Comparison of Ceria-Supported Catalysts for Attaining NO - NO2 Equilibrium at Industrial Nitric Acid Plant Conditions

Nitric acid is a key component in the production of nitrate fertilisers and is industrially produced using the Ostwald process. The Ostwald process can be further intensified by oxidising nitric oxide to nitrogen dioxide using heterogeneous catalysts. We have explored various monometallic and bimetallic catalysts for NO to NO2 oxidation and found ruthenium supported on ceria, containing 10 wt.% manganese to be a promising catalyst for oxidising NO to NO2 at low temperatures at industrially relevant conditions. For a feed comprising 10% NO, 6% O2, 15% H2O and rest Ar, and 8% NO, 2% NO2 5% O2, 15% H2O and rest Ar, the ruthenium-manganese catalysts attained NO-NO2 equilibrium below 400∘C. For the 5wt.% ruthenium and 10 wt.% manganese on ceria catalyst, an apparent activation energy of 39.4 kJ/mol and 85.4 kJ/mol were observed in the absence and presence of NO2, respectively. These findings demonstrate the potential of supported bimetallic ruthenium-manganese catalysts for efficient oxidation of NO to NO2 at low temperatures which can lead to significant process intensification of nitric acid plants.