Effect of thermal pretreatment and reduction on acidity and metal state in doped NiH and CuH mordenites

Thermal pretreatment such as calcination and steaming as well as the reduction of cations by hydrogen, affect the zeolitic acidity and activity of nickel- and copper-doped mordenites in heterogeneously catalyzed reactions such as the conversion of n-hexane. Data on acidity changes were obtained by IR spectroscopy, and information on ionic and metallic states by temperature-programmed reduction, CO chemisorption and transmission electron microscopy (TEM). The findings were compared with reaction results from conversion of n-hexane. Trimethylamine (TMA) was selected as a standardization molecule for semi-quantitative determination of acidity. Correlation of relative acidity values with experimental results was possible only to a very limited extent. Results of CO chemisorption, TPR and TEM allow conclusions to be drawn on metallic crystallites, Ni+ and Cu+ ions and clusters, which appear to exert a stabilizing influence on zeolitic activity. Nickel crystallites with d > 2 nm catalyze both hydrogenation and dehydrogenation of paraffins on the metal in bifunctional catalysis, as was also observed on platinum-doped zeolites.