The effect of the precursor structure on the catalytic properties of the nickel—chromium catalysts of hydrogenation reactions

Abstract

The influence of the Ni2+/Cr3+ ratio in the precursor compound on the formation of the catalyst structure and its transformation upon the thermal treatment and reductive activation in hydrogen was studied. The precursors with the cation ratio Ni2+/Cr3+ = (2.3–3)/1 represent a homogeneous system of the stichtite-type structure. The treatment of the precursors at T ∼400 °C in an inert atmosphere forms a nanosized phase of the NiO-type structure with the lattice parameter a = 4.186±0.005 A. At 600 °C the lattice parameter of this phase decreases to the tabulated value (a = 4.177±0.005 A). The phase of nickel chromite of the cubic spinel structure with the lattice parameter a = 8.320±0.005 A is also observed. Hydrogen activation of the catalyst preheated at 300 °C in an inert gas leads to the formation of Ni0 crystallites with a size of ∼5.5 nm and a specific surface area of ∼7.0 m2 g−1. This catalyst exhibits high activity and selectivity in benzene hydrogenation and preferential CO hydrogenation in the presence of CO2. The catalysts with the ratio Ni2+/Cr3+ = 1/(2−3) containing nickel and chromium hydroxocarbonates as precursors are less active in the hydrogenation of benzene to cyclohexane.