Effect of Surface Acidic and Basic Properties of the Supported Nickel Catalysts on the Hydrogenation of Pyridine to Piperidine

Ni/Al2O3, Ni/MgAlO, and Ni/MgO catalysts were studied for the hydrogenation of pyridine to piperidine. Microcalorimetric adsorption and infrared spectroscopy were used to study the adsorption of CO, H2, pyridine, and piperidine on the catalysts. It was found that the basic support (MgO) increased the heat of adsorption of CO on Ni, due to the increased surface electron density of Ni, while weakened the strength of H–Ni, which might be a reason for the decreased activity of Ni/MgO for the hydrogenation of pyridine. In contrast, the acidic support (Al2O3) caused the electron-deficient surface metallic Ni that enhanced the adsorption of H2 and pyridine and thus favored the hydrogenation of pyridine. In addition, it was found that pyridine was more strongly adsorbed on Ni than piperidine although piperidine is a stronger base than pyridine, indicating that the electron-enriched aromatic ring of pyridine might be involved in the adsorption of pyridine on Ni, which was favored on the electron-deficient surface Ni and acidic support.