Gold, Copper, and Platinum Nanoparticles Dispersed on CeOx/TiO2(110) Surfaces: High Water-Gas Shift Activity and the Nature of the Mixed-Metal Oxide at the Nanometer Level

CeO2 nanorods supported CuOx-RuOx bimetallic catalysts for low temperature CO oxidation

Bimetallic catalysts often outperform monometallic catalysts due to changeable structural orientation, synergistic effects, and integration of two different metal or metal oxide properties. Here, a series of CeO2 nanorods (NR) supported bimetallic CuOx and RuOx catalysts (Cu: Ru ratios of 9:1, 7:3, and 5:5) were prepared using a wet impregnation method. In situ DRIFTS, H2 temperature programmed reduction (H2-TPR), CO temperature programmed desorption (CO-TPD), and other characterization techniques were used to investigate the effect of the Cu:Ru ratio on the activity of low-temperature CO oxidation. Among three catalysts, CeO2 NR supported 7 wt% Cu-3 wt% Ru catalyst after a reduction activation treatment showed the best performance with 100 % CO conversion at 166 °C and the lowest activation energy of 18.37 kJ mol-1. Raman and XPS profiles revealed that the origin of the superior performance is at least partially related to the high surface oxygen vacancy concentration and other distinct oxygen species (physi-/chemi-sorbed oxygen and bulk lattice oxygen), leading to outstanding adsorption and oxidation property of CO.

Dynamic behaviour of platinum and copper dopants in gold nanoclusters supported on ceria catalysts

Understanding the behaviour of active catalyst sites at the atomic level is crucial for optimizing catalytic performance. Here, the evolution of Pt and Cu dopants in Au25 clusters on CeO2 supports is investigated in the water-gas shift (WGS) reaction, using operando XAFS and DRIFTS. Different behaviour is observed for the Cu and Pt dopants during the pretreatment and reaction. The Cu migrates and builds clusters on the support, whereas the Pt creates single-atom active sites on the surface of the cluster, leading to better performance. Doping with both metals induces strong interactions and pretreatment and reaction conditions lead to the growth of the Au clusters, thereby affecting their catalytic behaviour. This highlights importance of understanding the behaviour of atoms at different stages of catalyst evolution. These insights into the atomic dynamics at the different stages are crucial for the precise optimisation of catalysts, which ultimately enables improved catalytic performance.

CeO2/Cu2O/Cu Tandem Interfaces for Efficient Water-Gas Shift Reaction Catalysis

Metal-oxide interfaces on Cu-based catalysts play very important roles in the low-temperature water-gas shift reaction (LT-WGSR). However, developing catalysts with abundant, active, and robust Cu-metal oxide interfaces under LT-WGSR conditions remains challenging. Herein, we report the successful development of an inverse copper-ceria catalyst (Cu@CeO₂), which exhibited very high efficiency for the LT-WGSR. At a reaction temperature of 250 °C, the LT-WGSR activity of the Cu@CeO₂ catalyst was about three times higher than that of a pristine Cu catalyst without CeO₂. Comprehensive quasi-in situ structural characterizations indicated that the Cu@CeO₂ catalyst was rich in CeO₂/Cu₂O/Cu tandem interfaces. Reaction kinetics studies and density functional theory (DFT) calculations revealed that the Cu⁺/Cu⁰ interfaces were the active sites for the LT-WGSR, while adjacent CeO₂ nanoparticles play a key role in activating H₂O and stabilizing the Cu⁺/Cu⁰ interfaces. Our study highlights the role of the CeO₂/Cu₂O/Cu tandem interface in regulating catalyst activity and stability, thus contributing to the development of improved Cu-based catalysts for the LT-WGSR.

A review study on methanol steam reforming catalysts: Evaluation of the catalytic performance, characterizations, and operational parameters

Conventional fossil-based energy sources have numerous environmental demerits; sustainable and renewable sources are attracting the undivided attention of researchers owing to their valuable physical and chemical features. Several industrial-scale technologies are employing hydrogen as a green energy source as the most preferential source. Not only is hydrogen a potent energy carrier but also it is not detrimental to the environment. Among many other hydrogen production processes, steam reforming of methanol (SRM) is deemed a practical method due to its low energy consumption. Cu, Ni, noble metals, etc., are the salient catalysts in SRM. Many researchers have conducted thorough studies incorporating improvement of the catalysts’ activity, mechanism predictions, and the impacts of operational parameters and reformers. This review concentrates on the SRM catalysts, supports, promoters, and the effect of the operational parameters on the process efficiency and H2 production yield. In this regard, the methanol conversion, H2 and CO selectivity, and operating parameters are notably contingent on the surface characterization and chemistry of the catalysts. Herein, Cu-, Ni-, and noble metal-based catalysts on various metal oxide supports, such as Al2O3 and ZnO, are assessed meticulously in the SRM process from the standpoint of mechanism and catalyst characterization. Most of the peer-reviewed studies had encountered agglomeration, metal particle sintering at high temperatures, coke formation, and deactivation of catalysts as the prevalent barriers. Hence, the novel methods of conquering the above-mentioned obstacles are evaluated in this review. Employment of diverse synthetic methods, bimetallic catalysts, distinct catalyst promoters, and unconventional supports, such as metal–organic frameworks, carbon nanotubes, and zeolites, are the salient routes to overcome the metal dispersion and thermal stability issues. In addition, the influence of operational parameters (temperature of the process, steam/carbon ratio, and feed flow rate) has been weighed painstakingly, along with introducing the research gap and future perspectives in the territory of SRM catalysts.

Hydrogen Production on Pt/TiO2: Synergistic Catalysis between Pt Clusters and Interfacial Adsorbates

Understanding the mechanism of hydrogen (H₂) formation from the conversion of water (H₂O) and renewables on TiO₂ surfaces with cocatalysts via either photocatalysis or other catalytic processes is of significant importance to the successful design of efficient catalysts. Herein, we have investigated H₂ production from H₂O, CH₃OH, and C₂H₅OH on a Pt cluster covered rutile (R)-TiO₂(110) surface (Pt_clut/R-TiO₂(110)) to address the mechanism of H₂ production. Experimental results demonstrate that surface adsorbates not only help H atom diffusion on Pt_clut/R-TiO₂(110) but also take part in H₂ production directly. Further density functional theory (DFT) calculations suggest that H₂ production on Pt_clut/R-TiO₂(110) occurs via a synergistic catalysis process between Pt clusters and interfacial adsorbates rather than a recombination reaction of H atoms on Pt clusters. This work provides new insight into H₂ production from H₂O and renewables with Pt/TiO₂ catalysts, which may be applicable to H₂ production on other Pt cluster deposited metal oxide catalysts.

Heterostructured Ceria-Titania-Supported Platinum Catalysts for the Water Gas Shift Reaction

The water gas shift (WGS) reaction is a key process in the industrial hydrogen production and the development and application of the proton exchange membrane fuel cell. Metal oxide-supported highly dispersed Pt has been proved as an efficient catalyst for the WGS reaction. In this work, a series of supported 0.5Pt/xCe-10Ti (x = 1, 3, or 5) catalysts with different Ce/Ti molar ratios were prepared by a simple deposition-precipitation method. Compared with single TiO₂- or CeO₂-supported Pt catalysts, it was found that the 0.5Pt/3Ce-10Ti catalyst showed an obvious advantage in activity for the WGS reaction. In this catalyst, dispersed CeO₂ nanoparticles were supported on the TiO₂ sheets, and Pt single atoms and nanoparticles were located on CeO₂ and at the boundary of TiO₂ and CeO₂, respectively. It found that the reduction ability of the supported Pt catalyst was remarkably improved; meanwhile, the adsorption strength of CO on the surface of 0.5Pt/3Ce-10Ti was moderate. The heterostructured CeO₂-TiO₂ support gave an effective regulation on the Pt status and further influenced the CO adsorption ability, inducing excellent WGS reaction activity. This work provides a reference for the development and application of heterostructured materials in heterogeneous catalysis.

Au and Pt Remain Unoxidized on a CeO2-Based Catalyst during the Water-Gas Shift Reaction

The active forms of Au and Pt in CeO₂-based catalysts for the water-gas shift (WGS) reaction are an issue that remains unclear, although it has been widely studied. On one hand, ionic species might be responsible for weakening the Ce-O bonds, thus increasing the oxygen mobility and WGS activity. On the other hand, the close contact of Au or Pt atoms with CeO₂ oxygen vacancies at the metal-CeO₂ interface might provide the active sites for an efficient reaction. In this work, using in situ X-ray absorption spectroscopy, we demonstrate that both Au and Pt remain unoxidized during the reaction. Remarkable differences involving the dynamics established by both species under WGS atmospheres were recognized. For the prereduced Pt catalyst, the increase of the conversion coincided with a restructuration of the Pt atoms into cuboctahedrical metallic particles without significant variations on the overall particle size. Contrary to the relatively static behavior of Pt⁰, Au⁰ nanoparticles exhibited a sequence of particle splitting and agglomeration while maintaining a zero oxidation state despite not being located in a metallic environment during the process. High WGS activity was obtained when Au atoms were surrounded by oxygen. The fact that Au preserves its unoxidized state indicates that the chemical interaction between Au and oxygen must be necessarily electrostatic and that such an electrostatic interaction is fundamental for a top performance in the WGS process.

CeO2/CuO/TiO2heterojunction photocatalysts for conversion of CO2to ethanol

An attempt to reduce CO₂emissions has led to the development of CeO₂/CuO/TiO₂heterojunction photocatalysts for photoconversion of CO₂to useful products, e.g. ethanol. Composite photocatalysts were simply prepared by mixing TiO₂(P25) with different mass ratios of CeO₂(1 wt%) and CuO (2 or 3 wt%) by ball milling. The prepared photocatalysts had uniformly distributed CeO₂and CuO phases, throughout the TiO₂phase. The integration of CeO₂and CuO into TiO₂at 1 wt% CeO₂and 3 wt% CuO produced a composite, with a reduced band gap of 2.88 eV, allowing absorption of lower energy light and a lower electron-hole recombination rate. The 1%CeO₂/3%CuO/TiO₂photocatalysts yielded ethanol at 30.5μmol g_cat^-1h^-1, almost three times higher than the yield from pure TiO₂. This improved CO₂conversion efficiency was due to contributions from properties of both additives: CeO₂increased light absorption, while CuO acted as an electron trap and enhanced CO₂adsorption. In addition, the heterojunction at the interfaces facilitated the photogenerated charge separation, which, in turn, increased the charge participation in the catalyzed conversion reactions.

Manipulation of CO adsorption over Me1/CeO2 by heterocation doping: Key roles of single-atom adsorption energy

The performance of metal atoms chemically bonded to oxide supports cannot be explained solely by the intrinsic properties of the metals such as the d-band center. Herein, we present an in-depth study of the correlation between metal-oxide interactions and the properties of the supported metal using CO adsorption on Me₁ (Fe₁, Co₁, and Ni₁) loaded over CeO₂ (111) doped with divalent (Ca, Sr, and Ba), trivalent (Al, Ga, Sc, Y, and La), and quadrivalent (Hf and Zr) heterocations. CO adsorption over Me₁ is strongly dependent on the binding energies of Me₁. Two factors led to this trend. First, the extent of the Me₁-surface oxygen (Me₁-O) bond relaxation during CO adsorption played a key role. Second, the d-band center shifted drastically because of charge transfer to the oxides. The shift is related to the oxophilicity of metals. Adsorption energies of Me₁ over oxides include the contributions of the factors described above. Therefore, we can predict the activities of Me₁ using the strength of anchoring by oxide supports. Results show that smaller ionic radii of the doped heterocations were associated with more tightly bound Me₁. This finding sheds light on the possibility of heterocation-doping manipulating the reactivity of the Me₁ catalyst based on theoretical predictions.

A study on the effect of CeO2 addition to a Pt/TiO2 catalyst on the reverse water gas shift reaction

In this study, a series of catalysts with the composition 1 wt% Pt/X% CeO₂-Y% TiO₂ (where X and Y range from 0 to 20%) was prepared via impregnation. The effects of different ratios of CeO₂/TiO₂ on the catalytic activity were examined during the reverse water gas shift reaction (RWGS). The catalytic activities of the Pt-impregnated catalysts were enhanced by increasing CeO₂ loading. The activity tests, temperature-programmed reduction via H₂, and step test of an elementary RWGS reaction over the catalysts confirmed that the catalytic activity depends on the number of TiO₂ or CeO₂ sites, which participate in the RWGS reaction, on the surface of the support.

Au-Decorated Ce-Ti Mixed Oxides for Efficient CO Preferential Photooxidation

We investigated the photocatalytic behavior of gold nanoparticles supported on CeO2-TiO2 nanostructured matrixes in the CO preferential oxidation in H2-rich stream (photo-CO-PROX), by modifying the electronic band structure of ceria through addition of titania and making it more suitable for interacting with free electrons excited in gold nanoparticles through surface plasmon resonance. CeO2 samples with different TiO2 concentrations (0-20 wt %) were prepared through a slow coprecipitation method in alkaline conditions. The synthetic route is surfactant-free and environmentally friendly. Au nanoparticles (<1.0 wt % loading) were deposited on the surface of the CeO2-TiO2 oxides by deposition-precipitation. A benchmarking sample was also considered, prepared by standard fast coprecipitation, to assess how a peculiar morphology can affect the photocatalytic behavior. The samples appeared organized in a hierarchical needle-like structure, with different morphologies depending on the Ti content and preparation method, with homogeneously distributed Au nanoparticles decorating the Ce-Ti mixed oxides. The morphology influences the preferential photooxidation of CO to CO2 in excess of H2 under simulated solar light irradiation at room temperature and atmospheric pressure. The Au/CeO2-TiO2 systems exhibit much higher activity compared to a benchmark sample with a non-organized structure. The most efficient sample exhibited CO conversions of 52.9 and 80.2%, and CO2 selectivities equal to 95.3 and 59.4%, in the dark and under simulated sunlight, respectively. A clear morphology-functionality correlation was found in our systematic analysis, with CO conversion maximized for a TiO2 content equal to 15 wt %. The outcomes of this study are significant advancements toward the development of an effective strategy for exploitation of hydrogen as a viable clean fuel in stationary, automotive, and portable power generators.

Studies of CO2 hydrogenation over cobalt/ceria catalysts with in situ characterization: the effect of cobalt loading and metal–support interactions on the catalytic activity

Metal–oxide interactions affect the catalytic properties of Co/CeO₂ and can be used to control activity and selectivity.

The catalytic mechanism of the Au@TiO2−x/ZnO catalyst towards a low-temperature water-gas shift reaction

A redox mechanism towards the water-gas shift reaction was certified based on in situ/operando experiments and density functional theory calculation studies.

The influence of ceria on Cu/TiO2 catalysts to produce abundant oxygen vacancies and induce highly efficient CO oxidation

Ce and Cu species deposited on TiO₂ can apparently provide a higher turnover frequency rate and lower activation energy than the Cu/TiO₂ catalyst and the Ce and Cu species on SiO₂ catalysts.

CO2 Hydrogenation over Nanoceria-Supported Transition Metal Catalysts: Role of Ceria Morphology (Nanorods versus Nanocubes) and Active Phase Nature (Co versus Cu)

In this work we report on the combined impact of active phase nature (M: Co or Cu) and ceria nanoparticles support morphology (nanorods (NR) or nanocubes (NC)) on the physicochemical characteristics and CO2 hydrogenation performance of M/CeO2 composites at atmospheric pressure. It was found that CO2 conversion followed the order: Co/CeO2 > Cu/CeO2 > CeO2, independently of the support morphology. Co/CeO2 catalysts demonstrated the highest CO2 conversion (92% at 450 °C), accompanied by 93% CH4 selectivity. On the other hand, Cu/CeO2 samples were very selective for CO production, exhibiting 52% CO2 conversion and 95% CO selectivity at 380 °C. The results obtained in a wide range of H2:CO2 ratios (1-9) and temperatures (200-500 °C) are reaching in both cases the corresponding thermodynamic equilibrium conversions, revealing the superiority of Co- and Cu-based samples in methanation and reverse water-gas shift (rWGS) reactions, respectively. Moreover, samples supported on ceria nanocubes exhibited higher specific activity (µmol CO2·m-2·s-1) compared to samples of rod-like shape, disclosing the significant role of support morphology, besides that of metal nature (Co or Cu). Results are interpreted on the basis of different textural and redox properties of as-prepared samples in conjunction to the different impact of metal entity (Co or Cu) on CO2 hydrogenation process.

Enhanced Activity and Stability of Gold/Ceria-Titania for the Low-Temperature Water-Gas Shift Reaction

Gold supported on ceria-zirconia is one of the most active low temperature water-gas shift catalysts reported to date but rapid deactivation occurs under reaction conditions. In this study, ceria-titania was evaluated as an alternative catalyst support. Materials of different Ce:Ti compositions were synthesized using a sol-gel methodology and gold was supported onto these using a deposition-precipitation method. They were then investigated as catalysts for the low-temperature water-gas shift reaction. Au/Ce_0.2Ti_0.8O₂ exhibited superior activity and stability to a highly active, previously reported gold catalyst supported on ceria-zirconia. High activity and stability was found to be related to the support comprising a high number of oxygen defect sites and a high specific surface area. These properties were conducive to forming a highly active catalyst with well-dispersed Au species.

Understanding the Photocatalytic Properties of Pt/CeOx /TiO2 : Structural Effects on Electronic and Optical Properties

Ceria-titania interfaces play a crucial role in different chemical processes but are especially promising for the photocatalytic splitting of water using light in the visible wavelength region when Pt is added to the system. However, the complexity of this hierarchical structure hampers the study of the origin of its outstanding properties. In this article, the structural, electronic and optoelectronic properties of CeO₂ /TiO₂ systems containing 1D, 2D, and 3D particles of ceria are analyzed by means of density functional calculations. Adsorption sites and vacancy effects have been studied to model Pt adsorption. Density of states calculations and absorption spectra simulations explain the behavior of these systems. Finally, these models are used for the screening of other metals that can be combined with this heterostructure to potentially find more efficient water splitting photocatalysts.

Adsorption of CO2 on Heterostructures of Bi2O3 Nanocluster-Modified TiO2 and the Role of Reduction in Promoting CO2 Activation

The capture and conversion of CO₂ are of significant importance in enabling the production of sustainable fuels, contributing to alleviating greenhouse gas emissions. While there are a number of key steps required to convert CO₂, the initial step of adsorption and activation by the catalyst is critical. Well-known metal oxides such as oxidized TiO₂ or CeO₂ are unable to promote this step. In addressing this difficult problem, a recent experimental work shows the potential for bismuth-containing materials to adsorb and convert CO₂, the origin of which is attributed to the role of the bismuth lone pair. In this paper, we present density functional theory (DFT) simulations of enhanced CO₂ adsorption on heterostructures composed of extended TiO₂ rutile (110) and anatase (101) surfaces modified with Bi₂O₃ nanoclusters, highlighting in particular the role of heterostructure reduction in activating CO₂. These heterostructures show low coordinated Bi sites in the nanoclusters and a valence band edge that is dominated by Bi-O states, typical of the Bi³⁺ lone pair. The reduction of Bi₂O₃-TiO₂ heterostructures can be facile and produces reduced Bi²⁺ and Ti³⁺ species. The interaction of CO₂ with this electron-rich, reduced system can produce CO directly, reoxidizing the heterostructure, or form an activated carboxyl species (CO₂ ^-) through electron transfer from the reduced heterostructure to CO₂. The oxidized Bi₂O₃-TiO₂ heterostructures can adsorb CO₂ in carbonate-like adsorption modes, with moderately strong adsorption energies. The hydrogenation of the nanocluster and migration to adsorbed CO₂ is feasible with H-migration barriers less than 0.7 eV, but this forms a stable COOH intermediate rather than breaking C-O bonds or producing formate. These results highlight that a reducible metal oxide heterostructure composed of a semiconducting metal oxide modified with suitable metal oxide nanoclusters can activate CO₂, potentially overcoming the difficulties associated with the difficult first step in CO₂ conversion.

TiO2@Pt@CeO2 nanocomposite as a bifunctional catalyst for enhancing photo-reduction of Cr (VI) and photo-oxidation of benzyl alcohol

An solar-light-driven and bifunctional photocatalyst was designed for photo-reduction of Cr(VI) and selective photo-oxidation of benzyl alcohol into benzaldehyde in the presence of water under ambient conditions. Double-shelled and sandwiched TiO₂@Pt@CeO₂ hollow spheres were prepared by using functionalized polystyrene spheres, sol-gel, hydrothermal reaction, and calcination. The Pt nanoparticles (NPs) were controllably loaded between the TiO₂ shell and CeO₂ shell. Under solar-light irradiation, the photo-reduction rate of Cr(VI) (μmol h^-1) was in the order of TiO₂@Pt@CeO₂ (1.901) > TiO₂@CeO₂ (1.424) > TiO₂ (1.040) > CeO₂ (0.992). Among the above-mentioned photocatalysts, the conversion rate of benzyl alcohol for TiO₂@Pt@CeO₂ was also the best. These results were attributed to the combination of TiO₂ and CeO₂ as photocatalyst and oxygen buffer, the double-shelled and sandwiched nanostructure, and the addition of Pt NPs as cocatalyst and electron trap site, which could store and shuttle photo-generated electrons, reduce the recombination of the electron-hole, and then enhance photo-generation of active radicals. This conclusion was verified by the electron paramagnetic resonance (EPR) spectroscopy. Considering the versatile combination of photocatalyst, oxygen buffer and cocatalyst, this work could provide new insights into the design of high-performance bifunctional photocatalysts for heavy metal removal and selective synthesis.

Synthesis and CO Oxidation Activity of 1D Mixed Binary Oxide CeO2-LaO x Supported Gold Catalysts

One-dimensional (1D) Ce-La nanorods with different La contents (Ce and La in the molar ratio of 1:0, 3:1, 1:1, 1:3, and 0:1) were synthesized by hydrothermal process. Au/Ce-La nanorod catalysts were obtained by a modified deposition-precipitation method. The samples were characterized by N2 adsorption-desorption (BET), ICP, X-ray diffraction (XRD), SEM, TEM, EDX, X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), and temperature-programmed reduction (H2-TPR). It revealed that La existed as LaO x in the 1D nanorods. The catalysis results demonstrated that the mixed binary Ce-La nanorod oxides could be a good support for gold catalysts. The contents of La had an important influence on the catalytic performance of Au/Ce-La nanorod catalysts. Among the catalysts, when the Ce/La molar ratio was 3:1, the 1.0%Au/Ce0.75-La0.25 nanorods pretreated at 300 °C showed the best activity among the catalysts for CO oxidation, which could convert CO completely at 30 °C. The catalysts also performed high temperature resistance and good stability for CO oxidation at the reaction temperatures of 40, 70, and 200 °C.

Nanoengineering of aggregation-free and thermally-stable gold nanoparticles in mesoporous frameworks

Loading catalytically active, aggregation-free and thermally stable metal nanoparticles (NPs) on a high surface area support represents a major interest in heterogeneous catalysis. Current synthetic approaches to these hybrid catalysts, however, still lack controllability in the thermal stability of metal NPs, particularly at high temperatures in the absence of organic ligands. We herein report a facile "co-assembly" methodology to prepare aggregation-free, ligand-free and thermally stable mesoporous hybrid nanocatalysts of metal-oxides and metal-carbons. Immobilization of catalytically active gold NPs (AuNPs) within high surface area mesoporous frameworks was achieved via the polymer-directed co-assembly of chemically and structurally equivalent Pluronic P-123 and poly(ethylene oxide)-modified metallic gold NPs (AuNP-PEO) as co-structure-directing-agents. The in situ immobilization of AuNPs partially embedded into periodically ordered mesoporous frameworks imposed a three-dimensional "nanoconfinement" effect and essentially enhanced the long-term thermal stability of AuNPs up to 800 °C. The mesoporous hybrids retained a high surface accessibility of AuNPs and they had a fantastic high-temperature catalytic durability (>130 h at 375 °C) confirmed by two model catalytic reactions, including aerobic oxidation of benzyl alcohol and CO oxidation, respectively. Our results may offer a new realm of possibilities for the rational applications of thermally stable nanocatalysts in renewable energy technology and high-temperature catalysis.

Reversible Redox Cycling of Well-Defined, Ultrasmall Cu/Cu2O Nanoparticles

Exceptionally small and well-defined copper (Cu) and cuprite (Cu₂O) nanoparticles (NPs) are synthesized by the reaction of mesitylcopper(I) with either H₂ or air, respectively. In the presence of substoichiometric quantities of ligands, namely, stearic or di(octyl)phosphinic acid (0.1-0.2 equiv vs Cu), ultrasmall nanoparticles are prepared with diameters as low as ∼2 nm, soluble in a range of solvents. The solutions of Cu NPs undergo quantitative oxidation, on exposure to air, to form Cu₂O NPs. The Cu₂O NPs can be reduced back to Cu(0) NPs using accessible temperatures and low pressures of hydrogen (135 °C, 3 bar H₂). This striking reversible redox cycling of the discrete, solubilized Cu/Cu(I) colloids was successfully repeated over 10 cycles, representing 19 separate reactions. The ligands influence the evolution of both composition and size of the nanoparticles, during synthesis and redox cycling, as explored in detail using vacuum-transfer aberration-corrected transmission electron microscopy, X-ray photoelectron spectroscopy, and visible spectroscopy.

Metal/oxide interfacial effects on the selective oxidation of primary alcohols

A main obstacle in the rational development of heterogeneous catalysts is the difficulty in identifying active sites. Here we show metal/oxide interfacial sites are highly active for the oxidation of benzyl alcohol and other industrially important primary alcohols on a range of metals and oxides combinations. Scanning tunnelling microscopy together with density functional theory calculations on FeO/Pt(111) reveals that benzyl alcohol enriches preferentially at the oxygen-terminated FeO/Pt(111) interface and undergoes readily O–H and C–H dissociations with the aid of interfacial oxygen, which is also validated in the model study of Cu₂O/Ag(111). We demonstrate that the interfacial effects are independent of metal or oxide sizes and the way by which the interfaces were constructed. It inspires us to inversely support nano-oxides on micro-metals to make the structure more stable against sintering while the number of active sites is not sacrificed. The catalyst lifetime, by taking the inverse design, is thereby significantly prolonged.

Metals supported on metal oxides are common heterogeneous catalysts. Here the authors show that metal/oxide interfacial sites are highly active for alcohol oxidation—independent of the particle sizes—and use this information to design inverse oxide-on-metal particles with high activity and stability.

Controlled Growth of Ceria Nanoarrays on Anatase Titania Powder: A Bottom-up Physical Picture

The leading edge of catalysis research motivates physical understanding of the growth of nanoscale oxide structures on different supporting oxide materials that are themselves also nanostructured. This research opens up for consideration a diverse range of facets on the support material, versus the single facet typically involved in wide-area growth of thin films. Here, we study the growth of ceria nanoarchitectures on practical anatase titania powders as a showcase inspired by recent experiments. Density functional theory (DFT)-based methods are employed to characterize and rationalize the broad array of low energy nanostructures that emerge. Using a bottom-up approach, we are able to identify and characterize the underlying mechanisms for the facet-dependent growth of various ceria motifs on anatase titania based on formation energy. These motifs include 0D clusters, 1D chains, 2D plates, and 3D nanoparticles. The ceria growth mode and morphology are determined by the interplay of several factors including the role of the common cation valence, the interface template effect for different facets of the anatase support, enhanced ionic binding for more compact ceria motifs, and the local structural flexibility of oxygen ions in bridging the interface between anatase and ceria structures.

Ceria-based model catalysts: fundamental studies on the importance of the metal–ceria interface in CO oxidation, the water–gas shift, CO2 hydrogenation, and methane and alcohol reforming

Model metal/ceria and ceria/metal catalysts have shown to be excellent systems for studying fundamental phenomena linked to the operation of technical catalysts.

Activation of CO2 by supported Cu clusters

CO₂ forms a bent, negative anion upon adsorption near a Cu₃ cluster supported on TiO₂.

First-principles study of single transition metal atoms on ZnO for the water gas shift reaction

A single Ni atom substituted on a ZnO surface is a promising catalyst for the water gas shift reaction.