EFFECT OF PROMOTERS ON THE PROPERTIES OF Co/Ƴ-Al2O3 CATALYSTS PREPARED BY SOLID-STATE REACTION FOR CO2 HYDROGENATION

Abstract

The addition of different promoters (K, Mn, Cu, or Ce) over Co/Ƴ-Al2O3 catalysts was investigated. The catalysts were prepared by solid-state reaction and incipient wetness impregnation (IWI) method. The catalysts were characterized by various methods such as XRD, XPS, BET, ICP, TPR, SEM, and H2-chemisorption. Their catalytic performances were evaluated in the CO2 hydrogenation at atmospheric pressure and 270 °C in a fixed-bed reactor. The results show that under the reaction conditions, the addition of promoters increased the CO2 conversion in the order: 1KCo > 1MnCo > 1CeCo > Co > 1CuCo for 1 wt.% promoters loading. All the promoted catalysts exhibited 100% CH4 selectivity. The addition of promoters over Co/Ƴ-Al2O3 bring about the higher catalyst surface area and pore volume leading to higher Co dispersion and higher reducibility of Co3O4 crystallites. A series of Co/Ƴ-Al2O3 catalysts were also prepared with various amounts of K and Mn loading ranging from 0.5 to 2.0 wt.% by solid-state reaction and incipient wetness impregnation method. Conclusively, the addition of 1 wt.% of K and Mn was found to be appropriate for the CO2 hydrogenation. Excessive amount of promoter at 2 wt.% led to lower amount of the active metal and as a consequence the CH4 formation which was the desired product was decreased.