Microcalorimetric adsorption and infrared spectroscopic studies of KNi/MgAlO catalysts for the hydrogenation of acetonitrile

摘要

Ni/MgAlO and K_2CO_3Ni/MgAlO catalysts for the hydrogenation of acetonitrile to primary amine were studied. Microcalorimetric measurements and infrared spectroscopy were used to study the adsorption of CO, H_2, acetonitrile, and ethylamine onto the catalysts. It was found that the addition of K_2CO_3 led to an increase in the heat of adsorption of CO on Ni, due to increased surface electron density of Ni. The presence of K_2CO_3 weakened the strength of HNi and strengthened the bonding of CH_3CN onto Ni by changing adsorptive states of CH_3CN, which might be two main reasons for the decreased activity of Ni doped with K_2CO_3. Furthermore, the addition of K_2CO_3 decreased adsorptive strength of ethylamine on Ni, resulting in an increase in ethylamine selectivity. Finally, infrared spectra of CH_3CN adsorbed onto the Ni surface with preadsorbed hydrogen indicated that the hydrogenation might occur preferentially on carbon atoms in C=N, leading to the formation of surface species Ni-N=CH-CH_3 and Ni=N-CH_2CH_3.