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The surface electron density significantly affects the photocatalytic efficiency, especially the photocatalytic CO 2 reduction reaction, which involves multi-electron participation in the conversion process. Herein, we propose a conceptually different mechanism for surface electron density modulation based on the model of Au anchored CdS. We firstly manipulate the direction of electron transfer by regulating the vacancy types of CdS. When electrons accumulate on vacancies instead of single Au atoms, the adsorption types of CO 2 change from physical adsorption to chemical adsorption. More importantly, the surface electron density is manipulated by controlling the size of Au nanostructures. When Au nanoclusters downsize to single Au atoms, the strong hybridization of Au 5 d and S 2 p orbits accelerates the photo-electrons transfer onto the surface, resulting in more electrons available for CO 2 reduction. As a result, the product generation rate of Au SA /Cd 1−x S manifests a remarkable at least 113-fold enhancement compared with pristine Cd 1−x S. The electron density of reactive sites significantly affects catalytic performances. Here, authors demonstrate the electron density of different reactive sites can be modulated by regulating the type of vacancy and the size of Au, leading to effective CO 2 photoreduction.

Ammonia is a storage molecule for hydrogen, which can be released by catalytic decomposition. Inexpensive iron catalysts suffer from a low activity due to a too strong iron-nitrogen binding energy compared to more active metals such as ruthenium. Here, we show that this limitation can be overcome by combining iron with cobalt resulting in a Fe-Co bimetallic catalyst. Theoretical calculations confirm a lower metal-nitrogen binding energy for the bimetallic catalyst resulting in higher activity. Operando spectroscopy reveals that the role of cobalt in the bimetallic catalyst is to suppress the bulk-nitridation of iron and to stabilize this active state. Such catalysts are obtained from Mg(Fe,Co) 2 O 4 spinel pre-catalysts with variable Fe:Co ratios by facile co-precipitation, calcination and reduction. The resulting Fe-Co/MgO catalysts, characterized by an extraordinary high metal loading reaching 74 wt.%, combine the advantages of a ruthenium-like electronic structure with a bulk catalyst-like microstructure typical for base metal catalysts. Inexpensive iron catalysts often exhibit low activity in ammonia decomposition due to a strong iron-nitrogen binding energy. Here the authors demonstrate that combining iron with cobalt to form a Fe-Co bimetallic catalyst overcomes this limitation, presenting a promising solution for enhancing ammonia decomposition efficiency.

Under DAPHNE4NFDI, the X‐ray absorption spectroscopy (XAS) reference database, RefXAS, has been set up. For this purpose, we developed a method to enable users to submit a raw dataset, with its associated metadata, via a dedicated website for inclusion in the database. Implementation of the database includes an upload of metadata to the scientific catalogue and an upload of files via object storage, with automated query capabilities through a web server and visualization of the data and files. Based on the mode of measurements, quality criteria have been formulated for the automated check of any uploaded data. In the present work, the significant metadata fields for reusability, as well as reproducibility of results (FAIR data principles), are discussed. Quality criteria for the data uploaded to the database have been formulated and assessed. Moreover, the usability and interoperability of available XAS data/file formats have been explored. The first version of the RefXAS database prototype is presented, which features a human verification procedure, currently being tested with a new user interface designed specifically for curators; a user‐friendly landing page; a full list of datasets; advanced search capabilities; a streamlined upload process; and, finally, a server‐side automatic authentication and (meta‐) data storage via MongoDB, PostgreSQL and (data‐) files via relevant APIs. The RefXAS database under DAPHNE4NFDI enables users to access quality‐controlled, curated X‐ray absorption spectra of references along with important metadata and to share their data with the research community in easy steps.

Nitrogen oxide (NO x ) emissions are a major source of pollution, demanding ever-improving performance from catalytic after-treatment systems. However, catalyst development is often hindered by limited understanding of the catalyst at work, exacerbated by widespread use of model catalysts rather than technical catalysts, and by global rather than spatially resolved characterization tools. Here we combine operando X-ray absorption spectroscopy with microtomography to perform three-dimensional chemical imaging of the chemical state of copper species in a Cu-SSZ-13 washcoated monolith catalyst during NO x reduction. Gradients in copper oxidation state and coordination environment, resulting from an interplay of NO x reduction with adsorption–desorption of NH 3 and mass transport phenomena, were revealed at micrometre spatial resolution while simultaneously determining catalytic performance. Crucially, direct three-dimensional visualization of complex reactions on non-model catalysts is feasible only by the use of operando X-ray spectrotomography, which can improve our understanding of structure–activity relationships, including the observation of mass and heat transport effects. Obtaining spatially resolved spectroscopic information for catalysts under working conditions remains challenging. Here, an approach that combines X-ray absorption spectroscopy with microtomography is introduced and showcased for the selective catalytic reduction of NO x with ammonia over a Cu-SSZ-13 washcoated monolith catalyst.

Propane dehydrogenation (PDH) to propene is an important alternative to oil-based cracking processes, to produce this industrially important platform chemical . The commercial PDH technologies utilizing Cr-containing (refs. ) or Pt-containing (refs. ) catalysts suffer from the toxicity of Cr(VI) compounds or the need to use ecologically harmful chlorine for catalyst regeneration . Here, we introduce a method for preparation of environmentally compatible supported catalysts based on commercial ZnO. This metal oxide and a support (zeolite or common metal oxide) are used as a physical mixture or in the form of two layers with ZnO as the upstream layer. Supported ZnO species are in situ formed through a reaction of support OH groups with Zn atoms generated from ZnO upon reductive treatment above 550 °C. Using different complementary characterization methods, we identify the decisive role of defective OH groups for the formation of active ZnO species. For benchmarking purposes, the developed ZnO-silicalite-1 and an analogue of commercial K-CrO /Al O were tested in the same setup under industrially relevant conditions at close propane conversion over about 400 h on propane stream. The developed catalyst reveals about three times higher propene productivity at similar propene selectivity.

Propane dehydrogenation (PDH) to propene is an important alternative to oil-based cracking processes, to produce this industrially important platform chemical 1 , 2 . The commercial PDH technologies utilizing Cr-containing (refs. 3 , 4 ) or Pt-containing (refs. 5 – 8 ) catalysts suffer from the toxicity of Cr( vi ) compounds or the need to use ecologically harmful chlorine for catalyst regeneration 9 . Here, we introduce a method for preparation of environmentally compatible supported catalysts based on commercial ZnO. This metal oxide and a support (zeolite or common metal oxide) are used as a physical mixture or in the form of two layers with ZnO as the upstream layer. Supported ZnO x species are in situ formed through a reaction of support OH groups with Zn atoms generated from ZnO upon reductive treatment above 550 °C. Using different complementary characterization methods, we identify the decisive role of defective OH groups for the formation of active ZnO x species. For benchmarking purposes, the developed ZnO–silicalite-1 and an analogue of commercial K–CrO x /Al 2 O 3 were tested in the same setup under industrially relevant conditions at close propane conversion over about 400 h on propane stream. The developed catalyst reveals about three times higher propene productivity at similar propene selectivity. Propene is obtained through propane dehydrogenation using catalysts that are toxic, expensive or demanding to regenerate with ecologically harmful compounds, but the ZnO-based alternative reported here is cheap, clean and scalable.

In order to increase their stability and tune-sensing characteristics, metal oxides are often surface-loaded with noble metals. Although a great deal of empirical work shows that surface-loading with noble metals drastically changes sensing characteristics, little information exists on the mechanism. Here, a systematic study of sensors based on rhodium-loaded WO3, SnO2, and In2O3—examined using X-ray diffraction, high-resolution scanning transmission electron microscopy, direct current (DC) resistance measurements, operando diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, and operando X-ray absorption spectroscopy—is presented. Under normal sensing conditions, the rhodium clusters were oxidized. Significant evidence is provided that, in this case, the sensing is dominated by a Fermi-level pinning mechanism, i.e., the reaction with the target gas takes place on the noble-metal cluster, changing its oxidation state. As a result, the heterojunction between the oxidized rhodium clusters and the base metal oxide was altered and a change in the resistance was detected. Through measurements done in low-oxygen background, it was possible to induce a mechanism switch by reducing the clusters to their metallic state. At this point, there was a significant drop in the overall resistance, and the reaction between the target gas and the base material was again visible. For decades, noble metal loading was used to change the characteristics of metal-oxide-based sensors. The study presented here is an attempt to clarify the mechanism responsible for the change. Generalities are shown between the sensing mechanisms of different supporting materials loaded with rhodium, and sample-specific aspects that must be considered are identified.

Bifunctional Fe–Pt ammonia slip catalysts were studied by operando quick-scanning extended X-ray absorption fine structure spectroscopy (QEXAFS) under conditions mimicking rapid temperature variations that occur in an automotive exhaust gas aftertreatment system during real driving. Two catalysts, Pt/Al 2 O 3 and Fe-ZSM-5, were tested individually, as mixtures and in dual bed arrangements. Applying QEXAFS allowed to track changes of active metal state with high time resolution. It uncovered a strong dependence of the active metal state on reaction conditions and catalyst bed layout. For example, proximity to platinum stabilized iron species in their more active oxidized state and led to higher Fe-ZSM-5 activity. On the contrary, isolated iron species were more susceptible to overreduction by ammonia which led to deactivation and low selectivity. The use of transient conditions uncovered the influence of non-equilibrium phenomena on catalytic performance under industrially relevant conditions. Specifically, the effect of ammonia storage on the increase of activity was shown. This was also accompanied by elevated N 2 O production not observed during tests with gradual heating. Additionally, unusually high NO x selectivity was detected for Fe-ZSM-5 under these conditions. Lastly, tracking catalyst state under dynamic reaction conditions disclosed that Fe-ZSM-5 activity did not grow directly with temperature increase but rather depended on the oxidation state of Fe and surface concentration of ammonia.

For CO 2 hydrogenation over iron-based catalysts, revealing the promoting effect of manganese and the nature of catalytically active sites remains a challenge that hinders targeted catalyst design. Here we elucidate the manganese-modulated restructuring of such catalysts during preconditioning and CO 2 hydrogenation using in situ X-ray absorption spectroscopy. The reaction-induced decoration of the surface of iron carbide with a MnO-containing layer is essential to hinder methane formation in favour of C 2 –C 4 olefins and C 5+ hydrocarbons. The selectivity changes were rationalized via spatially resolved steady-state and time-resolved (micro)kinetic tests combined with density functional theory calculations. The promoter affects the ability of iron carbide to generate surface species from H 2 , CO 2 and C 2 H 4 , thus controlling the surface C/H ratio, which is decisive for product selectivity. Consequently, the design of efficient multi-component heterogeneous catalysts requires a thorough understanding of the optimal catalyst architecture and, in particular, how to generate and stabilize it under reaction conditions. Promoters are able to modulate the performance of catalysts for a given process, but this can be done through various mechanisms. Here the role of Mn as a promoter on Fe-based catalysts for CO 2 hydrogenation to olefins is comprehensively investigated via spectroscopic and kinetic analyses. The promoter induces a restructuring of the catalyst surface, balancing the strength of the adsorption of reactants and intermediates.

Despite the ongoing electrification trend seen especially in the passenger car segment, internal combustion engines will be used in the years to come in hybrid powertrains, heavy-duty and off-road markets, and shipping, etc. [...]the catalytic aftertreatment systems will continue to be developed in order to improve conversion efficiency, stability, and to reduce the amount of required precious metals. [...]it is equally important to precisely identify active species as well as to understand their structural dynamics and aging phenomena. Using temperature programmed desorption studies Villamaina et al. demonstrate and quantify the competition between water and ammonia—the primary NOx reducing agent—for adsorption on the active sites in state-of-the-art Cu-CHA zeolites used for NH3-SCR [7].