Catalytic Performance of Ni Catalysts Supported on α-, β-, and γ-Ga2O3 Polymorphs for CO2 Hydrogenation to Methanol

Nickel-based materials have garnered considerable attention owing to their potential as affordable, effective, and durable catalysts for CO2 hydrogenation. However, their propensity to favor methane production over more desirable methanol has posed a challenge. In this study, we endeavored to address this issue by synthesizing α-, β-, and γ-Ga2O3 supported Ni catalysts through the wet impregnation method. Notably, Ni supported on the α-Ga2O3 catalyst (referred to as 10Ni/α-Ga2O3) exhibited superior activity and methanol selectivity under typical CO2 hydrogenation conditions (3 MPa and 260 °C), reaching ca. 80% methanol selectivity at 0.72% CO2 conversion. This performance outpaced analogous counterparts utilizing β- and γ-Ga2O3 supports, which is attributed to the abundance of strong basic sites inherent in α-Ga2O3. We unveiled the intricate mechanism governing CO2 hydrogenation on 10Ni/α-Ga2O3 catalysts through ex situ characterizations and in situ FTIR. Evidently, H2 underwent dissociation over Ni nanoparticles. It spilts over onto the oxide support, while strong basic sites on the α-Ga2O3 support facilitate the adsorption of CO2, forming bidentate carbonate as a key intermediate and subsequently hydrogenated to yield methanol. Our findings propose a promising avenue for developing cost-effective and highly efficient catalyst systems for methanol synthesis through CO2 hydrogenation.