Abstract
PdZn-based catalysts have evolved as a very effective catalytic material for CO2 hydrogenation to methanol. ZrO2-supported PdZn and Ca-PdZn catalysts, synthesized by the simple impregnation method, exhibited excellent catalytic activity with impressive selectivity to methanol when tested for direct CO2 hydrogenation reaction. These catalysts were able to achieve up to 97-100 % methanol selectivity with significant CO2 conversion (single-pass of more than 10% in the case of Ca-doped PdZn/ZrO2) under reaction conditions of 20-30 bar, 2400 mL/g-h, H-2/CO2 = 3:1, 220-270 degrees C. Addition of calcium to PdZn/ZrO2 catalyst had a positive impact on overall catalytic performance and catalyst lifetime. Ca-doped PdZn/ZrO2 catalyst also showed high stability for at least 100 h (on stream) implying the catalyst was very stable and resistant to sintering. The catalysts were characterized using BET, CO-chemisorption, CO2-TPD, XRD, XPS, SEM-EDS and TPR. Whereas, in-situ DRIFT study identified surface reaction transient intermediates, formates and methoxy species, and therefore, a reaction mechanism of formate pathway is proposed based on the DRIFT analysis.