Experimental study of Cu-ZnO-ZrO₂/hydrotalcite catalyst for sorption-enhancing hydrogenation of CO₂ to methanol

CO2 utilization is increasingly seen as a potential mitigating component of CO2 emission control, in addition to carbon capture and storage (CCS). However, methanol synthesis via CO2 hydrogenation remains a challenge industrially due to the restricted CO2 conversion and methanol selectivity. Among traditional modifications, the sorption-enhancing strategy attracts our special interests as a consequence of its remarkable promotion by breaking the original equilibrium in reaction systems. Herein, Cu-ZnOZrO2 (CZZ), prepared by the co-precipitation method, and commercial hydrotalcite (HTC) were physically mixed varying the CZZ/HTC ratios to explore their interactions and thus impacts on catalysis performance, which were conducted on the micro-reactor apparatus equipped with a GC. Crystals of single CZZ and HT were confirmed by characteristic peaks in the XRD spectrum, and the CZZ/HTs simply show as overlays of single CZZ and HT. The BET surface areas of CZZ and activated HTC are 35.8 and 175.6 m²/g, respectively. The CZZ and HT still remain separate at the nanoscale after mixing. In a typical reaction, the CO2 conversion scores the similar level as single component Cu-ZnO-ZrO2 catalyst, yet the methanol selectivity is 50 % higher, reaching over 90 % at 523 K and 30 bars. The reason results from synergies between CZZ and HT. The former provides active sites for CO2 hydrogenation, while the later provides sites for CO2 and H2O adsorption. Accordingly, CO2 molecules are easily caught and react on copper sites and produced H2O molecules are then quickly removed from the copper surface. The present work provides an efficient and simple method to elevate catalytic performance of traditional copper-based catalysts by introducing hydrotalcites, promoting the catalytic properties in aspects of methanol selectivity. Since the as-obtained catalyst can also be easily fine-tuned by changing the CZZ:HTC ratio, it exhibits promising applications in methanol synthesis by CO2 hydrogenation.