A kinetic model was developed by taking into account the dynamic nature of the active sites in Mars-van Krevelen type catalytic reactions to predict the evolution of the reactant and product composition in the gas phase and the CuCl2 concentration in the solid catalyst. The kinetic model at the steady-state of ethylene oxychlorination was obtained by combining transient experiments of the two half-reactions in the redox cycle, namely CuCl2 reduced to Cud by ethylene and Cud oxidation by oxygen on the K-promoted CuCl2/gamma-Al2O3 catalyst. The dynamic transitions between CuCl2 and Cud of the active sites during the reactions are also modeled, and the contributions of two active sites, namely Cu coordination numbers of 4 and 3 in CuCl2 were distinguished and included in the kinetic model. The kinetic models describe well the transient response of the reduction and oxidation steps as well as the reaction at the steady-state at different reaction conditions. Moreover, by combining the reactor modeling through a steady-state approach, the spatial-time resolved CuCl2 profile and the C2H4 reaction rate can be well predicted in comparison with the experimental results. The approach of both transient and steady-state kinetic modeling and simulation is supposed to have general relevance for a better understanding of Mars-van Krevelen type reactions.

Monitoring and simulating the events occurring on the catalysts under the real reaction conditions has significant meaning for elucidating the dynamic changes of the active sites during the reactions and for a better understanding of the reaction mechanisms. Herein, we use the operando ultraviolet-visible and near-infrared (UV-vis-NIR) spectroscopy to study the CuCl2/gamma-Al2O3-based catalyst in ethylene oxychlorination, one of the most important processes for producing vinyl chloride in the industry, to elucidate the dynamic changes of the copper active sites. The full spectra of Cu species such as CuCl2, CuCl2 with vacancies, CuCl, and Cu2OCl2 were detected and identified for the first time, and their transient changes and contribution in the reduction, oxidation, and hydrochlorination steps as well as at the steady-state operation in the catalytic cycle can be accurately "imaged" by resolving the UV-vis-NIR spectra dataset using the multivariate curve resolution (MCR) analysis. The distribution and changes of the Cu species are correlated to the catalytic activity, selectivity, and stability. The time-resolved spectra and their correlation with the catalytic performance provide better insights into the dynamic nature of the active sites and their role in the Mars-van Krevelen-type reaction. This method is expected to be exploited to analyze the dynamics of the active sites and kinetic studies in other catalytic redox systems.

The defect plays a significant role in tuning the electronic structure of metal compounds such as oxides, chlorides, sulfides and nitrides, which is frequently used to explain the enhanced catalytic activity. However, the dynamic change of defect relating to the oxidation state change during the reaction is rarely addressed, and it is still not able to be appropriately predicted since the kinetic modeling of the redox reaction involving the in‐situ formation of defects is challenged by the dynamic evolution of the active sites and the complex kinetic phenomena. Here, for the first time, we present a general method to build a new kinetic model of the redox reaction cycle by combined kinetics of reduction‐ and oxidation steps to predict the time and spatially resolved formation of defects of solid catalysts and the reaction products in ethylene oxychlorination on CuCl2/Al2O3 catalyst. The defect concentration can be tuned by manipulating the relative rates of the reduction‐ and oxidation steps.

The use of a hydrophobic solvent in combination with water leads to significant suppression of H2O2 degradation pathways over a AuPd/C catalyst.

Potassium promoters are widely used in industrial catalysts of ethylene oxychlorination to achieve optimum performance. However, the origin of the promoter effect is not fully understood. Herein, we investigated the potassium promotion effect on CuCl2/gamma-Al2O3 catalyzed ethylene oxychlorination by kinetic experiments and DFT calculations. Kinetic experiments observed the effect of KCl on individual steps, and the evolution of the reaction mechanisms with Cl/Cu ratios. Further exploration via DFT found that KCl increases the formation energy of Cl vacancy (Delta E-v) and thus inhibits the reduction activity, which is attributed to the shift-down of Bader charge of Cl. Delta E-v boosts with the decline of Cl/Cu ratios; thus, ethylene can extract Cl atoms from the surface with a Cl/Cu ratio of 2, while it anchors to metal atoms at lower Cl/Cu ratios. The distinct adsorption modes reflect the evolution of reaction mechanisms with Cl/Cu ratios. KCl facilitates the adsorption of oxygen owing to the shift-up of the Bader charge of Cu atom. Potassium reduces the Gibbs free energy barrier of the oxidation step, which agrees with the experimental observation. It is concluded that the potassium promoter effect on the catalytic performance mainly results from the modification of the charge of surface atoms.

Alumina-supported copper chloride serves as an industrial catalyst for ethylene oxychlorination, resulting from its high activity and selectivity. A better understanding of the detailed active site structure and reaction mechanism is highly desired. The present work aims to explore the dependence of the structure of active sites and the adsorption of ethylene on differently sized (CuCl2)(n) (n = 1-4) clusters supported by gamma-Al2O3. The effect of the support facets (i.e., (110) and (100) surfaces) on the interface structures between the active component CuCl2 and the support was also investigated. The stronger CuCl2 support interaction was found on the (110) surface compared to the (100) surface, which is attributed to the stronger Lewis acidity of AI of the (110) surface. The adsorption strength of (CuCl2)(n)()) (n = 1-4) clusters becomes weak with the increment of cluster size on the (110) surface. The cluster size has a profound influence on the interaction between ethylene and the clusters. Ethylene binds to a copper atom on the small clusters (i.e., CuCl2 and (CuCl2)(2)), while it extracts two chlorine atoms to form dichloroethane from the large clusters (i.e., (CuCl2)(3) and (CuCl2)(4)), which explains the high activity of catalysts with high loadings upon exposure to ethylene. The effects of cluster size and alumina facets on the short d-band center and the Bader charge of the active sites result in the distinct formation energy of the chlorine vacancy and the interaction energy between C2H4 and the clusters. Thus, an improved catalyst could be achieved by the modification of the surface electronic structure via fine-tuning the support or adding promoters.

The energies involved in the diffusion of Cu2+ and Cu+ over hydroxylated gamma-alumina were modeled with density functional theory using explorative molecular dynamics. This is the first time that the mechanism for diffusion of ions over hydroxylated surfaces is studied. It is found that the crucial requirement for feasible activation energies for ion diffusion is the prevention of charge separation. This can be realized either by counterion codiffusion or proton contra-diffusion. Furthermore, the effects of the cation valency, hydroxylation level, and nature of the counterions were studied and general trends for diffusing cations on hydroxylated surfaces were postulated. At full hydroxylation, all charge compensation is performed by proton contradithision, while at intermediate hydroxylation levels, a combination of proton contradiffusion and counterion codiffusion occurs. Finally, energy barriers for codiffusion are related to the bonding strength of the counterions to the surface, which depends on the counterion and the hydroxylation level.

Hydrogen peroxide synthesis from hydrogen and oxygen in the gas phase is postulated to be a key reaction step in the gas phase epoxidation of propene using gold-titanium silicate catalysts. During this process H2O2 is consumed in a secondary step to oxidise an organic molecule so is typically not observed as a reaction product. We demonstrate that using AuPd nanoparticles, which are known to have high H2O2 synthesis rates in the liquid phase, it is possible to not only oxidise organic molecules in the gas phase but to detect H2O2 for the first time as a reaction product in both a fixed bed reactor and a pulsed Temporal Analysis of Products (TAP) reactor without stabilisers present in the gas feed. This observation opens up possibility of synthesising H2O2 directly using a gas phase reaction.

We present a novel approach to the dehydrochlorination of 1,2-dichloroethane using ionic liquid catalysts. After screening a wide range of ionic liquids, tetraalkylphosphonium chlorides show the best results, with much higher conversions compared with those of the current industrial "pyrolysis" process. This breakthrough approach has the remarkable advantage of operating at lower temperature while maintaining an excellent selectivity. This method shows high potential as a greener alternative for the current industrial process.

The effect of halide and acid addition on the direct synthesis of hydrogen peroxide is studied for magnesium oxide- and carbon-supported bimetallic gold-palladium catalysts. The addition of acids decreases the hydrogenation/decomposition of hydrogen peroxide, and the effect is particularly pronounced for the magnesium oxide-supported catalysts whilst for carbon-supported catalysts the pH requires close control to optimize hydrogen peroxide synthesis. The addition of bromide leads to a marked decrease in the hydrogenation/decomposition of hydrogen peroxide with either catalyst. These effects are discussed in terms of the structure of the gold-palladium alloy nanoparticles and the isoelectric point of the support. We conclude that with the highly active carbon-supported gold-palladium catalysts these additives are not required and that therefore this system presents the potential for the direct synthesis of hydrogen peroxide to be operated using green process technology.

We have investigated the effect of heat treatment in air on Au–Pd nanoparticles supported on titania and activated carbon prepared via the immobilisation of PVA-stabilised alloy nanoparticles. The catalytic activity of the gold–palladium nanoparticles was affected by both metal and PVA loading, as well as the degree of interaction of the nanoparticles with the support. The turnover frequency numbers for benzyl alcohol and hydrogen peroxide synthesis were also sensitive to the calcination procedure employed and find a doubling of catalytic activity when using activated carbon as opposed to TiO2 as the support material. These results illustrate the importance of understanding the precise metal–support interaction of catalyst systems designed for benzyl alcohol oxidation and hydrogen peroxide synthesis.

The direct synthesis of hydrogen peroxide (H2O2) represents a potential alternative to the currently industrially used anthraquinone process, and Au-Pd catalysts have been identified as effective catalysts. To obtain a direct process, a detailed understanding of the reaction conditions in a continuous flow system is needed. In this study, we use a flow reactor to study reaction conditions independently, including total gas flow rate, catalyst mass, reaction pressure, solvent flow rate, and H-2/O-2 molar ratio. The study was carried out without the addition of any halide or acid additives often used to suppress the sequential hydrogenation and decomposition reactions that allowed the kinetics of these reactions to be studied along with the synthesis reaction. A global kinetic model describing the net and gross synthesis rate is proposed, and on the basis of this model, we propose that the decomposition reaction suppresses the production of H2O2 to a greater extent than hydrogenation and that catalyst design studies should aim at blocking or generating catalysts without O-O dissociation sites.

The direct synthesis of hydrogen peroxide is investigated using silica supported Au, Pd and AuPd catalysts. Acid pre-treatment of the silica leads to an increase in the activity of the Pd-containing catalysts and also gives rise to a synergistic enhancement in activity when Au and Pd are combined that is absent in the untreated catalysts. The acid pre-treated mono and bi metallic catalysts show much reduced H2O2 hydrogenation activity compared to their untreated counterparts. The acid pre-treatment increases the concentration of the hydroxyl groups on the support, as demonstrated using inelastic neutron scattering, which helps to disperse the metals on the support. Pd can be dispersed effectively on silica, but Au is very poorly dispersed although this is enhanced marginally by the acid pre-treatment. The origin of the synergistic effect is discussed and is considered to be related to the incorporation of a small amount of Au within the Pd nanoparticles.

The direct synthesis of hydrogen peroxide has been studied using a highly active AuPd/C catalyst, where the activated carbon support has been pretreated with dilute HNO3 prior to metal deposition and consequently using standard reaction conditions this catalyst does not hydrogenate H2O2. The effect of reaction variables has been investigated on the synthesis and hydrogenation activity over this catalyst. The effect of H2/O2 molar ratio, temperature, total pressure and solvent composition has been studied and optimised conditions identified. The effect of these conditions on the hydrogenation activity was also evaluated; thereby permitting an optimal set of reaction conditions to be identified for both the synthesis of H2O2 and its hydrogenation/decomposition.

The direct synthesis of hydrogen peroxide using supported gold palladium catalysts prepared by incipient wetness impregnation is described and discussed. The effect of an acid pre-treatment step on the activated carbon support prior to the deposition of the metals, together with the effect of the calcination temperature, has been investigated. The acid pre-treated samples all show superior activity to those materials prepared with the omission of this acid pre-treatment stage. The calcination temperature affects both the re-usability and hydrogenation activity of the catalysts. Detailed characterisation using X-ray photoelectron spectroscopy and aberration-corrected scanning transmission electron microscopy is described. The enhanced activity is associated with a higher surface concentration of palladium in the acid pre-treated samples which is principally present as Pd2+. Calcination of the catalysts at 400 °C is required to achieve re-usable and stable catalysts, and this is associated with the morphology and dispersion of the metal nanoparticles. The surface ratio of Pd0/Pd2+ is found to be an important factor controlling the hydrogenation of hydrogen peroxide, and a series of controlled reduction and re-oxidation of a sample show how the Pd0/Pd2+ surface ratio can influence the relative rates of hydrogen peroxide synthesis and hydrogenation.

The direct synthesis of hydrogen peroxide from molecular H2 and O2 represents a green and economic alternative to the current anthraquinone process used for the industrial production of H2O2. In order for the direct process to compete with the anthraquinone process, there is a need for enhanced H2O2 yields and H2 selectivity in the process. We show that Au–Pd-exchanged and supported Cs-containing heteropolyacid catalysts with the Keggin structure are considerably more effective in achieving high H2O2 yields in the absence of acid or halide additives than previously reported catalysts. The Au–Pd-exchanged Cs-heteropolyacid catalysts also show superior H2O2 synthesis activity under challenging conditions (ambient temperature, water-only solvent and CO2-free reaction gas). Au plays a crucial role in achieving the improved performance of these heteropolyacid-based catalysts. The heteropolyacid limits the subsequential hydrogenation/decomposition of H2O2.

5-Hydroxymethyl-2-furfural (HMF) oxidation to furandicarboxylic acid (FDCA) was performed under mild reaction conditions using TiO2-supported Au and Au–Cu catalysts synthesized from pre-formed nanoparticles of different composition. Catalysts were characterized by BET, XRD and XPS. The Au3Cu1/TiO2 catalyst exhibited the best catalytic performance for FDCA yield. Moreover, after reaction, bimetallic Au–Cu catalysts with high gold content can be recovered by filtration and reused without significant loss of activity and selectivity; whereas, the monometallic gold materials are not stable.

The direct selective oxidation of long chain alkanes by O2 is a highly demanding reaction. We have shown that it is possible to oxidise n-decane in the presence of the oxygen-free radical initiator azobisisobutyronitrile. Formation of a range of oxygenated products has been observed under relatively mild conditions (70°C in air). Although the presence of a catalyst is not essential when the initiator is used, ceria-based catalysts have been found to increase the selectivity to alcohols by modifying the oxyfunctionalisation of decane.

The oxidation of 5-hydroxymethyl-2-furfural was studied under mild reaction conditions using TiO2-supported Au and Au–Cu catalysts synthesized from pre-formed nanoparticles. Bimetallic gold-copper catalysts display superior activity as compared to monometallic gold. Moreover, after reaction, the bimetallic Au–Cu catalysts can be recovered by filtration and reused without significant loss of activity and selectivity whereas gold materials are not stable. STEM-HAADF imagining and XEDS spectra obtained from bimetallic materials show that particles are homogeneous AuCu alloys. No AuCu ordering or segregation effects were noted from these analyses, and the Au:Cu ratio was quite consistent from particle-to-particle irrespective of its absolute size, proving the efficiency of the original method of synthesis utilized. Isolation effects of gold by copper in the alloy nanoparticles is imagined to play a pivotal role in the reaction. The effect of oxygen pressure, metal loading, reaction time, amount of base and temperature were studied in detail and a 99% yield of furandicarboxylic acid was achieved under optimized reaction conditions.