A Novel Sustainable Cobalt Catalyst for the Methane Pyrolysis Process

A Novel Sustainable Cobalt Catalyst for the Methane Pyrolysis Process | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article A Novel Sustainable Cobalt Catalyst for the Methane Pyrolysis Process Michal Wojtasik, Grażyna Żak, Renata Cicha-Szot This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7597996/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract This study investigates the use of biochar derived from pyrolyzed sewage sludge as a sustainable catalyst support for cobalt in the methane pyrolysis process aimed at clean hydrogen production. Biochar was obtained through fast pyrolysis of sewage sludge at 650°C and characterized for its morphological and textural properties. Catalysts with cobalt supported on biochar were synthesized and compared to conventional cobalt catalysts supported on alumina (Al₂O₃). The catalytic performance was evaluated based on methane conversion, hydrogen production efficiency, and selectivity at temperatures of 750°C, 850°C, and 950°C. Results demonstrate that while Co/Al₂O₃ catalysts exhibit higher maximum conversion and efficiency, Co/biochar catalysts show comparable or slightly better selectivity and significantly improved stability during prolonged operation at 850°C. The biochar-supported catalyst exhibited slower deactivation, attributed to the heterogeneous porous structure mitigating carbon deposition effects. Furthermore, the biochar production process has at least 50% lower greenhouse gas emissions compared to alumina, offering a promising environmental benefit. This research highlights the potential of sewage sludge-derived biochar as a cost-effective, sustainable alternative catalyst support for methane pyrolysis hydrogen production. Physical sciences/Chemistry Physical sciences/Energy science and technology Physical sciences/Engineering Earth and environmental sciences/Environmental sciences Physical sciences/Materials science methane pyrolysis biochar sewage sludge cobalt catalyst hydrogen production catalyst support sustainable catalyst catalyst stability pyrolysis greenhouse gas emissions Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 1. INTRODUCTION Hydrogen can be used as a raw material, fuel, carrier or energy storage. It also has many potential applications in the industrial, transport, energy and construction sectors. Most importantly, no carbon dioxide is produced during its use, thanks to which hydrogen seems to be the answer to the current situation in the global economy, which is in line with the desire of the population to live in a clean environment. As a result, global hydrogen consumption is projected to increase around sixfold in the coming decades. Currently, hydrogen is produced in fossil fuel processes (76% of global production) [ 1 ], mainly in the process of steam reforming of natural gas, coal gasification or by separation from coke oven gas. These hydrogen production methods generate large amounts of carbon dioxide – above 5.8 kg CO 2 eq/kg H 2 when using natural gas, and above 10 kg CO 2 eq/kg H 2 when the primary energy source is coal[ 2 ]. This type of hydrogen is called conventional hydrogen or gray hydrogen. Another type of hydrogen is low-carbon hydrogen, i.e. hydrogen produced from non-renewable or renewable energy sources with a low carbon footprint. The size of this trace has not yet been formally determined, but many studies indicate a size below 5.8 kg CO 2 eq/kg H 2 . This type of hydrogen is often referred to as blue hydrogen – defined as obtained from non-renewable fuels, but classified as low-carbon technologies through the production process. The methods of producing low-carbon hydrogen include: methane steam reforming with CO 2 capture and storage (CCS) or CO 2 capture and use (CCU), electrolysis with the use of electricity from RES, methane pyrolysis, chemical processes whose by-product is hydrogen, including the separation of hydrogen from coke oven gas. Methane pyrolysis is an endothermic process that requires temperatures of 1000°C and more to achieve high yields. However, in order to achieve reasonable reaction rates, temperatures above 1200°C [ 3 ] are usually required in the so-called thermal pyrolysis method. The methane pyrolysis process carried out by the thermal method is difficult to implement on a large scale due to the poor selectivity of H 2 and the difficulty in removing carbon that can block the reactor [ 4 ]. The high operating temperatures required also limit material options and increase the carbon footprint due to the high energy requirements for heating, further reducing the attractiveness of this method. The biggest advantage of the methane/natural gas pyrolysis method is that there is no need to capture and store CO 2 (sequestration), which significantly simplifies the process and brings the economic cost of hydrogen production using this method closer to the cost of its production from the steam reforming process [ 3 ]–[ 5 ]. The interest in methane pyrolysis as a potential way to obtain hydrogen has contributed to the further development of this method and currently its modifications are widely described in the scientific literature [ 6 ]–[ 8 ]. The use of a variety of metals as catalysts was studied, according to Jin et al.[ 9 ] A series of metal activities used without a carrier and promoter in the methane pyrolysis process are as follows: Ni > Co > Ru > Rh > Pt > Re > Ir > Pd > Cu > W > Fe > Mo Among them, Ni, Co, and Fe catalysts have gained great interest due to their advantages such as availability and low cost (Fe)[ 10 ] and superior activity and stability (Ni, Co) [ 11 ]–[ 13 ]. The explanation for the phenomenon of high nickel activity is seen in the crystallization temperature of this metal, which is directly related to the coking threshold (thermodynamic equilibrium constant), but rapid aggregation and encapsulation of carbon cause rapid inactivation of the Ni catalyst, especially at temperatures higher than 600 o C[ 14 ]. Otsuka et al. [ 4 ] showed that the iron catalyst, despite its lower activity, shows much higher stability at temperatures above 700 o C, moreover, in the presence of this catalyst, a by-product is formed in the form of thin-walled carbon nanotubes, which are a very valuable nanocarbon material [ 15 ]. Dupuis et al. [ 16 ] developed a theory according to which in the process of decomposing methane towards obtaining the highest possible amounts of hydrogen, active metallic catalysts are those characterized by partial filling of 3D orbitals (Fe, Co and Ni). This facilitates the dissociation of methane molecules by partially accepting electrons. It was also observed that when copper is used in the pyrolysis process (a completely filled 3d orbital), much less hydrogen is obtained. A similar phenomenon was observed for precious metals (Rh, Ru, Co and Pt) [ 17 ]. The article[ 18 ] presents the synthesis, characterization and evaluation of the catalytic activity of monometallic nickel (Ni), cobalt (Co) and iron (Fe) catalysts deposited on silica (SiO₂) microhulls obtained by the sol-gel method. The highest efficiency (~ 74%) of hydrogen production was obtained using the Ni/SiO₂ catalyst, but over time the catalyst was deactivated (down to 32% after 300 minutes) due to the deposition of nanocarbons on the surface. In contrast, the Co/SiO₂ catalyst showed a lower maximum hydrogen yield (~ 43%) but very high stability – no deactivation throughout the reaction. The most commonly used carrier for cobalt catalysts is alumina, which is a very good carrier, but its production is a real environmental burden [ 19 ]. Currently, it is produced using the Bayer or Pedersen process. The former is energy-efficient and less environmentally burdensome under conventional conditions, but the Pedersen process offers better use of mineral resources and the potential to reduce environmental impact under the right energy conditions and further technological development. Despite this, the aluminum oxide makes a significant contribution to the GHG emissions of the catalyst throughout its life cycle. The last step is to look for alternatives with a lower impact on the environment and climate. The use of sewage sludge seems to be an interesting alternative. Sewage sludge is a by-product of wastewater treatment. This solid product is produced in the treatment of both municipal and industrial wastewater. It is a problematic material, but it is becoming more and more popular, among others due to its energy potential and waste origin. Any use of sewage sludge is part of the circular economy, so it is expected that it will be a sought-after product on the market in the coming years. Sewage sludge is a waste with a very complex and variable composition, depending on the place of production and the wastewater treatment technology used: moreover, it has even been shown that its composition variably depends on the time (season) of its collection. One of the most interesting may be the production of biochar from it and then its use in other areas of the economy. One of the ways to obtain biochar is pyrolysis, i.e. thermal decomposition without access to air. In addition to biochar, the products of sewage sludge pyrolysis are gas consisting mainly of light hydrocarbons and hydrogen, and a liquid that is a mixture of hydrocarbons and aqueous phase. In a typical pyrolysis method, thermal decomposition is carried out in a furnace at a certain heating rate and final temperature in a stream of nitrogen or argon. The resulting biochar after pyrolysis is usually washed with a hydrochloric acid solution in order to reduce the content of inorganic substances on the surface [ 20 ]. This action also improves the porosity and specific surface area of biochar[ 20 ], [ 21 ]. Fang et al. [ 22 ] proved that the decomposition temperature of sewage sludge has a significant impact not only on the yield of the solid fraction, but above all on the morphological and physicochemical properties of the resulting biochar. Pyrolysis temperatures below 500°C result in a high content of uncarbonized mass, while pyrolysis at higher temperatures causes the resulting material to have a large number of cracks and surface porosity due to the release of volatile substances [ 23 ] However, heating above 800°C can reduce the surface area of pore deformation as a result [ 24 ]. Due to its stable composition and high porosity, biochar can be used as an adsorbent for adsorbing organometallic compounds or heavy metals [ 21 ], [ 25 ]. In addition, the high content of heavy metals makes it suitable for use as a catalyst or catalyst carrier. The literature describes the method of impregnation of such compounds constituting the active phase as: Fe 2 O 3 , Ti 3+ /Fe [ 26 ], Fe[ 27 ], TiO 2 [ 28 ], ZnO/Fe 3 O 4 [ 24 ], Fe 3 O 4 [ 24 ], [ 29 ]. The article presents the application of biochar obtained from the pyrolysis of sewage sludge as a catalyst support in the thermal pyrolysis of methane. The research focuses on comparing the composition, morphology, catalytic efficacy, and emission characteristics of cobalt catalysts impregnated on sewage sludge-derived carbon with those supported on alumina, used here as a reference material. Despite significant advances in methane pyrolysis catalysis, the environmental impact and sustainability of catalyst supports remain critical challenges. Traditional alumina supports contribute substantially to the overall greenhouse gas emissions in catalyst production processes. This study aims to investigate the potential use of biochar derived from pyrolyzed sewage sludge as a sustainable alternative catalyst support for cobalt catalysts in methane pyrolysis. The objective is to evaluate the catalytic performance, stability, and environmental footprint of Co/biochar catalysts compared to conventional Co/Al₂O₃ catalysts, thereby exploring a feasible approach towards greener hydrogen production technologies. 2. MATERIALS AND METHODS 2.1. Materials For the synthesis of catalysts were used: cobalt nitrate hexahydrate p.d.a., Co(NO3)2·6H2O (CAS: 10026-22-9) and Al 2 O 3 (CAS: (1344-28-1)) from Chempur, Poland. Other chemical reagents were obtained from Aldrich. Methane and technical gases were procured from Air Products, a reputable supplier of industrial gases. Sewage sludge with the properties listed in Table 1 was obtained from RIPOK Kielce, Poland. Table 1 Properties of sewage sludge used in research. Value moisture content in the analytical sample, wt% 10.9 ash content, wt% 35.1 total sulphur content, wt% 0.15 calorific value, kJ/kg 13 200 chlorine content, wt% 0.08 carbon content, wt. % 60.4 hydrogen content, wt% 4.08 nitrogen content, wt% 5.64 silica content, wt% 10.2 2.2 Methods 2.2.1. Biochar obtaining Sewage sludge was subjected to pyrolysis to produce biochar for use as a catalyst support. The process parameters were meticulously chosen to optimize biochar yield via fast pyrolysis, aiming to obtain a product with high carbon content and maximum porosity at a temperature of 650°C. Pyrolysis catalysts were deliberately omitted, and the operating temperature was limited to 650°C to mitigate excessive generation of the bioavailable fraction of polycyclic aromatic hydrocarbons (PAHs), which can result from recombination reactions. The pyrolysis was carried out in a laboratory setup, where 170 g of sewage sludge, ground to a particle size of 0.5 mm, was placed in an electrically heated, cylindrical reactor with a working volume of 2 dm³. Prior to heating, the reactor's contents were purged with nitrogen at a flow rate of 150 mL min⁻¹ for 60 minutes, subsequently reduced to 50 mL min⁻¹. The sample was then heated at a rate of 15°C min⁻¹ up to the target temperature of 650°C. After reaching the target temperature, it was maintained for 15 minutes. Then, the reactor was cooled for 2 hours under a constant flow of nitrogen (50 mL min⁻¹). Approximately 100 g of biochar was obtained. Additionally, 47.9 g of liquid was collected, which contained 20.4 g of the aqueous fraction. The mass loss was attributed to gaseous products. The typical composition of the pyrolysis gas was as follows: methane (CH₄) 0.135, ethane (C₂H₆) 0.035, propane (C₃H₈) 0.101, carbon dioxide (CO₂) 0.286, carbon monoxide (CO) 0.182, hydrogen (H₂) 0.009, hydrogen sulfide (H₂S) 0.026, and nitrogen (N₂) 0.225. The lower heating value (LHV) of the corrected gas mixture is approximately 16.29 MJ/kg. The concept of obtaining biochar from other biomasses has also been described in another of our papers[ 30 ]. 2.2.2. Synthesis of catalysts An aqueous solution containing 65.0 g of cobalt nitrate was mixed with an aqueous suspension comprising 30.0 g of the support material (Al 2 O 3 or biochar). The resulting suspension was stirred at 500 rpm in a closed vessel maintained at 60°C for 60 minutes. Subsequently, the vessel was opened, and the solvent was gently evaporated until a thick paste-like suspension was obtained. The samples were then dried at 120°C for 12 hours, ground in a mortar, and subjected to a second drying under the same conditions for another 12 hours. After a second grinding step, the sample was calcined at 700°C for 5 hours. Finally 65.2g of catalyst was obtained. The efficiency of process was 92.0%. 2.2.3. Methane pyrolysis process Methane pyrolysis (methane purity: 99.99%) was performed in a quartz reactor with a cylindrical shape of 1200mm in length, an inner diameter of 55mm and a wall thickness of 4mm. The tube was placed in a glass furnace model PRW 120x600/110MR with a power of 3.6kW (Czylok, Poland). The reactor was closed on two sides with sealed and cooled heads.(Fig. 1.) The process gases were directed through a multi-port valve either to the chromatograph for analysis or to the exhaust system. The flow rate of the reaction and process gas was set at 200Nmlmin − 1 for nitrogen and 200Nmlmin − for methane. The catalysts were placed in a loose form (about 2g) between two layers of rigid discs of heat-resistant quartz wool. The discs with the catalyst was inserted halfway up the reaction tube. The process was conducted at three different temperatures. In each case, the reactor containing the catalyst was heated to 750°C, 850°C, or 950°C at a heating rate of 15°C min⁻¹ under a nitrogen atmosphere with a flow rate of 200 mL min⁻¹. Upon reaching the target temperature, methane was introduced into the reactor at a flow rate of 200 mL min⁻¹. The process was carried out for 30 minutes, during which the post-process gas stream was directed to the chromatograph three times for analysis. 2.2.4. Gas chromatography The gaseous products of the process were analyzed using an SRI model gas chromatograph equipped with a valve-loop sampler and two detectors: a thermal conductivity detector (TCD) and a helium ionization detector (HID). The chromatograph was operated under isothermal conditions at 180°C, with helium and nitrogen carrier gases flowing at 10 mL min⁻¹. Calibration of the system was performed using standard gas mixtures from Multax s.c. as well as individual gas standards. Response factors for the thermal conductivity detector (TCD) were determined for each gas component and subsequently used to quantify the composition of gas samples obtained from the methane pyrolysis process. 2.2.5. Calculation of process parameters On the basis of the obtained post-process gas compositions (mass percentages), it was possible to determine:methane conversion (1), efficiency of the methane pyrolysis (2) and selectivity of the methane pyrolysis (3) calculated according to formulas shown below. \(\:Conversion,\:\%=\frac{products\:conc.}{substrate\:conc.\:}\bullet\:100\%\) (1) \(\:Efficiency,\:\%=\frac{hydrogen\:conc.}{substrate\:conc.}\:\bullet\:100\%\) (2) \(\:Selectivity,\:\%=\frac{Efficiency}{Conversion}\:\bullet\:100\%\) (3) 2.2.6. SEM Imaging and mapping of the structures of the catalysts was performed by SEM. It was used a Supra 35 microscope (Zeiss, Oberkochen, Germany) at accelerating voltages in the range of 2 to 10 kV. The microscope was equipped with an EDS detector. 3. RESULTS 3.1. Catalyst Analysis 3.1.1. SEM images The following figures show SEM images of the supports and catalysts at various magnifications. Figures 2 and 3 present the alumina (Al₂O₃) support and the Co/Al₂O₃ catalyst, respectively, while Figs. 4 and 5 display the biochar support and the catalyst prepared using it, Co/biochar. The alumina support images (Fig. 2) reveal a relatively uniform and porous surface morphology characteristic of γ-Al 2 O 3 materials[ 31 ]–[ 33 ]. The pores appear to be predominantly mesoporous with sizes in the nanometer to sub-micrometer range. The pore distribution is fairly homogeneous, which is advantageous for catalyst impregnation and active phase dispersion. The surface texture is rough and irregular, providing a high surface area for cobalt precursor adsorption during impregnation. In the images of the Co/Al 2 O 3 catalyst (Fig. 3), several notable changes are observed compared to the pure alumina support. The catalyst images show the presence of dispersed cobalt oxide or cobalt species on the surface. The cobalt crystallites appear as small, roughly spherical or slightly agglomerated nanoparticles with sizes estimated in the range of tens of nanometers. The cobalt particles are fairly well dispersed without large aggregates, indicating effective impregnation and distribution on the alumina substrate. This dispersion is critical for catalytic activity, as smaller particles generally offer more accessible active sites. The biochar support (Fig. 4) exhibits a distinctly different morphology compared to alumina. The surface is highly irregular with a heterogeneous porous structure including macropores and mesopores. The pores on the biochar support seem larger and more irregularly shaped, consistent with the carbonaceous, amorphous nature of biochar. This morphology can potentially enhance mass transport within the catalyst due to larger pore channels, but the surface heterogeneity might affect the uniformity of cobalt dispersion. In the images of the Co/biochar catalyst (Fig. 5), cobalt species are present but appear as somewhat larger and less uniformly shaped crystallites compared to the Co/Al 2 O 3 catalyst. The crystallites generally show a range of shapes from spherical to more irregular, indicating possible agglomeration or uneven dispersion on the biochar surface. The particle sizes are comparatively larger, which may reduce the total catalytic active surface area relative to the alumina-based catalyst. 3.1.2. SEM – Composition Analysis (EDS and mapping) Figure 6 presents the EDS analysis for the Co/Al₂O₃ catalyst sample. EDS analysis (Fig. 6) of Co/Al 2 O 3 catalyst revealed the following composition (weight, %): carbon 2.6%, oxygen 37.3%, aluminium 33.5%, and cobalt 26.9% This composition aligns well with expectations for cobalt impregnated on alumina support. The high Al content confirms the dominance of alumina as the support, while the significant presence of Co indicates effective cobalt impregnation. Oxygen is primarily associated with metal oxides present in the catalyst, including cobalt oxide. Elemental surface maps were generated to evaluate the distribution of elements in the Co/Al₂O₃ catalyst, with the results presented in the Fig. 7. The maps demonstrate a relatively uniform distribution of cobalt across the alumina surface, accompanied by even dispersion of aluminium. Uniform dispersion of cobalt on alumina suggests good distribution of active catalytic sites, which usually correlates with enhanced catalytic activity and durability. The data indicate a well-prepared and stable Co/Al₂O₃ catalyst system. Figure 8 presents the EDS analysis for the Co/biochar catalyst sample. EDS analysis (Fig. 8) of Co/biochar catalyst revealed the following composition (weight, %): carbon: 12.0%, oxygen: 31.0%, magnesium: 1.6%, phosphorus: 3.9%, sulfur: 1.0%, potassium: 0.7%, calcium: 5.1%, iron: 2.4%, silicon: 6.3%, aluminium: 1.9%, sodium: 0.5%, cobalt: 33.6%. The complex elemental composition reflects the heterogeneous nature of biochar derived from sewage sludge. The high cobalt content confirms the substantial loading of active metal. The presence of various elements such as P, S, K, Ca, Fe, and Si corresponds to mineral residues and impurities inherent to biochar. It is worth noting that carbon constitutes only 12% of the total catalyst mass, making it a kind of carbon-mineral composite material with a high content of silica and aluminosilicates. Elemental surface maps was performed for the Co/biochar catalyst (Fig. 9). However, the presentation of results is limited to the elemental maps of those elements found in the catalyst at the highest concentrations. Unlike the Co/Al₂O₃ catalyst, cobalt on biochar exhibits less uniform dispersion, with cobalt-rich clusters visible in certain regions. Carbon and oxygen remain widespread due to the carbonaceous nature of the support, with noticeable zones enriched in Ca, Si, and Fe, indicative of the intrinsic mineral heterogeneity in biochar. Although cobalt loading is higher in the Co/biochar catalyst, its uneven distribution and association with various mineral phases may influence catalytic behavior and active site accessibility. The mineral constituents may induce synergistic effects or impact catalytic stability but could also reduce the effective surface area of cobalt particles. 3.2.Testing the effectiveness of catalysts The calculated values of conversion, efficiency and selectivity for processes involving the developed catalysts are presented in Table 3. Each result is an average of the three post-processes gas analyses. Table 3 Conversion, yield and selectivity values for the developed cobalt catalysts. 750 o C 850 o C 950 o C Result, % Result, % Result, % Co/Al 2 O 3 conv., % 37.90 44.80 76.80 eff., % 32.50 40.10 69.40 sel., % 85.75 89.51 90.36 Co/biochar conv., % 38.70 45.20 71.00 eff., % 33.10 41.50 64.30 sel., % 85.53 91.81 90.56 The performance results for the developed cobalt catalysts—Co/Al₂O₃ and Co/biochar—are reported in terms of conversion, efficiency, and selectivity at three temperatures: 750°C, 850°C, and 950°C. All parameters—conversion, efficiency, and selectivity—increase with rising temperature for both catalysts. For the Co/Al₂O₃ catalyst, methane conversion rises from 37.9% at 750°C to 76.8% at 950°C, representing more than a twofold increase. Efficiency also improves substantially, from 32.5% to 69.4%, while selectivity increases moderately from 85.75% to 90.36%. Similarly, the Co/biochar catalyst shows an increase in conversion from 38.7% to 71.0% as the temperature rises, a 7.5% lower maximum conversion compared to Co/Al₂O₃ at 950°C. Efficiency follows this trend, increasing from 33.1% to 64.3%, which is around 7.3% lower at the highest temperature compared to Co/Al₂O₃. Selectivity for Co/biochar increases slightly more with temperature than for Co/Al₂O₃, rising from 85.53% to 90.56%, with a marginally higher selectivity (~ 0.2%) at 950°C compared to Co/Al₂O₃. Overall, Co/Al₂O₃ exhibits superior performance at higher temperatures, particularly for conversion and efficiency, however, both catalysts show very comparable selectivity above 850°C, with Co/biochar slightly outperforming Co/Al₂O₃ at the highest temperature tested. These results suggest that while Co/Al₂O₃ is more active overall, Co/biochar provides competitive selectivity and may offer advantages in other aspects such as cost or sustainability. 3.3. Catalyst Lifetime Study The catalysts were subjected to a lifetime study. For this purpose, an experiment was conducted at a temperature of 850°C lasting 10 hours according to the methodology described in section 2.2.3 . During the study, the composition of the post-process gases was analyzed every hour, and based on this, the process parameters—conversion, yield, and selectivity—were calculated for each measurement point according to the methodology described in section 2.2.5 . The catalyst lifetime tests at 850°C over a 10-hour period demonstrated a rapid deactivation of the Co/Al₂O₃ catalyst, with conversion and yield decreasing by approximately 90% and selectivity dropping by about 13%. In contrast, the Co/biochar catalyst exhibited notably greater stability, as its conversion and yield decreased by approximately 62% and 71%, respectively, and selectivity by about 23% over the same period. Throughout the experiment, the Co/biochar catalyst consistently maintained higher conversion, yield, and selectivity values compared to Co/Al₂O₃, indicating that the biochar-supported system is more resistant to deactivation under harsh reaction conditions and is a promising support for high-temperature methane pyrolysis catalysts. The slower deactivation of the biochar-based catalyst may be attributed to its heterogeneous pore structure and the presence of large pores, which are more difficult to block by the carbon generated during the process. Additionally, the phenomenon of faster selectivity loss for Co/biochar observed in the later stages of the experiment requires further attention, as it indicates a possible increase in the activity of competing side reactions leading to the formation of unexpected products. This trend highlights the need for more detailed investigation into the mechanisms of catalyst deactivation and process optimization to ensure consistent selectivity under prolonged high-temperature operating conditions 3.4. Climat impact Replacing the Al₂O₃ support with biochar derived from pyrolyzed sewage sludge offers a promising strategy for lowering the carbon intensity of catalyst production. The GHG emissions associated with biochar production are significantly lower than with commercial alumina due to the waste-derived nature of the feedstock and the relatively energy-efficient process conditions. To estimate the possible reduction in GHG emissions, the process of biochar production by pyrolysis was analyzed. Table 4 presents a simplified mass and energy balance of the sewage sludge pyrolysis process that allows producing 1 Mg of biochar for catalyst production. Table 4 Simplified mass and energy balance of sewage sludge pyrolysis process Inputs Balance value Drying sludge, kg 1700 Electricity, kWh 240 Outputs Biochar, kg 1000 Pyrolytic oil, kg 275 Waste water, g 204 Pyrolytic gas, g 221 According to IPCC guidelines, the carbon in sewage sludge is considered biogenic; however, the emissions of such material must be estimated based on the fuel and energy consumption required to prepare the material for product formation. The the thermal drying process, and the pyrolysis process consume 40 kWh and 118 kWh [ 34 ]. Considering the electricity emission factor in Poland (0.593 kgCO 2 eq/kWh) [ 35 ], the estimated GHG emission factor for dry (impregnation-ready) sewage sludge was about 0.21 kg CO 2 eq/kg. In the pyrolysis process, as described in section 2.2.1 , besides biochar, a liquid fraction, waste water, and gas fraction are produced. For emission estimation, it was assumed that the organic liquid fraction would be treated as a product and allocated part of the pyrolysis process emissions (mass allocation factor, 0.2159). The gas fraction formed was treated as an energy source that can reduce the electrical energy demand of the process. According to[ 36 ], up to 124 kWh can be recovered from the combustion of pyrolytic gas. Therefore, the total electricity demand was estimated at 244 kWh, consistent with the data [ 34 ]. The emission factor for wastewater was sourced from the European reference Life Cycle Database of the Joint Research Center, version 3.2. Based on the above data, the estimated emission of the biochar production process from sewage sludge by pyrolysis was 1.18 kg CO 2 eq/kg. This represents a reduction of at least 50% compared to Al₂O₃ support, which has an emission of about 2.4 kg CO 2 eq/kg[ 37 ]. CONCLUSION This study systematically explored the synthesis, characterization, performance, durability, and environmental impact of a novel cobalt catalyst supported on sewage sludge-derived biochar, compared directly with the conventional cobalt catalyst supported on alumina in the methane pyrolysis process for hydrogen generation. The research provides compelling evidence for the effectiveness and sustainability of using biochar as an alternative catalyst support, thereby contributing to cleaner hydrogen production and resource circularity. The Co/biochar catalyst exhibited hydrogen yields and methane conversions at all operational temperatures (750°C, 850°C, and 950°C) that were very close to those of the reference Co/Al₂O₃ catalyst, especially at 750°C and 850°C, with differences at the highest temperature being moderate (7–8% lower). Selectivity for hydrogen production using Co/biochar was slightly higher at increased temperatures, surpassing alumina-supported cobalt at 850°C and 950°C, suggesting that the unique pore structure and chemical nature of biochar support favor targeted reaction pathways. Despite the somewhat larger and less uniform cobalt crystallites identified by SEM on the biochar surface in comparison to alumina, the catalyst remained highly active, demonstrating that support composition and macrostructure can compensate for differences in active phase dispersion. A key outcome from the long-term performance (lifetime) tests was the substantially improved stability of Co/biochar under continuous operation at 850°C. Whereas Co/Al₂O₃ lost about 90% of its original activity and suffered a significant selectivity drop after 10 hours, Co/biochar retained higher conversion and selectivity, with its activity declining by only about 62%. The enhanced durability is linked to the heterogeneous and interconnected porosity of biochar, which appears less susceptible to rapid blockage by carbonaceous deposits generated during methane decomposition. This finding highlights that waste-based carbon supports can serve not only as a “greener” but also a technically robust, long-lived alternative to conventional oxide carriers in high-temperature catalytic reactions. The environmental assessment performed in this work further underscores the potential of this approach. Life cycle emission calculations reveal that the greenhouse gas footprint involved in producing 1 kg of sewage sludge-derived biochar is at least 50% lower than that of commercial alumina, even when accounting for the energy required to dry and pyrolyze the sludge. This difference is primarily due to the valorization of a problematic waste stream, energy recovery from the process gases, and reduced need for high-temperature oxide synthesis. Such attributes are especially relevant in the context of global decarbonization targets and circular economy ambitions, as they enable catalyst manufacturers and hydrogen producers to reduce both operational and embedded emissions simultaneously. The multifunctional nature of sewage sludge biochar—which contains not only carbon but also minerals such as Si, Ca, Fe, and P provided by the parent material—may also support further catalyst improvements through synergistic effects, though the current study notes some heterogeneity in cobalt dispersion as a potential area for optimization. In practice, this may offer pathways to tune surface chemistry, resistance to deactivation, or even achieve valorization of additional elements present in the waste feedstock. The results presented provide a strong foundation for industrial implementation of biochar-supported catalysts, particularly in scenarios where sustainability, waste management, and carbon intensity reductions are priorities. However, some limitations and opportunities for future research remain. These include efforts to: Improve the uniformity of cobalt distribution on complex carbon-mineral matrices through tailored impregnation or activation protocols. Investigate in detail the deactivation mechanisms and product distributions observed during extended operation, especially to control selectivity loss at late stages. Assess long-term operational stability in larger-scale or continuous-flow systems with various real-waste-derived biochars. Further integrate life cycle assessment and techno-economic studies to support decision making for scale-up and commercialization. In summary, the use of sewage sludge-derived biochar as a support for cobalt catalysts in methane pyrolysis represents an innovative technological advance with clear technical, economic, and environmental merits. By transforming a problematic municipal waste into a valuable, high-performance catalyst support, this approach helps close resource loops while lowering both catalyst costs and the carbon footprint of large-scale hydrogen generation. With additional research and scale-up, biochar-supported catalysts could accelerate progress toward low-emission, circular hydrogen production, and set a precedent for other waste-driven catalyst systems in the chemical process industries. This work was supported by funding by the Republic of Poland Ministry of Education and Science; Project INiG-PIB no. 0059/2024. This research was funded in in part by National Science Centre, Poland, Grant number: 2025/09/X/ST5/00196. For the purpose of Open Access, the author has applied a CC-BY public copyright licence to any Author. Accepted Manuscript (AAM) version arising from this submission Declarations Author Contribution M.W. conceived and designed the research, carried out the experiments, analyzed the results, and wrote the manuscript. G.Ż. contributed to the analysis of results and the preparation of the figures. R.C.-S. participated in writing the manuscript. All authors reviewed the manuscript. Data Availability The datasets used and/or analysed during the current study available from the corresponding author on reasonable request References Ahn, S. Y. et al. From gray to blue hydrogen: Trends and forecasts of catalysts and sorbents for unit process. Renew. Sustain. Energy Rev. 186 10.1016/j.rser.2023.113635 (2023). Shokrollahi, M., Teymouri, N., Ashrafi, O., Navarri, P. & Khojasteh-Salkuyeh, Y. Methane pyrolysis as a potential game changer for hydrogen economy: Techno-economic assessment and GHG emissions. Int. J. Hydrogen Energy . 66 , 337–353. 10.1016/J.IJHYDENE.2024.04.056 (May 2024). Poirier, M. 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Available: https://www.kobize.pl/pl/fileCategory/id/28/wskazniki-emisyjnosci Kwapinska, M., Horvat, A., Agar, D. A. & Leahy, J. J. Energy recovery through co-pyrolysis of wastewater sludge and forest residues – The transition from laboratory to pilot scale. J. Anal. Appl. Pyrol. 158 10.1016/j.jaap.2021.105283 (2021). Ma, Y., Preveniou, A., Kladis, A. & Pettersen, J. B. Circular economy and life cycle assessment of alumina production: Simulation-based comparison of Pedersen and Bayer processes. J. Clean. Prod. 366 10.1016/j.jclepro.2022.132807 (2022). Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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11:54:30","extension":"png","order_by":26,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":129481,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-7597996/v1/9d73bd3b6b2a12d9f5d8a31b.png"},{"id":92258081,"identity":"6536b81f-7eba-40e8-bfb4-474a2d7dea4b","added_by":"auto","created_at":"2025-09-26 11:54:30","extension":"xml","order_by":27,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":109899,"visible":true,"origin":"","legend":"","description":"","filename":"fe897f8f0f8246adbdccae14c49af9591structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-7597996/v1/b4797fcc082bc246301e3f1c.xml"},{"id":92258079,"identity":"6633a0b3-8ac6-4832-bcae-652314951ceb","added_by":"auto","created_at":"2025-09-26 11:54:30","extension":"html","order_by":28,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":117990,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7597996/v1/0f89bb59387ba87d69abba4e.html"},{"id":92258084,"identity":"308ce4f7-0f2f-49b8-9695-d85830940673","added_by":"auto","created_at":"2025-09-26 11:54:32","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":31714,"visible":true,"origin":"","legend":"\u003cp\u003eMethane pyrolysis process scheme\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7597996/v1/6754df702b38bf7080def053.png"},{"id":92258062,"identity":"ec0e70b5-694c-4cd9-a9da-a38473446d5e","added_by":"auto","created_at":"2025-09-26 11:54:27","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":688959,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eCatalyst Support - Al\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003cem\u003eO\u003c/em\u003e\u003csub\u003e\u003cem\u003e3 \u003c/em\u003e\u003c/sub\u003e\u003cem\u003eSEM images: a) 100k mag., b) 10k mag., c) 2.5k mag. d) 0.5k mag.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7597996/v1/405e353a849443baf58eed20.png"},{"id":92258059,"identity":"ca55dac4-40d1-4e1a-b00f-6548261fa754","added_by":"auto","created_at":"2025-09-26 11:54:27","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":657406,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eCatalyst Co/ Al\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003cem\u003eO\u003c/em\u003e\u003csub\u003e\u003cem\u003e3 \u003c/em\u003e\u003c/sub\u003e\u003cem\u003eSEM images: a) 100k mag., b) 50k mag., c) 5k mag. d) 1k mag.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7597996/v1/f420174757ecf5e81b6201e5.png"},{"id":92258054,"identity":"584443c5-15de-409c-afc5-eb36a384d11e","added_by":"auto","created_at":"2025-09-26 11:54:26","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":717226,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eCatalyst Support - biochar\u003c/em\u003e\u003csub\u003e\u003cem\u003e \u003c/em\u003e\u003c/sub\u003e\u003cem\u003eSEM images: a) 100k mag., b) 50k mag., c) 5k mag. d) 2.5k mag.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7597996/v1/93762e4828590c864d1f17c0.png"},{"id":92258251,"identity":"f497cfbe-bab2-47d4-8030-e8a7f59adb26","added_by":"auto","created_at":"2025-09-26 12:02:26","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":723133,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eCatalyst Co/biochar\u003c/em\u003e\u003csub\u003e\u003cem\u003e \u003c/em\u003e\u003c/sub\u003e\u003cem\u003eSEM images: a) 200k mag., b) 50k mag., c) 2.5k mag. d) 0.5k mag.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-7597996/v1/7be729fcbbe495a035341b86.png"},{"id":92258083,"identity":"8396d4bc-73c1-4e04-9f46-2162724819f9","added_by":"auto","created_at":"2025-09-26 11:54:31","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":143497,"visible":true,"origin":"","legend":"\u003cp\u003eCo/Al₂O₃ catalyst EDS analysis – a) analysis, b) analysed area\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-7597996/v1/40a3f777933a367ccf9e4160.png"},{"id":92258068,"identity":"3c5163ac-0fb1-438f-a1f8-e4da59139b0d","added_by":"auto","created_at":"2025-09-26 11:54:27","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":343882,"visible":true,"origin":"","legend":"\u003cp\u003eCo/Al₂O₃ catalyst elemental surface maps: a) Co, b) Al\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-7597996/v1/455094b480942078b7159192.png"},{"id":92258067,"identity":"4d1ef2a0-0a8c-46c7-ac29-7cd5e9eb0083","added_by":"auto","created_at":"2025-09-26 11:54:27","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":162859,"visible":true,"origin":"","legend":"\u003cp\u003eCo/biochar catalyst EDS analysis – a) analysis, b) analysed area\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-7597996/v1/b36837fdc5372c257ceddbd3.png"},{"id":92258252,"identity":"164ef804-f7a9-4358-b722-5d6f2d97c496","added_by":"auto","created_at":"2025-09-26 12:02:27","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":1532016,"visible":true,"origin":"","legend":"\u003cp\u003eCo/Al₂O₃ catalyst elemental surface maps: a) Co, b) C, c) Si, d Al), e) Fe, f) Ca, g) S, h) P\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-7597996/v1/507779505ed06a9c496daf08.png"},{"id":92258061,"identity":"cd290c8b-f3c2-405f-8a5a-4e22ecd53b61","added_by":"auto","created_at":"2025-09-26 11:54:27","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":101726,"visible":true,"origin":"","legend":"\u003cp\u003eCatalyst lifetime study – 10 hours test.\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-7597996/v1/e82ea4240efd936a5ff2ca2d.png"},{"id":103406900,"identity":"cf9165a3-fb37-48f7-b392-011c89a7e8df","added_by":"auto","created_at":"2026-02-25 10:13:13","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5880445,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7597996/v1/06bd49c0-49e7-4123-9087-e08434d35a54.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"A Novel Sustainable Cobalt Catalyst for the Methane Pyrolysis Process","fulltext":[{"header":"1. INTRODUCTION","content":"\u003cp\u003eHydrogen can be used as a raw material, fuel, carrier or energy storage. It also has many potential applications in the industrial, transport, energy and construction sectors. Most importantly, no carbon dioxide is produced during its use, thanks to which hydrogen seems to be the answer to the current situation in the global economy, which is in line with the desire of the population to live in a clean environment. As a result, global hydrogen consumption is projected to increase around sixfold in the coming decades. Currently, hydrogen is produced in fossil fuel processes (76% of global production) [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e], mainly in the process of steam reforming of natural gas, coal gasification or by separation from coke oven gas. These hydrogen production methods generate large amounts of carbon dioxide \u0026ndash; above 5.8 kg CO\u003csub\u003e2\u003c/sub\u003e eq/kg H\u003csub\u003e2\u003c/sub\u003e when using natural gas, and above 10 kg CO\u003csub\u003e2\u003c/sub\u003e eq/kg H\u003csub\u003e2\u003c/sub\u003e when the primary energy source is coal[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. This type of hydrogen is called conventional hydrogen or gray hydrogen. Another type of hydrogen is low-carbon hydrogen, i.e. hydrogen produced from non-renewable or renewable energy sources with a low carbon footprint. The size of this trace has not yet been formally determined, but many studies indicate a size below 5.8 kg CO\u003csub\u003e2\u003c/sub\u003e eq/kg H\u003csub\u003e2\u003c/sub\u003e. This type of hydrogen is often referred to as blue hydrogen \u0026ndash; defined as obtained from non-renewable fuels, but classified as low-carbon technologies through the production process. The methods of producing low-carbon hydrogen include: methane steam reforming with CO\u003csub\u003e2\u003c/sub\u003e capture and storage (CCS) or CO\u003csub\u003e2\u003c/sub\u003e capture and use (CCU), electrolysis with the use of electricity from RES, methane pyrolysis, chemical processes whose by-product is hydrogen, including the separation of hydrogen from coke oven gas.\u003c/p\u003e\u003cp\u003eMethane pyrolysis is an endothermic process that requires temperatures of 1000\u0026deg;C and more to achieve high yields. However, in order to achieve reasonable reaction rates, temperatures above 1200\u0026deg;C [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e] are usually required in the so-called thermal pyrolysis method. The methane pyrolysis process carried out by the thermal method is difficult to implement on a large scale due to the poor selectivity of H\u003csub\u003e2\u003c/sub\u003e and the difficulty in removing carbon that can block the reactor [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. The high operating temperatures required also limit material options and increase the carbon footprint due to the high energy requirements for heating, further reducing the attractiveness of this method.\u003c/p\u003e\u003cp\u003eThe biggest advantage of the methane/natural gas pyrolysis method is that there is no need to capture and store CO\u003csub\u003e2\u003c/sub\u003e (sequestration), which significantly simplifies the process and brings the economic cost of hydrogen production using this method closer to the cost of its production from the steam reforming process [\u003cspan additionalcitationids=\"CR4\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]\u0026ndash;[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe interest in methane pyrolysis as a potential way to obtain hydrogen has contributed to the further development of this method and currently its modifications are widely described in the scientific literature [\u003cspan additionalcitationids=\"CR7\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]\u0026ndash;[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe use of a variety of metals as catalysts was studied, according to Jin et al.[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] A series of metal activities used without a carrier and promoter in the methane pyrolysis process are as follows:\u003c/p\u003e\u003cp\u003eNi\u0026thinsp;\u0026gt;\u0026thinsp;Co\u0026thinsp;\u0026gt;\u0026thinsp;Ru\u0026thinsp;\u0026gt;\u0026thinsp;Rh\u0026thinsp;\u0026gt;\u0026thinsp;Pt\u0026thinsp;\u0026gt;\u0026thinsp;Re\u0026thinsp;\u0026gt;\u0026thinsp;Ir\u0026thinsp;\u0026gt;\u0026thinsp;Pd\u0026thinsp;\u0026gt;\u0026thinsp;Cu\u0026thinsp;\u0026gt;\u0026thinsp;W\u0026thinsp;\u0026gt;\u0026thinsp;Fe\u0026thinsp;\u0026gt;\u0026thinsp;Mo\u003c/p\u003e\u003cp\u003eAmong them, Ni, Co, and Fe catalysts have gained great interest due to their advantages such as availability and low cost (Fe)[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] and superior activity and stability (Ni, Co) [\u003cspan additionalcitationids=\"CR12\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u0026ndash;[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. The explanation for the phenomenon of high nickel activity is seen in the crystallization temperature of this metal, which is directly related to the coking threshold (thermodynamic equilibrium constant), but rapid aggregation and encapsulation of carbon cause rapid inactivation of the Ni catalyst, especially at temperatures higher than 600\u003csup\u003eo\u003c/sup\u003eC[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Otsuka et al. [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e] showed that the iron catalyst, despite its lower activity, shows much higher stability at temperatures above 700\u003csup\u003eo\u003c/sup\u003eC, moreover, in the presence of this catalyst, a by-product is formed in the form of thin-walled carbon nanotubes, which are a very valuable nanocarbon material [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eDupuis et al. [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] developed a theory according to which in the process of decomposing methane towards obtaining the highest possible amounts of hydrogen, active metallic catalysts are those characterized by partial filling of 3D orbitals (Fe, Co and Ni). This facilitates the dissociation of methane molecules by partially accepting electrons. It was also observed that when copper is used in the pyrolysis process (a completely filled 3d orbital), much less hydrogen is obtained. A similar phenomenon was observed for precious metals (Rh, Ru, Co and Pt) [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe article[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] presents the synthesis, characterization and evaluation of the catalytic activity of monometallic nickel (Ni), cobalt (Co) and iron (Fe) catalysts deposited on silica (SiO₂) microhulls obtained by the sol-gel method. The highest efficiency (~\u0026thinsp;74%) of hydrogen production was obtained using the Ni/SiO₂ catalyst, but over time the catalyst was deactivated (down to 32% after 300 minutes) due to the deposition of nanocarbons on the surface. In contrast, the Co/SiO₂ catalyst showed a lower maximum hydrogen yield (~\u0026thinsp;43%) but very high stability \u0026ndash; no deactivation throughout the reaction.\u003c/p\u003e\u003cp\u003eThe most commonly used carrier for cobalt catalysts is alumina, which is a very good carrier, but its production is a real environmental burden [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Currently, it is produced using the Bayer or Pedersen process. The former is energy-efficient and less environmentally burdensome under conventional conditions, but the Pedersen process offers better use of mineral resources and the potential to reduce environmental impact under the right energy conditions and further technological development. Despite this, the aluminum oxide makes a significant contribution to the GHG emissions of the catalyst throughout its life cycle. The last step is to look for alternatives with a lower impact on the environment and climate. The use of sewage sludge seems to be an interesting alternative.\u003c/p\u003e\u003cp\u003eSewage sludge is a by-product of wastewater treatment. This solid product is produced in the treatment of both municipal and industrial wastewater. It is a problematic material, but it is becoming more and more popular, among others due to its energy potential and waste origin. Any use of sewage sludge is part of the circular economy, so it is expected that it will be a sought-after product on the market in the coming years. Sewage sludge is a waste with a very complex and variable composition, depending on the place of production and the wastewater treatment technology used: moreover, it has even been shown that its composition variably depends on the time (season) of its collection. One of the most interesting may be the production of biochar from it and then its use in other areas of the economy. One of the ways to obtain biochar is pyrolysis, i.e. thermal decomposition without access to air. In addition to biochar, the products of sewage sludge pyrolysis are gas consisting mainly of light hydrocarbons and hydrogen, and a liquid that is a mixture of hydrocarbons and aqueous phase. In a typical pyrolysis method, thermal decomposition is carried out in a furnace at a certain heating rate and final temperature in a stream of nitrogen or argon. The resulting biochar after pyrolysis is usually washed with a hydrochloric acid solution in order to reduce the content of inorganic substances on the surface [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. This action also improves the porosity and specific surface area of biochar[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Fang et al. [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] proved that the decomposition temperature of sewage sludge has a significant impact not only on the yield of the solid fraction, but above all on the morphological and physicochemical properties of the resulting biochar. Pyrolysis temperatures below 500\u0026deg;C result in a high content of uncarbonized mass, while pyrolysis at higher temperatures causes the resulting material to have a large number of cracks and surface porosity due to the release of volatile substances [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e] However, heating above 800\u0026deg;C can reduce the surface area of pore deformation as a result [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Due to its stable composition and high porosity, biochar can be used as an adsorbent for adsorbing organometallic compounds or heavy metals [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. In addition, the high content of heavy metals makes it suitable for use as a catalyst or catalyst carrier. The literature describes the method of impregnation of such compounds constituting the active phase as: Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, Ti\u003csup\u003e3+\u003c/sup\u003e/Fe [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e], Fe[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e], TiO\u003csub\u003e2\u003c/sub\u003e [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e], ZnO/Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe article presents the application of biochar obtained from the pyrolysis of sewage sludge as a catalyst support in the thermal pyrolysis of methane. The research focuses on comparing the composition, morphology, catalytic efficacy, and emission characteristics of cobalt catalysts impregnated on sewage sludge-derived carbon with those supported on alumina, used here as a reference material.\u003c/p\u003e\u003cp\u003eDespite significant advances in methane pyrolysis catalysis, the environmental impact and sustainability of catalyst supports remain critical challenges. Traditional alumina supports contribute substantially to the overall greenhouse gas emissions in catalyst production processes. This study aims to investigate the potential use of biochar derived from pyrolyzed sewage sludge as a sustainable alternative catalyst support for cobalt catalysts in methane pyrolysis. The objective is to evaluate the catalytic performance, stability, and environmental footprint of Co/biochar catalysts compared to conventional Co/Al₂O₃ catalysts, thereby exploring a feasible approach towards greener hydrogen production technologies.\u003c/p\u003e"},{"header":"2. MATERIALS AND METHODS","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1. Materials\u003c/h2\u003e\u003cp\u003eFor the synthesis of catalysts were used: cobalt nitrate hexahydrate p.d.a., Co(NO3)2\u0026middot;6H2O (CAS: 10026-22-9) and Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (CAS: (1344-28-1)) from Chempur, Poland. Other chemical reagents were obtained from Aldrich. Methane and technical gases were procured from Air Products, a reputable supplier of industrial gases.\u003c/p\u003e\u003cp\u003eSewage sludge with the properties listed in Table\u0026nbsp;1 was obtained from RIPOK Kielce, Poland.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eProperties of sewage sludge used in research.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"2\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eValue\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003emoisture content in the analytical sample, wt%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e10.9\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eash content, wt%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e35.1\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003etotal sulphur content, wt%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.15\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ecalorific value, kJ/kg\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e13 200\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003echlorine content, wt%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.08\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ecarbon content, wt. %\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e60.4\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ehydrogen content, wt%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e4.08\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003enitrogen content, wt%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e5.64\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003esilica content, wt%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e10.2\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Methods\u003c/h2\u003e\u003cdiv id=\"Sec5\" class=\"Section3\"\u003e\u003ch2\u003e2.2.1. Biochar obtaining\u003c/h2\u003e\u003cp\u003eSewage sludge was subjected to pyrolysis to produce biochar for use as a catalyst support. The process parameters were meticulously chosen to optimize biochar yield via fast pyrolysis, aiming to obtain a product with high carbon content and maximum porosity at a temperature of 650\u0026deg;C. Pyrolysis catalysts were deliberately omitted, and the operating temperature was limited to 650\u0026deg;C to mitigate excessive generation of the bioavailable fraction of polycyclic aromatic hydrocarbons (PAHs), which can result from recombination reactions. The pyrolysis was carried out in a laboratory setup, where 170 g of sewage sludge, ground to a particle size of 0.5 mm, was placed in an electrically heated, cylindrical reactor with a working volume of 2 dm\u0026sup3;. Prior to heating, the reactor's contents were purged with nitrogen at a flow rate of 150 mL min⁻\u0026sup1; for 60 minutes, subsequently reduced to 50 mL min⁻\u0026sup1;. The sample was then heated at a rate of 15\u0026deg;C min⁻\u0026sup1; up to the target temperature of 650\u0026deg;C. After reaching the target temperature, it was maintained for 15 minutes. Then, the reactor was cooled for 2 hours under a constant flow of nitrogen (50 mL min⁻\u0026sup1;). Approximately 100 g of biochar was obtained. Additionally, 47.9 g of liquid was collected, which contained 20.4 g of the aqueous fraction. The mass loss was attributed to gaseous products. The typical composition of the pyrolysis gas was as follows: methane (CH₄) 0.135, ethane (C₂H₆) 0.035, propane (C₃H₈) 0.101, carbon dioxide (CO₂) 0.286, carbon monoxide (CO) 0.182, hydrogen (H₂) 0.009, hydrogen sulfide (H₂S) 0.026, and nitrogen (N₂) 0.225. The lower heating value (LHV) of the corrected gas mixture is approximately 16.29 MJ/kg. The concept of obtaining biochar from other biomasses has also been described in another of our papers[\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section3\"\u003e\u003ch2\u003e2.2.2. Synthesis of catalysts\u003c/h2\u003e\u003cp\u003eAn aqueous solution containing 65.0 g of cobalt nitrate was mixed with an aqueous suspension comprising 30.0 g of the support material (Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e or biochar). The resulting suspension was stirred at 500 rpm in a closed vessel maintained at 60\u0026deg;C for 60 minutes. Subsequently, the vessel was opened, and the solvent was gently evaporated until a thick paste-like suspension was obtained. The samples were then dried at 120\u0026deg;C for 12 hours, ground in a mortar, and subjected to a second drying under the same conditions for another 12 hours. After a second grinding step, the sample was calcined at 700\u0026deg;C for 5 hours. Finally 65.2g of catalyst was obtained. The efficiency of process was 92.0%.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section3\"\u003e\u003ch2\u003e2.2.3. Methane pyrolysis process\u003c/h2\u003e\u003cp\u003eMethane pyrolysis (methane purity: 99.99%) was performed in a quartz reactor with a cylindrical shape of 1200mm in length, an inner diameter of 55mm and a wall thickness of 4mm. The tube was placed in a glass furnace model PRW 120x600/110MR with a power of 3.6kW (Czylok, Poland). The reactor was closed on two sides with sealed and cooled heads.(Fig.\u0026nbsp;1.) The process gases were directed through a multi-port valve either to the chromatograph for analysis or to the exhaust system. The flow rate of the reaction and process gas was set at 200Nmlmin\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for nitrogen and 200Nmlmin\u003csup\u003e\u0026minus;\u003c/sup\u003efor methane. The catalysts were placed in a loose form (about 2g) between two layers of rigid discs of heat-resistant quartz wool. The discs with the catalyst was inserted halfway up the reaction tube.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe process was conducted at three different temperatures. In each case, the reactor containing the catalyst was heated to 750\u0026deg;C, 850\u0026deg;C, or 950\u0026deg;C at a heating rate of 15\u0026deg;C min⁻\u0026sup1; under a nitrogen atmosphere with a flow rate of 200 mL min⁻\u0026sup1;. Upon reaching the target temperature, methane was introduced into the reactor at a flow rate of 200 mL min⁻\u0026sup1;. The process was carried out for 30 minutes, during which the post-process gas stream was directed to the chromatograph three times for analysis.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section3\"\u003e\u003ch2\u003e2.2.4. Gas chromatography\u003c/h2\u003e\u003cp\u003eThe gaseous products of the process were analyzed using an SRI model gas chromatograph equipped with a valve-loop sampler and two detectors: a thermal conductivity detector (TCD) and a helium ionization detector (HID). The chromatograph was operated under isothermal conditions at 180\u0026deg;C, with helium and nitrogen carrier gases flowing at 10 mL min⁻\u0026sup1;. Calibration of the system was performed using standard gas mixtures from Multax s.c. as well as individual gas standards. Response factors for the thermal conductivity detector (TCD) were determined for each gas component and subsequently used to quantify the composition of gas samples obtained from the methane pyrolysis process.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec9\" class=\"Section3\"\u003e\u003ch2\u003e2.2.5. Calculation of process parameters\u003c/h2\u003e\u003cp\u003eOn the basis of the obtained post-process gas compositions (mass percentages), it was possible to determine:methane conversion (1), efficiency of the methane pyrolysis (2) and selectivity of the methane pyrolysis (3) calculated according to formulas shown below.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Taba\" border=\"1\"\u003e\u003ccolgroup cols=\"2\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:Conversion,\\:\\%=\\frac{products\\:conc.}{substrate\\:conc.\\:}\\bullet\\:100\\%\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003e(1)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:Efficiency,\\:\\%=\\frac{hydrogen\\:conc.}{substrate\\:conc.}\\:\\bullet\\:100\\%\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e(2)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:Selectivity,\\:\\%=\\frac{Efficiency}{Conversion}\\:\\bullet\\:100\\%\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e(3)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section3\"\u003e\u003ch2\u003e2.2.6. \u003cem\u003eSEM\u003c/em\u003e\u003c/h2\u003e\u003cp\u003eImaging and mapping of the structures of the catalysts was performed by SEM. It was used a Supra 35 microscope (Zeiss, Oberkochen, Germany) at accelerating voltages in the range of 2 to 10 kV. The microscope was equipped with an EDS detector.\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e"},{"header":"3. RESULTS","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1. Catalyst Analysis\u003c/h2\u003e\n \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e\n \u003ch2\u003e3.1.1. SEM images\u003c/h2\u003e\n \u003cp\u003eThe following figures show SEM images of the supports and catalysts at various magnifications. Figures 2 and 3 present the alumina (Al₂O₃) support and the Co/Al₂O₃ catalyst, respectively, while Figs. 4 and 5 display the biochar support and the catalyst prepared using it, Co/biochar.\u003c/p\u003e\n \u003cp\u003eThe alumina support images (Fig.\u0026nbsp;2) reveal a relatively uniform and porous surface morphology characteristic of \u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e materials[\u003cspan class=\"CitationRef\"\u003e31\u003c/span\u003e]\u0026ndash;[\u003cspan class=\"CitationRef\"\u003e33\u003c/span\u003e]. The pores appear to be predominantly mesoporous with sizes in the nanometer to sub-micrometer range. The pore distribution is fairly homogeneous, which is advantageous for catalyst impregnation and active phase dispersion. The surface texture is rough and irregular, providing a high surface area for cobalt precursor adsorption during impregnation.\u003c/p\u003e\n \u003cp\u003eIn the images of the Co/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst (Fig. 3), several notable changes are observed compared to the pure alumina support. The catalyst images show the presence of dispersed cobalt oxide or cobalt species on the surface. The cobalt crystallites appear as small, roughly spherical or slightly agglomerated nanoparticles with sizes estimated in the range of tens of nanometers. The cobalt particles are fairly well dispersed without large aggregates, indicating effective impregnation and distribution on the alumina substrate. This dispersion is critical for catalytic activity, as smaller particles generally offer more accessible active sites.\u003c/p\u003e\n \u003cp\u003eThe biochar support (Fig.\u0026nbsp;4) exhibits a distinctly different morphology compared to alumina. The surface is highly irregular with a heterogeneous porous structure including macropores and mesopores. The pores on the biochar support seem larger and more irregularly shaped, consistent with the carbonaceous, amorphous nature of biochar. This morphology can potentially enhance mass transport within the catalyst due to larger pore channels, but the surface heterogeneity might affect the uniformity of cobalt dispersion.\u003c/p\u003e\n \u003cp\u003eIn the images of the Co/biochar catalyst (Fig.\u0026nbsp;5), cobalt species are present but appear as somewhat larger and less uniformly shaped crystallites compared to the Co/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst. The crystallites generally show a range of shapes from spherical to more irregular, indicating possible agglomeration or uneven dispersion on the biochar surface. The particle sizes are comparatively larger, which may reduce the total catalytic active surface area relative to the alumina-based catalyst.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e\n \u003ch2\u003e3.1.2. SEM \u0026ndash; Composition Analysis (EDS and mapping)\u003c/h2\u003e\n \u003cp\u003eFigure 6 presents the EDS analysis for the Co/Al₂O₃ catalyst sample.\u003c/p\u003e\n \u003cp\u003eEDS analysis (Fig.\u0026nbsp;6) of Co/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst revealed the following composition (weight, %): carbon 2.6%, oxygen 37.3%, aluminium 33.5%, and cobalt 26.9%\u003c/p\u003e\n \u003cp\u003eThis composition aligns well with expectations for cobalt impregnated on alumina support. The high Al content confirms the dominance of alumina as the support, while the significant presence of Co indicates effective cobalt impregnation. Oxygen is primarily associated with metal oxides present in the catalyst, including cobalt oxide.\u003c/p\u003e\n \u003cp\u003eElemental surface maps were generated to evaluate the distribution of elements in the Co/Al₂O₃ catalyst, with the results presented in the Fig. 7.\u003c/p\u003e\n \u003cp\u003eThe maps demonstrate a relatively uniform distribution of cobalt across the alumina surface, accompanied by even dispersion of aluminium.\u003c/p\u003e\n \u003cp\u003eUniform dispersion of cobalt on alumina suggests good distribution of active catalytic sites, which usually correlates with enhanced catalytic activity and durability. The data indicate a well-prepared and stable Co/Al₂O₃ catalyst system.\u003c/p\u003e\n \u003cp\u003eFigure 8 presents the EDS analysis for the Co/biochar catalyst sample.\u003c/p\u003e\n \u003cp\u003eEDS analysis (Fig.\u0026nbsp;8) of Co/biochar catalyst revealed the following composition (weight, %): carbon: 12.0%, oxygen: 31.0%, magnesium: 1.6%, phosphorus: 3.9%, sulfur: 1.0%, potassium: 0.7%, calcium: 5.1%, iron: 2.4%, silicon: 6.3%, aluminium: 1.9%, sodium: 0.5%, cobalt: 33.6%. The complex elemental composition reflects the heterogeneous nature of biochar derived from sewage sludge. The high cobalt content confirms the substantial loading of active metal. The presence of various elements such as P, S, K, Ca, Fe, and Si corresponds to mineral residues and impurities inherent to biochar. It is worth noting that carbon constitutes only 12% of the total catalyst mass, making it a kind of carbon-mineral composite material with a high content of silica and aluminosilicates.\u003c/p\u003e\n \u003cp\u003eElemental surface maps was performed for the Co/biochar catalyst (Fig. 9). However, the presentation of results is limited to the elemental maps of those elements found in the catalyst at the highest concentrations.\u003c/p\u003e\n \u003cp\u003eUnlike the Co/Al₂O₃ catalyst, cobalt on biochar exhibits less uniform dispersion, with cobalt-rich clusters visible in certain regions. Carbon and oxygen remain widespread due to the carbonaceous nature of the support, with noticeable zones enriched in Ca, Si, and Fe, indicative of the intrinsic mineral heterogeneity in biochar.\u003c/p\u003e\n \u003cp\u003eAlthough cobalt loading is higher in the Co/biochar catalyst, its uneven distribution and association with various mineral phases may influence catalytic behavior and active site accessibility. The mineral constituents may induce synergistic effects or impact catalytic stability but could also reduce the effective surface area of cobalt particles.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2.Testing the effectiveness of catalysts\u003c/h2\u003e\n \u003cp\u003eThe calculated values of conversion, efficiency and selectivity for processes involving the developed catalysts are presented in Table 3. Each result is an average of the three post-processes gas analyses.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eConversion, yield and selectivity values for the developed cobalt catalysts.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"2\" rowspan=\"2\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e750\u003csup\u003eo\u003c/sup\u003eC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e850\u003csup\u003eo\u003c/sup\u003eC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e950\u003csup\u003eo\u003c/sup\u003eC\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eResult, %\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eResult, %\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eResult, %\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" rowspan=\"3\"\u003e\n \u003cp\u003eCo/Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003econv., %\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e37.90\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e44.80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e76.80\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eeff., %\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e32.50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e40.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e69.40\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003esel., %\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e85.75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e89.51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e90.36\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" rowspan=\"3\"\u003e\n \u003cp\u003eCo/biochar\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003econv., %\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e38.70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e45.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e71.00\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eeff., %\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e33.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e41.50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e64.30\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003esel., %\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e85.53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e91.81\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e90.56\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eThe performance results for the developed cobalt catalysts\u0026mdash;Co/Al₂O₃ and Co/biochar\u0026mdash;are reported in terms of conversion, efficiency, and selectivity at three temperatures: 750\u0026deg;C, 850\u0026deg;C, and 950\u0026deg;C.\u003c/p\u003e\n \u003cp\u003eAll parameters\u0026mdash;conversion, efficiency, and selectivity\u0026mdash;increase with rising temperature for both catalysts. For the Co/Al₂O₃ catalyst, methane conversion rises from 37.9% at 750\u0026deg;C to 76.8% at 950\u0026deg;C, representing more than a twofold increase. Efficiency also improves substantially, from 32.5% to 69.4%, while selectivity increases moderately from 85.75% to 90.36%. Similarly, the Co/biochar catalyst shows an increase in conversion from 38.7% to 71.0% as the temperature rises, a 7.5% lower maximum conversion compared to Co/Al₂O₃ at 950\u0026deg;C. Efficiency follows this trend, increasing from 33.1% to 64.3%, which is around 7.3% lower at the highest temperature compared to Co/Al₂O₃. Selectivity for Co/biochar increases slightly more with temperature than for Co/Al₂O₃, rising from 85.53% to 90.56%, with a marginally higher selectivity (~\u0026thinsp;0.2%) at 950\u0026deg;C compared to Co/Al₂O₃.\u003c/p\u003e\n \u003cp\u003eOverall, Co/Al₂O₃ exhibits superior performance at higher temperatures, particularly for conversion and efficiency, however, both catalysts show very comparable selectivity above 850\u0026deg;C, with Co/biochar slightly outperforming Co/Al₂O₃ at the highest temperature tested. These results suggest that while Co/Al₂O₃ is more active overall, Co/biochar provides competitive selectivity and may offer advantages in other aspects such as cost or sustainability.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3. Catalyst Lifetime Study\u003c/h2\u003e\n \u003cp\u003eThe catalysts were subjected to a lifetime study. For this purpose, an experiment was conducted at a temperature of 850\u0026deg;C lasting 10 hours according to the methodology described in section \u003cspan class=\"InternalRef\"\u003e2.2.3\u003c/span\u003e. During the study, the composition of the post-process gases was analyzed every hour, and based on this, the process parameters\u0026mdash;conversion, yield, and selectivity\u0026mdash;were calculated for each measurement point according to the methodology described in section \u003cspan class=\"InternalRef\"\u003e2.2.5\u003c/span\u003e.\u003c/p\u003e\n \u003cp\u003eThe catalyst lifetime tests at 850\u0026deg;C over a 10-hour period demonstrated a rapid deactivation of the Co/Al₂O₃ catalyst, with conversion and yield decreasing by approximately 90% and selectivity dropping by about 13%. In contrast, the Co/biochar catalyst exhibited notably greater stability, as its conversion and yield decreased by approximately 62% and 71%, respectively, and selectivity by about 23% over the same period. Throughout the experiment, the Co/biochar catalyst consistently maintained higher conversion, yield, and selectivity values compared to Co/Al₂O₃, indicating that the biochar-supported system is more resistant to deactivation under harsh reaction conditions and is a promising support for high-temperature methane pyrolysis catalysts. The slower deactivation of the biochar-based catalyst may be attributed to its heterogeneous pore structure and the presence of large pores, which are more difficult to block by the carbon generated during the process. Additionally, the phenomenon of faster selectivity loss for Co/biochar observed in the later stages of the experiment requires further attention, as it indicates a possible increase in the activity of competing side reactions leading to the formation of unexpected products. This trend highlights the need for more detailed investigation into the mechanisms of catalyst deactivation and process optimization to ensure consistent selectivity under prolonged high-temperature operating conditions\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\n \u003ch2\u003e3.4. Climat impact\u003c/h2\u003e\n \u003cp\u003eReplacing the Al₂O₃ support with biochar derived from pyrolyzed sewage sludge offers a promising strategy for lowering the carbon intensity of catalyst production. The GHG emissions associated with biochar production are significantly lower than with commercial alumina due to the waste-derived nature of the feedstock and the relatively energy-efficient process conditions. To estimate the possible reduction in GHG emissions, the process of biochar production by pyrolysis was analyzed.\u003c/p\u003e\n \u003cp\u003eTable 4 presents a simplified mass and energy balance of the sewage sludge pyrolysis process that allows producing 1 Mg of biochar for catalyst production.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eSimplified mass and energy balance of sewage sludge pyrolysis process\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eInputs\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eBalance value\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDrying sludge, kg\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1700\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eElectricity, kWh\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e240\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eOutputs\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBiochar, kg\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1000\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePyrolytic oil, kg\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e275\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eWaste water, g\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e204\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePyrolytic gas, g\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e221\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eAccording to IPCC guidelines, the carbon in sewage sludge is considered biogenic; however, the emissions of such material must be estimated based on the fuel and energy consumption required to prepare the material for product formation.\u003c/p\u003e\n \u003cp\u003eThe the thermal drying process, and the pyrolysis process consume 40 kWh and 118 kWh [\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e]. Considering the electricity emission factor in Poland (0.593 kgCO\u003csub\u003e2\u003c/sub\u003eeq/kWh) [\u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e], the estimated GHG emission factor for dry (impregnation-ready) sewage sludge was about 0.21 kg CO\u003csub\u003e2\u003c/sub\u003eeq/kg.\u003c/p\u003e\n \u003cp\u003eIn the pyrolysis process, as described in section \u003cspan class=\"InternalRef\"\u003e2.2.1\u003c/span\u003e, besides biochar, a liquid fraction, waste water, and gas fraction are produced. For emission estimation, it was assumed that the organic liquid fraction would be treated as a product and allocated part of the pyrolysis process emissions (mass allocation factor, 0.2159). The gas fraction formed was treated as an energy source that can reduce the electrical energy demand of the process. According to[\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e], up to 124 kWh can be recovered from the combustion of pyrolytic gas.\u003c/p\u003e\n \u003cp\u003eTherefore, the total electricity demand was estimated at 244 kWh, consistent with the data [\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e]. The emission factor for wastewater was sourced from the European reference Life Cycle Database of the Joint Research Center, version 3.2.\u003c/p\u003e\n \u003cp\u003eBased on the above data, the estimated emission of the biochar production process from sewage sludge by pyrolysis was 1.18 kg CO\u003csub\u003e2\u003c/sub\u003eeq/kg. This represents a reduction of at least 50% compared to Al₂O₃ support, which has an emission of about 2.4 kg CO\u003csub\u003e2\u003c/sub\u003eeq/kg[\u003cspan class=\"CitationRef\"\u003e37\u003c/span\u003e].\u003c/p\u003e\n\u003c/div\u003e"},{"header":"CONCLUSION","content":"\u003cp\u003eThis study systematically explored the synthesis, characterization, performance, durability, and environmental impact of a novel cobalt catalyst supported on sewage sludge-derived biochar, compared directly with the conventional cobalt catalyst supported on alumina in the methane pyrolysis process for hydrogen generation. The research provides compelling evidence for the effectiveness and sustainability of using biochar as an alternative catalyst support, thereby contributing to cleaner hydrogen production and resource circularity.\u003c/p\u003e\u003cp\u003eThe Co/biochar catalyst exhibited hydrogen yields and methane conversions at all operational temperatures (750\u0026deg;C, 850\u0026deg;C, and 950\u0026deg;C) that were very close to those of the reference Co/Al₂O₃ catalyst, especially at 750\u0026deg;C and 850\u0026deg;C, with differences at the highest temperature being moderate (7\u0026ndash;8% lower). Selectivity for hydrogen production using Co/biochar was slightly higher at increased temperatures, surpassing alumina-supported cobalt at 850\u0026deg;C and 950\u0026deg;C, suggesting that the unique pore structure and chemical nature of biochar support favor targeted reaction pathways. Despite the somewhat larger and less uniform cobalt crystallites identified by SEM on the biochar surface in comparison to alumina, the catalyst remained highly active, demonstrating that support composition and macrostructure can compensate for differences in active phase dispersion.\u003c/p\u003e\u003cp\u003eA key outcome from the long-term performance (lifetime) tests was the substantially improved stability of Co/biochar under continuous operation at 850\u0026deg;C. Whereas Co/Al₂O₃ lost about 90% of its original activity and suffered a significant selectivity drop after 10 hours, Co/biochar retained higher conversion and selectivity, with its activity declining by only about 62%. The enhanced durability is linked to the heterogeneous and interconnected porosity of biochar, which appears less susceptible to rapid blockage by carbonaceous deposits generated during methane decomposition. This finding highlights that waste-based carbon supports can serve not only as a \u0026ldquo;greener\u0026rdquo; but also a technically robust, long-lived alternative to conventional oxide carriers in high-temperature catalytic reactions.\u003c/p\u003e\u003cp\u003eThe environmental assessment performed in this work further underscores the potential of this approach. Life cycle emission calculations reveal that the greenhouse gas footprint involved in producing 1 kg of sewage sludge-derived biochar is at least 50% lower than that of commercial alumina, even when accounting for the energy required to dry and pyrolyze the sludge. This difference is primarily due to the valorization of a problematic waste stream, energy recovery from the process gases, and reduced need for high-temperature oxide synthesis. Such attributes are especially relevant in the context of global decarbonization targets and circular economy ambitions, as they enable catalyst manufacturers and hydrogen producers to reduce both operational and embedded emissions simultaneously.\u003c/p\u003e\u003cp\u003eThe multifunctional nature of sewage sludge biochar\u0026mdash;which contains not only carbon but also minerals such as Si, Ca, Fe, and P provided by the parent material\u0026mdash;may also support further catalyst improvements through synergistic effects, though the current study notes some heterogeneity in cobalt dispersion as a potential area for optimization. In practice, this may offer pathways to tune surface chemistry, resistance to deactivation, or even achieve valorization of additional elements present in the waste feedstock.\u003c/p\u003e\u003cp\u003eThe results presented provide a strong foundation for industrial implementation of biochar-supported catalysts, particularly in scenarios where sustainability, waste management, and carbon intensity reductions are priorities. However, some limitations and opportunities for future research remain. These include efforts to:\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003eImprove the uniformity of cobalt distribution on complex carbon-mineral matrices through tailored impregnation or activation protocols.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eInvestigate in detail the deactivation mechanisms and product distributions observed during extended operation, especially to control selectivity loss at late stages.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eAssess long-term operational stability in larger-scale or continuous-flow systems with various real-waste-derived biochars.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eFurther integrate life cycle assessment and techno-economic studies to support decision making for scale-up and commercialization.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cp\u003eIn summary, the use of sewage sludge-derived biochar as a support for cobalt catalysts in methane pyrolysis represents an innovative technological advance with clear technical, economic, and environmental merits. By transforming a problematic municipal waste into a valuable, high-performance catalyst support, this approach helps close resource loops while lowering both catalyst costs and the carbon footprint of large-scale hydrogen generation. With additional research and scale-up, biochar-supported catalysts could accelerate progress toward low-emission, circular hydrogen production, and set a precedent for other waste-driven catalyst systems in the chemical process industries.\u003c/p\u003e\u003cp\u003eThis work was supported by funding by the Republic of Poland Ministry of Education and Science; Project INiG-PIB no. 0059/2024.\u003c/p\u003e\u003cp\u003eThis research was funded in in part by National Science Centre, Poland, Grant number: 2025/09/X/ST5/00196. For the purpose of Open Access, the author has applied a CC-BY public copyright licence to any Author. Accepted Manuscript (AAM) version arising from this submission\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eM.W. conceived and designed the research, carried out the experiments, analyzed the results, and wrote the manuscript. G.Ż. contributed to the analysis of results and the preparation of the figures. R.C.-S. participated in writing the manuscript. All authors reviewed the manuscript.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe datasets used and/or analysed during the current study available from the corresponding author on reasonable request\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAhn, S. Y. et al. From gray to blue hydrogen: Trends and forecasts of catalysts and sorbents for unit process. \u003cem\u003eRenew. Sustain. 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Prod.\u003c/em\u003e \u003cb\u003e366\u003c/b\u003e \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.jclepro.2022.132807\u003c/span\u003e\u003cspan address=\"10.1016/j.jclepro.2022.132807\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2022).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"methane pyrolysis, biochar, sewage sludge, cobalt catalyst, hydrogen production, catalyst support, sustainable catalyst, catalyst stability, pyrolysis, greenhouse gas emissions","lastPublishedDoi":"10.21203/rs.3.rs-7597996/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7597996/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study investigates the use of biochar derived from pyrolyzed sewage sludge as a sustainable catalyst support for cobalt in the methane pyrolysis process aimed at clean hydrogen production. Biochar was obtained through fast pyrolysis of sewage sludge at 650\u0026deg;C and characterized for its morphological and textural properties. Catalysts with cobalt supported on biochar were synthesized and compared to conventional cobalt catalysts supported on alumina (Al₂O₃). The catalytic performance was evaluated based on methane conversion, hydrogen production efficiency, and selectivity at temperatures of 750\u0026deg;C, 850\u0026deg;C, and 950\u0026deg;C. Results demonstrate that while Co/Al₂O₃ catalysts exhibit higher maximum conversion and efficiency, Co/biochar catalysts show comparable or slightly better selectivity and significantly improved stability during prolonged operation at 850\u0026deg;C. The biochar-supported catalyst exhibited slower deactivation, attributed to the heterogeneous porous structure mitigating carbon deposition effects. Furthermore, the biochar production process has at least 50% lower greenhouse gas emissions compared to alumina, offering a promising environmental benefit. This research highlights the potential of sewage sludge-derived biochar as a cost-effective, sustainable alternative catalyst support for methane pyrolysis hydrogen production.\u003c/p\u003e","manuscriptTitle":"A Novel Sustainable Cobalt Catalyst for the Methane Pyrolysis Process","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-26 11:54:11","doi":"10.21203/rs.3.rs-7597996/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"e4ed5a95-93b1-423a-8903-ecfe3a770b0f","owner":[],"postedDate":"September 26th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":55286573,"name":"Physical sciences/Chemistry"},{"id":55286574,"name":"Physical sciences/Energy science and technology"},{"id":55286575,"name":"Physical sciences/Engineering"},{"id":55286576,"name":"Earth and environmental sciences/Environmental sciences"},{"id":55286577,"name":"Physical sciences/Materials science"}],"tags":[],"updatedAt":"2026-02-25T10:12:21+00:00","versionOfRecord":[],"versionCreatedAt":"2025-09-26 11:54:11","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7597996","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7597996","identity":"rs-7597996","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}