The structure and dynamics of adsorbed atoms (adatoms) at solid-liquid interfaces determine the performance of advanced catalysts, electrochemical devices, molecular separation technologies, and metal extraction from waste streams. However, in situ investigations of atomically dispersed metals in various chemical environments have been prevented by insufficient imaging resolution and solvent incompatibility. In this study, we combined a specimen design that provides atomic resolution in liquid-phase electron microscopy with deep learning-enabled analysis to explore the interactions between gold adatoms, graphite support, and the solvent collectively. We tracked the locations of >106 graphite-supported gold adatoms, dimers, and larger clusters in five solvents. Although their initial atomic dispersion was determined by the solvent polarity, fast drying kinetics at low temperature was required for optimizing catalytic performance.

Liquid-phase heterogeneous catalysis underpins numerous chemical manufacturing processes, ranging from essential products to renewable energy sources, such as hydrogen. Despite the differences in reactor setups and the driving forces between thermos- and electro-catalysis, it is commonly overlooked that the two disciplines are fundamentally governed by the same underlying fundamentals. In this tutorial review, we explore the similarities between electro- and thermocatalysis and introduce how electrochemical methodologies can be applied to characterize thermocatalysis to gain both fundamental and experimental insights. Here, we discuss the recent discovery of Cooperative Redox Enhancement (CORE), a phenomenon whereby selectivity differences for two electrochemical half reactions on two physically separated but electrochemically connected dissimilar metal catalyst particles lead to acceleration of the overall catalytic rate. This approach suggests a new paradigm for the design of heterogeneous catalysis.

Heterogeneous catalysts consistently suffer from the leaching of active components into the fluid phase, causing loss in activity and lifetime. Here we demonstrate, exemplified with the thermocatalytic oxidation of 1,2-propanediol, a metal stabilization mechanism arising from electrochemical coupling of half reactions between physically separated carbon-supported Au and Pd catalysts. When electrochemically coupled, polarization of each metal to an operating mixed potential occurs as a function of the Au:Pd molar ratio that, at pH 9-10, significantly reduces Pd leaching. At pH 14, where this stabilization no longer holds, we clearly show that an active redox mechanism can exist between disparate catalytic species in the liquid and solid phase, and that this leads to the cycling of Pd speciation as well as considerable enhancements in the rate of oxidation.

Replacement of mercuric chloride catalysts to produce vinyl chloride monomer from acetylene, the precursor to PVC, is needed due to widespread environmental damage of leached mercury. Cationic gold catalysts, which have been recently commercialised, represent a more environmentally benign alternative. However, new catalysts are required to limit the atomically dispersed cationic Au from agglomeration due to reduction under reaction conditions. Several strategies are available to stabilise the Au active sites such as the use of sulphur containing ligands or to use heteroatom doped carbon as the support. Here we prepared two types of doped carbon supports; spheres derived via a hard template methodology and secondly, doped commercial activated carbon. In both cases the Au supported on S-doped carbon was superior in comparison to the undoped analogue; the acetylene conversion was enhanced by 1.6 times over the S-doped carbon sphere catalyst and 2 times over the S-doped Norit catalyst at 60 min time-on-line. The stability and activity of the gold centres are discussed with respect to the heteroatom used, in this case either sulphur, nitrogen, or a combination of the two, and compared to the unmodified supports.

Understanding solid-liquid interfaces at the atomic-scale is key to improved performance of heterogeneous catalysts, electrodes and membranes. Here we combine unique specimen design, record atomic resolution in situ electron microscopy, and artificial intelligence-enabled analysis to achieve a step change in quantitative understanding of interfacial atomic behaviour. We create the first graphene liquid cells with organic solvents and employ them to track over 106 gold adatoms and clusters at a graphene surface immersed in acetone and cyclohexanone. We reveal dynamic correlated behaviour of gold adatom monomers, dimers, trimers and clusters, strongly influenced by each other, the solvent properties, and the atomic lattice of the substrate, in good agreement with theoretical calculations. We use the results to interpret differences in catalytic activity towards the industrially important acetylene hydrochlorination reaction. This new capability for exploration of atomic scale chemistry could enable rational design of future catalysts, membranes and electrodes with improved functionality.

The Cooperative Redox Enhancement (CORE) mechanism, driven by electrochemical coupling between physically separated yet electrically connected catalytically active sites, underpins significant rate enhancements in liquid-phase thermocatalytic reactions. In this study, we use galvanic coupling measurements to accurately predict the magnitude of this rate enhancement in Au-Pd bimetallic systems using the conversion of 1,4-butanediol as a model system. This electrochemical method enables the determination of the optimal ratio of Au/C to Pd/C monometallic catalysts and serves as a predictive approach across a range of reaction conditions. These findings underscore the utility of electrochemical measurements to evaluate and optimize bimetallic thermocatalytic systems, advancing strategies for liquid-phase redox reaction design.

The formation of C-C bonds through coupling reactions is an important industrial process. The ability of Au to catalyze such reactions has been reported, with both homogeneous and heterogeneous catalyst examples. Previous work has shown that carbon-supported cationic and nanoparticulate Au are active for the homocoupling of phenylboronic acid to biphenyl. However, the stability of supported cationic Au is short-lived, and the formed nanoparticles were suggested to be the active species. Through the synthesis of two types of supported cationic Au catalysts, utilizing either aqua regia or acetone solvents, we show that both catalysts develop nanoparticulate Au species early in the reaction; however, only the aqua regia prepared catalyst is active. We ascribe the activity of the aqua regia prepared Au catalyst to excess Cl and the presence of C-Cl surface species in combination with Au. Carbon treated with aqua regia was inactive; however, when used as a support for Au deposited with acetone or via a sol immobilization method, activity was comparable to the aqua regia prepared catalyst. The role of C-Cl and Au nanoparticles is discussed with respect to their correlation to the biphenyl yield, which is shown to be significant only when the C-Cl species are present on the catalyst.

The development of titianosilicates is considered a major milestone in oxidative catalysis due to the ability of framework Ti sites to co-ordinate hydrogen peroxide/peroxy species. Herein, we demonstrate that interfacial Ti sites can be constructed through the vertical intergrowth of two MFI-type zeolite surfaces along [100] and [010] projections, with the assistance of UV-induced hydroxyl radicals. The application of these intergrown titanosilicalites as supports for Au species are observed to simultaneously offer a 2.1-fold and 3.0-fold increase in propene oxide (PO) formation rate and Au efficiency, respectively, when compared to standard Au/TS-1 catalysts. Mechanistic studies reveal that the intergrown interface Ti sites allow for lower-energy epoxidation pathways with more efficient activation of key oxygen-transfer intermediates. These results provide insights into the development of zeolite intergrown interface sites (e.g., titanosilicalite/silicalite-1/ZSM-5) and may allow for further advancements in the epoxidation of a range of key feedstocks.

ConspectusElectro- and thermo-catalysis are frequently considered as disparate fields of research. The former is critical for the future electrified green chemical industry where renewable electrical energy will power production in place of fossil-derived sources; however, the necessary scale-up from the laboratory to commodity chemical production is in its infancy. In contrast, thermo-catalysis is at the heart of the modern chemical industry with the associated capital investments in infrastructure and technology. It is, however, far more energy intensive and typically requires the use of elevated temperatures and pressures to obtain economically viable productivity. Our recent discovery of a new approach to catalyst design, termed Cooperative Redox Enhancement (CORE), bridges the gap between these traditionally distinct fields. In this Account, we outline how CORE can facilitate a unifying approach to these fields and describe how electrochemical methods can provide detailed thermochemical mechanistic information.Industrial heterogeneous catalysts often comprise supported precious metal nanoparticles with alloys frequently providing superior performance over monometallic counterparts. However, we have found that spatial separation of the two metals on an electronically conductive support leads to substantial enhancement in activity through electrochemical coupling. This CORE effect demonstrates that thermochemical redox reactions can, and often do, operate like nanoscale electrochemical fuel cells. The electrochemical coupling in systems containing at least two discrete active sites accelerates both half reactions in a mechanism analogous to galvanic coupling in corrosion science. CORE demonstrates that leveraging electrocatalytic approaches is a key tool for the development of the next generation of thermochemical catalysts and vice versa.Here, our primary aim is to provide a critical overview of CORE effects that are exhibited in thermocatalytic redox reactions over bimetallic catalysts. We will provide a chronological timeline of the research in this area that led to this discovery. This will include comparing CORE to other effects which are commonly exhibited by bimetallic catalysts, e.g., the synergistic electronic and geometric effects observed through the formation of nanoalloys. We will provide a detailed overview of CORE, how it can be studied, and how thermochemical enhancements can be predicted by utilizing electrochemical methods. Specifically, we will discuss the importance of using linear sweep voltammetry, Tafel analysis, and mixed potential theory to acquire a host of new electrochemical terms that we have defined, such as ECORE (operating mixed potential for bimetallic catalysts) and jCORE (operating current density for bimetallic catalysts), which underpin the electrochemical study of CORE. Primarily, the discussion will be centered on the CORE effects observed in coupled systems that involve dehydrogenation and oxygen reduction, as this is the primary model system we have studied to date. However, we also include examples of how CORE has relevance in other redox reactions, demonstrating the generality of the effect. Finally, we provide a short perspective on the future directions of this field and the impact that can be expected on catalysis over the coming decade.

Correction for 'Adipic acid formation from cyclohexanediol using platinum and vanadium catalysts: elucidating the role of homogeneous vanadium species' by Owen Rogers et al., Catal. Sci. Technol., 2020, 10, 4210-4218, https://doi.org/10.1039/D0CY00914H

Correction for ‘Adipic acid formation from cyclohexanediol using platinum and vanadium catalysts: elucidating the role of homogeneous vanadium species’ by Owen Rogers et al., Catal. Sci. Technol., 2020, 10, 4210–4218, https://doi.org/10.1039/D0CY00914H

Cooperative redox enhancement (CORE) between physically separated but electrochemically connected catalysts promotes thermocatalytic reactions. Using the oxidative dehydrogenation of ethanol as a model reaction, we showcase two electrochemical approaches that predict monometallic and (CORE-enabled) bimetallic thermocatalytic activities. The common approach of linear sweep voltammetry can accurately determine the activity of individual half-reactions but does not account for competitive adsorption. This can lead to the underprediction of thermocatalytic rates and to overlooking the possibility of leveraging CORE effects. In contrast, adapting utilizing the Tafel method, with both reactants present, can accurately predict thermocatalytic rates and the coupling between separated catalysts.

Developing highly active catalysts for the decomposition of ammonia to produce hydrogen is an important goal in the context of renewable energy. Allied with this is a need for identification strategies to efficiently design novel catalysts integral to ensuring rapid progress in this research field. We investigated the efficacy of N–binding energy and periodic table interpolation to predict active bimetallic nanoparticle catalysts. Supported iron-platinum and iron-palladium were identified and experimentally shown to be more active than their monometallic analogues. Atomic resolution electron microscopy indicated that the most active catalyst (5 wt% Fe 80 Pt 20 /γ-Al 2 O 3 ) was principally formed of alloyed nanoparticles. It restructured during testing, yet no activity loss was noted at 20 h time-on-line. While these findings show that periodic table interpolation may be a viable tool for identifying active combinations of metals, the activity of the catalysts in the current work were not able to outperform the Ru/Al 2 O 3 benchmark. Further catalyst optimization or refinement of reaction descriptors may facilitate the development of catalysts with higher intrinsic activity than the current state-of-the-art catalysts. Graphical Abstract

The spatial separation of Au and Pd nanoparticles supported on carbon has been demonstrated to be highly effective in facilitating aqueous-phase alcohol oxidation reactions, wherein OH- is the oxidant terminal for the oxidative dehydrogenation reaction. However, the application of this methodology in nonaqueous environments has not yet been explored. Supported alloyed Au-Pd nanoparticles are known to be highly active in the solvent-free oxidation of benzyl alcohol with oxygen as the terminal oxidant, leading to benzaldehyde by direct oxidation and toluene by disproportionation. Here, we show that by physically separating Au and Pd nanoparticles supported on carbon, the reaction rate for solvent-free benzyl alcohol oxidation can be further enhanced by coupling the oxidation and disproportionation reactions via H-transfer from Pd to Au.

The aerobic oxidation of alcohols and aldehydes over supported heterogeneous catalysts can be considered as comprising two complementary and linked processes: dehydrogen-ation and oxygen reduction. Significant rate enhancements can be observed when these processes are catalyzed by independent active sites, coupled by electron transport between the two catalysts. This effect, termed cooperative redox enhancement (CORE), could significantly influence how researchers approach catalyst design, but a greater understanding of the factors which influence it is required. Herein, we demonstrate that the Au/Pd ratio used in physical mixtures of monometallic catalysts and phase-separated Au and Pd bimetallic catalysts dramatically influences the degree to which CORE effects can promote alcohol oxidation. Perhaps more interestingly, the roles of Au and Pd in this coupled system are determined to be interchangeable. Preliminarily, we hypothesize that this is attributed to the relative rates of the coupled reactions and demonstrate how physical properties can influence this. This deeper understanding of the factors which influence CORE is an important development in bimetallic catalysis.

We investigate the effect of chlorides on the photocatalytic degradation of phenol by titania polymorphs (anatase and rutile). We demonstrate how solubilised chlorides can affect the hydroxyl radical formation on both polymorphs with an overall effect on their photodegradative activity. Initially, the photocatalytic activity of anatase and rutile for phenol degradation is investigated in both standard water and brines. With anatase, a significant reduction of the phenol conversion rate is observed (from a pseudo-first-order rate constant k = 5.3 × 10-3 min-1 to k = 3.5 × 10-3 min-1). In contrast, the presence of solubilised chlorides results in enhancement of rutile activity under the same reaction conditions (from 2.3 × 10-3 min-1 to 4.8 × 10-3 min-1). Periodic DFT methods are extensively employed and we show that after the generation of charge separation in the modelled titania systems, adsorbed chlorides are the preferential site for partial hole localisation, although small energy differences are computed between partially localised hole densities over adsorbed chloride or hydroxyl. Moreover, chlorides can reduce or inhibit the ability of r-TiO2 (110) and a-TiO2 (101) systems to localise polarons in the slab structure. These results indicate that both mechanisms - hole scavenging and the inhibition of hole localisation - can be the origin of the effect of chlorides on photocatalytic activity of both titania polymorphs. These results provide fundamental insight into the photocatalytic properties of titania polymorphs and elucidate the effect of adsorbed anions over radical formation and oxidative decomposition of organic pollutants.

Heterogeneous catalysis is immensely important, providing access to materials essential for the well-being of society, and improved catalysts are continuously required. New catalysts are frequently tested under different conditions making it difficult to determine the best catalyst. Here we describe a general approach to identify the best catalyst using a data set based on all reactions under kinetic control to calculate a set of key performance indicators (KPIs). These KPIs are normalized to take into account the variation in reaction conditions. Plots of the normalized KPIs are then used to demonstrate the best catalyst using two case studies: (i) acetylene hydrochlorination, a reaction of current interest for vinyl chloride manufacture, and (ii) the selective oxidation of methane to methanol using O2 in water, a reaction that has attracted very recent attention in the academic literature.

Supported bimetallic catalysts commonly exhibit higher rates of reaction compared to their monometallic counterparts, but the origin of these enhancements is often poorly defined. The recent discovery that cooperative redox enhancement effects in Au-Pd systems promote bimetallic catalysis in thermochemical oxidation is an important development in this field. This effect aligns two important research fields, thermo- and electrocatalysis, but questions relating to the generality and origin of the effect remain. Here, we demonstrate that these effects can be observed in reactions over a range of bimetal combinations and reveal the origin using a combination of electrochemical and material characterization. We disclose that the observed activity enhancement in thermochemical systems is a result of the electrochemical polarization of two disparate catalytic sites. This forms an alternative operating potential for a given bimetallic system that increases the driving force of each of the composite half reactions in oxidative dehydrogenation. We therefore uncover the physicochemical descriptors that dictate whether these enhancement effects will be exhibited by a particular combination of supported metal catalysts and determine the magnitude of the effect.

Stabilizers are commonly employed to synthesize nanocrystals with well-defined morphologies and size distributions, making them ideal tools to study structure-activity relationships in heterogeneous catalysts. Whilst it is well documented that stabilizers can influence both the structure and size of the nanocrystals; little emphasis has been placed on how the properties of these species influence catalytic performance. Herein, different polymers (poly-sodium acrylate (PVNaA), poly-vinyl alcohol (PVA) and -vinylpyrrolidone (PVP)) and the monomer sodium acrylate (NaA) were used as stabilizers for the synthesis of Au nanoparticles, supported on TiO 2 . The mean Au particle size in all the catalysts were comparable regardless of the stabilizer used, however, the activity of these catalysts towards CO oxidation differed markedly. The activity decreased in the following sequence: Au/TiO 2 (NaA)> Au/TiO 2 (PNaA)> Au/TiO 2 (none)> Au/TiO 2 (PVA)> Au/TiO 2 (PVP), despite the Au/TiO 2 (none) catalyst possessing a larger Au mean particle size, suggesting that active site blocking due to the steric nature of the polymer species. According to UV-vis, XPS, in situ DRIFTS, HRTEM, XAS and composition analysis experiments, it was concluded that the enhanced activity of Au/TiO 2 (NaA) and Au/TiO 2 (PNaA) catalysts were attributed to the large proportions of low coordinate step/kink Au sites. It is to be noted that the electronic interactions between NaA and HAuCl 4 facilitated the production of active Au nanoparticles. Our findings highlight that the physicochemical properties of stabilizer can profoundly influence the reactivity of supported metal catalysts prepared by sol-immobilisation. These observations highlight the influence that various stabilizers have on the morphology of supported metal nanoparticles and provides an explanation for the low activity of catalysts prepared using common forms such as PVA and PVP.

Abstract Supported bimetallic catalysts commonly exhibit higher rates of reaction compared to their monometallic counterparts, but the origin of these enhancements is often poorly defined. The recent discovery that cooperative redox enhancement effects in Au-Pd systems promote bimetallic catalysis in thermochemical transformations is an important development in this field, but questions relating to the generality and origin of the effect remain. Here, we demonstrate that these effects can be observed in reactions over a range of bi-metal combinations and reveal the origin of the effect using a combination of electrochemical and materials characterisation. In doing so, we uncover the physicochemical descriptors that (i) dictate whether such effects will be exhibited by a particular combination of supported metal catalysts, and (ii) determine the magnitude of the effect.