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The promoting effects of SO42− on N2 selectivity for selective catalytic oxidation (SCO) of ammonia to nitrogen over RuO2/ZrO2 catalyst were systematically investigated. The catalysts were measured by different characterization methods (BET, XRD, TEM, NH3–TPD and in situ DRIFTS). The results showed that the introduction of SO42− into RuO2/ZrO2 presented obvious effects on the structure, surface acidity and N2 selectivity of RuO2/ZrO2. The introduction of SO42− obviously increased the amount of surface acid sites, which could promote the adsorption of ammonia species and prevent the excessive oxidation of ammonia to NOx, improving the N2 selectivity dramatically. The DRIFTS results confirmed that the SCO of ammonia over RuO2/ZrO2–SO42− followed the in situ selective catalytic reduction of NOx (i-SCR) mechanism, involving NH3 oxidation to NO species and –NH2 reacted with NO to form the main product N2. The presence of SO42− not only increased the surface acid sites of the catalyst, but also inhibited the production of nitrate species, which was beneficial to improve the N2 selectivity. [ABSTRACT FROM AUTHOR]

The catalyzed hydrolysis of HCN has become one of the most promising methods for the purification of HCN emissions. Three types of reaction mechanisms (named path A, B and C) for HCN hydrolysis were considered, and a total of 51 geometries including 20 transition states were optimized using ab initio MP2 methods with the 6-31++G(d,p) basis set. They share the first step of water attack for path A and B. In the following process, the proton of oxygen atom shifts to the nitrogen atom first for path A, while in path B, the proton of carbon atom shifts first. The path C contains the structural tautomer interconversion from HCN to HNC, and it turns out to be the most favorable pathway. Additionally, the water-assisted hydrolysis reaction mechanisms were examined for the three types of reaction processes. The inclusion of the auxiliary water decreases most of the Gibbs free energy barriers, and the formamide is the most stable intermediate on the free energy surface. The Gibbs free energy barrier of w-path A (50.39 kcal/mol) becomes the lowest. It is found that the process with the transfer of H atom from the C atom to the N atom is the rate-controlling step, and the efficient catalyst should activate C–N bond and assist the proton transfer. This information may help in designing new catalysts for this important reaction. [ABSTRACT FROM AUTHOR]