Gallium-Mediated Switch in Product Selectivity for Co2 Hydrogenation Over Ni/Ceo2 Catalysts

Abstract

Achieving high activities and selectivity for the reverse water-gas shift (RWGS) reaction at low-temperatures continues to pose a significant challenge. Ni-based catalysts have been widely employed in CO2 hydrogenation due to their strong capacity to dissociate H2, but they exhibit low selectivity for CO. Herein, we successfully altered the product selectivity for CO2 hydrogenation via controlling the distribution of Ga species on Ni/CeO2 catalysts. When Ga was combined with Ni to form the spinel of NiGa2O4 (NiGa2O4/CeO2), the main product selectivity was CO. While, the Ga was doped into CeO2 to support Ni (Ni/Ga4-CeO2), the product selectivity was the CH4. The NiGa2O4 spinel supported on CeO2 exhibited excellent performance in the RWGS reaction, with a CO selectivity over 99%, and a production rate as high as 74.5 mmol/gcat·h at 450 oC and 24000 mL/gcat·h, without any loss of activity after 72 h. The Ni/Ga4-CeO2, containing metallic Ni species and abundant oxygen vacancies, enhanced the methanation process, with a CO2 conversion as high as 81.38%, and a CH4 production rate of 136 mmol/gcat·h. The CO-TPD analysis revealed that the NiGa2O4/CeO2 catalyst exhibited weak adsorption of CO*, which played a key role in enhancing the selectivity towards CO. Subsequent in-situ DRIFTS analysis further confirmed that the differences in CO2 hydrogenation product obtained from NiGa4/CeO2 and Ni/Ga4-CeO2 were due to the formation of different intermediate species over their surface, leading to a change in the selectivity of CO2 hydrogenation products. This study provides a new idea to switch the product selectivity for CO2 reduction by controlling the distribution of Ga species.

Keywords: Reverse water-gas shift, CO2 reduction, CO selectivity, NiGa2O4 spinel