Influence of nickel content on structural and surface properties, reducibility and catalytic behavior of mesoporous γ-alumina-supported Ni–Mg oxides for pre-reforming of liquefied petroleum gas

Abstract

Mesoporous γ-alumina-supported Ni–Mg oxides (xNiO–MgO/γ-MA) with various mass percentage contents of nickel (x = 0, 5, 10, 15, 18 and 21) were prepared through one-pot hydrolysis of metal nitrate salts without surfactants. The influences of nickel content on the catalyst structure, surface properties, interaction between Ni species and the support, reducibility of Ni²⁺ ions and Ni particle dispersion were investigated in detail using XRD, N₂ sorption, TEM, XPS, CO₂-TPD, H₂-TPR, hydrogen chemisorption and TG techniques. The xNiO–MgO/γ-MA materials showed wormhole-like mesoporous structures with large surface areas and narrow pore size distributions. The dominant NiO species were homogeneously dispersed and had an attenuated interaction with the support with the increase in Ni content, producing uniform Ni nanoparticles throughout γ-alumina frameworks after H₂ reduction. The Ni particle sizes decreased with increasing Ni content and showed a minimum at 18 wt%, likely due to Ni crystallite growth by Ostwald ripening rather than by migration of Ni nanoparticles. The reduced xNi–MgO/γ-MA catalysts were investigated for their catalytic behaviors in pre-reforming of liquefied petroleum gas. The results demonstrated that the Ni surface areas were mainly responsible for their catalytic activities; smaller Ni nanoparticles promoted steam reforming of hydrocarbons, methanation of carbon oxides and water gas shift reaction, but inhibited hydrocracking of hydrocarbons and lowered the rate of coke deposition, improving the catalytic activity and stability.