Sara Faiz Hanna Tasfy

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 H₂-TPR peaks from 315 °C for the un-promoted catalyst to 284 °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 °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 µmol/g), which resulted in the highest CO₂ conversion (15.9%) and methanol selectivity (68.8%).

Promoted Cu/ZnO catalyst was synthesized on Al₂O₃-ZrO₂ support. Effects of calcination conditions on the catalytic performance in a CO₂ hydrogenation reaction were studied systematically using the response surface methodology (RSM). The application of RSM with rotatable central composite design (RCCD) for optimization on the influence of catalyst’s calcination variables on the CO₂ conversion and methanol selectivity is presented. The calcination variables studied include temperature, A (181–518 °C), ramping rate, B (1–30 °C/min), and duration, C (1–7 h). From the RSM-generated model, the optimum calcination condition for this catalyst was 350 °C with 17.5 °C/min ramping rate for a 4 h duration. At the optimum calcination condition, the catalyst exhibited a Brunauer–Emmett–Teller (BET) surface area of 147 m²/g, a pore volume of 0.31 cm³/g, and a pore diameter of 8.1 nm.