Catalytic oxidation of NO to NO2 for industrial nitric acid production using Ag-promoted MnO2/ZrO2 catalysts

Abstract

The Ostwald process is the most common industrial process to produce nitric acid (HNO₃). It involves three main steps; ammonia oxidation in air over Pt–Rh gauze catalysts to produce nitric oxide, homogeneous gas-phase conversion of NO to NO₂, and subsequent absorption of the NO₂ by water to produce nitric acid. Turning the homogeneous gas-phase NO oxidation reaction catalytic may lead to a significant reduction in footprint and capital expenditure. However, no industrial catalyst yet exists for this process. In this work, we focus on catalytic oxidation of NO to NO₂ using silver-promoted manganese on zirconia catalysts at industrially relevant conditions (10% NO, 6% O₂ and 15% H₂O). Silver was found to promote the low-temperature activity of manganese catalysts in both dry and wet conditions compared to unpromoted manganese. The results demonstrate that manganese catalysts are able to work at low temperatures and concentrations relevant to industrial catalytic oxidation of NO.