Influence of the conditions of thermal treatments and of storage on the size of the gold particles in Au/TiO2 samples

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.

Temperature-driven evolution of ceria-zirconia-supported AuPd and AuRu bimetallic catalysts under different atmospheres: insights from IL-STEM studies

The evolution of the structure and composition of the system of particles in two Ce0.62Zr0.38O2-supported bimetallic catalysts based on Au and a 4d metal (Ru or Pd) under high temperature conditions and different reducing and oxidizing environments has been followed by means of Identical Location Scanning Transmission Electron Microscopy (IL-STEM). As an alternative to in situ microscopy, this technique offers valuable insights into the structural modifications occurring in chemical environments with the characteristics of a macro-scale reactor. By tracking exactly the same areas on a large number of metallic entities, it has been possible to reveal the influence of particle size and the nature of the redox environment on the temperature-driven mobilization of the different metals involved. Thus, oxidizing environments evidenced a much higher capacity to mobilize the three metals, preferentially Au. Moreover, the typical storage conditions (under air) of catalysts during the prolonged exposure time has been proved to induce significant modifications in these bimetallic systems, even at room temperature. Regardless of the type of redox environment, bimetallic systems showed better thermal resistance, which demonstrates a beneficial effect of the second metal. In summary, IL-STEM is an invaluable and complementary methodology for characterizing heterogeneous catalysts under realistic reaction conditions and is within the reach of most laboratories.

Catalytic behavior of gold nanoparticles supported on a TiO2-Al2O3 mixed oxide for CO oxidation at low temperature

The present work highlights the versatility of a TiO₂-Al₂O₃ mixed oxide bearing highly dispersed gold nanoparticles that was applied in the CO oxidation reaction at room temperature. The TiO₂, Al₂O₃, and TiO₂-Al₂O₃ supports were synthesized by the sol-gel method, while gold nanoparticles were added by the deposition-precipitation with urea method using a theoretical Au loading of 2 wt.%. A promotional effect of the TiO₂-Al₂O₃ support on the activity of gold catalysts with respect to TiO₂ and Al₂O₃ was observed; Au/TiO₂-Al₂O₃ showed outstanding CO oxidation, being active from 0 °C and stable throughout a 24-h test. As for the alumina content (5, 10, and 15 wt.%) in TiO₂, it improved the textural properties by retarding the crystal growth and anatase-rutile phase transformation of TiO₂, suppressing the deposition of carbon on the catalyst surface and stabilizing the Au nanoparticles even at high temperatures. Gold was highly dispersed with nanoparticle sizes ranging from 1 to 2 nm when H₂ was used to treat thermally the Au/TiO₂-Al₂O₃, Au/TiO_2, and Au/Al₂O₃ materials. In addition, the XPS technique helped elicit that Au⁰ and Au¹⁺ boosted their interaction with the TiO₂, Al₂O₃, and TiO₂-Al₂O₃ supports by means of charge transfer, which resulted in outstanding CO oxidation activity from 0 °C. Likewise, the key factors that control the peculiar catalytic performance in the CO oxidation reaction are discussed, which represents a step forward in the versatility behavior of gold catalysts supported on mixed oxide catalysts.

Controllable Microemulsion Synthesis of Hybrid TiO2-SiO2 Hollow Spheres and Au-Doped Hollow Spheres with Enhanced Photocatalytic Activity

Hollow structures in TiO₂ materials can enhance the photocatalytic properties by reducing the diffusion length and improving the accessibility of active sites for the reactants. However, existing approaches for preparing hollow TiO₂ materials have two drawbacks that restrict their engineering applicability: first, a heavy reliance on templates to form a hollow structure, which makes the preparation laborious, complicated, and costly; second, difficult-to-achieve high crystallization while maintaining the small grain size in calcinated TiO₂, which is crucial for enhancing photocatalytic activity. Herein, a simple, effective method is proposed that not only enables the preparation of hybrid TiO₂-SiO₂ hollow spheres without the template fabrication and removal process via microemulsion technology but also achieves both high crystallization and a small grain size in calcinated TiO₂ at once through the calcination of amorphous TiO₂ with organosilane at a high temperature of 850 °C. The prepared TiO₂-SiO₂ hollow spheres with tunable sizes demonstrate high photocatalytic activity with a maximum k value of 133.74 × 10^-3 min^-1, which is superior to commercial photocatalyst P25 (k = 114.97 × 10^-3 min^-1). In addition, Au can be doped in the hybrid TiO₂-SiO₂ shell to gain Au-doped hollow spheres that show a high k value of up to 694.14 × 10^-3 min^-1, which is 6 times larger than that of P25 and much better than that reported in the literature. This study not only provides an effective approach to stabilize and tune the grain growth of the TiO₂ photocatalyst during calcination but also enables the simple preparation of hollow TiO₂-based materials with controllable hollow nanostructures.

Insight into the Properties of Plasmonic Au/TiO2 Activated by O2/Ar Plasma

The performance of CO oxidation over plasmonic Au/TiO₂ photocatalysts is largely determined by the electric discharge characteristics and physicochemical properties of discharge gas. To explore the activation mechanism of Au/TiO₂, an O₂ and Ar mixture gas as a discharge gas was employed to activate Au/TiO₂. The photocatalytic activity in CO oxidation over activated Au/TiO₂ was obtained, and the electric discharge characteristics, Au nanoparticle size, surface chemical state, optical property and CO chemisorption were thoroughly characterized. As the O₂ content increases from 10% to 50%, the amplitude of the current pulses increases, but the number of pulses and the discharge power decrease. The photocatalytic activity of Au/TiO₂ rises rapidly at first and then remains constant at 75% when the O₂ content is above 50%. Compared with the discharge gas of 10% and 30% O₂/Ar, the sample activated by 50% O₂/Ar plasma possesses less metallic Au and more surface oxygen species and carbonate species by X-ray photoelectron spectroscopy, which is consistent with UV-vis diffuse reflectance spectra and CO chemisorption. The CO chemisorption capacities of the activated samples are the same at a long exposure time due to the approximate Au nanoparticle size observed by transmission electron microscopy. An increase in carbonate species generated from the oxygen species on the surface of TiO₂ is discovered.

Localized surface plasmon resonance for enhanced electrocatalysis

Electrocatalysis plays a vital role in energy conversion and storage in modern society. Localized surface plasmon resonance (LSPR) is a highly attractive approach to enhance the electrocatalytic activity and selectivity with solar energy. LSPR excitation can induce the transfer of hot electrons and holes, electromagnetic field enhancement, lattice heating, resonant energy transfer and scattering, in turn boosting a variety of electrocatalytic reactions. Although the LSPR-mediated electrocatalysis has been investigated, the underlying mechanism has not been well explained. Moreover, the efficiency is strongly dependent on the structure and composition of plasmonic metals. In this review, the currently proposed mechanisms for plasmon-mediated electrocatalysis are introduced and the preparation methods to design supported plasmonic nanostructures and related electrodes are summarized. In addition, we focus on the characterization strategies used for verifying and differentiating LSPR mechanisms involved at the electrochemical interface. Following that are highlights of representative examples of direct plasmonic metal-driven and indirect plasmon-enhanced electrocatalytic reactions. Finally, this review concludes with a discussion on the remaining challenges and future opportunities for coupling LSPR with electrocatalysis.

Effect of the Metal Deposition Order on Structural, Electronic and Catalytic Properties of TiO2-Supported Bimetallic Au-Ag Catalysts in 1-Octanol Selective Oxidation

Au and Ag were deposited on TiO2 modified with Ce, La, Fe or Mg in order to obtain bimetallic catalysts to be used for liquid-phase oxidation of 1-octanol. The effects of the deposition order of gold and silver, and the nature of the support modifying additives and redox pretreatments on the catalytic properties of the bimetallic Au-Ag catalysts were studied. Catalysts were characterized by low-temperature nitrogen adsorption–desorption, energy dispersive spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy and ultraviolet-visible diffuse reflectance spectroscopy. It was found that pretreatments with hydrogen and oxygen at 300 °C significantly decreased the activity of AuAg catalysts (silver was deposited first) and had little effect on the catalytic properties of AgAu samples (gold was deposited first). The density functional theory method demonstrated that the adsorption energy of 1-octanol increased for all positively charged AuxAgyq (x + y = 10, with a charge of q = 0 or +1) clusters compared with the neutral counterparts. Lanthanum oxide was a very effective promoter for both monometallic and bimetallic gold and silver catalysts in the studied process.

Titanium-Anchored Gold on Silica for Enhanced Catalytic Activity in Aqueous Ethanol Oxidation

The heterogeneously catalyzed oxidation of bioethanol offers a promising route to bio-based acetic acid. Here, we assess an alternative method to support gold nanoparticles, which aims to improve selectivity to acetic acid through minimizing over-oxidation to carbon dioxide. The most promising support system is 5 wt % titanium on silica, which combines the high surface area of silica with the stabilizing effect of titania on the gold particles. Compared to gold–silica systems, which require a complex synthesis method, small quantities of titanium promoted the formation of gold nanoparticles during a simple deposition–precipitation. Characterization of the catalyst with X-ray absorption spectroscopy shows that titanium is highly dispersed in the form of small, possibly dimeric, titanium(IV) structures, which are isolated and stabilize gold nanoparticles, possibly minimizing sintering effects during synthesis. The size of the gold particles depends on the pre-treatment of the titanium–silica support before gold deposition, with larger titanium structures hosting larger gold particles. Acetic acid yield over the titanium–silica-supported gold systems improved by about 1.6 times, compared to pure titania-supported gold. The high activity of those catalysts suggests that bulk, crystalline titania is not required for the reaction, encouraging the use of mixed supports to combine their benefits. Those support systems, besides improving selectivity, offer high surface area and a low-cost filler material, which brings ethanol oxidation one step further to the industry. Additionally, the low loading of titanium permits studying the reaction mechanisms on the gold–titanium interface with bulk characterization techniques.

Effect of Gold Electronic State on the Catalytic Performance of Nano Gold Catalysts in n-Octanol Oxidation

This study aims to identify the role of the various electronic states of gold in the catalytic behavior of Au/M_xO_y/TiO₂ (where M_xO_y are Fe₂O₃ or MgO) for the liquid phase oxidation of n-octanol, under mild conditions. For this purpose, Au/M_xO_y/TiO₂ catalysts were prepared by deposition-precipitation with urea, varying the gold content (0.5 or 4 wt.%) and pretreatment conditions (H₂ or O₂), and characterized by low temperature nitrogen adsorption-desorption, X-ray powder diffraction (XRD), energy dispersive spectroscopy (EDX), scanning transmission electron microscopy-high angle annular dark field (STEM HAADF), diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy of CO adsorption, temperature-programmable desorption (TPD) of ammonia and carbon dioxide, and X-ray photoelectron spectroscopy (XPS). Three states of gold were identified on the surface of the catalysts, Au⁰, Au¹⁺ and Au³⁺, and their ratio determined the catalysts performance. Based on a comparison of catalytic and spectroscopic results, it may be concluded that Au⁺ was the active site state, while Au⁰ had negative effect, due to a partial blocking of Au⁰ by solvent. Au³⁺ also inhibited the oxidation process, due to the strong adsorption of the solvent and/or water formed during the reaction. Density functional theory (DFT) simulations confirmed these suggestions. The dependence of selectivity on the ratio of Brønsted acid centers to Brønsted basic centers was revealed.

Boosting the catalysis of gold by O2 activation at Au-SiO2 interface

Supported gold (Au) nanocatalysts have attracted extensive interests in the past decades because of their unique catalytic properties for a number of key chemical reactions, especially in (selective) oxidations. The activation of O₂ on Au nanocatalysts is crucial and remains a challenge because only small Au nanoparticles (NPs) can effectively activate O₂. This severely limits their practical application because Au NPs inevitably sinter into larger ones during reaction due to their low Taman temperature. Here we construct a Au-SiO₂ interface by depositing thin SiO₂ layer onto Au/TiO₂ and calcination at high temperatures and demonstrate that the interface can be not only highly sintering resistant but also extremely active for O₂ activation. This work provides insights into the catalysis of Au nanocatalysts and paves a way for the design and development of highly active supported Au catalysts with excellent thermal stability.

The development of sintering resistant supported Au catalysts with high activity still remains a challenge. Here the authors construct a Au-SiO₂ interface by depositing SiO₂ thin layer onto Au/TiO₂ catalyst which shows very high activity in CO oxidation even after calcination at 800 °C.

C. Ribeiro A, Kolobova E, M. D. R. S. Martins L, A. C. Carabineiro S, German D, Pichugina D, Jiang C, J. L. Pombeiro A, Bogdanchikova N, Cortés Corberán V, Pestryakov A. Supported Gold Nanoparticles as Catalysts in Peroxidative and Aerobic Oxidation of 1-Phenylethanol under Mild Conditions

The efficiency of Au/TiO₂ based catalysts in 1-phenylethanol oxidation was investigated. The role of support modifiers (La₂O₃ or CeO₂), influence of gold loading (0.5% or 4%) and redox pretreatment atmosphere, catalyst recyclability, effect of oxidant: tert-butyl hydroperoxide (TBHP) or O₂, as well as the optimization of experimental parameters of the reaction conditions in the oxidation of this alcohol were studied and compared with previous studies on 1-octanol oxidation. Samples were characterized by temperature-programmed oxygen desorption (O₂-TPD) method. X-ray photoelectron spectroscopy (XPS) measurements were carried out for used catalysts to find out the reason for deactivation in 1-phenylethanol oxidation. The best catalytic characteristics were shown by catalysts modified with La₂O₃, regardless of the alcohol and the type of oxidant. When O₂ was used, the catalysts with 0.5% Au, after oxidative pretreatment, showed the highest activity in both reactions. The most active catalysts in 1-phenylethanol oxidation with TBHP were those with 4% Au and the H₂ treatment, while under the same reaction conditions, 0.5% Au and O₂ treatment were beneficial in 1-octanol oxidation. Despite the different chemical nature of the substrates, it seems likely that Au⁺(Au^δ+) act as the active sites in both oxidative reactions. Density functional theory (DFT) simulations confirmed that the gold cationic sites play an essential role in 1-phenylethanol adsorption.

Synthesis of a CeO2/Co3O4 catalyst with a remarkable performance for the soot oxidation reaction

A highly active catalyst based on CeO₂/Co₃O₄ for soot oxidation at low temperatures with complete selectivity toward CO₂.

Ultrastable Au nanoparticles on titania through an encapsulation strategy under oxidative atmosphere

Supported gold catalysts play a crucial role in the chemical industry; however, their poor on-stream stability because of the sintering of the gold nanoparticles restricts their practical application. The strong metal-support interaction (SMSI), an important concept in heterogeneous catalysis, may be applied to construct the structure of catalysts and, hence, improve their reactivity and stability. Here we report an ultrastable Au nanocatalyst after calcination at 800 °C, in which Au nanoparticles are encapsulated by a permeable TiO_x thin layer induced by melamine under oxidative atmosphere. Owning to the formed TiO_x overlayer, the resulting Au catalyst is resistant to sintering and exhibits excellent activity and stability for catalytic CO oxidation. Furthermore, this special strategy can be extended to colloidal Au nanoparticles supported on TiO₂ and commercial gold catalyst denoted as RR2Ti, providing a universal way to engineer and develop highly stable supported Au catalysts with tunable activity.

Sintering-resistant Au nanoparticles are highly desirable due to their low Tammann temperature. Here, the authors report an ultrastable titania-supported Au nanocatalyst through an encapsulation strategy under oxidative atmosphere.

Supported Gold Nanoparticles as Catalysts for the Oxidation of Alcohols and Alkanes

Supporting gold nanoparticles have shown to be extremely active for many industrially important reactions, including oxidations. Two representative examples are the oxidation of alcohols and alkanes, that are substrates of industrial interest, but whose oxidation is still challenging. This review deals with these reactions, giving an insight of the first studies performed by gold based catalysts in these reactions and the most recent developments in the field.

A Study of Catalytic Oxidation of a Library of C₂ to C₄ Alcohols in the Presence of Nanogold

The classical stoichiometric oxidation of alcohols is an important tool in contemporary organic chemistry. However, it still requires huge modifications in order to comply with the principles of green chemistry. The use of toxic chemicals, hazardous organic solvents, and the large amounts of toxic wastes that result from the reactions are a few examples of the problems that must be solved. Nanogold alone or conjugated with palladium were supported on different carriers (SiO₂, C) and investigated in order to evaluate their catalytic potential for environmentally friendly alcohol oxidation under solvent-free and base-free conditions in the presence H₂O₂ as a clean oxidant. We tested different levels of Au loading (0.1⁻1.2% wt.) and different active catalytic site forms (monometallic Au or bimetallic Au⁻Pd sites). This provided new insights on how the structure of the Au-dispersions affected their catalytic performance. Importantly, the examination of the catalytic performance of the resulting catalysts was oriented toward a broad scope of alcohols, including those that are the most resistant to oxidation-the primary aliphatic alcohols. Surprisingly, the studies proved that Au/SiO₂ at a level of Au loading as low as 0.1% wt. appeared to be efficient and prospective catalytic system for the green oxidation of alcohol. Most importantly, the results revealed that 0.1% Au/SiO₂ might be the catalyst of choice with a wide scope of utility in the green oxidation of various structurally different alcohols as well as the non-activated aliphatic ones.

Classical strong metal-support interactions between gold nanoparticles and titanium dioxide

Supported metal catalysts play a central role in the modern chemical industry but often exhibit poor on-stream stability. The strong metal-support interaction (SMSI) offers a route to control the structural properties of supported metals and, hence, their reactivity and stability. Conventional wisdom holds that supported Au cannot manifest a classical SMSI, which is characterized by reversible metal encapsulation by the support upon high-temperature redox treatments. We demonstrate a classical SMSI for Au/TiO₂, evidenced by suppression of CO adsorption, electron transfer from TiO₂ to Au nanoparticles, and gold encapsulation by a TiO _x overlayer following high-temperature reduction (reversed by subsequent oxidation), akin to that observed for titania-supported platinum group metals. In the SMSI state, Au/TiO₂ exhibits markedly improved stability toward CO oxidation. The SMSI extends to Au supported over other reducible oxides (Fe₃O₄ and CeO₂) and other group IB metals (Cu and Ag) over titania. This discovery highlights the general nature of the classical SMSI and unlocks the development of thermochemically stable IB metal catalysts.

Superior Stability of Au/SiO2 Compared to Au/TiO2 Catalysts for the Selective Hydrogenation of Butadiene

Supported gold nanoparticles are highly selective catalysts for a range of both liquid-phase and gas-phase hydrogenation reactions. However, little is known about their stability during gas-phase catalysis and the influence of the support thereon. We report on the activity, selectivity, and stability of 2-4 nm Au nanoparticulate catalysts, supported on either TiO₂ or SiO₂, for the hydrogenation of 0.3% butadiene in the presence of 30% propene. Direct comparison of the stability of the Au catalysts was possible as they were prepared via the same method but on different supports. At full conversion of butadiene, only 0.1% of the propene was converted for both supported catalysts, demonstrating their high selectivity. The TiO₂-supported catalysts showed a steady loss of activity, which was recovered by heating in air. We demonstrated that the deactivation was not caused by significant metal particle growth or strong metal-support interaction, but rather, it is related to the deposition of carbonaceous species under reaction conditions. In contrast, all the SiO₂-supported catalysts were highly stable, with very limited formation of carbonaceous deposits. It shows that SiO₂-supported catalysts, despite their 2-3 times lower initial activities, clearly outperform TiO₂-supported catalysts within a day of run time.

Photocatalytic Properties of TiO2 Composites Immobilized with Gold Nanoparticle Assemblies Using the Streptavidin-Biotin Interaction

A method using biomolecules to precisely fabricate the morphology of metal nanoparticles immobilized on the surface of a semiconductor using biomolecules is described. A biotin moiety (Biot) is introduced onto the surface of a gold nanoparticle (AuNP) by covalent coupling with α-lipoic acid to assemble AuNPs in the presence of streptavidin (STV). The assembly of Biot-AuNP/STV is immobilized on the surface of TiO2 chemically modified with 1-(3-aminopropyl)silatrane (APS) to provide a positively charged surface. The Au content immobilized on the surface of TiO2 is clearly increased to 9.5 wt % (Au) as a result of the STV-biotin interaction and the electrostatic interaction between negatively charged Biot-AuNPs and the positively charged surface of APS/TiO2. Transmission electron microscopy (TEM) analysis reveals that the composite has an ordered surface geometry in which Biot-AuNPs are spread over the composite surface in two dimensions. The photocatalytic activity toward decomposition of methyl orange dye promoted by this composite is 55%, which is higher than that of the other composites. The Biot-AuNP/STV@APS/TiO2 composite efficiently reduces O2 molecules at Eonset = -0.23 V vs Ag|AgCl, which is more positive than that of other composites (Eonset = -0.40 to -0.32 V). The result suggests that an increased number of AuNPs immobilized in close contact with the TiO2 surface facilitates photoinduced charge transfer. This strategy, which takes advantage of the specific interactions provided by biomolecules and the chemical modification on the surface, has remarkable potential for efficient fabrication of metal nanoparticles on the surface of the semiconductor, which accelerates the reduction of oxygen molecules.

Identification of Subnanometric Ag Species, Their Interaction with Supports and Role in Catalytic CO Oxidation

The nature and size of the real active species of nanoparticulated metal supported catalysts is still an unresolved question. The technique of choice to measure particle sizes at the nanoscale, HRTEM, has a practical limit of 1 nm. This work is aimed to identify the catalytic role of subnanometer species and methods to detect and characterize them. In this frame, we investigated the sensitivity to redox pretreatments of Ag/Fe/TiO₂, Ag/Mg/TiO₂ and Ag/Ce/TiO₂ catalysts in CO oxidation. The joint application of HRTEM, SR-XRD, DRS, XPS, EXAFS and XANES methods indicated that most of the silver in all samples is in the form of Ag species with size <1 nm. The differences in catalytic properties and sensitivity to pretreatments, observed for the studied Ag catalysts, could not be explained taking into account only the Ag particles whose size distribution is measured by HRTEM, but may be explained by the presence of the subnanometer Ag species, undetectable by HRTEM, and their interaction with supports. This result highlights their role as active species and the need to take them into account to understand integrally the catalysis by supported nanometals.

Causes of Activation and Deactivation of Modified Nanogold Catalysts during Prolonged Storage and Redox Treatments

The catalytic properties of modified Au/TiO₂ catalysts for low-temperature CO oxidation are affected by deactivation and reactivation after long-term storage and by redox treatments. The effect of these phenomena on the catalysts was studied by HRTEM, BET, SEM, FTIR CO, XPS and H₂ TPR methods. The main cause for the deactivation and reactivation of catalytic properties is the variation in the electronic state of the supported gold, mainly, the proportion of singly charged ions Au⁺. The most active samples are those with the highest proportion of singly charged gold ions, while catalysts with a high content of trivalent gold ions are inactive at low-temperatures. Active states of gold, resistant to changes caused by the reaction process and storage conditions, can be stabilized by modification of the titanium oxide support with transition metals oxides. The catalyst modified with lanthanum oxide shows the highest stability and activity.

On the High Sensitivity of the Electronic States of 1 nm Gold Particles to Pretreatments and Modifiers

In this paper, the effect of modifiers and pretreatments on the electronic states of 1 nm gold nanoparticles (AuNPs) supported on silica was systematically studied. AuNPs deposited on silica (particle size of 2–4 nm) modified with Ce, La and Fe oxides, were studied by FTIR of adsorbed CO after different redox treatments at 100, 300 and 500 °C. This study was conducted at room temperature to allow detecting the electronic states of gold, which is more likely involved in CO oxidation at the same temperature. AuNP size distribution was measured by HRTEM. It is shown that the electronic state of gold species (Au_n^δ−, Au⁰, Au_n^δ+, Au⁺) in 1 nm AuNPs is sensitive to the modifier as well as to the temperatures of redox pretreatments. Supports modified with the same additives but containing larger AuNPs (~3, 4, 5, and 7 nm) were also studied. They showed that Au⁰ remains stable irrespective of additives and redox pretreatments, indicating no significant effect of such treatments on the electronic properties of larger AuNPs. Samples with a predominant AuNP size of 2 nm are an intermediate case between these two groups of materials.

C, N co-doping promoted mesoporous Au/TiO2 catalyst for low temperature CO oxidation

The doping of C and N into meso-structured TiO₂ increases the number of surface defects which could improve the absorption of oxygen, tune the metal-support interaction and promote the catalytic activities for CO oxidation.

Plasmonic Au/TiO2nanostructures for glycerol oxidation

Visible light irradiation of the reaction volume results in boosted conversion for glycerol oxidation due to plasmonic properties of Au/TiO₂.

Thermal activation process of Au/TiO2 system: a molecular spectroscopy study

Concatenated reactions involved in the thermal activation process of the AuNPs/TiO₂ system were evidenced by an in situ molecular spectroscopy study.