The big picture

Thermocatalytic CO₂ hydrogenation to methanol, a high-pressure gas-phase reaction that transforms greenhouse gases into useful platform chemicals, plays a crucial role in decarbonizing the hard-to-abate chemical sector. Although industrial copper-based catalysts in syngas-to-methanol production demonstrate high activity, they typically exhibit low methanol selectivity and suffer from severe water-induced deactivation under pure CO₂ feed. Consequently, the interest in CO₂ valorisation has propelled the quest for superior catalytic systems with high methanol selectivity and stability under CO₂ hydrogenation conditions. In this context, indium oxide (In₂O₃)-based systems, in particular mixed indium-zirconium oxide (InZrO_x), have emerged as the leading candidate since its discovery in 2015.^[1] This is because the strong oxide-support interaction stabilizes the active In₂O₃ phase, driving selective and stable methanol production.^[2,3] Crucially, ZrO₂ enhanced methanol productivity of the active indium phase by more than an order of magnitude with augmented interfacial oxygen vacancies, which have been suggested to be the active sites for this reaction.

A decade-long challenge in the field

Significant efforts worldwide have been dedicated to deepening the understanding of this exceptional oxide-oxide interfacial behaviour over the last decade, with the ultimate goal of improving the catalytic performance. Although different strategies such as catalyst design and reaction engineering have been reported to improve the performance of InZrO_x catalysts;^[4,5] fundamentally, no other oxides have showcased such a unique support promotional effect. Furthermore, various In₂O₃ architectures, such as monolayers and clusters, have been proposed to be the optimal active nanostructures. Indium single atoms have generally been considered less active than extended In₂O₃ nanostructures for methanol synthesis, precluding better utilization of the expensive element. Overall, two questions persist: is there an alternative support comparable or even superior to ZrO₂? And how can we maximize the atom efficiency by optimizing the catalytic performance of indium single atoms?

Breaking the long-standing limitation by coupling single atom catalysis and wide bandgap dielectrics

Writing in Nature Nanotechnology, we present the discovery of a new catalytic system that genuinely addresses these two long-standing challenges.^[6] We show that single atoms of indium on hafnia overcomes these hurdles by coupling the concepts of wideband gap dielectrics and single-atom catalysis. Hafnium oxide, or hafnia (HfO₂), is a metal oxide rarely explored in heterogeneous catalysis owing to its presumable chemical and electronic inertness. Notably, it has been widely applied in scalable electronics and ferroelectrics due to its wide bandgap, simultaneously minimizing current leakage and maximizing charge transport efficiency. We transferred this concept and revealed that a dielectric traditionally considered physiochemically inert can actively participate in interfacial catalysis, enabling efficient reactant activation and facilitating intermediates hydrogenation around the isolated indium sites. Using flame spray pyrolysis, we precisely controlled the indium dispersion on HfO₂, stabilizing isolated single-atom sites, and demonstrating that they are the most efficient hydrogen splitters.

Outlook and scientific impact

Extending this concept beyond In₂O₃, we uncovered that HfO₂ support also enhances the CO₂ hydrogenation performance of other families of reducible oxides, such as zinc- and gallium single atoms, by more than two orders of magnitude. Overall, these results show the broad application of HfO₂, justifying its role as an efficient and robust support for advancing sustainable chemical transformation and single-atom catalysis. For more details, please refer to the article^[6].

References

[1] Martin, O. et al. Indium oxide as a superior catalyst for methanol synthesis by CO₂ hydrogenation. Angew. Chem. Int. Ed. 55, 6261-6265 (2016).

[2] Frei, M. S. et al. Role of zirconia in indium oxide-catalyzed CO₂ hydrogenation to methanol. ACS Catal. 10, 1133-1145 (2019).

[3] Yang, C. et al. Strong electronic oxide–support interaction over In₂O₃/ZrO₂ for highly selective CO₂ hydrogenation to methanol. J. Am. Chem. Soc. 142, 19523-19531 (2020).

[4] Pinheiro Araújo, T. et al. Flame-made ternary Pd-In₂O₃-ZrO₂ catalyst with enhanced oxygen vacancy generation for CO₂ hydrogenation to methanol. Nat. Commun. 13, 5610 (2022).

[5] Gao, F. et al. Redox-mediated interfacial restructuring of supported In₂O₃ to drive CO₂ hydrogenation to methanol. ACS Catal. 15, 2785–2795 (2025).

[6] Chiang, Y.-T. et al. Single atoms of indium on hafnia enable superior CO₂-based methanol synthesis. Nat. Nanotechnol. doi:10.1038/s41565-026-02135-y (2026).