The hydrogenation of CO₂ to methanol is an interesting approach to decreasing the emissions of this gas. In this research, catalysts of Cu and Zn nanoparticles supported on composites of activated carbon (AC) or carbon nanotubes (CNT) and Al₂O₃ were developed, characterized and assessed in catalytic experiments. The results indicate this is a promising strategy to further improve catalyst's efficiency.

Abstract

The increase in CO₂ emissions contributes massively to the aggravation of climate change. The hydrogenation of CO₂ to methanol is a possible approach for reducing this gas emissions by converting emitted CO₂ into a value-added product. Therefore, the development of efficient catalysts for this reaction is fundamental. In this study, CuZn bimetallic catalysts supported on composites of AC-Al₂O₃ and CNT-Al₂O₃ were synthesized, and their catalytic performance was assessed. The catalytic experiments were conducted at 250 °C and 30 bar for 15 h, under a H₂:CO₂ ratio of 3. The catalysts CuZn/AC-Al₂O₃ (50:50) and CuZn/AC-Al₂O₃ (70:30) demonstrated an overall improved catalytic performance when compared to the catalyst supported on pristine AC, indicating that the increased presence of mesopores and the synergistic effect between AC and Al₂O₃ are beneficial. The catalyst CuZn/CNT-Al₂O₃ (90:10) performed similarly to the catalyst supported on pristine CNT. CuZn/CNT-Al₂O₃ (50:50) and CuZn/CNT-Al₂O₃ (70:30) displayed reduced CO₂ conversion but enhanced methanol selectivity compared to the reference catalyst, CuZn/Al₂O₃, suggesting that the presence of CNT is advantageous for methanol selectivity. The catalyst CuZn/CNT presented the highest methanol yield, and was stable for over 80 h on a TOS experiment.