Methanol synthesis by CO2 hydrogenation is attractive in view of avoiding the environmental implications associated with the production of the traditional syngas feedstock and mitigating global warming. However, there still is a lack of efficient catalysts for such alternative processes. Herein, we unveil the high activity, 100 % selectivity, and remarkable stability for 1000 h on stream of In2 O3 supported on ZrO2 under industrially relevant conditions. This strongly contrasts to the benchmark Cu-ZnO-Al2 O3 catalyst, which is unselective and experiences rapid deactivation. In-depth characterization of the In2 O3 -based materials points towards a mechanism rooted in the creation and annihilation of oxygen vacancies as active sites, whose amount can be modulated in situ by co-feeding CO and boosted through electronic interactions with the zirconia carrier. These results constitute a promising basis for the design of a prospective technology for sustainable methanol production.

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Graphitic carbon nitride (g-C3N4) exhibits unique properties as a support for single-atom heterogeneous catalysts (SAHCs). Understanding how the synthesis method, carrier properties, and metal identity impact the isolation of metal centers is essential to guide their design. This study compares the effectiveness of direct and postsynthetic routes to prepare SAHCs by incorporating palladium, silver, iridium, platinum, or gold in g-C3N4 of distinct morphology (bulk, mesoporous and exfoliated). The speciation (single atoms, dimers, clusters, or nanoparticles), distribution, and oxidation state of the supported metals are characterized by multiple techniques including extensive use of aberration-corrected electron microscopy. SAHCs are most readily attained via direct approaches applying copolymerizable metal precursors and employing high surface area carriers. In contrast, although post-synthetic routes enable improved control over the metal loading, nanoparticle formation is more prevalent. Comparison of the carrier morphologies also points toward the involvement of defects in stabilizing single atoms. The distinct metal dispersions are rationalized by density functional theory and kinetic Monte Carlo simulations, highlighting the interplay between the adsorption energetics and diffusion kinetics. Evaluation in the continuous three-phase semihydrogenation of 1-hexyne identifies controlling the metal–carrier interaction and exposing the metal sites at the surface layer as key challenges in designing efficient SAHCs

Monoclinic zirconia has been uncovered as a carrier able to substantially boost the activity of indium oxide for CO2 hydrogenation to methanol. Here, electronic, geometric, and interfacial phenomena associated with this unique effect are investigated. Generating mixed In-Zr oxides by coprecipitation does not improve performance, excluding a primary role of electronic parameters.Since even only 1 mol% of indium stabilizes the metastable tetragonal phase of zirconia, the relevance of its crystalline structure is explored in impregnated solids. Both tetragonal and monoclinic ZrO2 permit epitaxial growth of In2O3, but a delicate lattice mismatching leads to a slightly lower dispersion of the oxide on the second, which is observed in the form of subnanometric islands on the carrier. More importantly, compressive and tensile forces are exerted on In2O3, respectively, which inhibit and foster oxygen vacancy formation, in line with the low and greatly enhanced indium-specific activity of the catalysts prepared with the two polymorphs.Hence, a deposition synthesis method is essential to unlock the role of monoclinic zirconia.According to analyses with reference In2O3-based catalysts supported on alumina and ceria, which display diverse ability to activate CO2 on their surface, the direct participation of monoclinic zirconia in a parallel pathway to methanol is put forward as a second origin of activity boosting.The latter is likely enabled by the abundancy of indium active sites vicinal to the interface and/or by a more favorable CO2 adsorption geometry onto this carrier or onto an alternative bimetallic site possibly produced.

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