Microfabrication Enables Quantification of Interfacial Activity in Thermal Catalysis.

A myriad of heterogeneous catalysts comprises multiple phases that need to be precisely structured to exert their maximal contribution to performance through electronic and structural interactions at their peripheries. In view of the nanometric, tridimensional, and anisotropic nature of these materials, a quantification of the interface and the impact of catalytic sites located there on the global performance is a highly challenging task. Consequently, the true origin of catalysis often remains subject of debate even for widely studied materials. Herein, an integrated strategy based on microfabricated catalysts and a custom-designed reactor is introduced for determining interfacial contributions upon catalytic activity assessment under process-relevant conditions, which can be easily implemented in the common catalysis research infrastructure and will accelerate the rational design of multicomponent heterogeneous catalysts for diverse applications. The method is validated by studying the high-pressure continuous-flow hydrogenation of CO and CO2 over Cu-ZnO catalysts, revealing linear correlations between the methanol formation rate and the interface between the metal and the oxide. Characterization of fresh and used materials points to the model catalyst preparation as the current challenge of the methodology that can be addressed through further development of nanotechnological tools.

Nanostructure of nickel-promoted indium oxide catalysts drives selectivity in CO2 hydrogenation.

Metal promotion in heterogeneous catalysis requires nanoscale-precision architectures to attain maximized and durable benefits. Herein, we unravel the complex interplay between nanostructure and product selectivity of nickel-promoted In2O3 in CO2 hydrogenation to methanol through in-depth characterization, theoretical simulations, and kinetic analyses. Up to 10 wt.% nickel, InNi3 patches are formed on the oxide surface, which cannot activate CO2 but boost methanol production supplying neutral hydrogen species. Since protons and hydrides generated on In2O3 drive methanol synthesis rather than the reverse water-gas shift but radicals foster both reactions, nickel-lean catalysts featuring nanometric alloy layers provide a favorable balance between charged and neutral hydrogen species. For nickel contents >10 wt.%, extended InNi3 structures favor CO production and metallic nickel additionally present produces some methane. This study marks a step ahead towards green methanol synthesis and uncovers chemistry aspects of nickel that shall spark inspiration for other catalytic applications.

Methanol as a Hydrogen Carrier: Kinetic and Thermodynamic Drivers for its CO2 -Based Synthesis and Reforming over Heterogeneous Catalysts.

Methanol is an attractive energy vector in a closed loop including its synthesis from CO2 and H2 and on-demand reforming to the starting feedstocks. Catalytic materials for the two reactions were mostly studied separately, with very few works assessing the feasibility of the same system for both. Here, key kinetic drivers of methanol synthesis (MS) and methanol steam reforming (MSR) were identified for the main catalyst families, with special focus on Cu-ZnO-Al2 O3 , In2 O3 , and Pd/ZrO2 . It was shown that the relative activity level was preserved in either direction, whereas the distinctly favored (reverse) water-gas shift modulated selectivity differently. Low selectivity in kinetically controlled MS could be overcome in MSR by exploiting thermodynamics as the driving force, with many catalysts unfit for MS still comprising appealing candidates for MSR and only few being suited for MS as well as MSR. Overall, readily identifiable properties describing catalyst behavior in the forward and backward reactions were highlighted, effectively linking research in the two fields and setting a stronger basis for developing a methanol-based hydrogen storage unit with a single reactor.

Development of In2O3-based Catalysts for CO2-based Methanol Production.

CO2 valorization into chemicals and fuels is a key area in current academic and industrial research, with thermocatalytic hydrogenation to methanol comprising one of the most advanced routes. Life-cycle analysis coupled to the framework of planetary boundaries has recently confirmed the sustainability of this process in absolute terms, emphasizing the need for cheaper CO2 and renewable H2 and for a catalytic system embracing high activity, selectivity, and durability to meet economic requirements. Herein, our research efforts aimed to gather atomic-level understanding of electronic and geometric properties of active sites in breakthrough In2O3-based catalytic systems guiding their development are reviewed. In-depth mechanistic elucidations identified limited hydrogen activation ability as well as water-driven sintering as limitations of pure In2O3. The former aspect was successfully addressed by adding through coprecipitation a minimal amount of palladium, forming tiny clusters strongly anchored to the oxide lattice leading to an unprecedented sustained methanol productivity. The use of monoclinic zirconia as a carrier, enabling high In2O3 dispersion in two-dimensional nanostructures, inducing the formation of additional active sites on In2O3, and contributing to CO2 activation, offered an efficient way to further boost activity and tackle In2O3 sintering. Overall, our findings set solid grounds to rationally design a supported and promoted In2O3 catalyst holding bright prospects for use at a large scale.

Atomic-scale engineering of indium oxide promotion by palladium for methanol production via CO2 hydrogenation.

Metal promotion is broadly applied to enhance the performance of heterogeneous catalysts to fulfill industrial requirements. Still, generating and quantifying the effect of the promoter speciation that exclusively introduces desired properties and ensures proximity to or accommodation within the active site and durability upon reaction is very challenging. Recently, In2O3 was discovered as a highly selective and stable catalyst for green methanol production from CO2. Activity boosting by promotion with palladium, an efficient H2-splitter, was partially successful since palladium nanoparticles mediate the parasitic reverse water-gas shift reaction, reducing selectivity, and sinter or alloy with indium, limiting metal utilization and robustness. Here, we show that the precise palladium atoms architecture reached by controlled co-precipitation eliminates these limitations. Palladium atoms replacing indium atoms in the active In3O5 ensemble attract additional palladium atoms deposited onto the surface forming low-nuclearity clusters, which foster H2 activation and remain unaltered, enabling record productivities for 500 h.