CO2 methanation over Ni supported on Carbon-ZrO2: An optimization of the composite composition

Currently, the most common catalysts for CO2 methanation reaction are based on Ni supported on metal oxides. However, such catalysts require high operation temperatures and present stability issues, which have been tackled by the use of expensive metal oxides such as CeO2 or ZrO2. In this study, the decrease in the amount of ZrO2 in ZrO2-based catalysts was addressed through the prepa-ration of composites of ZrO2 and carbon materials (activated carbon (AC) and carbon nanotubes (CNTs)). The optimization of the carbon:ZrO2 ratio demonstrated an optimal value of 50:50 in the case of AC:ZrO2, and 70:30 for CNT:ZrO2. With this composite composition, the possibility of enhancing the performance of the catalyst by functionalizing the carbon material was evaluated, and it was demonstrated that reduced AC (AC-R) with increased Lewis basic sites showed the best performance for AC-based composites, achieving a CO2 conversion of 79 % and CH4 selectivity of 98.9 % at 400 degrees C, whereas the catalysts supported on the pristine CNT:ZrO2 com-posite presented the highest CO2 conversion of 82.1 % and CH4 selectivity of 99.3 % at 400 degrees C. Notably, promotion with Fe was studied in the best performing support (CNT:ZrO2 (70:30) and it was shown that it enabled an improvement in terms of CO2 conversion and optimal temperature, achieving a CO2 conversion of 85 % and CH4 selectivity of 99.5 % at a lower temperature of 370 degrees C. This catalyst demonstrated to be highly stable for 70 h of time on stream with no apparent modifications on its chemical composition or microstructure. This work demonstrates that combining the properties of carbon materials and ZrO2 can be an interesting approach to obtain high performing catalysts for CO2 methanation.