Catalytic activity of rare earth and alkali metal promoted (Ce, La, Mg, K) Ni/Al2O3 nanocatalysts in reverse water gas shift reaction

Abstract

Nanocrystalline Ni/Al2O3 catalysts and promoted Ni-M/Al2O3 (M = Ce, La, Mg, K) catalysts were employed a in reverse water gas shift reaction. Among the prepared nickel catalysts 5% Ni/Al2O3 catalyst showed high CO2 conversion and CO selectivity. To improve the CO2 conversion and CO selectivity of 5% Ni/Al2O3, 1 or 2 wt% Ce, La, Mg or K were used. One percent La and 2% K showed highest CO2 conversion and CO selectivity. The high activity and CO selectivity of promoted catalysts can be accredited to the increase of Ni dispersion (or smaller Ni particles), concentration of surface active sites and CO2 adsorption by basic nature of promoters. The prepared samples were characterized by X-ray diffraction, inductively coupled plasma emission spectroscopy, N2 adsorption–desorption (BET), temperature programmed reduction (TPR), scanning electron microscopy and transmission electron microscopy (TEM) techniques. The BET surface area of prepared γ-alumina support was 126.81 m2 g−1, impregnation of the support with Ni and promotion of 5 wt% Ni with K and La reduced the specific surface area. The support and catalysts possessed mesoporous structure. The TPR-H2 analysis revealed higher Ni dispersion and reducibility for promoted nickel catalysts; 5Ni–2K showed highest reducibility. TEM images of 5Ni and 5Ni–2K showed increase of Ni dispersion and decrease of Ni particle size for the promoted catalyst. After 50 h on stream at 600 °C, 5Ni–1La and 5Ni–2K performed great catalytic stability.