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The strong metal-support interaction (SMSI) is one of the most important concepts in heterogeneous catalysis, which has been widely investigated between metals and active oxides triggered by reductive atmospheres. Here, we report the oxidative strong metal-support interaction (O-SMSI) effect between Pt nanoparticles (NPs) and inert hexagonal boron nitride (h-BN) sheets, in which Pt NPs are encapsulated by oxidized boron (BO

Oxygen vacancies (Vos) play a vital role in the physical and chemical properties of oxide materials and their applications. Because Vos are first produced on oxide surfaces, it has been often recog...

Bimetallic nanoparticle catalysts attract extensive attention for relevant catalysis processes due to their flexible structures, while the structure evolution under specific conditions is ambiguous...

Summary Propane dehydrogenation (PDH) is a commercial propylene production technology that has received much attention, but high reaction temperatures result in a decrease of propylene selectivity and catalyst stability. This paper describes a single-site [PtZn4] catalyst by assembling atomically ordered intermetallic alloy (IMA) as a selective and ultrastable PDH catalyst. The catalyst enables more than 95% of propylene selectivity from 520°C to 620°C. No obvious deactivation is observed within the 160-h test, superior to PtSn/Al2O3 and state-of-the-art Pt-based catalysts. Based on in situ X-ray absorption fine structure, X-ray photoelectron spectroscopy measurements, and density functional theory calculations, we reveal that the surface [PtZn4] ensembles in PtZn IMAs serve as the key active site structures, wherein the geometry-isolated and electron-rich Pt1 site in [PtZn4] ensembles readily promotes the first and second C–H cleavage of propane but inhibits further dehydrogenation of surface-bounded propylene. This significantly improves the selectivity and stability by prohibiting coke side reactions.

Well-defined manganese oxide (MnOx) overlayers with a controlled chemical state and coverage were deposited on Au(111), and CO activation at the model MnOx/Au(111) surfaces was explored by combinin...

Chemical looping provides an energy- and cost-effective route for alkane utilization. However, there is considerable CO2 co-production caused by kinetically mismatched O2- bulk diffusion and surface reaction in current chemical looping oxidative dehydrogenation systems, rendering a decreased olefin productivity. Sub-monolayer or monolayer vanadia nanostructures are successfully constructed to suppress CO2 production in oxidative dehydrogenation of propane by evading the interference of O2- bulk diffusion (monolayer versus multi-layers). The highly dispersed vanadia nanostructures on titanium dioxide support showed over 90 % propylene selectivity at 500 °C, exhibiting turnover frequency of 1.9×10-2 s-1 , which is over 20 times greater than that of conventional crystalline V2 O5 . Combining in situ spectroscopic characterizations and DFT calculations, we reveal the loading-reaction barrier relationship through the vanadia/titanium interfacial interaction.

Defects are ubiquitous in oxide supports and can often tune the catalytic property of supported metal catalysts. This work describes the distinct role of titanium and oxygen vacancies of TiO2 supports in the catalytic performance of supported Pt catalysts for CO oxidation. Pt was loaded on the TiO2 supports with oxygen vacancies (VO-TiO2) and titanium vacancies (VTi-TiO2). It was found that different defects of TiO2 could distinctively modify the electron property of Pt and thereby CO adsorption strength. The strength of CO adsorption on Pt/VTi-TiO2 is enhanced, while that of Pt/VO-TiO2 becomes weaker. Additionally, the presence of defects would also promote the reducibility of catalysts. On the account of the superior redox ability, both Pt/VTi-TiO2 and Pt/VO-TiO2 exhibit a higher activity than Pt supported on normal TiO2 for CO oxidation.

This paper describes the design of a FeWOx-based oxygen carrier for the chemical partial oxidation of methane (CLPOM). Thermodynamic screening and kinetic analyses both forecast the FeWOx-based oxygen carrier as a promising candidate for the production of syngas. The total methane conversion and syngas yield can be dramatically increased with this catalyst compared to the case with the unmodified WO3/SiO2, thereby enabling CLPOM with 62% methane conversion, 93% CO gas-phase selectivity, 94% H2 selectivity, and a 2.4 H2/CO ratio. The catalyst has the advantages of high availability of lattice oxygen to oxidize carbonaceous intermediates in time, together with the formation of an Fe-W alloy to promote the surface reaction. Consequently, it demonstrates excellent catalytic performance with no catalyst deactivation at 900 dC and 1 atm. The excellent structural stability plays an essential role in CLPOM. As revealed via XPS and ICP, the phase segregation has not been observed due to the strong interaction between Fe and W, which resulted in the formation of the Fe-W alloy during the reduction processes and the match between the ion oxidation rates of the Fe and W ions in the oxidation stage. The results provide fundamental information on the reaction mechanism of FeWOx/SiO2, and present it as a promising candidate for CLPOM.

Pt–Mn bimetallic catalysts exhibit high activity in many heterogeneous catalytic and electrocatalytic reactions. However, the surface structure of Pt–Mn catalysts under different reaction condition...

Modulating lattice oxygen in metal oxides that conducts partial oxidation of methane in balancing C-H activation and syngas selectivity remains challenging. This paper describes the discovery of distorting FeO6 octahedra in La1-xCexFeO3 (x = 0, 0.25 0.5, 0.75, 1) orthorhombic perovskites for the promotion of lattice oxygen activation. By combined electrical conductivity relaxation measurements and density functional theory calculations studies, this paper describes the enhancement of FeO6 octahedral distortion in La1-xCexFeO3 promoting their bulk oxygen mobility and surface oxygen exchange capability. Consequently, La0.5Ce0.5FeO3 with the highest FeO6 distortion achieves exceptional syngas productivity of ∼3 and 8 times higher than LaFeO3 and CeFeO3, respectively, in CH4 partial oxidation step with simultaneous high CO2 conversion (92%) in the CO2-splitting step at 850 °C. The results exemplify the feasibility to tailor the active lattice oxygen of perovskite by modulating the distortion of BO6 in ABO3, which ultimately influences their reaction performance in chemical looping processes.

Understanding of thin film growth mechanism is crucial for tailoring film growth behaviors, which in turn determine physicochemical properties of the resulting films. Here, vapor-growth of tungsten carbide overlayers on W(110) surface is investigated by real time low energy electron microscopy. The surface growth is strongly confined by surface steps, which is in contrast with overlayer growth crossing steps in a so-called carpet-like growth mode for example in graphene growth on metal surfaces. Density functional theory calculations indicate that the step-confined growth is caused by the strong interaction of the forming carbide overlayer with the substrate blocking cross-step growth of the film. Furthermore, the tungsten carbide growth within each terrace is facilitated by the supply of carbon atoms from near-surface regions at high temperatures. These findings suggest the critical role of near-surface atom diffusion and step confinement effects in the thin film growth, which may be active in many film growth systems.

Oxygen chemistry plays a pivotal role in numerous chemical reactions. In particular, selective cleavage of C-H bonds by metal oxo species is highly desirable in dehydrogenation of light alkanes. However, high selectivity of alkene is usually hampered through consecutive oxygenation reactions in a conventional oxidative dehydrogenation (ODH) scheme. Herein, we show that dual-functional Mo-V-O mixed oxides selectively convert propane to propylene via an alternative chemical looping oxidative dehydrogenation (CL-ODH) approach. At 500 °C, we obtain 89% propylene selectivity at 36% propane conversion over 100 dehydrogenation-regeneration cycles. We attribute such high propylene yield-which exceeds that of previously reported ODH catalysts-to the involvement and precise modulation of bulk lattice oxygen via atomic-scale doping of Mo and show that increasing the binding energy of V-O bonds is critical to enhance the selectivity of propylene. This work provides the fundamental understanding of metal-oxygen chemistry and a promising strategy for alkane dehydrogenation.

Metal oxide-promoted Rh-based catalysts have been widely used for CO2 hydrogenation, especially for the ethanol synthesis. However, this reaction usually suffers low CO2 conversion and alcohols selectivity due to the formation of byproducts methane and CO. This paper describes an efficient vanadium oxide promoted Rh-based catalysts confined in mesopore MCM-41. The Rh-0.3VOx/MCM-41 catalyst shows superior conversion (~12%) and ethanol selectivity (~24%) for CO2 hydrogenation. The promoting effect can be attributed to the synergism of high Rh dispersion by the confinement effect of MCM-41 and the formation of VOx-Rh interface sites. Experimental and theoretical results indicate the formation of til-CO at VOx-Rh interface sites is easily dissociated into *CHx, and then *CHx can be inserted by CO to form CH3CO*, followed by CH3CO* hydrogenation to ethanol.

The search for efficient nontoxic catalysts able to perform industrial hydrogenations is a topic of interest, with relevance to many catalytic processes. Herein, we describe a mechanistic phenomenon for the activation and spillover of hydrogen for remarkable selectivity in the semi-hydrogenation of acetylene over sub-1 nm Pd nanoclusters confined within sodalite (SOD) zeolite (Pd@SOD). Specifically, hydrogen is dissociated on the Pd nanoclusters to form hydrogen species (i.e., hydrogen atoms and hydroxyl groups) that spill over the SOD surfaces. The design and utilization of the small-pore zeolite SOD (six-membered rings with 0.28×0.28 nm channels) is crucial as it only allows H2 diffusion into the channels to reach the encapsulated Pd nanoclusters and thus avoids over-hydrogenation to form ethane. Pd@SOD exhibits an ethylene selectivity of over 94.5 %, while that of conventional Pd/SOD is approximately 21.5 %.

Oxide-supported Rh nanoparticles have been widely used for CO2 hydrogenation, especially for ethanol synthesis. However, this reaction operates under high pressure, up to 8 MPa, and suffers from low CO2 conversion and alcohol selectivity. This paper describes the crucial role of hydroxyl groups bound on Rh-based catalysts supported on TiO2 nanorods (NRs). The RhFeLi/TiO2 NR catalyst shows superior reactivity (≈15% conversion) and ethanol selectivity (32%) for CO2 hydrogenation. The promoting effect can be attributed to the synergism of high Rh dispersion and high-density hydroxyl groups on TiO2 NRs. Hydroxyls are proven to stabilize formate species and protonate methanol, which is easily dissociated into *CHx, and then CO obtained from the reverse water–gas shift reaction (RWGS) is inserted into *CHx to form CH3CO*, followed by CH3CO* hydrogenation to ethanol.

Artificial photosynthesis can be used to store solar energy and reduce CO2 into fuels to potentially alleviate global warming and the energy crisis. Compared to the generation of gaseous products, it remains a great challenge to tune the product distribution of artificial photosynthesis to liquid fuels, such as CH3 OH, which are suitable for storage and transport. Herein, we describe the introduction of metallic Cu nanoparticles (NPs) on Cu2 O films to change the product distribution from gaseous products on bare Cu2 O to predominantly CH3 OH by CO2 reduction in aqueous solutions. The specifically designed Cu/Cu2 O interfaces balance the binding strengths of H* and CO* intermediates, which play critical roles in CH3 OH production. With a TiO2 model photoanode to construct a photoelectrochemical cell, a Cu/Cu2 O dark cathode exhibited a Faradaic efficiency of up to 53.6 % for CH3 OH production. This work demonstrates the feasibility and mechanism of interface engineering to enhance the CH3 OH production from CO2 reduction in aqueous electrolytes.

Ruthenium dioxide is used extensively as a co-catalyst in a wide range of photocatalytic water splitting systems. As such, understanding how it promotes the evolution of hydrogen and oxygen is of high importance. In this study, we employ scanning tunneling microscopy to study the adsorption and reaction of hydrogen on a model RuO2(110) surface. We find that at low coverages H2 dissociates heterolytically to hydride‑hydroxyl pairs even at 5 K. The onset temperature for the low coverage H2 dissociation is surprising as it is not expected based on prior temperature programmed desorption studies. At higher coverages, H2 chemisorbs molecularly on bare ruthenium sites that are neighboring the hydride‑hydroxyl pairs. Upon annealing, the chemisorbed H2 disappears by 120 K, primarily due to H2 desorption from the surface. Further annealing between 120 and 295 K leads to the conversion of hydride species to bridging hydroxyls. The bridging hydroxyls ultimately recombine between 450 and 600 K to form water, yielding clean RuO2(110) with oxygen vacancies.

Oxidative dispersion has been widely used in regeneration of sintered metal catalysts and fabrication of single atom catalysts, which is attributed to an oxidation-induced dispersion mechanism. However, the interplay of gas-metal-support interaction in the dispersion processes, especially the gas-metal interaction has not been well illustrated. Here, we show dynamic dispersion of silver nanostructures on silicon nitride surface under reducing/oxidizing conditions and during carbon monoxide oxidation reaction. Utilizing environmental scanning (transmission) electron microscopy and near-ambient pressure photoelectron spectroscopy/photoemission electron microscopy, we unravel a new adsorption-induced dispersion mechanism in such a typical oxidative dispersion process. The strong gas-metal interaction achieved by chemisorption of oxygen on nearly-metallic silver nanoclusters is the internal driving force for dispersion. In situ observations show that the dispersed nearly-metallic silver nanoclusters are oxidized upon cooling in oxygen atmosphere, which could mislead to the understanding of oxidation-induced dispersion. We further understand the oxidative dispersion mechanism from the view of dynamic equilibrium taking temperature and gas pressure into account, which should be applied to many other metals such as gold, copper, palladium, etc. and other reaction conditions., Designing ultra small metal nanoclusters or single atoms with metallic state is a challenge. Here, the authors demonstrate the stabilization of ultra small silver clusters in the nearly-metallic state by oxygen adsorption at high temperature, using in situ spectroscopy and microscope technologies.

The rational design and controlled construction of active centers remain grand challenges in heterogeneous catalysis, in particular for oxide catalysts with complex surface and interface structures. This work describes a facile way in the design of highly active Ni-O Lewis pairs for water activation where Ni and O sites act as Lewis acid and base, respectively. Surface science experiments indicate that dissociative adsorption of water occurs at edges of NiOx nanoislands grown on Au(111) and NiOx-Ni interfaces formed by further depositing metallic Ni layers along the edges of NiOx nanoislands. Enhanced activity of Ni-O Lewis pairs at the NiOx-Ni interface has been demonstrated by theoretical calculations, which are attributed to the higher Lewis acidity of metallic Ni sites and synergy of the metal and oxide components. Moreover, proton can migrate away from the NiOx-Ni interface and refresh the O base sites, leading to further hydroxylation of the neighboring Ni acid sites.

Noble-metal alloys are widely used as heterogeneous catalysts. However, due to the existence of scaling properties of adsorption energies on transition metal surfaces, the enhancement of catalytic activity is frequently accompanied by side reactions leading to a reduction in selectivity for the target product. Herein, we describe an approach to breaking the scaling relationship for propane dehydrogenation, an industrially important reaction, by assembling single atom alloys (SAAs), to achieve simultaneous enhancement of propylene selectivity and propane conversion. We synthesize γ-alumina-supported platinum/copper SAA catalysts by incipient wetness co-impregnation method with a high copper to platinum ratio. Single platinum atoms dispersed on copper nanoparticles dramatically enhance the desorption of surface-bounded propylene and prohibit its further dehydrogenation, resulting in high propylene selectivity (~90%). Unlike previous reported SAA applications at low temperatures (, Enhancing the catalytic activity of noble-metal alloys is frequently accompanied by side reactions. Here, the authors describe an approach to break the scaling relationship for propane dehydrogenation, by assembling single atom alloys, to achieve simultaneous enhancement of propylene selectivity and propane conversion.

Electroreduction (ER) of carbon dioxide (CO2) is a promising way to curb excessive CO2 emission and produce value-added products. Gold–copper (AuCu) alloys are known to exhibit eminent CO production performance toward CO2ER. However, it still remains a grand challenge to balance *COOH and *CO bonding and to further decrease CO onset potential. This Letter describes the construction of Cu vacancies at an abrupt surface over a dealloyed AuCu catalyst to effectively decrease the overpotential and increase CO faradaic efficiency. Dealloyed Au3Cu exhibited a 90.2% CO faradaic efficiency at −0.38 V vs RHE and a 418.60 A/g CO mass current density at −0.8 V. vs RHE, achieving the record for CO production among AuCu catalysts. Combining the experimental and theoretical results, we concluded that the improved performance primarily results from the enhanced *COOH absorption.

Thermal diffusion of CO adsorbed on rutile TiO2(110) was studied in the 20–110 K range using photon-stimulated desorption (PSD), temperature-programmed desorption (TPD), and scanning tunneling microscopy. During UV irradiation, CO desorbs from certain photoactive sites (e.g., oxygen vacancies). This phenomenon was exploited to study CO thermal diffusion in three steps: first, empty these sites during a first irradiation cycle, then replenish them with CO during annealing, and finally probe the active site occupancy in the second PSD cycle. The PSD and TPD experiments show that the CO diffusion rate correlates with the CO adsorption energy—stronger binding corresponds to slower diffusion. Increasing the CO coverage from 0.06 to 0.44 monolayer (ML) or hydroxylation of the surface decreases the CO binding and increases the CO diffusion rate. Relative to the reduced surface, the CO adsorption energy increases and the diffusion decreases on the oxidized surface. The CO diffusion kinetics can be modeled satisfa...

Supported vanadium oxides are one of the most promising alternative catalysts for propane dehydrogenation (PDH) and efforts have been made to improve its catalytic performance. However, unlike Pt-based catalysts, the nature of the active site and surface structure of the supported vanadium catalysts under reductive reaction conditions still remain elusive. This paper describes the surface structure and the important role of surface-bound hydroxyl groups on VOx / γ-Al2 O3 catalysts under reaction conditions employing in situ DRIFTS experiments and DFT calculations. It is shown that hydroxyl groups on the VOx /Al2 O3 catalyst (V-OH) are produced under H2 pre-reduction, and the catalytic performance for PDH is closely connected to the concentration of V-OH species on the catalyst. The hydroxyl groups are found to improve the catalyst that leads to better stability by suppressing the coke deposition.

Carbon dioxide (CO2 ) reduction in aqueous solutions is an attractive strategy for carbon capture and utilization. Cuprous oxide (Cu2 O) is a promising catalyst for CO2 reduction as it can convert CO2 into valuable hydrocarbons and suppress the side hydrogen evolution reaction (HER). However, the nature of the active sites in Cu2 O remains under debate because of the complex surface structure of Cu2 O under reducing conditions, leading to limited guidance in designing improved Cu2 O catalysts. This paper describes the functionality of surface-bonded hydroxy groups on partially reduced Cu2 O(111) for the CO2 reduction reaction (CO2 RR) by combined density functional theory (DFT) calculations and experimental studies. We find that the surface hydroxy groups play a crucial role in the CO2 RR and HER, and a moderate coverage of hydroxy groups is optimal for promotion of the CO2 RR and suppression of the HER simultaneously. Electronic structure analysis indicates that the charge transfer from hydroxy groups to coordination-unsaturated Cu (CuCUS ) sites stabilizes surface-adsorbed COOH*, which is a key intermediate during the CO2 RR. Moreover, the CO2 RR was evaluated over Cu2 O octahedral catalysts with {111} facets and different surface coverages of hydroxy groups, which demonstrates that Cu2 O octahedra with moderate coverage of hydroxy groups can indeed enhance the CO2 RR and suppress the HER.

Mixed-metal oxides are one of the most frequently used catalysts in chemical industry, because the superior catalytic reactivity can be achieved by taking advantage of the synergetic effects of their parent oxides. However, the interfacial electronic interactions between metal oxides remain unclear, because of their structural complexity. This paper describes the modulation of catalytic performance of mixed RuO2/TiO2 catalysts via adjusting the loading amount of RuO2. We show that, at very low loadings, the majority of RuO2 catalysts can be anchored at the defective sites of TiO2 substrates. Spectroscopic studies, combined with density functional calculations, indicate that electrons transfer from defective sites of substrates to RuO2, causing an increase in the apparent reaction barrier of CO oxidation. As the loading of Ru increases, RuO2 starts to appear on the terrace of TiO2, and the apparent reaction barrier of CO oxidation decreases. At the medium loading of ∼0.75 wt %, the lowest apparent reaction...

The existence of acetylene impurities in ethylene feedstock is harmful to downstream polymerization reactions. The removal of acetylene can be achieved via semihydrogenation reaction, which is normally catalyzed by Pd-based catalysts. This paper describes the coverage effect on the activity of acetylene hydrogenation reactions over Pd and PdSn alloy surfaces. High-coverage models are presented to construct coverage-dependent adsorption energies of C2H2, C2H4, and H2 on Pd(111) and Pd3Sn(111) surfaces. It has been validated that the downshift of d-band center caused by preadsorbed molecules makes the adsorption weaker along with the increase of coverage, and the geometric effect can be neglected. An iterative method has been applied to predict surface coverages of reaction intermediates. Previous calculations with low-coverage models indicate that alloying Pd with late or post-transition metals, in general, enhances ethylene selectivity, accompanied with lower hydrogenation activity. However, by applying a...

The adsorption and photochemistry of CO on rutile TiO2(110) are studied with scanning tunneling microscopy (STM), temperature-programmed desorption, and angle-resolved photon-stimulated desorption (PSD) at low temperatures. Site occupancies, when weighted by the concentration of each kind of adsorption site on the reduced surface, show that the adsorption probability is the highest for the bridging oxygen vacancies (VO). The probability distribution for the different adsorption sites corresponds to very small differences in CO adsorption energies (

Supported VOx catalysts are promising non-oxidative propane dehydrogenation (PDH) materials for their commercially attractive activity and propylene selectivity. However, they frequently suffer from rapid deactivation caused by coke deposition. This paper describes the promoting role of magnesium on the stability of VOx/Al2O3 catalysts for PDH. A series of VOx/Al2O3 and Mg-modified VOx/Al2O3 catalysts were synthesized by an incipient wetness impregnation method. The catalysts were carefully characterized by Raman spectra, UV-Vis spectra, STEM, TGA and in situ DRIFTS. We showed that the stability of a 12V/Al2O3 catalyst was significantly improved upon addition of small amounts of MgO. Experimental evidences indicate that V2O5 nanoparticles emerge in the 12V/Al2O3 samples, and appropriate Mg addition helps dispersing the V2O5 nanoparticles into 2D VOx species thus decreasing coke formation and improving stability in non-oxidative dehydrogenation of propane. This article is protected by copyright. All rights reserved.

Understanding adsorbed water and its dissociation to surface hydroxyls on oxide surfaces is key to unraveling many physical and chemical processes, yet the barrier for its deprotonation has never been measured. In this study, we present direct evidence for water dissociation equilibrium on rutile-TiO2(110) by combining supersonic molecular beam, scanning tunneling microscopy (STM), and ab initio molecular dynamics. We measure the deprotonation/protonation barriers of 0.36 eV and find that molecularly bound water is preferred over the surface-bound hydroxyls by only 0.035 eV. We demonstrate that long-range electrostatic fields emanating from the oxide lead to steering and reorientation of the molecules approaching the surface, activating the O–H bonds and inducing deprotonation. The developed methodology for studying metastable reaction intermediates prepared with a high-energy molecular beam in the STM can be readily extended to other systems to clarify a wide range of important bond activation processes.

This paper describes a detailed understanding of the influence of surface defects of TiO2 supports on the catalytic properties of Pt catalysts., In heterogeneous catalysis, it is widely believed that the surface states of catalyst supports can strongly influence the catalytic performance, because active components are generally anchored on supports. This paper describes a detailed understanding of the influence of surface defects of TiO2 supports on the catalytic properties of Pt catalysts. Pt was deposited on reduced (r-), hydroxylated (h-), and oxidized (o-) TiO2 surfaces, respectively, and the different surface states of TiO2 not only lead to differences in metal dispersion, but also distinct electronic interactions between the metal and the support. The highest reactivity for catalytic CO oxidation can be achieved over the Pt catalyst supported on reduced TiO2 with surface oxygen vacancies. The turnover frequency (TOF) of this catalyst is determined to be ∼11 times higher than that of Pt supported on oxidized TiO2. More importantly, the reactivity is seen to increase in the sequence of Pt/o-TiO2 < Pt/h-TiO2 < Pt/r-TiO2, which is well consistent with the trend of the calculated Bader charge of Pt.

Sorption enhanced steam reforming of methanol (SESRM) can significantly promote the hydrogen production process with simultaneous CO2 sorption. The mechanical mixture of catalysts and sorbents as a conventional approach is complex and requires high temperatures for regeneration, which results in serious sintering of Cu-based catalysts. This paper describes a novel Cu-MgO/Al2O3 bifunctional catalysts (xCMA, x is denoted as the mass fraction of Cu, 0%–10%) via a sol–gel method for the SESRM process. We find that Cu species, including metallic Cu and Cu ions, co-exist on the catalyst. The metallic Cu on the catalyst surface is an active site for methanol steam reforming while the Cu ion in MgO lattice promotes the CO2 sorption capacity. Moreover, the incorporation of Cu ion into MgO also facilitates CO2 desorption by forming more bidentate carbonates. Due to the strong interaction between Cu and MgO, the Cu sintering is inhabited in comparison with the mechanical mixture of catalysts and sorbents. Meanwhile, MgO is found to induce more formate species to inhibit the generation of carbon monoxide. As a result, the optimal bifunctional catalyst, 8 wt% Cu-MgO/Al2O3 (8CMA) shows a superior performance in both catalytic reforming and CO2 sorption with a highest H2 selectivity of 99.3% and lowest CO selectivity (

The coordination of H2 to a metal center via polarization of its σ bond electron density, known as a Kubas complex, is the means by which H2 chemisorbs at Ru(4+) sites on the rutile RuO2(110) surface. This distortion of electron density off an interatomic axis is often described as a 'banana-bond.' We show that the Ru-H2 banana-bond can be destabilized and split using visible light. Photodesorption of H2 (or D2) is evident by mass spectrometry and scanning tunneling microscopy. From time-dependent density functional theory, the key optical excitation splitting the Ru-H2 complex involves an interband transition in RuO2 which effectively diminishes its Lewis acidity, thereby weakening the Kubas complex. Such excitations are not expected to affect adsorbates on RuO2 given its metallic properties. Therefore, this common thermal cocatalyst employed in photocatalysis is, itself, photoactive.

Modulating electronic structure of graphene overlayers is highly demanding for its potential applications in microelectronics, sensors, and catalysis, which however remains a grand challenge. Here, we report electrochemistry-involved treatments to tune the electronic structure of graphene overlayers. Both galvanic corrosion and potential-aided intercalation of H2O were employed to change the graphene/Cu interfaces to graphene/Cu2O/Cu and graphene/H2O/Cu interfaces, respectively. Electronic properties and structural changes of the graphene/Cu interfaces were investigated by X-ray photoelectron spectroscopy, in-situ Raman, and atomic force microscopy. The formed Cu2O interlayer blocks the charge transfer between graphene overlayer and Cu substrate, which turns n-type doping of the as-grown graphene to free-standing state. In contrast, the intercalated H2O interlayer induces much stronger n-type doping in graphene through the electrostatic field effect generated by confined H2O. This work offers efficient but mild methods to modulate the doping state of graphene layers.

Conversion of CO2 into methanol is a promising strategy to solve the urgent energy and environment problems, but the efficiency of this reaction is still limited due to the difficulty in CO2 activation. Here, we report a strategic Al doping in Pd/ZnO catalysts for enhancing methanol synthesis via CO2 hydrogenation. When the loading amount of Al is below 3.93 wt.%, CO2 conversion and CH3OH yield increase as Al content increases. The best catalytic performance is observed over Pd/ZnO catalysts with 3.93 wt.% Al, where the CO2 conversion and CH3OH yield are increased to 2.5 times and 1.7 times that of Pd/ZnO, respectively. Combined with a variety of experimental characterizations and density functional theory calculations, the enhanced performance is attributed to the Al doping in ZnO which can facilitate the adsorption and activation of CO2, and thus improving the catalytic performance of Pd/ZnO catalysts. Further increasing the loading amount of Al to higher than 3.93 wt.%, the CO2 conversion and CH3OH yield decrease, which can be attributed to the formation of ZnAl2O4 spinel and amorphous Al2O3 on the surface of ZnO.

Hydroxylated oxide surfaces play an important role in many catalysis, energy, and environment processes. In this work, surface hydroxylation of Zn oxide (ZnOx) overlayers grown on Pt(1 1 1) has been studied by X-ray photoelectron spectroscopy and high resolution electron energy loss spectroscopy in ultrahigh vacuum, H2, and H2O atmospheres, respectively. Surface science measurements and H-D exchange experiments confirm that surface dissociation of H2 and H2O results in the surface hydroxylation of ZnOx overlayers. Bare Pt surface and interface between ZnOx and Pt are critical in surface hydroxylation by H2, whereas ZnOx surface itself is active for H2O dissociation. H2O mainly reacts with O-deficient ZnOx overlayer, while reaction with H2 or atomic H species becomes dominant on O-rich ZnOx overlayer.

Subsurface Fe, Co, and Ni can promote the Pt-catalyzed propane dehydrogenation while exposed adversely on the surface., Progress in heterogeneous catalysis is often hampered by the difficulties of constructing active architectures and understanding reaction mechanisms at the molecular level due to the structural complexity of practical catalysts, in particular for multicomponent catalysts. Although surface science experiments and theoretical simulations help understand the detailed reaction mechanisms over model systems, the direct study of the nature of nanoparticle catalysts remains a grand challenge. This paper describes a facile construction of well-defined Pt-skin catalysts modified by different 3d transition metal (3dTM) atoms in subsurface regions. However, on the catalyst containing both surface and subsurface 3dTMs, the selectivity of propane dehydrogenation decreases in the sequences of Pt ~ PtFe > PtCo > PtNi due to the easier C–C cracking on exposed Co and Ni sites. After the exposed 3dTMs were removed completely, the C3H6 selectivity was found to increase markedly in the row Pt < PtNi@Pt < PtCo@Pt < PtFe@Pt, which is in line with the calculated trend of d-band center shifting. The established relationship between reactivity and d-band center shifting illustrates the role of subsurface catalysis in dehydrogenation reaction.

CO poisoning is a major problem for Pt-based catalysts in various catalytic processes. Thus, the prediction of CO binding energies over Pt alloy surfaces is fundamentally important to evaluate their CO poisoning tolerance. This article describes the effect of surface and subsurface coordination environments on the CO binding strength over PtCu alloy surfaces by employing density functional theory calculations. We show that the existence of surface Pt neighbors weakens the CO binding strength on Pt, whereas the subsurface Pt neighbors play the opposite role. Crystal orbital Hamilton population analysis suggests a stronger antibonding interaction for the Ptsurface–Ptsubsurface bond than for the Ptsurface–Ptsurface bond, which indicates less stable subsurface Pt atoms that hence generate an activated surface Pt that attracts CO more strongly. On the basis of the calculated CO binding energies, an empirical formula, with Pt–Pt coordination numbers as the variables, has been fitted to achieve a fast prediction...

Understanding water/solid interactions is of great importance in a variety of fundamental and technological processes, such as photocatalytic water splitting, heterogeneous catalysis, electrochemistry, and corrosion. This review describes recent advancements in the molecular-level understanding of water adsorption, dissociation and clustering on model surfaces of metal oxides, achieved primarily by combining scanning probe microscopies with ensemble-averaged techniques and density functional theory calculations. Factors controlling how water binds and clusters on the coordinatively unsaturated metal cations of different oxide surfaces are discussed. We start by reviewing the fundamental differences in the relative stability of molecularly and dissociatively-bonded water monomers and clusters on isostructural rutile TiO2(110) and RuO2(110) surfaces and on different surfaces and polymorphs of TiO2. We further discuss how oxide interfaces (both exposed and buried) with metals affect water dissociation. Subsequently, we focus on high coverage water overlayers such as one-dimensional water chain structures that result from different substrate morphologies, and water monolayer structures. We conclude with novel studies of interfacial water in liquids.

The ability to synthesis well-ordered two-dimensional materials under ultra-high vacuum and directly characterize them by other techniques in-situ can greatly advance our current understanding on their physical and chemical properties. In this paper, we demonstrate that iso-oriented {\alpha}-MoO3 films with as low as single monolayer thickness can be reproducibly grown on SrTiO3(001) (STO) substrates by molecular beam epitaxy ( (010)MoO3 || (001)STO, [100]MoO3 || [100]STO or [010]STO) through a self-limiting process. While one in-plane lattice parameter of the MoO3 is very close to that of the SrTiO3 (aMoO3 = 3.96 {\AA}, aSTO = 3.905 {\AA}), the lattice mismatch along other direction is large (~5%, cMoO3 = 3.70 {\AA}), which leads to relaxation as clearly observed from the splitting of streaks in reflection high-energy electron diffraction (RHEED) patterns. A narrow range in the growth temperature is found to be optimal for the growth of monolayer {\alpha}-MoO3 films. Increasing deposition time will not lead to further increase in thickness, which is explained by a balance between deposition and thermal desorption due to the weak van der Waals force between {\alpha}-MoO3 layers. Lowering growth temperature after the initial iso-oriented {\alpha}-MoO3 monolayer leads to thicker {\alpha}-MoO3(010) films with excellent crystallinity., Comment: One supporting figure is attached at the end of the manuscript