Au-based Catalysts Research Articles

Harvesting low-cost gold-based catalysts from e-waste by a cationic covalent triazine organic framework for 4-nitrophenol reduction

Gold (Au)-based catalysts are commonly used for the hydrogenation of 4-nitrophenol, however, the high cost of Au has limited their widespread application. Therefore, developing affordable Au-based catalysts is highly desirable yet challenging. Herein, we synthesized a cationic covalent triazine framework to recover Au from e-waste, leading to the creation of cost-effective Au NPs@iCTF-TPM catalysts. Adsorption experiments demonstrate that cationic iCTF-TPM exhibits exceptional Au adsorption capabilities, with a maximum capacity of 1919 mg g−1. Notably, the iCTF-TPM selectively recovers Au from the e-waste leaching solution, achieving 99 % removal of Au within just 5 min. Moreover, the adsorbed AuCl4− can be self-reduced to form fine Au nanoparticles, resulting in the formation of Au NPs@iCTF-TPM catalysts. Remarkably, Au NPs@iCTF-TPM could convert 4-nitrophenol to 4-nitroaniline with a low activation energy of 26.15kJ mol−1 and a high rate constant of 1.73 × 10−2 s−1. Electron paramagnetic resonance spectroscopy indicates that the high catalytic activity is primarily due to the generation of active hydrogen radicals facilitated by Au NPs@iCTF-TPM. This study opens new avenues for developing low-cost Au-based catalysts from e-waste leaching solutions.

Machine-learning-aided Au-based single-atom alloy catalysts discovery for electrochemical NO reduction reaction to NH3

Machine-learning-aided Au-based single-atom alloy catalysts discovery for electrochemical NO reduction reaction to NH3

MIL-101(Fe) supported Au-Cu nanoalloy for enhanced electrochemical nitrogen fixation in gas–liquid-solid three-phase reactor

Low-temperature electrocatalytic nitrogen fixation technology is a green artificial nitrogen fixation technology. Here, we designed and synthesized AuxCuy/MIL-101 series catalysts, i.e., using simple alloy engineering strategy, the synthesized AuCu nanoalloy particles were efficiently loaded onto MIL-101(Fe) by one-step co-reduction. Experiments and calculations show that (Ⅰ) MIL-101(Fe) as support not only enhances the N2 enrichment ability of catalysts, but also facilitates the high dispersion of AuCu nanoparticles. (II) In AuCu nanoalloy, the strong coupling between Au-Cu sites bridges its effective electron transfer, improves the charge structure of Au sites, thereby enhancing the Au 5d-N2 π* interaction, which not only facilitates the adsorption of N2 by catalysts, but also weakens the N≡N triple bond and reduces RDS (N2 → NNH*, 0.38 eV). (III) Au-Cu alloying increases the hydrogen adsorption free energy (0.76 eV), which weakens the competitive adsorption between H+ and N2 by catalysts, and optimizes the charge transfer efficiency of AuxCuy/MIL-101 catalysts. Therefore, the overall NH3 yield and FE of AuxCuy/MIL-101 catalysts are higher than those of MIL-101, Cu/MIL-101 and Au/MIL-101. After optimization, Au1Cu1/MIL-101 with the highest ECSA and suitable Rct has the highest NRR activity (NH3 yield: 161.07 μg h−1 mg-1cat., FE: 58.86 %), which exceeds most Au-based catalysts. Meanwhile, the in-situ FTIR test results further indicate that Au-Cu alloying can accelerate the cleavage of N≡N and the adsorption of N2 by catalysts. This study demonstrates that the gold-copper alloying strategy not only promotes Au 5d feedback to N≡N bond, reduces RDS but also increases ΔGH*, inhibits proton adsorption, ultimately promoting Au1Cu1/MIL-101 catalyst to perform highly efficient NRR performance.

Au-Based Bimetallic Catalysts for Aerobic Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid under Base-Free Reaction Conditions.

The aerobic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) plays a pivotal role in the synthesis of renewable, biodegradable plastics and sustainable chemicals. Although supported gold nanoclusters (NCs) exhibit significant potential in this process, they often suffer from low selectivity. To address this challenge, a series of gold-M (M means Ni, Fe, Cu, and Pd) bimetallic NCs catalysts were designed and synthesized to facilitate the selective oxidation of HMF to FDCA. Our findings indicate that the introduction of doped metals, particularly Ni and Pd, not only improves the reaction rates for HMF tandem oxidation but also promotes high yields of FDCA. Various characterizations techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), in situ diffuse reflectance infrared Fourier transform spectroscopy of CO adsorption (CO-DRIFTS), and temperature-programmed desorption of oxygen (O2-TPD), were employed to scrutinize the structural and electronic properties of the prepared catalysts. Notably, an electronic effect was observed across the Au-based bimetallic catalysts, facilitating the activation of reactant molecules and enhancing the catalytic performance. This study provides valuable insights into the alloy effects, aiding in the development of highly efficient Au-based bimetallic catalysts for biomass conversions.

Alkali treatment modulated borate anions in layered double hydroxides as precursors of highly efficient Au-based catalysts for water-gas shift reaction

Layered double hydroxides (LDHs) as an adjustable layered materials were considered as good candidates for the supports of water-gas Shift (WGS) catalysts. However, there is rare report about the exfoliation preparation and WGS application of LDHs containing BO33− as intercalated anions. Herein, we reported a mild alkali treatment modulation of the intercalated borate anions in LDHs for improving the WGS catalytic performance of Au-based catalysts. Compared with inactive Au supported LDHs without alkali treatment, the moderate alkali treatment consumes intercalated BO33− anions in LDHs, arousing the WGS activities of Au-based catalysts. Among the different alkali treatment concentration, Au-LDHs-1M treated with 1 M NaOH present the highest WGS activity and excellent stability with a reduction of only 10 % for 60 h. The moderate alkali treatment promotes the exfoliation of LDHs into nanosheets covered Co3O4 small nanoparticles, which facilitated the high dispersion of Au species and also easily converted into active Fe3O4 and metallic Co phases. While Au-LDHs-5M presents such large Au particles that it exhibits low activity, and Au-LDHs-0M is inactive due to the formation of B2O and Fe23B6 poison phases for the WGS reaction.

Engineering hydrophobicity and high-index planes of gold nanostructures for highly selective electrochemical CO2 reduction to CO and efficient CO2 capture

In current study, we demonstrate a strategy for improving the catalytic performance of gold (Au) for carbon dioxide reduction reaction (CO2RR), specifically enhancing selectivity for CO over hydrogen evolution reaction (HER) and increasing low-level CO2 capture efficiency. This involved controlling nanostructures without any further modification. Au nanostructures having four different morphologies (i.e., degree of roughness) were fabricated via electrodeposition at varied deposition potential, resulting in different intrinsic surface hydrophobicity and exposure of high-index planes depending on the actual morphology. The roughest Au, with its combination of the most hydrophobic feature and abundant high-index planes, generated greater partial current density (jCO) and faradaic efficiency for CO (FECO) than the other Au deposits within a tested potential region: The roughest Au showed 6-fold higher FECO (95.8 %) and 327-fold higher jCO (normalized to electrode geometric surface area) at −0.75 VRHE compared to the smoothest Au. Moreover, the roughest Au exhibited excellent CO2 capture ability even at low CO2 concentration, confirmed with scanning electrochemical microscopy. These improvement at hierarchical Au for CO2RR could be ascribed to two factors. Firstly, the morphology-driven hydrophobicity provides an optimal gas–liquid-solid triple-phase interfaces, increasing the local CO2 concentration near the Au catalyst surface due to its superb CO2 capture ability. Secondly, the abundant high-index planes serve as stable active sites for CO2RR, expediting the reaction rates. Remarkably, Au with the highest hydrophobicity and enriched high-index planes, even without any chemical modification, showed excellent CO2RR catalytic performance comparable to or even better than the other previously reported Au-based catalysts.

Thiol Ligand-Modified Au for Highly Efficient Electroreduction of Nitrate to Ammonia.

Electroreduction of nitrate (NO3 -) to ammonia (NH3) is an environmentally friendly route for NH3 production, serving as an appealing alternative to the Haber-Bosch process. Recently, various noble metal-based electrocatalysts have been reported for electroreduction of NO3 -. However, the application of pure metal electrocatalysts is still limited by unsatisfactory performance, owing to the weak adsorption of nitrogen-containing intermediates on the surface of pure metal electrocatalysts. In this work, we report thiol ligand-modified Au nanoparticles as the effective electrocatalysts toward electroreduction of NO3 -. Specifically, three mercaptobenzoic acid (MBA) isomers, thiosalicylic acid (ortho-MBA), 3-mercaptobenzoic acid (meta-MBA), and 4-mercaptobenzoic acid (para-MBA), were employed to modify the surface of the Au nanocatalyst. During the NO3 - electroreduction, para-MBA modified Au (denoted as para-Au/C) displayed the highest catalytic activity among these Au-based catalysts. At -1.0 V versus reversible hydrogen electrode (vs RHE), para-Au/C exhibited a partial current density for NH3 of 472.2 mA cm-2, which was 1.7 times that of the pristine Au catalyst. Meanwhile, the Faradaic efficiency (FE) for NH3 reached 98.7% at -1.0 V vs RHE for para-Au/C. The modification of para-MBA significantly improved the intrinsic activity of the Au/C catalyst, thus accelerating the kinetics of NO3 - reduction and giving rise to a high NH3 yield rate of para-Au/C.

Theoretical insights into oxygen reduction reaction on Au-based single-atom alloy cluster catalysts

Developing highly active alloy catalysts that surpass the performance of platinum group metals in the oxygen reduction reaction (ORR) is critical in electrocatalysis. Gold-based single-atom alloy (AuSAA) clusters are gaining recognition as promising alternatives due to their potential for high activity. However, enhancing its activity of AuSAA clusters remains challenging due to limited insights into its actual active site in alkaline environments. Herein, we studied a variety of Au54M1 SAA cluster catalysts and revealed the operando formed MOx(OH)y complex acts as the crucial active site for catalyzing the ORR under the basic solution condition. The observed volcano plot indicates that Au54Co1, Au54M1, and Au54Ru1 clusters can be the optimal Au54M1 SAA cluster catalysts for the ORR. Our findings offer new insights into the actual active sites of AuSAA cluster catalysts, which will inform rational catalyst design in experimental settings.

Oxygen vacancy-regulated atomic dispersed Au on CeFeOx for preferential oxidation of CO in H2-rich stream

CO preferential oxidation in H2-rich stream (CO-PROX) is a critical reaction for H2 purification in emerging hydrogen economy including advanced fuel cell technology. Au-based catalysts are viewed as some of the most promising catalysts but achieving high catalytic efficiency and selectivity is still challenging. Defect engineering is deemed as a powerful strategy to improve the intrinsic catalytic activity. Herein, CeFeOx-supported Au catalysts with controllable oxygen vacancy (Ov) concentrations were obtained and applied to CO-PROX. The results of characterizations showed that the Ovs were preferentially generated in conjunction with Au single atoms (SAs) rather than nanoparticles (NPs), which further modulated the surface electronic properties via surplus electrons in Ovs and enhanced the interfical interaction between Ovs and Au SAs. The CO-PROX results indicated that the reduced Au SA catalyst (Au1/CeFeOx-R) with the highest Ov concentration completely converted CO at temperature of 80 °C with relatively low reactivity towards H2 oxidation. The remarkable catalytic activity and selectivity were attributed to the modified electronic properties by Ovs that played a bridging role in electron transfer and accelerated reaction process, as well as the coupling effect of Ovs and Au SAs that enhanced the dissociative adsorption of O2 and the adsorption-oxidation of CO, resulting in a reduced reaction energy barrier and making CO oxidation more favorable than H2 oxidation. This research opens up an alternative strategy to simultaneously stabilize and activate single-atom catalysts.

Surface Redox Dynamics in Gold-Zinc CO2 Hydrogenation Catalysts.

Au-Zn catalysts have previously been shown to promote the hydrogenation of CO2 to methanol, but their active state is poorly understood. Here, silica-supported bimetallic Au-Zn alloys, prepared by surface organometallic chemistry (SOMC), are shown to be proficient catalysts for hydrogenation of CO2 to methanol. In situ X-ray absorption spectroscopy (XAS), in conjunction with gas-switching experiments, is used to amplify subtle changes occurring at the surface of this tailored catalyst during reaction. Consequently, an Au-Zn alloy is identified and is shown to undergo subsequent reversible redox changes under reaction conditions according to multivariate curve resolution alternating least-squares (MCR-ALS) analysis. These results highlight the role of alloying and dealloying in Au-based CO2 hydrogenation catalysts and illustrate the role of these reversible processes in driving reactivity.

Steering the Au−FexCo1Oy interface for efficient imine synthesis at low temperature via oxidative coupling reaction

Low-temperature imine formation through oxidative coupling of alcohols with amines under base-free conditions is very important for fine-chemical synthesis. Supported-Au catalysts show superior performances toward selective oxidation reactions but are scarcely reported for the above application. In this work, the finely-dispersed Au nanoparticles (ca. 2.4 nm) loaded on magnetic FexCo1Oy oxides were developed as novel, efficient and reusable heterogeneous catalyst. Varying the Fe/Co molar ratio allowed tuning the Au−FexCo1Oy interface and further boosting the selective oxidation performance of Au. The optimum Au/Fe0.25Co1Oy catalyst showed >99% yield of benzylideneaniline and 20.1 molimine molAu−1 h−1 productivity using the model reaction at 30 °C under air atmosphere without alkaline additives. This was the best result compared to benchmark Au-based catalysts in the literature. In addition, this catalyst exhibited superior performances towards gram-scaled synthesis and diverse substrates. XRD, N2-physisorption, TEM, H2-TPR, O2-TPD, EPR, pyridine-adsorbed FT-IR, and kinetic investigations were used to study this Au catalytic system. It was found that the synergy between Fe2O3 and Co3O4 can induce formation of abundantly mobile and reactive oxygen species (i.e., O2− and O− related to oxygen vacancies) and electron-rich metallic Au species on the surface of mesoporous FexCo1Oy oxides. These interfacial features were disclosed to be vital to activating molecular O2 and O H bond in an alcohol. Besides, it was demonstrated that the surface Lewis acidic sites associated with coordinatively unsaturated Co3+ ions can help facilitate the tandem oxidation-condensation reactions.

Theoretical study on the adsorption and oxidation of glucose on Au(111) surface.

While Au-based catalysts recently have shown tremendous potential in glucose oxidation to gluconic acid, the detailed reaction mechanism is still unclear, which impedes the development of direct glucose fuel cell (DGFC). Using density functional theory (DFT), we exhibit some new adsorption configurations and oxidation mechanisms by considering both the open chain form and the ring form of glucose on Au(111) surface in the presence of OH. The strong interactions between glucose and the OH adsorbed surface are obtained. Moreover, form the calculated energy pathways, the oxidation of glucose in the open chain involves the dissociation of the formyl C - H bond by the adsorbed OH, while the ring form glucose oxidation is initiated by O - H bond rupture rather than C - H bond scission and preferentially undergoes the ring-open process to generate the open chain form glucose. Meanwhile, the results demonstrate that the adsorbed OH assists in reducing the activation energy of reaction process.

Plasmonic Au nanoparticles anchored 2D WS2@RGO for high-performance photoelectrochemical nitrogen reduction to ammonia

The photoelectrochemical reduction of nitrogen to ammonia (NH3) is a sustainable and cost-effective process. The photoelectrocatalysts adsorb light, activate N2, and transport electrons efficiently to achieve high-yield NH3. In the present work, gold-tungsten sulfide-anchored reduced graphene oxides (Au-WS2@RGO) are developed as highly efficient photoelectrocatalysts for the N2 reduction reaction (NRR) to synthesize NH3. The effect of Au nanoparticles loaded on WS2@RGO is optimized to achieve hierarchical 2D Au-WS2@RGO with excellent electrical conductivity, large active surface area, and unique porous network. Photoelectrocatalytic NRR of Au-WS2@RGO achieves remarkable NH3 production rates with ultrahigh NH3 yield of 34 μgh-1mgcat-1 at −0.6 V, tremendous faradaic efficiency (FE) of 16.2 %, long durability for about 14 h, and prolonged lifetime of photo-carriers. DFT calculations support the experimental findings and demonstrate that Au-WS2@RGO as an effeient NRR catalyst with low overpotential. The Au-WS2@RGO shows the highest NRR performances even in atmospheric air (AirRR) and outperforms the state-of-the-art NRR catalysts. The high AirRR performance and durability of Au-WS2@RGO make it a promising alternative to Au-based NRR catalysts in photo electrolyzers. Further, an innovative methodology will be proposed for high-efficiency urea fertilizer production using Au-WS2@RGO-based NRR photocatalysts.

Cationic Covalent Triazine Network: A Metal-Free Catalyst for Effective Acetylene Hydrochlorination

Vinyl chloride, the monomer of polyvinyl chloride, is produced primarily via acetylene hydrochlorination catalyzed by environmentally toxic carbon-supported HgCl2. Recently, nitrogen-doped carbon materials have been explored as metal-free catalysts to substitute toxic HgCl2. Herein, we describe the development of a cationic covalent triazine network (cCTN, cCTN-700) that selectively catalyzes acetylene hydrochlorination. cCTN-700 exhibited excellent catalytic activity with initial acetylene conversion, reaching ~99% and a vinyl chloride selectivity of >98% at 200 °C during a 45 h test. X-ray photoelectron spectroscopy, temperature programmed desorption, and charge calculation results revealed that the active sites for the catalytic reaction were the carbon atoms bonded to the pyridinic N and positively charged nitrogen atoms (viologenic N+) of the viologen moieties in cCTN-700, similar to the active sites in Au-based catalysts but different from the those in previously reported nitrogen-doped carbon materials. This research focuses on using cationic covalent triazine polymers for selective acetylene hydrochlorination.

Ligand-assisted morphology regulation of AuNi bimetallic nanocrystals for efficient hydrogen evolution.

We report the controllable synthesis of AuNi core-shell (c-AuNi) and Janus (j-AuNi) nanocrystals (NCs) with uniform shape, tunable size and compositions in the presence of trioctylphosphine (TOP) or triphenylphosphine (TPP). The morphology of the AuNi bimetallic NCs could be regulated by varying the structure and concentration of phosphine ligands. The ligand-directed structural evolution mechanism of AuNi bimetallic NCs was investigated and discussed in detail. When loaded on graphitic carbon nitride (GCN) for photocatalytic hydrogen generation, the obtained j-AuNi NCs showed much higher activity for hydrogen evolution than the monometallic (Au and Ni) counterparts, owing to the synergistic effect of plasmon enhanced light absorption from the Au portion and additional electron sink effect from the Ni portion. This work provides a promising route for preparing low-cost Au-based bimetallic catalysts with controllable morphologies and high activities for hydrogen production.

Gold nanoparticles self-assemble on the thiol-functionalized fibrous silica microspheres to produce a robust catalyst

A new type of catalyst based on thiol-functionalized fibrous nano-silica material (DFNS-SH) with unique fibrous structure as support and gold nanoparticles (Au NPs) as active sites (DFNS-SH/Au) has been prepared through a facile and environment-friendly self-assembly approach. The synthetic procedure involves the Au NPs prepared in mild conditions instantaneously self-assembled onto the DFNS-SH. The as-synthesized catalyst exhibits a remarkable higher catalytic activity in the reduction of 4-nitrophenol compared with other recently reported related catalysts. Furthermore, DFNS-SH/Au has an outstanding recyclability, after repeated use for many times, obvious activity loss did not occur until the eleventh time. The excellent catalytic activity and robust recyclability are attributed to the synergistic effect between the DFNS-SH and Au NPs. Numerous nano-fibers appear on DFNS-SH, which effectively enhance the mass diffusion and transport in catalytic reactions. Additionally, the enough strong interaction between the Au NPs and thiol groups onto the surface of DFNS can efficiently protect the Au NPs from aggregation and also endow the DFNS-SH/Au with enhanced stability. Thiol groups are also beneficial for improving the Au loading, decreasing the NPs size, reducing their aggregation and improving the catalytic performance of Au NPs anchored on the DFNS-SH as much as possible. This synthetic method discovers an eco-friendly path to effectively prepare low-budget Au-based catalysts and is promising for the development of other excellent materials.

Interfacial Auδ--OV-Zr3+ structure promoted C[sbnd]H bond activation for oxidative esterification of methacrolein to Methyl methacrylate

Constructing abundant metal-support interfacial active sites is an effective strategy to boost catalytic performance toward interfacial electronic structure-sensitive reactions, such as oxidative esterification of oxygenates. Herein, we successfully promote the generation of the interfacial active sites via tuning the crystal phases of Au/ZrO2 catalysts. Multi-characterizations (such as in-situ FT-IR spectra and reaction kinetics) and density functional theory (DFT) calculations demonstrated that the interfacial Auδ--OV-Zr3+ structure with the synergistic effect exhibits strong electrons transfer from tetragonal-ZrO2 to Au atom. Specifically, the OV-Zr3+ could facilitate the adsorption of methacrolein substrate, and the electron-rich Auδ- species could promote the CH bond activation of the CH2C(CH3)CHOOCH3 intermediate. Therefore, the interface-rich Au/t-ZrO2 catalyst achieved nearly 90 % yield of MMA and excellent catalyst stability without the incorporation of second promoter. The outcome of this work could provide some insights into developing an efficient Au-based catalyst in the oxidative esterification system.

A Facile Strategy to Obtain Low-Cost and High-Performance Gold-Based Catalysts from Artificial Electronic Waste by [Zr48 Ni6 ] Nano-Cages in MOFs for CO2 Electroreduction to CO.

Expensive gold-based catalysts are frequently used for electrochemical CO2 reduction into CO. A feasible approach to obtain low-cost Au-based catalysts is needed. Herein, a novel framework 1 assembled from [Zr48 Ni6 ] nano-cages is prepared. It exhibits a high BET surface area of 1569 m2 g-1 and high solvents/pH stability. 1 can not only selectively extract AuCl4 - from artificial electronic waste, but can then be transformed into low-cost catalyst Au nanoparticle@1-x (Au NPs@1-x, x=1, 2, 3, 4) with tuneable Au NPs sizes. The CO2 RR investigations revealed that the Au NPs@1-3 displayed an excellent FECO of 95.2 % with a current density of 102.9 mA cm-2 at -1.1 V, and such high catalytic activity can be maintained for at least 15 h without obvious decrease because the confinement effect of [Zr48 Ni6 ] nano-cages prevents Au NPs agglomeration. This work offers a facile strategy to obtain low-cost and high-performance Au-based catalysts for various reactions activated by Au.

Electrochemical Reduction of Carbon Dioxide: Recent Advances on Au-Based Nanocatalysts

The electrocatalytic reduction of CO2 to other high value-added chemicals under ambient conditions is a promising and ecofriendly strategy to achieve sustainable carbon recycling. However, the CO2 reduction reaction (CO2RR) is still confronted with a large number of challenges, such as high reaction overpotential and low product selectivity. Therefore, the rapid development of appropriate electrocatalysts is the key to promoting CO2 electroreduction. Over the past few decades, Au-based nanocatalysts have been demonstrated to be promising for the selective CO2RR to CO owing to their low reaction overpotential, good product selectivity, high Faraday efficiency and inhibition of the hydrogen evolution reaction. In this respect, this review first introduces the fundamentals of the electrochemical reduction of CO2 and then focuses on recent accomplishments with respect to Au-based nanocatalysts for CO2RR. The manipulation of various factors, e.g., the nanoporous structure, nanoparticle size, composition, morphology, support and ligand, allows for the identification of several clues for excellent Au-based nanocatalysts. We hope that this review will offer readers some important insights on Au-based catalyst design and provide new ideas for developing robust electrocatalysts.

Role of interfacial oxygen vacancies in low-loaded Au-based catalysts for the low-temperature reverse water gas shift reaction

Gold-based catalysts have shown high catalytic activity for reverse water gas shift (RWGS) reactions at low temperatures. Despite extensive studies, the RWGS reaction on Au-based catalysts with very low Au content (< 0.1 wt%) has not yet been investigated. In this study, TiO2 and ZrO2 supported gold catalysts with such low gold loading have been synthesized and tested for RWGS. The catalysts were investigated by a series of in/ex-situ characterization techniques, including ICP-OES, XRD, BET, XPS, STEM, STEM-EELS, TAP, in-situ DRIFTS and in-situ EPR. At 250 oC, the Au/TiO2 catalyst showed almost 10 times higher activity than Au/ZrO2. In-situ DRIFTS results suggest that the formate mechanism is the predominant mechanism over Au/ZrO2, while over Au/TiO2 the reaction proceeds via the formation of hydroxycarbonyl intermediates. A combined study including STEM, STEM-EELS, XPS, and in-situ EPR suggests that the interfacial Au–Ov–Ti3+ sites are responsible for the superior activity of Au/TiO2.