Shamil Shaikhutdinov

We investigated the effect of catalyst pretreatment with "cold" plasmas on the catalytic performance of Pt single-atom catalyst (SAC) precursors supported on Al₂O₃ for the propane dehydrogenation reaction. We found that the catalysts treated with a hydrogen plasma before the conventional calcination/reduction steps showed considerably increased propane conversion without loss of selectivity, whereas exposure to an argon plasma did not result in such an effect. Moreover, the H₂ plasma-treated catalyst showed a lower deactivation rate, suggesting better long-term stability. The structural and chemical evolution of the catalysts studied by TEM, XAS, XPS, and DRIFTS showed that the H₂ plasma: (i) partially reduces singly dispersed Pt²⁺ species and promotes Pt clustering; (ii) decreases the amount of Cl remaining after the use of the hexachloroplatinic acid precursor; and (iii) enhances surface defects in the alumina support. We propose that the promotional effect of the H₂ plasma lies in the specific modification of the alumina surface, which in turn alters the metal-support interaction and leads to the formation of a more active Pt/Al₂O₃ interface during the subsequent oxidation and reduction steps. The results show that nonthermal plasma treatments of single-atom precursors can become a tool for tuning the catalytic performance of highly dispersed metal catalysts.

We investigated the structure and reactivity of cubic Cu₂O nanoparticles (nanocubes) in the ethanol dehydrogenation (EDH) reaction, which is considered as an ecofriendly process for production of “green” hydrogen and valuable chemicals such as acetaldehyde. High-loaded catalysts prepared by physical mixing of nc-Cu₂O and SiO₂ demonstrated activity considerably higher than that of those prepared by conventional impregnation/calcination. Reactivity tests revealed the catalytic performance (conversion and selectivity) to be independent of the initial state of the catalyst, i.e., oxidized or reduced, due to the facile reduction of the Cu­(I) oxide to metallic Cu in the ethanol atmosphere, as observed by operando XRD, DRIFTS, and near ambient pressure (NAP) XPS. The reduction of nc-Cu₂O is accompanied by strong morphological changes, i.e., the transformation of the nanocubes into roundish nanoparticles and their sintering as shown by TEM and SEM. The Cu­(I) oxide catalyst is initially active in EDH, but the Cu(0) phase formed in situ is considerably more active, and the Cu(0) phase is the only one that exists at the steady state. Analysis of the Cu surface by NAP XPS and CO DRIFTS revealed only the metallic state, with no indication for surface Cu oxide formation under the reaction conditions. The catalysts are stable at relatively low temperatures (∼170 °C) but deactivate, most notably at temperatures above 230 °C, due to coke (mostly amorphous carbon) formation. The results suggest that nc-Cu₂O can be used as a well-defined precursor for the synthesis of high-loaded Cu catalysts for alcohol dehydrogenation at moderate temperatures.

This review critically discusses recent in situ and operando studies on Fe-based catalysts in CO ₂ hydrogenation, in particular focusing on the effect of composition, promoters, support and particle size.

Alloys of gallium with transition metals have recently received considerable attention for their applications in microelectronics and catalysis. Here, we investigated the initial stages of the Ga-Cu alloy formation on Cu(111) and Cu(001) surfaces using scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and low energy electron diffraction (LEED). The results show that Ga atoms deposited using physical vapor deposition readily intermix with the Cu surface, leading to a random distribution of the Ga and Cu atoms within the surface layer, on both terraces and monolayer-thick islands formed thereon. However, as the Ga coverage increases, several ordered structures are formed. The (√3×√3)R30° structure is found to be thermodynamically most stable on Cu(111). This structure remains after vacuum annealing at 600 K, independent of the initial Ga coverage (varied between 0.5 and 3 monolayers), indicating a self-limited growth of the Ga-Cu alloy layer, with the rest of the Ga atoms migrating into the Cu crystal. For Ga deposited on Cu(001), we observed a (1 × 5)-reconstructed surface, which has never been observed for surface alloys on Cu(001). The experimental findings were rationalized on the basis of density functional theory (DFT) calculations, which provided structural models for the most stable surface Ga-Cu alloys on Cu(111) and Cu(001). The study sheds light on the complex interaction of Ga with transition metal surfaces and the interfaces formed thereon that will aid in a better understanding of surface alloying and chemical reactions on the Ga-based alloys.

Carbon monoxide adsorption experiments were performed to probe surface atoms on the MnO surface, followed by water adsorption experiments that revealed molecule dissociation occurring at oxygen vacancies mediated by nearby Mn²⁺ sites.

Gallium-containing alloys have recently been reported to hydrogenate CO₂ to methanol at ambient pressures. However, a full understanding of the Ga-promoted catalysts is still missing due to the lack of information about the surface structures formed under reaction conditions. Here, we employed near ambient pressure scanning tunneling microscopy and x-ray photoelectron spectroscopy to monitor the evolution of well-defined Cu-Ga surfaces during CO₂ hydrogenation. We show the formation of two-dimensional Ga(III) oxide islands embedded into the Cu surface in the reaction atmosphere. The islands are a few atomic layers in thickness and considerably differ from bulk Ga₂O₃ polymorphs. Such a complex structure, which could not be determined with conventional characterization methods on powder catalysts, should be used for elucidating the reaction mechanism on the Ga-promoted metal catalysts.

Ultrathin silica films are considered suitable two-dimensional model systems for the study of fundamental chemical and physical properties of all-silica zeolites and their derivatives, as well as novel supports for the stabilization of single atoms. In the present work, we report the creation of a new model catalytic support based on the surface functionalization of different silica bilayer (BL) polymorphs with well-defined atomic structures. The functionalization is carried out by means of in situ H-plasma treatments at room temperature. Low energy electron diffraction and microscopy data indicate that the atomic structure of the films remains unchanged upon treatment. Comparing the experimental results (photoemission and infrared absorption spectra) with density functional theory simulations shows that H2 is added via the heterolytic dissociation of an interlayer Si-O-Si siloxane bond and the subsequent formation of a hydroxyl and a hydride group in the top and bottom layers of the silica film, respectively. Functionalization of the silica films constitutes the first step into the development of a new type of model system of single-atom catalysts where metal atoms with different affinities for the functional groups can be anchored in the SiO2 matrix in well-established positions. In this way, synergistic and confinement effects between the active centers can be studied in a controlled manner.

Atomically dispersed precious metals on oxide supports have recently become increasingly interesting catalytic materials. Nonetheless, their non‐trivial preparation and limited thermal and environmental stability constitutes an issue for their potential applications. Here we demonstrate that an oxygen plasma pre‐treatment of the ceria (CeO ₂ ) surface serves to anchor Pt single atoms, making them active and resistant towards sintering in the CO oxidation reaction. Through a combination of experimental results obtained on well‐defined CeO ₂ films and theory, we show that the O ₂ plasma causes surface nanostructuring and the formation of surface peroxo (O ₂ ²⁻ ) species, favoring the uniform and dense distribution of isolated strongly bonded Pt ²⁺ atoms. The promotional effect of the plasma treatment was further demonstrated on powder Pt/CeO ₂ catalysts. We believe that plasma functionalization can be applied to other metal/oxide systems to achieve tunable and stable catalysts with a high density of active sites.

Atomically dispersed precious metals on oxide supports have recently become increasingly interesting catalytic materials. Nonetheless, their non‐trivial preparation and limited thermal and environmental stability constitutes an issue for their potential applications. Here we demonstrate that an oxygen plasma pre‐treatment of the ceria (CeO ₂ ) surface serves to anchor Pt single atoms, making them active and resistant towards sintering in the CO oxidation reaction. Through a combination of experimental results obtained on well‐defined CeO ₂ films and theory, we show that the O ₂ plasma causes surface nanostructuring and the formation of surface peroxo (O ₂ ²⁻ ) species, favoring the uniform and dense distribution of isolated strongly bonded Pt ²⁺ atoms. The promotional effect of the plasma treatment was further demonstrated on powder Pt/CeO ₂ catalysts. We believe that plasma functionalization can be applied to other metal/oxide systems to achieve tunable and stable catalysts with a high density of active sites.