Understanding the structure-performance relationship of active sites at atomic scale

Recycling CO2 as a renewable carbon source for the production of high-value fuels and chemicals has drawn global attention lately as a promising method to mitigate climate change and lessen depende...

Recycling Carbon Dioxide through Catalytic Hydrogenation: Recent Key Developments and Perspectives

In recent years, noble metals atomically dispersed on solid oxide supports have become a frontier of heterogeneous catalysis. In pursuit of an ultimate atom efficiency, the stability of single-atom catalysts is pivotal. Here we compare two Pd/CeO2 single-atom catalysts that are active in low-temperature CO oxidation and display drastically different structural dynamics under the reaction conditions. These catalysts were obtained by conventional impregnation on hydrothermally synthesized CeO2 and one-step flame spray pyrolysis. The oxidized Pd atoms in the impregnated catalyst were prone to reduction and sintering during CO oxidation, whereas they remained intact on the surface of the Pd-doped CeO2 derived by flame spray pyrolysis. A detailed in situ characterization linked the stability of the Pd single atoms to the reducibility of the Pd–CeO2 interface and the extent of reverse oxygen spillover. To understand the chemical phenomena that underlie the metal–support interactions is crucial to the rational design of stable single-atom catalysts. Single-atom catalysts have become a frontier of heterogeneous catalysis, but to achieve a high stability under turnover is often a challenge. Now, a Pd/CeO2 single-atom catalyst prepared using flame spray pyrolysis is able to stabilize the isolated Pd species during CO oxidation due to a high mobility of surface lattice oxygen.

Interface dynamics of Pd–CeO2 single-atom catalysts during CO oxidation

Carbon dioxide (CO2) hydrogenation to methanol with H2 produced with renewable energy represents a promising path for the effective utilization of a major anthropogenic greenhouse gas, in which cat...

CO2Hydrogenation to Methanol over In2O3-Based Catalysts: From Mechanism to Catalyst Development

Spillover is a well-known phenomenon in heterogeneous catalysis and is involved in many important reactions. The establishment of the spillover concept opened up a new research field for an in-dept...

Spillover in Heterogeneous Catalysis: New Insights and Opportunities

Metal–support interactions have a strong impact on the performance of heterogeneous catalysts. Specific sites at the metal–support interface can give rise to unusual high reactivity, and there is a growing interest in optimizing not only the properties of metal particles but also the metal–support interface. Here, we demonstrate how varying the particle size of the support (ceria–zirconia) can be used to tune the metal–support interactions, resulting in a substantially enhanced CO2 hydrogenation rate. A combination of X-ray diffraction, X-ray absorption spectroscopy, near-ambient pressure X-ray photoelectron spectroscopy, transmission electron microscopy and infrared spectroscopy provides insight into the active sites at the interface between cobalt and ceria–zirconia involved in CO2 hydrogenation to CH4. Reverse oxygen spillover from the support during treatment in hydrogen results in the generation of oxygen vacancies. Stabilization of cobalt particles by ceria–zirconia particles of intermediate size leads to oxygen spillover to the support during the CO2 and CO dissociation steps, followed by further hydrogenation of the resulting intermediates on cobalt. Metal–support interactions can effectively modify the catalytic properties of heterogeneous composites. Here, the authors report the possibility of controlling the interaction between cobalt and a ceria–zirconia support by changing the particle size of the latter, resulting in a superior CO2 hydrogenation system.

Boosting CO2 hydrogenation via size-dependent metal-support interactions in cobalt-ceria-based catalysts

One of the well-known observations in the Fischer–Tropsch (FT) reaction is that the CH4 selectivity for cobalt catalysts is always higher than the value expected on the basis of the Anderson–Schulz–Flory (ASF) distribution. Depositing graphitic carbon on a cobalt catalyst strongly suppresses this non-ASF CH4, while the formation of higher hydrocarbons is much less affected. Carbon was laid down on the cobalt catalyst via the Boudouard reaction. We provide evidence that the amorphous carbon does not influence the FT reaction, as it can be easily hydrogenated under reaction conditions. Graphitic carbon is rapidly formed and cannot be removed. This unreactive form of carbon is located on terrace sites and mainly decreases the CO conversion by limiting CH4 formation. Despite nearly unchanged higher hydrocarbon yield, the presence of graphitic carbon enhances the chain-growth probability and strongly suppresses olefin hydrogenation. We demonstrate that graphitic carbon will slowly deposit on the cobalt catalys...

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Tobias F. Kimpel

Papers

Boosting CO2 hydrogenation via size-dependent metal-support interactions in cobalt-ceria-based catalysts

Influence of Carbon Deposits on the Cobalt-Catalyzed Fischer-Tropsch Reaction: Evidence of a Two-Site Reaction Model.

Mechanistic aspects of n-paraffins hydrocracking: Influence of zeolite morphology and acidity of Pd(Pt)/ZSM-5 catalysts

Breaking structure sensitivity in CO2 hydrogenation by tuning metal–oxide interfaces in supported cobalt nanoparticles

Pressure dependence and mechanism of Mn promotion of silica-supported Co catalyst in the Fischer-Tropsch reaction