Tuning of perovskite composition for NO oxidation
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Nitric acid (HNO3) is an important building block in the chemical industry, and special for production of fertilizers. It is manufactured by the Ostwald process, where oxidizing NO to NO2 is one of the three chemical steps. The reaction is carried out as a homogeneous gas phase reaction. Introducing a catalyst for this reaction can lower the capital investment and increase the heat recovery from the reaction. The aim of this project was to investigate a non-noble metal based catalyst for oxidation of NO at industrial conditions. Lanthanum based perovskites have shown promising catalytic oxidation activity at low concentration of NO, conditions similar to diesel engine exhaust. Thus, lanthanum based perovskites with manganese, nickel and cobalt (LaMnO3, LaNiO3 and LaCoO3), were synthesized and tested at conditions similar to the industrial conditions. LaCoO3 had the highest activity of these with a conversion level of 34% at 405°C, and further tuning of LaCoO3 with substituting the A- and B-site in the structure to increase the catalytic activity was carried out. The A-site was substituted with both barium and cerium. The B-site was substituted with manganese and nickel. The perovskites were prepared by the sol-gel method and characterized by BET, XRD and H2-TPR. All samples had low surface area, between 6-15m2/g. The formation of perovskites was confirmed by the XRD. The XRD revealed small amounts of secondary phases formed for the A-site substituted perovskites, which were confirmed by H2-TPR. Activity tests under conditions close to industrial conditions were performed. The feed composition was 10% NO, 6% O2 and argon in balance. The best perovskites at 300°C were LaCo1.05O3, LaCe0.1O3 and LaCoNi0.25O3, with conversion level of 20.3% 19.7% and 19.3% respectively. Initial work on the effect of NO and O2 variations and the effect of water in the feed was done. The conversion over La0.9Ce0.1O3 decreased from 13.6% to 10.1% for La0.9Ce0.1O3, but it was reversible, in water compared to without water. The result showed that perovskites are promising catalysts for NO oxidation at industrial conditions.