Effects of Promoter's Composition on the Physicochemical Properties of Cu/ZnO/Al2O3-ZrO2 Catalyst

Cu/ZnO catalysts were synthesized via an impregnation method on an Al2O3-ZrO2 support and modified by the addition of manganese and niobium as promoters. The effect of the selected promoters on the physicochemical properties and performance toward the hydrogenation of CO2 to methanol are presented in this paper. The Mn and Nb promoters improved the reducibility of the catalyst as evidenced by the shifting of the H-2-TPR peaks from 315 degrees C for the un-promoted catalyst to 284 degrees C for the Mn- and Nb-promoted catalyst. The catalytic performance in a CO2 hydrogenation reaction was evaluated in a fixed-bed reactor system at 22.5 bar and 250 degrees C for 5 h. Amongst the catalysts investigated, the catalyst with equal ratio of Mn and Nb promoters exhibited the smallest particle size of 6.7 nm and highest amount of medium-strength basic sites (87 mu mol/g), which resulted in the highest CO2 conversion (15.9%) and methanol selectivity (68.8%).