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

Ni/MgAlO and K2CO3Ni/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, H2, acetonitrile, and ethylamine onto the catalysts. It was found that the addition of K2CO3 led to an increase in the heat of adsorption of CO on Ni, due to increased surface electron density of Ni. The presence of K2CO3 weakened the strength of HNi and strengthened the bonding of CH3CN onto Ni by changing adsorptive states of CH3CN, which might be two main reasons for the decreased activity of Ni doped with K2CO3. Furthermore, the addition of K2CO3 decreased adsorptive strength of ethylamine on Ni, resulting in an increase in ethylamine selectivity. Finally, infrared spectra of CH3CN adsorbed onto the Ni surface with preadsorbed hydrogen indicated that the hydrogenation might occur preferentially on carbon atoms in CN, leading to the formation of surface species NiNCHCH3 and NiNCH2CH3.

The addition of K2CO3 significantly increased the heat of adsorption of CH3CN onto Ni and changed the adsorption structures from that involving the π bond in CN to di-σ bonded CH3CN. The strong adsorption of CH3CN might be an important factor in the decreased activity of Ni doped with K2CO3 for the hydrogenation of acetonitrile to ethylamine.Figure optionsDownload high-quality image (101 K)Download as PowerPoint slideHighlights
► Addition of K2CO3 increased electron density on Ni and strengthened CO adsorption.
► Addition of K2CO3 weakened H2 adsorption on Ni and decreased hydrogenation activity.
► Addition of K2CO3 weakened adsorption of ethylamine and increased its selectivity.
► Addition of K2CO3 changed adsorption structures of CH3CN on Ni.
► Addition of K2CO3 strengthened adsorption of CH3CN and decreased catalytic activity.