Heterogeneous catalysts play a pivotal role in the chemical industry. The strong metalsupport interaction (SMSI), which affects the catalytic activity, is a phenomenon researched for decades. However, detailed mechanistic understanding on real catalytic systems is lacking. Here, this surface phenomenon was studied on an actual platinum-titania catalyst by state-of-the-art in situ electron microscopy, in situ X-ray photoemission spectroscopy and in situ X-ray diffraction, aided by density functional theory calculations, providing a novel real time view on how the phenomenon occurs. The migration of reduced titanium oxide, limited in thickness, and the formation of an alloy are competing mechanisms during high temperature reduction. Subsequent exposure to oxygen segregates the titanium from the alloy, and a thicker titania overlayer forms. This role of oxygen in the formation process and stabilization of the overlayer was not recognized before. It provides new application potential in catalysis and materials science.

In spite of numerous works in the field of chemical valorization of carbon dioxide into methanol, the nature of high activity of Cu/ZnO catalysts, including the reaction mechanism and the structure of the catalyst active site, remains the subject of intensive debate. By using high-pressure operando techniques: steady-state isotope transient kinetic analysis coupled with infrared spectroscopy, together with time-resolved X-ray absorption spectroscopy and X-ray powder diffraction, and supported by electron microscopy and theoretical modeling, we present direct evidence that zinc formate is the principal observable reactive intermediate, which in the presence of hydrogen converts into methanol. Our results indicate that the copper-zinc alloy undergoes oxidation under reaction conditions into zinc formate, zinc oxide and metallic copper. The intimate contact between zinc and copper phases facilitates zinc formate formation and its hydrogenation by hydrogen to methanol.

Copper-zinc-alumina catalysts are the industrially-used formulation for methanol synthesis from carbon monoxide and carbon dioxide containing feedstock. Its high performance stems from synergies that develop between its components. This important catalytic system has been investigated with a myriad of approaches, however, no comprehensive agreement has emerged as to the fundamental source of its high activity. One potential source of the disagreements is the considerable variation in pressure used in studies to understand a process that is industrially performed at pressures above 20 bar. Here, by systematically studying the catalyst state during temperature-programmed reduction and under carbon dioxide hydrogenation with in situ and operando X-ray absorption spectroscopy over four orders of magnitude in pressure, we show how the state and evolution of the catalyst is defined by its environment. Especially below 1 bar, the structure of the catalyst shows a strong pressure dependence. As pressure gaps are a general problem in catalysis, these observations have wide-ranging ramifications.The improvement of heterogeneous catalysts is central to a sustainable development of energy conversion and the production of chemicals. Historically, such development relied heavily on trial-and-error based research. More recently, advances in characterization methods allowed the study of catalysts under pretreatment and catalytic conditions, thus in situ and operando. This has permitted the possibility to derive fundamental understanding of the state of the catalyst whilst it is actually working 1 . Ideally, a detailed comprehension of the reaction mechanisms of the desired catalytic reaction emerges. Many of these methods, such as electron microscopy and X-ray photoelectron spectroscopy, remain limited in their routine application to pressure regimes in the millibar range [2][3][4][5] ; others, however, such as X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD), suffer no

This study reports a thorough investigation of nanosized CuO/CeO 2 materials as an efficient catalyst for decomposition of N 2 O, which is a strong greenhouse gas largely produced by chemical industry. Effect of terminating CeO 2 crystalline planes ({100}, {110} and {111}) on the behavior of CuO dispersed over CeO 2 nanocubes, nanorods and polyhedral crystallites was examined in detail by using a variety of catalyst characterization techniques. The 4 wt. % Cu was found as the most advantageous metal loading, whereas higher Cu content resulted in lower dispersion and formation of significantly less active, segregated bulk CuO phase. It was discovered that CuO/CeO 2 solids should enable both excessive oxygen mobility on the catalyst surface as well as formation of highly reducible Cu defect sites, in order to ensure high intrinsic activity. Detailed studies further revealed that CeO 2 morphology needs to be tailored to expose {100} and {110} high-energy surface planes, as present in CeO 2 nanorods. Oxygen mobility and regeneration of active Cu phase on these surface planes is easier, which in turn facilitates higher catalytic activity through the recombination of surface oxygen atoms and desorption as molecular oxygen that replenishes active sites for subsequent catalytic cycles. As a consequence, CuO supported on CeO 2 nanorods demonstrated lower activation energy (87 kJ/mol) in N 2 O decomposition reaction compared to catalysts based on CeO 2 nanocubes (102 kJ/mol) or polyhedral CeO 2 (92 kJ/mol).

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