Modulation of supported Ni catalysts with phosphorus for the hydrogenation of diethyl oxalate to ethyl glycolate

Abstract

In this study, 13-Ni/ZrO₂, 13-Ni₃P/ZrO₂, 13-Ni/SiO₂, and 13-Ni₃P/SiO₂ catalysts were used in the hydrogenation of diethyl oxalate (DEO) to ethyl glycolate (Egly) to investigate the modulating effect of phosphorus. XRD, TEM, and FT-IR spectroscopy results indicated that phosphorus acts as a distributor of Ni metallic particles and thereby shows a segregation effect. The presence of P transformed the linkage of surface metals from an original Ni–Ni–Ni–Ni– to a P–Ni–P–Ni–P state, and FT-IR spectra showed that the former adsorbed CO in a combination of linear and bridging adsorption modes, whereas the latter predominantly in CO linear adsorption. Bridging adsorption occurs via dual sites and makes preliminary hydrogenation products less likely to detach from the catalyst surface, thus facilitating deep hydrogenation, while linear adsorption facilitates partial hydrogenation via rapid detachment of intermediate products such as Egly. Different loadings of Ni₃P/SiO₂ catalysts show incomplete phosphorylation with an increase in nickel loading, giving rise to a state of coexistence of Ni and Ni₃P crystalline phases. This may lead to a coexistence of surface Ni–Ni–Ni–Ni and P–Ni–P–Ni–P and an increase in the corresponding bridging adsorption/linear adsorption ratios, making deep hydrogenation occur partially besides stepwise hydrogenation.