Deciphering the Metal-Support Interaction of Au/ZnO Catalyst Induced by H2 and O2 Pretreatment

Metal-support interaction (MSI) provides great possibilities to tune the activity, selectivity, and stability of heterogeneous catalysts. Herein, the Au/ZnO catalyst is prepared by commercial ZnO and chloroauric acid, and the structure evolution of the catalyst pretreated by H2 and O2 gas at varied temperature is investigated to provide mechanistic insights of MSI. It is found that the H2 treatment at 300 °C and above can induce the formation of both the ZnOx overlayer and bulk Au-Zn alloy. In contrast, the O2 treatment can form the ZnOx overlayer at 500 °C and above without the formation of Au-Zn alloy. It is also revealed that the ZnOx overlayer is dynamically stable (permeable), which can provide access for reactant molecules during the reaction process. And, the Au-Zn alloy can recover to Au and ZnO under the CO oxidation reaction condition, which can be deemed as a re-activation process that endows H2 -treated samples with the superior activity and stability.

Enhanced performance of glycerol electro-oxidation in alkaline media using bimetallic Au-Cu NPs supported by MWCNTs and reducible metal oxides

Electrochemical technologies for valorizing glycerol, a byproduct of biodiesel production, into electric energy and value-added chemical products continue to be technologically and economically challenging. In this field, an ongoing challenge is developing more active, stable, and low-cost heterogeneous catalysts for the glycerol electro-oxidation reaction (GlyEOR). This paper reports the influence of the preparation procedure, which involves intermatrix synthesis (Cu and Au NPs), followed by galvanic displacement (Cu-Au NPs) in previously functionalized multi-walled carbon nanotubes (MWCNTs). It also discusses the role of the supports, CeO₂ NPs, and TiO₂ NPs, obtained by a hydrothermal microwave-assisted procedure, on the electroactivity of a hybrid bimetallic Cu-Au/MWCNT/MO₂ catalyst in the GlyEOR in alkaline media. The electrocatalytic behavior was studied and discussed in terms of structure, composition, and electroactivity of the synthesized materials, which were determined by Fourier-transform infrared spectroscopy (FTIR), flame atomic absorption spectroscopy (FAAS), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), X-ray photoelectronic spectroscopy (XPS), and cyclic voltammetry (CV). In addition, the role of the oxidation states of Cu and Au in the as-prepared catalysts (Cu/MWCNT, Au/MWCNT, Cu-Au/MWCNT, Cu-Au/MWCNT-CeO₂, and Cu-Au/MWCNT-TiO₂) was demonstrated. It was concluded that the preparation method of metal NPs for the controlled formation of the most catalytically active oxidation states of Cu and Au, together with the presence of a conductive and oxophilic microenvironment provided by carbon nanotubes and facile reducible oxides in optimized compositions, allows for an increase in the catalytic performance of synthesized catalysts in the GlyEOR.

Sonochemical engineering of highly efficient and robust Au nanoparticle-wrapped on Fe/ZrO2 nanorods and their controllable product selectivity in dimethyl oxalate hydrogenation

A facile sonochemical approach is adopted for the synthesis of Fe/ZrO₂ and Au decorated Fe/ZrO₂ NRs catalysts and their outstanding stability and catalytic performance for the synthesis of EtOH and MG from DMO hydrogenation were reported.

Size- and shape-dependent catalytic performances of oxidation and reduction reactions on nanocatalysts

Heterogeneous catalysis is one of the most important chemical processes of various industries performed on catalyst nanoparticles with different sizes or/and shapes. In the past two decades, the catalytic performances of different catalytic reactions on nanoparticles of metals and oxides with well controlled sizes or shapes have been extensively studied thanks to the spectacular advances in syntheses of nanomaterials of metals and oxides. This review discussed the size and shape effects of catalyst particles on catalytic activity and selectivity of reactions performed at solid-gas or solid-liquid interfaces with a purpose of establishing correlations of size- and shape-dependent chemical and structural factors of surface of a catalyst with the corresponding catalytic performances toward understanding of catalysis at a molecular level.

A facile synthesis strategy to couple porous nanocubes of CeO2 with Ag nanoparticles: an excellent catalyst with enhanced reactivity for the ‘click reaction’ and carboxylation of terminal alkynes

CeO₂–Ag nanocomposite was synthesized by modifying the surface of CeO₂ with DMP and its catalytic activity was shown for click reaction and carboxylation of terminal alkynes.

How do the unique Au/α-Fe2O3 interfacial structures determine activity in CO oxidation?

Unique Au/α-Fe₂O₃ interfacial structures and the interface-associated intermediates critically determine the activity of CO oxidation.

The synergy between atomically dispersed Pd and cerium oxide for enhanced catalytic properties

We report a photochemical synthesis of Pd/CeO₂ catalysts with atomically dispersed Pd. Compared to atomically dispersed Pd/CeO₂ with a cubic CeO₂ support (Pd/CeO₂-CP), atomically dispersed Pd/CeO₂ with a truncated octahedral CeO₂ support (Pd/CeO₂-TOP) exhibited higher activity and selectivity, owing to the synergy between Pd atoms and the (111) surface of CeO₂. When compared to Pd/CeO₂ with Pd clusters and nanoparticles via chemical reduction, Pd/CeO₂-TOP showed excellent activity with an enhancement factor of 324 in CO oxidation, as well as an activity enhancement by a factor of 344 in selective oxidation of benzyl alcohol.

Sterical ligand stabilization of nanocrystals versus electrostatic shielding by ionic compounds: a principle model study with TEM and XPS

Electrostaticversussterical ligand stabilization: competitive stabilization mechanism play a key role in the control of nanomaterial properties.

Room-temperature catalytic oxidation of formaldehyde on catalysts

Room-temperature catalytic oxidative decomposition of harmful formaldehyde (HCHO) in indoor air is summarized.

Nano-sized mesoporous sodium iron hydroxyphosphate supported gold: an effective catalyst for the oxidation of sulfides

Nano-sized mesoporous sodium iron hydroxyphosphate (SIHP) was synthesized as a support. The supported gold catalyst showed excellent performance for the oxidation of sulfides to sulfoxides.

Unusual behaviour of Au/ZnO catalysts in selective hydrogenation of butadiene due to the formation of a AuZn nanoalloy

The loss of activity observed when Au/ZnO was activated under H₂ was explained by the formation of AuZn alloy.

Selective hydrogenation of 1,3-butadiene on platinum-copper alloys at the single-atom limit

Platinum is ubiquitous in the production sectors of chemicals and fuels; however, its scarcity in nature and high price will limit future proliferation of platinum-catalysed reactions. One promising approach to conserve platinum involves understanding the smallest number of platinum atoms needed to catalyse a reaction, then designing catalysts with the minimal platinum ensembles. Here we design and test a new generation of platinum–copper nanoparticle catalysts for the selective hydrogenation of 1,3-butadiene,, an industrially important reaction. Isolated platinum atom geometries enable hydrogen activation and spillover but are incapable of C–C bond scission that leads to loss of selectivity and catalyst deactivation. γ-Alumina-supported single-atom alloy nanoparticle catalysts with <1 platinum atom per 100 copper atoms are found to exhibit high activity and selectivity for butadiene hydrogenation to butenes under mild conditions, demonstrating transferability from the model study to the catalytic reaction under practical conditions.

Reducing the platinum content of industrial catalysts is an important research target. Here, the authors present a nanocatalyst containing less than 1% platinum, where the isolated platinum atoms contribute to both the catalyst activity and selectivity for butadiene hydrogenation.

A 2D-3D structure transition of gold clusters on CeO2-X(111) surfaces and its influence on CO and O2 adsorption: a comprehensive DFT + U investigation

Detailed knowledge of the structures of gold nanoparticles on ceria surfaces is of fundamental importance to understand their extraordinary activities in catalysis. In this work, we employ density functional theory with the inclusion of the on-site Coulomb interaction (DFT + U) to investigate the structure evolution of small-sized gold (Au, Au4, Au8 and Au12) clusters on four types of reduced CeO2-X(111) surfaces: SSV (single surface oxygen vacancy), LSVT (linear surface oxygen vacancy trimer), dLSVC (double linear surface oxygen vacancy with a surface vacancy dimer and a subsurface vacancy), and TSVT (triangular surface oxygen vacancy trimer). Our results indicate that the relative stabilities of multilayer (3D) structures are strengthened gradually compared with the monolayer (2D) structures with increasing the number of gold atoms. In addition, the 2D-3D structure transition occurs on the size order of Au(2D → 3D)@TSVT > Au(2D → 3D)@dLSVC ∼ Au(2D → 3D)@LSVT > Au(2D → 3D)@SSV, which is determined by the charge transfer magnitude between the CeO2 surfaces and gold clusters. Meanwhile, two competitive nucleation patterns are observed, fcc-like nucleation and hcp-like nucleation, which highly affect the morphology of supported gold clusters. Further site-by-site investigations indicate that the coordination number and the charges of Au atoms are the dominant factors to influence the adsorption strength of CO and O2, and the interface plays a relatively minor role. These findings not only enrich our knowledge of the relationship between surface defects, gold cluster structures and small molecule adsorptions, but also provide a theoretical perspective to help design the optimal Au/CeO2 systems possessing high catalytic efficiency.

Review: monoclinic zirconia, its surface sites and their interaction with carbon monoxide

This review is focused on the surface sites of monoclinic zirconia, especially surface hydroxyls and their manipulation, and the interaction of CO with zirconia to form linearly adsorbed CO and formates.

Water-gas shift on gold catalysts: catalyst systems and fundamental studies

Since the pioneering finding by Haruta et al. that small gold nanoparticles on reducible supports can be highly active for low-temperature CO oxidation, the synthesis, characterization, and application of supported gold catalysts have attracted much attention. The water-gas shift reaction (WGSR: CO + H2O = CO2 + H2) is important for removing CO and upgrading the purity of H2 for fuel cell applications, ammonia synthesis, and selective hydrogenation processes. In recent years, much attention has been paid to exploration the possibility of using supported gold nanocatalysts for WGSR and understanding the fundamental aspects related to catalyst deactivation mechanisms, nature of active sites, and reaction mechanisms. Here we summarize recent advances in the development of supported gold catalysts for this reaction and fundamental insights that can be gained, and furnish our assessment on the status of research progress.

Shape-controlled ceria-based nanostructures for catalysis applications

Among oxide catalysts, ceria is a technologically important material because of its wide applications as a promoter in three-way catalysts for the elimination of toxic exhaust gases, low-temperature water-gas-shift reaction, oxygen sensors, oxygen permeation membrane systems, and fuel cells. The catalytic activities of cerium oxide are highly dependent on interfacial structures and nanocrystal morphologies. This Minireview highlights the recent progress in the research of ceria nanoshapes as both catalysts and catalyst supports, including the synthesis, structure characterization, catalytic properties, surface chemistry, as well as reaction mechanisms. Insights from in situ spectroscopy study and theoretical modeling of nanostructured ceria-based materials have shed light on the origin of the ceria shape effect. It is suggested that the surface structure of ceria controls the catalytic activity and selectivity through structure-dependent surface-site geometry, surface vacancy formation energy, defect sites, and coordinatively unsaturated sites on ceria. The morphology-dependent catalysis in ceria has offered a new strategy to finely tune the catalytic activity and selectivity through shape control without altering the catalyst composition. A brief summary and an outlook on this research field will be presented at the end.

Shape-controlled nanostructures in heterogeneous catalysis

Nanotechnologies have provided new methods for the preparation of nanomaterials with well-defined sizes and shapes, and many of those procedures have been recently implemented for applications in heterogeneous catalysis. The control of nanoparticle shape in particular offers the promise of a better definition of catalytic activity and selectivity through the optimization of the structure of the catalytic active site. This extension of new nanoparticle synthetic procedures to catalysis is in its early stages, but has shown some promising leads already. Here, we survey the major issues associated with this nanotechnology-catalysis synergy. First, we discuss new possibilities associated with distinguishing between the effects originating from nanoparticle size versus those originating from nanoparticle shape. Next, we survey the information available to date on the use of well-shaped metal and non-metal nanoparticles as active phases to control the surface atom ensembles that define the catalytic site in different catalytic applications. We follow with a brief review of the use of well-defined porous materials for the control of the shape of the space around that catalytic site. A specific example is provided to illustrate how new selective catalysts based on shape-defined nanoparticles can be designed from first principles by using fundamental mechanistic information on the reaction of interest obtained from surface-science experiments and quantum-mechanics calculations. Finally, we conclude with some thoughts on the state of the field in terms of the advances already made, the future potentials, and the possible limitations to be overcome.