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Well-defined bimetallic heterogeneous catalysts are not only difficult to synthesize in a controlled manner, but their elemental distributions are also notoriously challenging to define. Knowledge of these distributions is required for both the as-synthesized catalyst and its activated form under reaction conditions, where various types of reconstruction can occur. Success in this endeavor requires observation of the active catalyst via in situanalytical methods. As a step toward this goal, we present a composite material composed of bimetallic nickel–ruthenium nanoparticles supported on a protonated zeolite (Ni–Ru/HZSM-5) and probe its evolution and function as a photoactive carbon dioxide methanation catalyst using in situX-ray absorption spectroscopy (XAS). The working Ni–Ru/HZSM-5, as a selective and durable photothermal CO2methanation catalyst, comprises a corona of Ru nanoparticles decorating a Ni nanoparticle core. The specific Ni–Ru interactions in the bimetallic particles were confirmed by in situXAS, which reveals significant electron transfer from Ni to Ru. The light-harvesting Ni nanoparticle core and electron-accepting Ru nanoparticle corona serve as the CO2and H2dissociation centers, respectively. These Ni and Ru nanoparticles also promote synergistic photothermal and hydrogen atom transfer effects. Collectively, these effects enable an associative CO2methanation reaction pathway while hindering coking and fostering high selectivity toward methane.

Harnessing solar energy for CO2conversion to fuels presents a sustainable alternative to fossil fuels. However, finding an economical, stable, non-toxic nanomaterial catalyst poses a significant challenge. Understanding the catalyst’s active state is vital for optimal performance due to potential structural changes during reactions. Herein, we employ various in situcharacterizations to detail δ-FeOOH’s structural evolution during hydrogen activation, identifying its active phase while catalyzing the heterogeneous reduction of CO2by H2. Using in situenvironmental transmission electron microscopy, δ-FeOOH is first dehydrated to α-Fe2O3, then reduced to Fe3O4, and finally to α-Fe. Other in situcharacterizations revealed that the active state of the catalyst (Fe-350-H2) is a mixture of Fe3O4and α-Fe. A detailed investigation into the photocatalytic CO2reduction using batch, flow, and LED reactors unveiled that the Fe-350-H2catalyst exhibits superior activity and selectivity in activating the reverse water gas shift reaction compared with similar iron-based catalysts.

Herein is developed a ternary heterostructured catalyst, based on a periodic array of 1D TiN nanotubes, with a TiO2nanoparticulate intermediate layer and a In2O3–x(OH)ynanoparticulate shell for improved performance in the photocatalytic reverse water gas shift reaction. It is demonstrated that the ordering of the three components in the heterostructure sensitively determine its activity in CO2photocatalysis. Specifically, TiN nanotubes not only provide a photothermal driving force for the photocatalytic reaction, owing to their strong optical absorption properties, but they also serve as a crucial scaffold for minimizing the required quantity of In2O3–x(OH)ynanoparticles, leading to an enhanced CO production rate. Simultaneously, the TiO2nanoparticle layer supplies photogenerated electrons and holes that are transferred to active sites on In2O3–x(OH)ynanoparticles and participate in the reactions occurring at the catalyst surface.

Turanite, Cu5(VO4)2(OH)4, is a naturally occurring mineral whose physical and chemical properties are of interest for magnetic data storage, battery applications, and catalysis. In this study, the reduction of nanostructured Cu5(VO4)2(OH)4by H2is investigated using a combination of scanning transmission electron microscopy–electron energy-loss spectroscopy, X-ray photoelectron spectroscopy, in situdiffuse reflectance infrared Fourier transform spectroscopy, in situX-ray absorption spectroscopy, first-principles calculations, and kinetic analysis based on thermogravimetry. A two-step mechanism is proposed, in which Cu5(VO4)2(OH)4is first reduced, following exponential growth kinetics, to form a stable intermediate consisting of a mix of Cu3VO4, Cu2O, and CuV2O5. The intermediate phase is then subsequently reduced in a 3-D diffusion-limited process to form two segregated phases consisting of Cu metal and V2O3particles. The apparent energy barriers for these two steps, obtained from the kinetic analysis, were found to be 52.5 and 71.2 kJ mol–1for Stages 1 and 2 of the reduction, respectively. These results highlight the importance of developing a rigorous understanding of the reduction processes involved in metal oxide catalyst preparation.

Bimetallic nanoparticles with tailored structures constitute a desirable model system for catalysts, as crucial factors such as geometric and electronic effects can be readily controlled by tailoring the structure and alloy bonding of the catalytic site. Here we report a facile colloidal method to prepare a series of platinum–gold (PtAu) nanoparticles with tailored surface structures and particle diameters on the order of 7 nm. Samples with low Pt content, particularly Pt4Au96, exhibited unprecedented electrocatalytic activity for the oxidation of formic acid. A high forward current density of 3.77 A mgPt−1was observed for Pt4Au96, a value two orders of magnitude greater than those observed for core–shell structured Pt78Au22and a commercial Pt nanocatalyst. Extensive structural characterization and theoretical density functional theory simulations of the best-performing catalysts revealed densely packed single-atom Pt surface sites surrounded by Au atoms, which suggests that their superior catalytic activity and selectivity could be attributed to the unique structural and alloy-bonding properties of these single-atomic-site catalysts.

Currently, the direct photocatalytic transformation of gaseous CO2and H2into renewable methanol is attracting great attention. The research on this topic has rapidly grown in recent years, but very few photocatalysts have yet to be discovered to enable CO2hydrogenation to methanol at ambient pressures. Therefore, further exploring and designing materials that have efficient and stable performance for this purpose still pose a significant challenge. Herein, a photocatalyst, CaCu3Ti4O12, is discovered that enables CO2hydrogenation to methanol at atmospheric pressure with performance that can compete with commercial Cu/ZnO/Al2O3. Moreover, CaCu3Ti4O12exhibits pronounced activity under the pressurized conditions required for industrial-scale processes. During CO2hydrogenation, this methanol photocatalyst acts as a “storage-and-release device” able to interconvert reversibly and sustainably between the photoactive Cu/CaTiO3/TiO2functioning composite catalyst and the precursor CaCu3Ti4O12phase. This discovery inspires creative strategies for the design of sustainable CO2hydrogenation to methanol at ambient pressures.

A novel nanoparticulate polyacetylene-supported Pd(II) catalyst (NP-Pd(II)) for use in the aqueous Suzuki-Miyaura cross coupling reaction was successfully synthesized by simply treating an aqueous solution of PdCl42–with acetylene under ambient conditions. Electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy were employed to characterize the NP-Pd(II) structure in detail. These analyses demonstrated that the Pd atoms in the NP-Pd(II) were present as Pd(II) and were coordinated with both the Cl atoms and the C=C bonds of the polyacetylene. Both the homogeneous distribution of the Pd(II) along the polyacetylene backbone and the aggregation of the NP-Pd(II) in solution work in conjunction to make this material an ideal catalyst, combining the advantages of both homogeneous and heterogeneous catalysts.

The electrochemical stability of platinum–iron oxide nanoparticles has been studied using X-ray absorption spectroscopy. Samples were monitored for changes in their surface structure and elemental composition after electrochemical cycling in acidic media, which were then correlated with their electronic properties and a thorough analysis of their electrocatalytic activities. In addition to the observation of significant surface restructuring, greater Fe content following electrochemical treatment was found to be associated with higher half-wave potentials and specific current densities (up to 0.965 ± 0.001 VRHEand 1.32 ± 0.03 × 10–5mA cm–2, respectively). This work highlights the potential to improve the electrocatalytic activity of platinum–iron oxide nanoparticles by controlling the Fe content and platinum–iron bonding, and demonstrates the critical importance of characterizing these nanocatalysts both before and after use.

Bimetallic nanoparticles (NPs) consisting of small Pt clusters on the surface of larger metal NPs are potential catalysts that combine the advantages of reduced cost, high surface area, and a strong alloying interaction between Pt and the substrate. Herein we report the preparation of a series of small Pt clusters deposited on the surface of Ag NPs with systematically varied compositions (Ag93Pt7, Ag81Pt19, Ag72Pt28, and Ag65Pt35) via a galvanic replacement reaction. UV–vis spectroscopy, transmission electron microscopy, and inductively coupled plasma optical emission spectroscopy are used to provide evidence of NPs formation and evaluate their gross structural and compositional characteristics. Extended X-ray absorption fine structure (EXAFS) measurements at the Pt L3- and Ag K-edges are then used to elucidate the structural evolution of small surface Pt clusters as the Pt concentration is increased, allowing the formation mechanism of the bimetallic NPs to be deduced. X-ray absorption near-edge structure (XANES) provides further information regarding the electronic properties of the bimetallic NPs from both Ag and Pt perspectives. Finally, the Pt L3-edge XANES spectra are used in conjunction with ab initiocalculations to verify the accuracy of structural models based on the EXAFS fitting results and to provide insight into the size-dependent nature of the Ag–Pt bonding interaction.

A series of platinum–iron oxide nanoparticles was synthesized using a “clean” CO-reduction method that employed different ratios of Pt−Fe precursor salts in oleylamine at elevated temperatures. High-resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray spectroscopy (EDS) studies revealed that nearly monodisperse (i.e., with relative standard deviations of less than 15%) nanoparticles with mean diameters of 3.5–4.4 nm and varied elemental compositions (Pt54Fe46Pt70Fe30, and Pt87Fe13) were obtained. X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) measurements at the Pt L3- and Fe K-edges revealed that these nanoparticles all consisted of a Pt core with amorphous iron oxide on the surface. Furthermore, it was observed that the local structure (e.g., Pt–Pt bond distance and coordination number) and electronic behavior of the Pt–FeO nanoparticles (e.g., Pt d electron density and Fe valence state) are dependent on the Pt−Fe precursor ratios used in their synthesis. Quantum mechanical ab initio calculations were employed to interpret the results from X-ray spectroscopy and help elucidate the relationships between local structure and electronic properties in the nanoparticle samples. Finally, the surface reactivity of these nanoparticles in the oxygen reduction reaction (ORR) was explored, demonstrating higher electrocatalytic activity for all three platinum–iron oxide samples in comparison with a commercial Pt catalyst. The surface reactivity was also found to be sensitive to the Pt−Fe ratios of the nanoparticles and could be correlated with their local structure and electronic behavior.

Three supported Pt/Fe2O3catalysts were prepared by depositing platinum colloids with discrete particle sizes onto the surface of Fe(OH)3powders, which were then calcined at an elevated temperature. Pt nanoparticle colloids with mean diameters of 1.1, 1.9, or 2.7 nm were synthesized in order to investigate the effects of particle size on the structure and CO oxidation properties of these Pt/Fe2O3catalysts. All Pt/Fe2O3catalysts demonstrated activity in low-temperature CO oxidation, with the sample containing Pt nanoparticles with a mean diameter of 1.9 nm (designated Pt/Fe2O3-b) exhibiting relatively higher catalytic activity. Compared with the other two catalysts, Pt/Fe2O3-b exhibited an increased ability to activate oxygen and maintain the stability of Pt species, correlating with its higher catalytic activity. The results of various characterization techniques revealed that the mean particle size of the Pt nanoparticles could influence the chemical states of Pt species and the strength of metal–support interactions of the Pt/Fe2O3catalysts. It was observed that the metal–support interactions in Pt/Fe2O3catalysts were able to adjust the redox properties and the O2-activation abilities of the catalysts. Finally, it is proposed that the interacting Pt and Fe species located at the Pt–FeOxinterface are the primary active sites for the activation of CO and O2, respectively.

The reactions and structural evolution of FeF3during cell cycling are investigated in an in situ cell by using Fe K-edge X-ray absorption fine-structure (XAFS) spectroscopy. The results of X-ray absorption near-edge structure spectroscopic analysis demonstrate that there are three stages in the reaction of FeF3with Li: (1) a two-phase intercalation reaction in the range of x= 0 to 0.46 Li, (2) a single-phase intercalation reaction in the range of x= 0.46 to 0.92 Li, and (3) a conversion reaction in the range of x= 0.92 to 2.78 Li. The coordination numbers (CNs) and bond lengths of the Fe–F bonds or Fe–Fe bonds for the lithiated FeF3are obtained by performing XAFS fitting. The splitting trends of the Fe–F bond lengths and the Fe–F CNs in the range of x= 0 to 0.92 Li support the proposal that R-3c-structured FeF3is transformed into R3c-structured Li0.92FeF3after the intercalation of 0.92 equiv. of Li, and that the intermediate Li0.46FeF3may be R3-structured. The small Fe–Fe CNof Li2.78FeF3indicates that the average diameter of the Fe crystallites formed during discharge is <1 nm.