Tailoring the atomic structural configuration at metal and oxide interface offers an effective route for the development of catalysts with optimized properties. Here, we report the design of a unique structural configuration of yolk-shell-like FePt-FeOx nanoparticles (NPs), that exhibits notably enhanced activity and stability towards CO oxidation at relatively low temperatures (< 100 degrees C) compared with Pt NPs. The optimized FePt-FeOx catalysts were produced by partially reducing core-shell FePt-FeOx NPs under H-2 at 200 degrees C. The structural configuration was interrogated by advanced electron microscopy, which clearly reveals the evolution of the morphology, elemental segregation, and phase transition of FePt-FeOx NPs after the post-synthesis treatment. The generation of voids, partial crystallization of the FeOx shell and increased electron density on Pt were identified as key contributors to the enhanced activity and stability towards CO oxidation in FePt-FeOx NPs. This unique structural configuration allows for CO and O-2 diffusion through the FeOx shell with an increased exposure for CO and O-2 adsorption onto the core as well as an enhanced activation of O-2 compared with the core-shell FePt-FeOx without voids, which collectively boost the catalytic performance.

The water gas shift (WGS) reaction is of paramount importance for the chemical industry, as it constitutes, coupled with methane reforming, the main industrial route to produce hydrogen. Copper-chromium-iron oxide-based catalysts have been widely used for the high-temperature WGS reaction industrially. The WGS reaction mechanism by the CuCrFeO x catalyst has been debated for years, mainly between a "redox" mechanism involving the participation of atomic oxygen from the catalyst and an "associative" mechanism proceeding via a surface formate-like intermediate. In the present work, advanced in situ characterization techniques (infrared spectroscopy, temperature-programmed surface reaction (TPSR), near-ambient pressure XPS (NAP-XPS), and inelastic neutron scattering (INS)) were applied to determine the nature of the catalyst surface and identify surface intermediate species under WGS reaction conditions. The surface of the CuCrFeO x catalyst is found to be dynamic and becomes partially reduced under WGS reaction conditions, forming metallic Cu nanoparticles on Fe3O4. Neither in situ IR not INS spectroscopy detect the presence of surface formate species during WGS. TPSR experiments demonstrate that the evolution of CO2 and H2 from the CO/H2O reactants follows different kinetics than the evolution of CO2 and H2 from HCOOH decomposition (molecule mimicking the associative mechanism). Steady-state isotopic transient kinetic analysis (SSITKA) (CO + H216O → CO + H218O) exhibited significant 16O/18O scrambling, characteristic of a redox mechanism. Computed activation energies for elementary steps for the redox and associative mechanism by density functional theory (DFT) simulations indicate that the redox mechanism is favored over the associative mechanism. The combined spectroscopic, computational, and kinetic evidence in the present study finally resolves the WGS reaction mechanism on the industrial-type high-temperature CuCrFeO x catalyst that is shown to proceed via the redox mechanism.

CO oxidation is an important reaction both experimentally and industrially, and its performance is usually dominated by the charge states of catalysts. For example, CO oxidation on the platinum (Pt) surface requires a properly charged state for the balance of adsorption and activation of CO and O2. Here, we present "Mott-Schottky modulated catalysis" on Pt nanoparticles (NPs) via an electron-donating carbon nitride (CN) support with a tunable Fermi level. We demonstrate that properly-charged Pt presents an excellent catalytic CO oxidation activity with an initial conversion temperature as low as 25 °C and total CO conversion below 85 °C. The tunable electronic structure of Pt NPs, which is regulated by the Fermi level of CN, is a key factor in dominating the catalytic performance. This "Mott-Schottky modulated catalysis" concept may be extended to maneuver the charge state on other metal catalysts for targeted catalytic reactions.

To gain an in-depth understanding of the surface properties relevant for catalysis using ternary oxides, we report the acid-base pair reactivity of shape-controlled SrTiO3 (STO) nanocrystals for the dehydrogenation of ethanol, Cubes, truncated cubes, dodecahedra, and etched cubes of STO with varying ratios of (001) and (110) crystal facets were synthesized using a hydrothermal method. Low-energy ion scattering (LEIS) analysis revealed that the (001) surface on cubes of STO is enriched with SrO due to surface reconstruction, resulting in a high ratio of strong base sites. Chemical treatment with dilute nitric acid to form etched cubes of STO resulted in a surface enriched with Ti cations and strong acidity. Furthermore, the strength and distribution of surface acidic sites increase with the ratio of (110) facet from cubes to truncated cubes to dodecahedra for STO. Kinetic, isotopic, and spectroscopy methods show that the dehydrogenation of ethanol proceeds through the facile dissociation of the alcohol group, followed by the cleavage of the C-alpha-H bond, which is the rate-determining step. Co-feeding of various probe molecules during catalysis, such as NH3, 2,6-di-tert-butylpyridine, CO2, and SO2, reveals that a pair of Lewis acid site and basic surface oxygen atom is involved in the dehydrogenation reaction. The surface density of acid-base site pairs was measured using acetic acid as a probe molecule, allowing initial acetaldehyde formation turnover rates to be obtained. Comparison among various catalysts reveals no simple correlation between ethanol turnover rate and the percentage of either surface facet ((001) or (110)) of the STO nanocrystals. Instead, the reaction rate is found to increase with the strength of acid sites but reversely with the strength of base sites. The acid-base property is directly related to the surface composition as a result from different surface reconstruction behaviors of the shaped STO nanocrystals. The finding in this work underscores the importance of characterizing the top surface compositions and sites properties when assessing the catalytic performance of shape controlled complex oxides such as perovskites.

Core–shell heterostructures have been utilized as a catalyst that is thermally stable and exhibits a synergistic effect between core and shell, resulting in increased catalytic activity. Here we report on the synthetic procedure involving a Au144 core with an iron oxide shell which can be varied in thickness. The Au144@Fe2O3 particles with Au:Fe mass ratios of 1:2, 1:4, and 1:6 were synthesized and then deposited onto silica via colloidal deposition. Using CO oxidation, each Au144@Fe2O3/SiO2 catalyst gave varying degrees of full CO conversion depending on the thickness of the iron oxide layer. The 1:4 Au144@Fe2O3/SiO2 catalyst produced the best catalytic activity and was further investigated via thermal treatments, where calcination at 300 °C presented the best results, and the 1:4 ratio was still active at 100 °C after thermal treatments.

Methane conversion has received renewed interest due to the rapid growth in production of shale gas. Methane combustion for power generation and transportation is one of the alternatives for methane utilization. However, complete conversion of methane is critical to minimize negative environmental effects from unburned methane, whose noxious effect is 25 times greater than that of CO2. Although perovskite catalysts have high thermal stability, their low activities for methane combustion prevent them from being utilized on a commercial basis. In this work, we show the impact from reconstruction of surface and subsurface monolayers of perovskite catalysts on methane combustion, using SrTiO3 (STO) as a model perovskite. Several STO samples obtained through different synthetic methods and subjected to different post synthetic treatments were tested for methane combustion. Through top surface characterization, kinetic experiments (including isotope labeling experiments) and density functional theory calculations, it is shown that both surface segregation of Sr and creation of step surfaces of STO can impact the rate of methane combustion over an order of magnitude. This work highlights the role of surface reconstruction in tuning perovskite catalysts for methane activation.

Although perovskites have been widely used in catalysis, tuning of their surface termination to control reaction selectivity has not been well established. In this study, we employed multiple surface-sensitive techniques to characterize the surface termination (one aspect of surface reconstruction) of SrTiO3 (STO) after thermal pretreatment (Sr enrichment) and chemical etching (Ti enrichment). We show, by using the conversion of 2-propanol as a probe reaction, that the surface termination of STO can be controlled to greatly tune catalytic acid/base properties and consequently the reaction selectivity over a wide range, which is not possible with single-metal oxides, either SrO or TiO2 . Density functional theory (DFT) calculations explain well the selectivity tuning and reaction mechanism on STO with different surface termination. Similar catalytic tunability was also observed on BaZrO3 , thus highlighting the generality of the findings of this study.

The atomistic structure and morphology (shape and size) of nanomaterials have strong influences on their physical and chemical properties. However, many characterization techniques focus exclusively on one length-scale regime or another when developing quantitative morphology/structural models. In this article, we demonstrate that powder X-ray diffraction and neutron pair distribution function (PDF) can be used to obtain accurate average morphology and atomistic structure of {001} and {101} faceted anatase TiO2 nanocrystals based on differential evolution refinements using Debye scattering equation calculations. It is also demonstrated that the morphology polydispersity of TiO2 nanocrystals can be effectively obtained from the diffraction data via a numerical refinement routine. The morphology refinement results are in good agreement with those from transmission electron microscopy and the modeling of small angle neutron scattering data. This method is successfully used to quantify the facet-specified photocatalytic hydrogen evolution activity of anatase TiO2 nanocrystals with different {001} to {101} ratios. It is found that the sample with an intermediate amount of both {001} and {101} facets shows the best photocatalytic hydrogen evolution reaction (HER) activity. It is expected that the simultaneous structure and morphology refinement technique can be generally used to study the relationship between morphology and functionality of nanomaterials.

1.3 wt% Pt/HBEA and HBEA were studied as catalysts for the hydrodeoxygenation of pine pyrolysis vapors at 500 degrees C. Both catalysts showed high initial conversion of oxygenated pyrolysis products into aromatic hydrocarbons, while Pt/HBEA showed higher stability in terms of hydrocarbon productivity and deferred breakthrough of oxygenated compounds. Among 1-, 2- and 3-ring aromatic hydrocarbons, Pt/HBEA had a significantly higher selectivity than HBEA towards unalkylated aromatics (e.g., benzene) as compared to the corresponding alkylated aromatics (e.g., toluene and xylene). Additionally, Pt addition to HBEA decreased coke deposition and improved resistance to pore and acid site blockage as determined by TPO, N-2 physisorption, and NH3 TPD. The ability of Pt to promote cleavage and hydrogenation of methoxy and methyl groups was observed by increased methane production over Pt/HBEA relative to HBEA. A progressive decrease in the methane production over Pt/HBEA correlated with deactivation in terms of reduced benzene formation, breakthrough of oxygenated products, and increased formation of polynuclear aromatics and their degree of substitution, which indicate coke formation. The increased methane yield and suppressed coke formation with the addition of Pt is attributed to hydrogen spillover, through which hydrogen activated on Pt can subsequently migrate to the HBEA support to reverse the coke-forming hydrogen abstraction reaction. (C) 2017 Elsevier B.V. All rights reserved.

An ultrastable Au nanocatalyst based on a heterostructured perovskite support with high surface area and uniform LaFeO3 nanocoatings was successfully synthesized and tested for CO oxidation. Strikingly, small Au nanoparticles (4-6 nm) are obtained after calcination in air at 700 degrees C and under reaction conditions. The designed Au catalyst not only possessed extreme sintering resistance but also showed high catalytic activity and stability because of the strong interfacial interaction between Au and the heterostructured perovskite support.

Taming interfacial electronic effects on Pt nanoparticles modulated by their concomitants has emerged as an intriguing approach to optimize Pt catalytic performance. Here, we report Pt nanoparticles assembled on vacancy-abundant hexagonal boron nitride nanosheets and their use as a model catalyst to embrace an interfacial electronic effect on Pt induced by the nanosheets with N-vacancies and B-vacancies for superior CO oxidation catalysis. Experimental results indicate that strong interaction exists between Pt and the vacancies. Bader charge analysis shows that with Pt on B-vacancies, the nanosheets serve as a Lewis acid to accept electrons from Pt, and on the contrary, when Pt sits on N-vacancies, the nanosheets act as a Lewis base for donating electrons to Pt. The overall-electronic effect demonstrates an electron-rich feature of Pt after assembling on hexagonal boron nitride nanosheets. Such an interfacial electronic effect makes Pt favour the adsorption of O 2 , alleviating CO poisoning and promoting the catalysis.

Although perovskite catalysts are well-known for their excellent redox property, their acid base reactivity remains largely unknown. To explore the potential of perovskites in acid-base catalysis, we made a comprehensive investigation in this work on the acid base properties and reactivity of a series of selected perovskites, SrTiO3, BaTiO3, SrZrO3, and BaZrO3, via a combination of various approaches including adsorption microcalorimetry, in situ FTIR spectroscopy, steady state kinetic measurements, and density functional theory (DFT) modeling. The perovskite surfaces are shown to be dominated with intermediate and strong basic sites with the presence of some weak Lewis acid sites, due to the preferred exposure of SrO/BaO on the perovskite surfaces as evidenced by low energy ion scattering (LEIS) measurements. Using the conversion of 2-propanol as a probe reaction, we found that the reaction is more selective to dehydrogenation over dehydration due to the dominant surface basicity of the perovskites. Furthermore, the adsorption energy of 2-propanol (Delta H-ads,H-2-propanol) is found to be related to both a bulk property (tolerance factor) and the synergy between surface acid and base sites. The results from in situ FTIR and DFT calculations suggest that both dehydration and dehydrogenation reactions occur mainly through the E-1cB pathway, which involves the deprotonation of the alcohol group to form a common alkoxy intermediate on the perovskite surfaces. The results obtained in this work pave a path for further exploration and understanding of acid-base catalysis over perovskite catalysts.

The nature of the surface species formed through the adsorption of CO2 on amine-grafted mesoporous silica is investigated through in situ FTIR spectroscopy with the aid of 15 N dynamic nuclear polarization (DNP) and 13 C NMR spectroscopy. Primary, secondary, and tertiary amines are functionalized onto a mesoporous SBA-15 silica. Both isotopically labeled 13 CO2 and natural-abundance CO2 are used for accurate FTIR peak assignments, which are compared with assignments reported previously. The results support the formation of monomeric and dimeric carbamic acid species on secondary amines that are stabilized differently to the monocarbamic acid species on primary amines. Furthermore, the results from isotopically labelled 13 CO2 experiments suggest the existence of two carbamate species on primary amines, whereas only one species is observed predominantly on secondary amines. The analysis of the IR peak intensities and frequencies indicate that the second carbamate species on primary amines is probably more asymmetric in nature and forms in a relatively smaller amount. Only the formation of bicarbonate ions at a low concentration is observed on tertiary amines; therefore, physisorbed water on the surface plays a role in the hydrolysis of CO2 even if water is not added intentionally and dry gases are used. This suggests that a small amount of bicarbonate ions could be expected to form on primary and secondary amines, which are more hydrophilic than tertiary amines, and these low concentration species are difficult to observe on such samples.

Ceria has recently shown intriguing hydrogenation reactivity in catalyzing alkyne selectively to alkenes. However, the mechanism of the hydrogenation reaction, especially the activation of H2, remains experimentally elusive. In this work, we report the first direct spectroscopy evidence for the presence of both surface and bulk Ce-H species upon H2 dissociation over ceria via in situ inelastic neutron scattering spectroscopy. Combined with in situ ambient-pressure X-ray photoelectron spectroscopy, IR, and Raman spectroscopic studies, the results together point to a heterolytic dissociation mechanism of H2 over ceria, leading to either homolytic products (surface OHs) on a close-to-stoichiometric ceria surface or heterolytic products (Ce-H and OH) with the presence of induced oxygen vacancies in ceria. The finding of this work has significant implications for understanding catalysis by ceria in both hydrogenation and redox reactions where hydrogen is involved.

The exchanged Ga(iii) sites are the active sites for promoting BTX formation during ethanol conversion.