Cecilia Mondelli

Ternäre Pd‐In₂O₃/ZrO₂ Katalysatoren beweisen technologisches Potenzial für die CO₂‐basierte Methanolsynthese, wobei die Entwicklung skalierbarer Systeme und das Verständnis komplexer dynamischer Wechselwirkungen zwischen der aktiven Phase, des Promotors und des Trägers der Schlüssel zur Erreichung einer hohen Produktivität sind. Hier zeigen wir, dass durch einfache Imprägnierung hergestellte Pd‐In₂O₃/ZrO₂ Katalysatoren unter CO₂‐Hydrierbedingungen eine stabile und selektive Nanoarchitektur bilden, unabhängig von der Reihenfolge der Zugabe von Pd‐ und In‐Komponenten auf den Zirkonoxidträger. Detaillierte operando Charakterisierung und Simulationen deuten auf eine schnelle Umstrukturierung, dessen Treiber die Energie der Metall‐Metalloxid‐Wechselwirkung ist. Die Nähe von InO_x‐Schichten auf den entstehenden InPd_x‐Partikeln verhindern Leistungsverluste durch Pd‐Sinterung. Weiterhin unterstreichen die Ergebnisse die entscheidende Rolle der reaktionsinduzierten Umstrukturierung in komplexem CO₂‐Hydrierkatalysatoren und bieten Einblicke in die optimale Integration von Säure‐Base‐ und Redoxfunktionen für die technische Umsetzung.

Ternary Pd‐In₂O₃/ZrO₂ catalysts exhibit technological potential for CO₂‐based methanol synthesis, but developing scalable systems and comprehending complex dynamic behaviors of the active phase, promoter, and carrier are key for achieving high productivity. Here, we show that the structure of Pd‐In₂O₃/ZrO₂ systems prepared by wet impregnation evolves under CO₂ hydrogenation conditions into a selective and stable architecture, independent of the order of addition of Pd and In phases on the zirconia carrier. Detailed operando characterization and simulations reveal a rapid restructuring driven by the metal‐metal oxide interaction energetics. The proximity of InPd_x alloy particles decorated by InO_x layers in the resulting architecture prevents performance losses associated with Pd sintering. The findings highlight the crucial role of reaction‐induced restructuring in complex CO₂ hydrogenation catalysts and offer insights into the optimal integration of acid‐base and redox functions for practical implementation.

Palladium promotion and deposition on monoclinic zirconia are effective strategies to boost the performance of bulk In₂O₃ in CO₂-to-methanol and could unlock superior reactivity if well integrated into a single catalytic system. However, harnessing synergic effects of the individual components is crucial and very challenging as it requires precise control over their assembly. Herein, we present ternary Pd-In₂O₃-ZrO₂ catalysts prepared by flame spray pyrolysis (FSP) with remarkable methanol productivity and improved metal utilization, surpassing their binary counterparts. Unlike established impregnation and co-precipitation methods, FSP produces materials combining low-nuclearity palladium species associated with In₂O₃ monolayers highly dispersed on the ZrO₂ carrier, whose surface partially transforms from a tetragonal into a monoclinic-like structure upon reaction. A pioneering protocol developed to quantify oxygen vacancies using in situ electron paramagnetic resonance spectroscopy reveals their enhanced generation because of this unique catalyst architecture, thereby rationalizing its high and sustained methanol productivity.

A plethora of metal promoters have been applied to enhance the performance of In₂O₃ in CO₂ hydrogenation to methanol, a prospective energy carrier. However, the lack of systematic catalyst preparation and evaluation precludes a direct comparison of their speciation and promotional effects, and consequently, the design of an optimal system. Herein, flame spray pyrolysis (FSP) is employed as a standardized synthesis method to introduce nine metal promoters (0.5 wt.%) into In₂O₃. Methanol productivity generally increased on M‐In₂O₃ with selectivity following Pd ≈ Pt > Rh ≈ Ru ≈ Ir > Ni ≈ Co > Ag ≈ In₂O₃ > Au. In‐depth characterization, kinetic analyses, and theoretical calculations reveal a range of metal‐dependent speciation which dictate catalyst architecture and degree of promotion. Atomically‐dispersed promoters (Pd, Pt, Rh, Ru, and Ir) grant the highest improvement in performance, particularly Pd and Pt, which markedly promote hydrogen activation while hindering undesired CO formation. In contrast, metals in clustered (Ni and Co) and nanoparticle (Ag and Au) forms display moderate and no promotion, respectively. This study provides an atomic‐level understanding of In₂O₃ promotion based on a unified protocol, and highlights the potential of FSP to engineer complex catalytic systems toward more efficient energy transformations.

The impact of carbon monoxide on CO₂‐to‐methanol catalysts has been scarcely investigated, although CO will comprise up to half of the carbon feedstock, depending on the origin of CO₂ and process configuration. In this study, copper‐based systems and ZnO−ZrO₂ are assessed in cycling experiments with hybrid CO₂−CO feeds and their CO sensitivity is compared to In₂O₃‐based materials. All catalysts are found to be promoted upon CO addition. Copper‐based systems are intrinsically more active in CO hydrogenation and profit from exploiting this carbon source for methanol production, whereas CO induces surplus formation of oxygen vacancies (i. e., the catalytic sites) on ZnO−ZrO₂, as in In₂O₃‐based systems. Mild‐to‐moderate deactivation occurs upon re‐exposure to CO₂‐rich streams, owing to water‐induced sintering for all catalysts except ZnO−ZrO₂, which responds reversibly to feed variations, likely owing to its more hydrophobic nature and the atomic mixing of its metal components. Catalytic systems are categorized for operation in hybrid CO₂−CO feeds, emphasizing the significance of catalyst and process design to foster advances in CO₂ utilization technologies.