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Abstract: Excessively strong adsorption of CO onto a Pt-based catalyst results in the poisoning effect during numerous CO-containing catalysis reactions, including the dehydrogenation process of alcohols. Traditional strategies via modifying the electronic state of Pt atoms are beneficial for weakening CO adsorption; however, they are normally detrimental to C–H cracking, thereby degrading catalytic efficiency toward alcohol dehydrogenation reaction. In this work, we present a synergistic function of Pt1 single atoms and heterostructured MoOx/Mo2N for efficiently dehydrogenating alcohols, allowing high CO resistance along with excellent capacity for C–H and O–H activation. This conjunction renders electron transfer via a strong Pt-MoOx/Mo2N interaction and thus induces the low 5d occupancy of Pt sites, enabling the facile CO desorption, which thereby boosts the efficiency of entire reaction cycles. Based on in situ structural characterizations and isotopic labeling analysis, we found that the spontaneously formed thin MoOx-Ov layer enables the barrierless breakage of O–H bonds even at as low as room temperature, which further energetically facilitates C–H cracking on interfacial Pt1 sites. Therefore, this strategy can be applied to fabricate CO-tolerant Pt-based catalysts toward numerous CO-containing reactions without compromising reactivity by coupling the advantages of single-atom and defective support materials.

Open Access

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Abstract: Selective catalytic oxidation (SCO) of NH3 to N2 is one of the most effective methods used to eliminate NH3 emissions. However, achieving high conversion over a wide operating temperature range while avoiding over-oxidation to NOx remains a significant challenge. Here, we report a bi-metallic surficial catalyst (PtSCuO/Al2O3) with improved Pt atom efficiency that overcomes the limitations of current catalysts. It achieves full NH3 conversion at 250 °C with a weight hourly space velocity of 600 ml NH3·h−1·g−1, which is 50 °C lower than commercial Pt/Al2O3, and maintains high N2 selectivity through a wide temperature window. Operando XAFS studies reveal that the surface Pt atoms in PtSCuO/Al2O3 enhance the redox properties of the Cu species, thus accelerating the Cu2+ reduction rate and improving the rate of the NH3-SCO reaction. Moreover, a synergistic effect between Pt and Cu sites in PtSCuO/Al2O3 contributes to the high selectivity by facilitating internal selective catalytic reduction.

Open Access

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Abstract: Ambient pressure X-ray photoelectron spectroscopy (AP-XPS) was employed to investigate the effect of applied potential on the interface of TiO2(110) with 0.1 M HCl. The study, which involved operando electrochemical characterization, enabled real-time monitoring and analysis of electrochemical processes. There is a significant influence on the interface composition; in particular, the surface Cl– surface coverage varies with electrochemical potential. Moreover, there appears to be a reaction of evolved Cl with adventitious carbon to form C–Cl and C–Cl2 species.

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Abstract: Hydrocarbons such as gasoline and short olefins are among the most important chemical raw materials in industry. They are used as energy sources and to power most means of transport and machines worldwide. For a long time, these chemicals were produced almost exclusively in the petrochemical industry. However, the over-exploitation of these resources has led to various environmental problems and has been shown to play a crucial role in greenhouse gas emissions into the atmosphere. As a possible environmentally friendly alternative, hydrocarbons can also be synthesized through the catalytic reduction of CO2 with green H2. This process has the great advantage that the CO2 can be used as a raw material. It is particularly attractive if the CO2 is extracted directly from the atmosphere in order to generate a neutral CO2 cycle. This work deals with the characterization of iron-based catalysts for the hydrogenation of CO2 to hydrocarbons. In particular, a combination of real catalysts (powder catalysts) and flat model catalysts (planar catalysts) is used. The advantage of such an approach is that surface science tools and methods can be used in addition to the conventional methods commonly used to characterize catalysts. The reason for this work is the numerous contradictions regarding the parameters controlling the catalytic performance of CO2 hydrogenation with Fe-based catalysts. My goal is to gain a better understanding of the fundamental behavior of the active catalytic Fe phase for the CO2 hydrogenation reaction. For this purpose, a combination of operando, in situ and ex situ characterizations are carried out and correlated with the catalytic performance of the various catalysts produced. Particular attention was paid to in situ surface characterization using X-ray photoelectron spectroscopy (NAP-XPS) and operando characterization using X-ray absorption spectroscopy (XAS). The first part of this work addresses the role of the oxide support in the catalytic performance of Fe-based nanoparticles. It is shown how the traditionally considered inert substrates (Al2O3 and SiO2) alter the selectivity of small Fe nanoparticles during CO2 hydrogenation. The selectivity changes depending on the substrate are associated with the interaction and influence of the carrier on the Fe nanoparticles and how the carrier defines the chemical state of the active Fe phase. The second section focuses on how the size of Fe nanoparticles affects the catalytic performance in CO2 hydrogenation. In particular, the size of the Fe nanoparticles influences the reducibility of the Fe precursors during the activation of the catalyst and thus directly affects the chemical state of the Fe under the reaction conditions. In this way, it determines the observed catalytic performance. This work ends by linking both effects in Fe-based catalysts (size and support effects) as they are coupled with each other. In summary, my work shows that the catalytic performance of Fe-based materials is highly dependent on parameters such as their support and the size of the nanoparticles. This results in a deeper understanding of the complex behaviors of these Fe-based systems described in the literature.

Open Access

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Abstract: Single-atom catalysts have garnered significant attention due to their exceptional atom utilization and unique properties. However, the practical application of these catalysts is often impeded by challenges such as sintering-induced instability and poisoning of isolated atoms due to strong gas adsorption. In this study, we employed the mechanochemical method to insert single Cu atoms into the subsurface of Fe2O3 support. By manipulating the location of single atoms at the surface or subsurface, catalysts with distinct adsorption properties and reaction mechanisms can be achieved. It was observed that the subsurface Cu single atoms in Fe2O3 remained isolated under both oxidation and reduction environments, whereas surface Cu single atoms on Fe2O3 experienced sintering under reduction conditions. The unique properties of these subsurface single-atom catalysts call for innovations and new understandings in catalyst design.