Catalytic hydrogenation of CO2 to methanol offers a promising route to convert captured carbon — whether from the air or waste streams — into a valuable industrial chemical and fuel. Among catalysts developed so far, In2O3 supported on monoclinic ZrO2 stands out for its excellent methanol selectivity and stability; however, the underlying reasons for this exceptional performance are not well understood, and catalysts on alternative supports have not been able to match its performance. Addressing this issue, Javier Pérez-Ramírez and colleagues in Switzerland and Spain report that replacing the ZrO2 support with another monoclinic structured oxide, HfO2, leads to InHfOx-based catalysts that can outperform the established InZrOx system.
The researchers synthesize nanostructured InHfOx catalysts with a range of In2O3 loadings using flame spray pyrolysis. At a 2 wt% loading, In atoms are highly dispersed on the catalyst surface and the methanol production rate peaks at 9.3 g h−1 gIn−1 — a 70% improvement over InZrOx. The team attribute this performance, in part, to the wide bandgap and high dielectric constant of the HfO2 allowing hydride–proton pairs — species key to the catalytic mechanism — to be electronically stabilized at the surface. Moreover, the highly stable monoclinic surface and the formation of hydroxylated indium species appear to further contribute to the high performance of InHfOx catalysts. The researchers note that the relative scarcity of hafnium may limit wide deployment, but that the design principles of using reducible oxides on wide-bandgap dielectrics may apply more broadly.
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