Alexey Boubnov

Karlsruhe Institute of Technology | KIT · Institute of Nanotechnology

Water and NO reversibly inhibit catalytic methane oxidation to CO 2 over Pd/Al 2 O 3 and Pd‐Pt/Al 2 O 3 at temperatures near 50% conversion. Modulation‐excitation X‐ray absorption spectroscopy (ME‐XAS) was used to characterize the interaction of the inhibitors with the Pd and Pt components. Simulated X‐ray absorption near‐edge structure (XANES) spe...

Despite intensive investigations for unravelling the water splitting reaction, the catalyst behavior during the oxygen evolution reaction (OER) is still not fully understood. This is especially true under more demanding conditions like high potentials and high temperatures. Rotating disk electrode measurements show a gradual increase of OER current...

The microkinetics of the electrocatalytic oxygen evolution reaction substantially determines the performance in proton-exchange membrane water electrolysis. State-of-the-art nanoparticulated rutile IrO2 electrocatalysts present an excellent trade-off between activity and stability due to the efficient formation of intermediate surface species. To r...

The role of proton exchange membrane water electrolysers (PEMWE) in providing clean and reliable green hydrogen is undeniable in a fully decarbonized energy system. Indeed, the ambitious “Hydrogen Shot” initiative by the U.S. DoE seeks to decrease in a decade green hydrogen pricing down to 1$/Kg H 2 .(1) Such endeavour will require a mass-scale imp...

Chalcogenides in perovskite and the related layered Ruddlesden-Popper crystal structures (chalcogenide perovskites for brevity) are an exciting family of semiconductors but remain experimentally little studied. Chalcogenide perovskites share crystal structures and some physical properties with ionic compounds such as oxide and halide perovskites, b...

CO oxidation on Pt group metals is affected by the metal size and reducibility of the oxide support. Here, we report that Ir supported on MgAl 2 O 4 , traditionally considered non-reducible, exhibits...

X‐ray absorption spectroscopy (XAS) is one of the powerful operando tools to track structural variations in heterogeneous catalysts. The nature of active sites in catalyst research is of great relevance, especially given the growing importance of energy storage using CO2 as feedstock and the need for dynamic availability of electric power. Due to t...

This work probes the effects of La on reactions involving CuO sorbents and H2S in gaseous streams. La‐CuO sorbents with nominal La/Cu atomic ratios of 1:2 achieved higher capacities (27 and 36 g H2S per 100 g sorbent) compared to CuO sorbents (25 g H2S per 100 g sorbent). Comparison of the La‐CuO sorbents using energy dispersive X‐ray spectroscopy...

Designing acid‐stable oxygen evolution reaction electrocatalysts is key to developing sustainable energy technologies such as polymer electrolyte membrane electrolyzers but has proven challenging due to the high applied anodic potentials and corrosive electrolyte. This work showcases advanced nanoscale microscopy techniques supported by complementa...

The structure of IrO2 during the oxygen evolution reaction (OER) was studied by operando X-ray absorption spectroscopy (XAS) at the Ir L3-edge to gain insight into the processes that occur during the electrocatalytic reaction at the anode during water electrolysis. For this purpose, calcined and uncalcined IrO2 nanoparticles were tested in an opera...

The increasing scarcity of iridium (Ir) and its rutile-type oxide (IrO 2), the current state-of-the-art oxygen evolution reaction (OER) catalysts, is driving the transition toward the use of mixed Ir oxides with a highly active yet inexpensive metal (Ir x M 1−x O 2). Ruthenium (Ru) has been commonly employed due to its high OER activity although it...

We report on an inverse model Cu/MgO methanol catalyst modified with 5% zinc oxide at the Cu surface to element‐specifically probe the interplay of metallic copper and zinc oxide during reductive activation. The structure of copper and zinc was unraveled by in situ X‐ray diffraction (XRD) and in situ X‐ray absorption spectroscopy (XAS) supported by...

The atomic scale structure of the active sites in heterogeneous catalysts is central to their reactivity and selectivity. Therefore, understanding active site stability and evolution under different reaction conditions is key to the design of efficient and robust catalysts. Herein we describe theoretical calculations which predict that carbon monox...

Although Cu/ZnO-based catalysts have been long used for the hydrogenation of CO2 to methanol, open questions still remain regarding the role and the dynamic nature of the active sites formed at the metal-oxide interface. Here, we apply high-pressure operando spectroscopy methods to well-defined Cu and Cu0.7Zn0.3 nanoparticles supported on ZnO/Al2O3...

Operando X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) were performed on a Co/TiO2 Fischer–Tropsch synthesis (FTS) catalyst at 16 bar for (at least) 48 h time-on-stream in both a synchrotron facility and a laboratory-based X-ray diffractometer. Cobalt carbide formation was observed earlier during FTS with operando XAS than with XR...

The Cover Feature illustrates the significant effects of trace impurities on the structure and syngas conversion reactivity of SiO2‐supported Co2C catalysts. In their Full Paper, A. S. Asundi et al. show that low concentrations of Na impurities in a commercial SiO2 support play an important role in stabilizing the Co2C phase resulting in a catalyst...

The design of supported heterogeneous catalysts requires a detailed understanding of the structure and chemistry of the active surface. Although the chemical components of the active phase, support material, and process feed are typically considered to be the most important factors governing catalyst structure and performance, many common commercia...

Co 2 C, an emerging catalyst for the conversion of syngas to oxygenates, shows support‐sensitive behavior that has not yet been fully explained. Here, we characterize Co catalysts modified with ZnO atomic layer deposition on SiO 2 , carbon, CeO 2 , and Al 2 O 3 supports. We find that under syngas conditions, ZnO‐promoted Co transforms into Co 2 C o...

Recently metal carbide catalysts have attracted attention as alternatives to pure metals for the conversion of syngas to higher oxygenates, a process which could enable the sustainable production of fuels, polymers, and chemicals. Although Mo and Co carbides have both shown promise for higher oxygenate production, they have not achieved the requisi...

An understanding of the fundamentals of the reaction between CuO with trace amounts of H2S to form CuS products is critical for the optimal utilization of this process in sulfur removal applications. Unfortunately, CuS is a complex material, featuring various Cu2-xS compounds (with 0 ≤ x ≤ 1), distorted crystal phases, and varying electronic struct...

Dopants enhance the catalytic properties of ceria. However, conventional techniques for synthesizing doped ceria have limitations in terms of structural homogeneity, surface area, and catalytic activity of the resulting oxide. Use of toxic and corrosive chemicals presents further challenges. The sol-gel method described in this work provides a faci...

Rh-based catalysts have shown promise for the direct conversion of syngas to higher oxygenates. Although improvements in higher oxygenate yield have been achieved by combining Rh with metal oxide promoters, details of the structure of the promoted catalyst and the role of the promoter in enhancing catalytic performance are not well understood. In t...

Metal organic frameworks (MOFs), with their crystalline, porous structures, can be synthesized to incorporate a wide range of catalytically active metals in tailored surroundings. These materials have potential as catalysts for conversion of light alkanes, feedstocks available in large quantities from shale gas that are changing the economics of ma...

Pd- and Pt-based catalysts are highly studied materials due to their widespread use in emissions control catalysis. However, claims continue to vary regarding the active phase and oxidation state of the metals. Different conclusions have likely been reached due to the heterogeneous nature of such materials containing various metal nanoparticle size...

Effective catalysts stabilize specific transition states and control the transport of species to and from catalytically active sites. Enzymes show these traits thanks to their diverse amino acid functional groups encapsulating metal centres, but are limited in the reaction conditions in which they can operate. Realizing a catalyst with this kinetic...

Supported metal single-atom catalysts have shown unique activity and selectivity for several reactions. Investigating the reaction mechanism on single-atom catalysts and unambiguous assignment of the activity and selectivity requires catalysts with exclusively single atoms. However, it is challenging to prepare pure single-atom catalysts with conve...

Catalytic CO2 reduction to fuels and chemicals is one of the major pursuits in reducing greenhouse gas emissions. One such popular approach utilizes the reverse water‐gas shift reaction, followed by Fischer‐Tropsch synthesis, and iron is a well‐known candidate for this process. Some attempts have been made to modify and improve its reactivity, but...

Catalytic CO2 reduction to fuels and chemicals is one of the major pursuits in reducing greenhouse gas emissions. One such popular approach utilizes the reverse water‐gas shift reaction, followed by Fischer‐Tropsch synthesis, and iron is a well‐known candidate for this process. Some attempts have been made to modify and improve its reactivity, but...

Hydrogen peroxide (H2O2) is a commodity chemical that serves as an oxidant and disinfectant for a number of historically important chemical end-use applications. Its synthesis can be made more sustainable, clean, and geographically distributed through technology based on the aqueous electrocatalytic two-electron reduction of O2, which produces H2O2...

Supported iridium complexes were synthesized on reduced graphene aerogel (rGA) by the reaction of Ir(CO)2(acac) [acac = acetonylacetonato] with oxygen-containing groups on the rGA. Characterization of the supported species by X-ray absorption, infrared, and X-ray photoelectron spectroscopies and atomic resolution aberration-corrected scanning trans...

The use of oxide-supported isolated Pt-group metal atoms as catalytic active sites is of interest due to their unique reactivity and efficient metal utilization. However, relationships between the structure of these active sites, their dynamic response to environments and catalytic functionality have proved difficult to experimentally establish. He...

The synthesis of zeolite-supported Mo carbide species was studied by testing different reduction/carburization conditions applied to a zeolite-supported Mo oxide catalyst, with the aim to find the optimized treatment conditions necessary to form stable supported Mo carbide catalysts ex situ for application in methane dehydroaromatization reaction....

The effect of dynamic reorganization and confinement of isolated TiIV catalytic centers supported on silicates is investigated for olefin epoxidation. Active sites consist of grafted single-site calix[4]arene-TiIV centers or their calcined counterparts. Their location is synthetically controlled to be either unconfined at terminal T-atom positions...

We acquired Pd K-edge and Au L3-edge EXAFS spectra of two libraries of titania-supported Pd-doped Au nanoparticle catalysts representing the as-prepared and post-catalysis state. The nanoparticles have narrow particle size distributions, in the range 2.8–6.6 nm, and were synthesized to preferentially locate the palladium atoms on the surface of a g...

The reactive surface sites of MoS2 hydrotreating catalysts (unpromoted as well as Co- and Ni-promoted) supported on MgAl2O4 spinel were investigated with respect to the substitution of sulfur by oxygen using in-situ XAS coupled with modulation excitation spectroscopy (MES). Specifically, MES experiments were carried out by periodically cycling betw...

Single-site Ir(CO)2 complexes bonded to high-surface-area metal oxide supports, SiO2, TiO2, Fe2O3, CeO2, MgO, and La2O3, were synthesized by chemisorption of Ir(CO)2(acac) (acac = acetylacetonate) followed by coating with each of the following ionic liquids (ILs): 1-n-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF4], 1-n-butyl-3-methylimida...

Controlling selectivity is a key goal in the design of a heterogeneous catalyst. Herein, we present detailed characterization and activity of silica‐supported cobalt catalysts both unmodified and a catalyst that has been modified by atomic layer deposition of ZnO. After reduction, the resulting catalyst exhibit substantial selectivity towards alcoh...

CO2 reduction to higher value products is a promising way to produce fuels and key chemical building blocks while reducing CO2 emissions. The reaction at atmospheric pressure mainly yields CH4 via methanation and CO via the reverse water gas shift (RWGS) reaction. Describing catalyst features that control the selectivity of these two pathways is im...

Selective oxidations are crucial for the creation of valuable chemical building blocks but often require expensive and unstable stoichiometric oxidants such as hydroperoxides and peracids. To date, many catalysts that contain a single type of active site have not been able to attain the desired level of selectivity for partially oxidized products o...

We studied the effect of 973 K heating in argon atmosphere on the magnetic and structural properties of a magnetite-bearing ore, which was previously exposed to laboratory shock waves between 5 and 30 GPa. For this purpose magnetic properties were studied using temperature-dependent magnetic susceptibility, magnetic hysteresis and low-temperature s...

This work reports on exploiting conventional and novel hard X-ray techniques for identifying the structure of catalysts in exhaust gas catalysis under working conditions. Operando X-ray absorption spectroscopy, high energy resolution fluorescence detected X-ray absorption near edge structure and valence-to-core (V2C) X-ray emission spectroscopy (XE...

Combined X-ray absorption spectroscopy (XAS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were applied to investigate the interaction between reaction atmosphere, adsorbates and Pt oxidation state of Pt/Al2O3 model diesel oxidation catalysts under CO/NO oxidation conditions. The Pt oxidation state was correlated to the a...

Representative Greek bauxite and red mud samples were studied by means of X-ray absorption spectroscopy (XAS) in order to investigate the oxidation state and the solid-state structural environment of the Fe atoms.

Analysis of the oxidation state and coordination geometry using pre-edge analysis is attractive for heterogeneous catalysis and materials science, especially for in situ and time-resolved studies or highly diluted systems. In the present study, focus is laid on iron-based catalysts. First a systematic investigation of the pre-edge region of the Fe...

An in-depth understanding of the active site requires advanced operando techniques and the preparation of defined catalysts. We elucidate here the mechanism of the selective catalytic reduction of NO by NH3 (NH3-SCR) over a Fe-ZSM-5 zeolite catalyst. 1.3 wt% Fe-ZSM-5 with low nuclearity Fe sites was synthesized, tested in the SCR reaction and chara...

MnOx and FeOx-based catalysts supported on γ-Al2O3 (0.1–20 wt %) were prepared by using two methods: incipient wetness impregnation and single-step flame spray pyrolysis. The effect of the structural properties and composition on the CO oxidation activity was systematically evaluated and correlated with the preparation methods. The characterization...

Fresh and mildly aged Pt/Al2O3 model diesel oxidation catalysts with small and large noble metal particle size have been studied during CO oxidation under lean burn reaction conditions to gain more insight into the structure and oscillatory reaction behaviour. The catalytic performance, CO adsorption characteristics using in situ DRIFTS and oxidati...

Structure–performance relationships for Pt/Al2O3 catalysts with mean Pt particle sizes of 1, 2, 3, 5 and 10 nm are investigated for the catalytic oxidation of CO and NO under lean-burning diesel exhaust conditions. The most active catalysts for CO oxidation exhibit Pt particles of 2–3 nm, having a large fraction of low-coordinated and reactive surf...

EXAFS and pre-edge information from the Fe K-edge absorption spectra is used in this study to characterise the local environment and geometry of Fe-centres in a 1% Fe/Al2O3 model catalyst. The EXAFS results reveal clusters of 2-3 Fe oxo-moieties dispersed on the Al2O3-support. The Fe3+ centres are coordinated by 6 O-atoms in a strongly distorted oc...