(514c) Catalytic Conversion of CO2 over Cu and Ni Metals Supported on CeO2 and La2O3 Via Reverse Water Gas Shift Reaction

Increasing levels of carbon dioxide in the atmosphere have contributed to global warming, triggering a lot of interest in capturing and utilizing carbon dioxide. While CO₂ is generally regarded as an inert molecule, several processes can be employed to activate it and turn it into useful compounds and fuels. Among the most promising methods for utilizing CO₂ is the reverse water-gas shift (RWGS) reaction, which occurs when CO₂ and H₂ combine to form CO and H₂O and upon mixing with H₂ as syngas, the mixture can be fed into another unit like the Fischer-Tropsch process to produce fuels and other value-added chemicals. Although RWGS is thermodynamically favourable at high temperatures, it saves energy and reduces capital and operating costs at low temperatures, so it is preferable to be performed at low temperatures, even though it competes with the highly exothermic CO₂ methanation reaction in this case; thus, developing selective catalysts for the RWGS reaction that can lead to cost-effective hydrogenation of CO₂ is still challenging. It has been proved that transition metal catalysts, such as Cu and Ni, are effective catalysts for both WGS and RWGS. The present study investigates the role of reducible ceria and lanthanum supports deposited with 1 wt.% Cu, 1 wt.% Ni, and 1 wt.% CuNi (Cu=0.5%, Ni=0.5%) active metals prepared via the solution combustion synthesis method (SCS) to evaluate the performance of these supports during the RWGS reaction at temperatures ranging from 100 to 600°C. The results showed that increasing the temperature improved CO₂ conversion in all cases, with a maximum CO₂ conversion of 70% at 600°C for 1wt.%Cu-CeO₂ catalyst, 100% selectivity toward CO, and stable performance for 1200 min time on stream (TOS) with a negligible amount of carbon deposition (less than 0.05%). The perfect synergistic interaction among the active species via Ce³⁺-oxygen vacancy-Cu⁰ may be the cause of the high catalytic activity. The highest overall CO₂ conversion rates for lanthanum-supported catalysts were 57%, 68%, and 74% for Cu-La₂O₃, CuNi-La₂O₃, and Ni-La₂O₃, respectively, at 600°C with high stability over a 1440-minute TOS and carbon depositions of less than 3wt.% for all the samples. Nonetheless, only the 1 wt.% Cu-La₂O₃ catalyst displayed a 100% CO selectivity at all investigated temperatures. For both fresh and used catalysts, several studies including XRD, TEM, SEM-EDX, and TPR were carried out in order to understand the morphological characteristics of the catalysts as well as the impact of the reaction on the surfaces of the catalysts. The findings may open up new possibilities for the support role of reducible oxides in RWGS and other hydrogenation processes.

Fig. 1: Catalytic performance in RWGS reaction (a) activity, (b) selectivity