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Epoxidation reactions are tremendously important for modern chemistry, as they lead to series of highly useful bulk and fine chemicals, monomers, and intermediates for organic synthesis. Progress in epoxidation processes goes hand in hand with the advancement made in catalysis science. In this context, heterogeneous catalysts, and particularly Ti‐based formulations, are playing a central role and have seen tremendous developments over the past two decades, leveraging on advanced materials science. The aim of this review is to illustrate the various strategies of titanosilicate catalysts preparation that can lead to more versatile, more performant, and greener epoxidation processes. We successively cover (i) supported catalysts, obtained by the grafting of Ti species onto preformed silica supports, (ii) microporous crystalline titanosilicates (zeolites), and (iii) amorphous titanosilicates obtained by sol‐gel chemistry. For each category, with an emphasis on catalyst preparation, the challenges that have to be tackled to boost catalyst performance are highlighted. From that point, we present a critical review of the different approaches that have been proposed in the primary literature to tailor the properties that govern catalysts performance (activity, selectivity, stability, ease of handling). This is done by better controlling the nature of the active surface species, adapting particles size and shape, optimizing texture, modifying surface chemistry, etc. These lines of attack encompass molecular approaches for the grafting of well‐defined species, top‐down and bottom‐up synthesis of hierarchically porous zeolites, advanced sol‐gel routes potentially performed in non‐conventional media or coupled with original processing, preparation of self‐standing monoliths, etc. Future research directions are discussed with emphasis on the application scope of new catalytic materials and possible approaches to increase catalyst performance. [ABSTRACT FROM AUTHOR]

Even after a century, ammonia (NH3) synthesis from nitrogen and hydrogen through Haber‐Bosch process is still energy intensive. Even with recently introduced second generation Ru based catalysts with superior performance over commercial Fe based catalysts, there is still place for upgrading with new approach using advanced materials in catalyst formulation. The alkali and alkaline metal promoted Ru supported carbon and metal oxide catalyst attracted attention at initial stage and extensively studied for NH3 synthesis in the 20th century. Until recently, advanced materials such as electrides, hydrides, nitrides, oxides and oxy‐hydrides‐nitrides studied as support and active component of catalyst fascinated much attention, with milder reaction conditions for NH3 synthesis. These materials with unique properties of reversible storage of electrons, hydrides, nitrides and oxygen vacancies enrich electron density on Ru catalyst and cleave N≡N bond with very low activation energy (<60 kJ/mol). The mechanistic understanding of these materials leads to the fact that activation N≡N bond is no more rate‐determining step (RDS). Instead, formation of N−H bond is RDS, pushing towards an innovative research directions and scientific basis for development of new catalysts. Enormous maturation of experimental and theoretical methods with improved precession over worldwide research effort helped in gaining a fundamental understanding of these materials in NH3 synthesis. The most of Ru supported on these advanced materials were better in performance compared to benchmark Cs−Ru/MgO and Ru/AC catalysts in NH3 synthesis. Insights on these materials and their mechanism are covered in this review, which digs towards finding a realistic catalyst for NH3 synthesis. [ABSTRACT FROM AUTHOR]

The picloram (PCM) adsorption on nontronite, illite and kaolinite was studied at pH 3, 5 and 7. The adsorption isotherms had well-fitted to Langmuir and Freundlich models equations. The interactions of PCM with the clay mineral surfaces exhibited an anionic profile adsorption, with a decrease in adsorption when the pH increases. The PCM adsorption capacity increases in the following order: kaolinite < illite < nontronite. The X-ray diffraction (XRD) analysis of PCM-clay samples revealed that the picloram molecule does not enter into the clays basal space. The interaction of PCM with clays surface sites through nitrogen of the pyridine ring was confirmed by X-ray photoelectron spectroscopy (XPS). Due to the anionic form of PCM, the adsorption onto the external and edges surface sites of the clay minerals was proposed. [ABSTRACT FROM AUTHOR]

H 3 PW 12 O 40 is a Keggin heteropolyacid (HPA) that nowadays attracts more and more attention as catalyst for the gas phase dehydration of methanol to dimethylether. Here, we investigate its performance in the latter reaction at 250–300 °C, namely under coking conditions. Actually, we address the question whether the elsewhere elucidated procedure allowing to activate the bulk of the H 3 PW 12 O 40 solid is beneficial or not under conditions leading to the rapid coking/deactivation of H 3 PW 12 O 40 ’s surface (through which the bulk gets accessed). Unprecedented, our results show that pre-activating the bulk is actually crucial in the latter conditions, as it allows drastically increasing H 3 PW 12 O 40 ’s lifetime (up to 5 times at 300 °C). Indeed, once activated, the bulk stays accessible beyond the deactivation of the surface. However, with its 24 times more protons than provided by the surface, and with the conversion over the latter protons being diffusion-limited, it then contains continuously enough fresh protons being able to take over the job of the other bulk protons that are deactivated (in the sense that they are capped within coke molecules) until having all been solicited/deactivated. As a consequence, the catalyst bed gets fully exploited until the last of its available bulk protons has contributed to the reaction, instead of getting only scarcely exploited as it is the case when the reaction is purely surface-type. So, the results of this work bring considerable insight on how to use a Keggin HPA-based catalyst in a more sustainable way. Furthermore, they allow understanding the performance obtained upon submitting a Keggin HPA to a temperature programmed reaction of methanol from 25 to 300 °C. Indeed, throughout such a reaction, the deactivation profile (e.g. drastic conversion drops vs slow ones) is governed by the nature of the protons (surface vs bulk-type) that are getting deactivated. [ABSTRACT FROM AUTHOR]

Characterizing catalysts under working conditions is crucial to understand and to optimize their behavior and performance. However, when Raman spectroscopy is used, attention has to be paid to laser-induced artefacts. While laser irradiation is often claimed to lead to a temperature gradient between the integral catalyst bed and the sampling point, neither the circumstances when such effect appears, nor if it systematically occurs or not, are really explored in details. The present paper shows that the sensitivity of a catalyst to laser-induced heating largely depends on the gas composition under which the analysis is done, in particular that it depends whether the catalyst has adsorbed reactant molecules or not. These aspects are here addressed via the Raman in situ exploration of H 3 PW 12 O 40 . This heteropolyacid is a widely used acid catalyst due to its very high Brönsted acidity, approaching the superacid region. In particular, we have investigated the impact of laser irradiation in the Raman monitoring of solid H 3 PW 12 O 40 at work under a flow of methanol in nitrogen at 50 °C. When 1 single spectrum of H 3 PW 12 O 40 was measured after 3 h of exposure to methanol, the characteristic C H vibration bands of adsorbed methanol appeared. However, when spectra were measured continuously throughout the experiment, the same C H vibration bands were observed only during the first hour, then they disappeared and the characteristic bands of polyaromatic molecules appeared. Under continuous laser irradiation, adsorbed methanol was thus converted into polyaromatic coke as resulting from a laser-induced heating. However, the spectra collected under pure nitrogen show that the laser does not heat the catalyst in the absence of methanol. UV–Vis revealed the reason of the laser-induced heating in the presence of methanol, and the subsequent formation of coke. Actually the catalyst gets reduced by the adsorbed methanol, what darkens the catalyst bed. Such a darkening renders the catalyst sensitive to laser-induced heating, which in turn leads to the formation of coke. Under continuous laser irradiation, methanol thus auto-initiated its own catalytic conversion, finally leading to the deposition of coke. Such artefact must be avoided if one wants to study the true behavior of the catalyst at work. This paper shows that, for reducible samples analyzed in the presence of reductive molecules, this is only possible by shining the laser intermittently and not continuously. More generally, it actually shows that the adequate way to irradiate a catalyst (continuous vs intermittent) in an in situ / operando Raman analysis depends on the gas flow composition. [ABSTRACT FROM AUTHOR]

Heteropolyacids (HPAs) are metal-oxygen clusters that are nowadays widely used in acid catalysis. Indeed, as they possess a very strong Brönsted acidity, approaching the superacid region, they generally allow performing reactions at lower temperatures than conventional catalysts. In the present paper, we use in situ/operando Raman spectroscopy to optimize the catalytic performance of H3PW12O40 the strongest Keggin-type HPA in the low temperature (150 °C) gas phase dehydration of methanol to dimethyl ether (DME), which is one of the most promising renewable fuels for the future. Precisely, we demonstrate that the ability of methanol to displace the HPA's crystallization water located in-between the Keggin units and thus to reach the acidic protons decreases with increasing temperature. Actually, we show that one and the same flow of methanol scarcely displaces the crystallization water at reaction temperature 150 °C, whereas, at a temperature as low as 25 °C, it succeeds to completely dehydrate the HPA. By exploiting this, namely by pre-exposing the initially hydrated HPA to methanol at 25 °C right before heating it to a reaction temperature of 150 °C, the conversion increases dramatically, precisely by a factor 3. As reflected by the spectra, the flow of methanol at 25 °C does not only dehydrate but also recrystallizes the HPA (so rendering its structure more rigid and the diffusion in-between the Keggin units later at 150 °C more difficult). As a consequence, the conversion obtained at 150 °C is not as high as after a thermal dehydration under inert atmosphere. However, to be complete, the latter requires a temperature as high as 320 °C which is not tolerated by all HPA-based catalysts. In other words, the present work shows how to pretreat an HPA-based catalyst in order to maximize its catalytic performance in the methanol-to-DME reaction, depending on its resistance or not to a harsh thermal pretreatment. [ABSTRACT FROM AUTHOR]

A spray method is proposed to improve the catalytic properties of ceramic papers to be used as catalytic filters for removing diesel soot particles. Small particles of Ce and Co oxides, acting as active centers for the combustion of the soot retained by the filter, are efficiently and homogeneously deposited. On the contrary, the application of the conventional drip method results in bigger particles mainly agglomerated at the crossings between the fibers of the ceramic paper. As a result, catalytic papers prepared by the spray method exhibit much higher performance with soot combustion temperatures decreased by ~ 30 °C. [ABSTRACT FROM AUTHOR]

Palladium nanoparticles of different sizes and supported on TiO2 (2 wt. %) were synthesized by using the water-in-oil microemulsion method. The control of palladium nanoparticles was investigated in terms of the nature of organic surfactant and solvent. Attention was paid to the reduction of palladium ions in solution during synthesis. Materials were characterized by N2-BET at low temperature, XRD, XPS, H2 chemisorption, and TEM and were tested in the gas phase oxidation of methanol. The results confirmed the effect of microemulsion composition on the size of palladium nanoparticles. The direct formation of methyl formate from methanol was observed. Supported palladium catalysts produced methyl formate at low temperature (<150 °C) with a very high selectivity, and, in some cases, a selectivity of approximately 100 %. At higher temperature, methyl formate is not formed at all and the total oxidation to CO2 occurs. A linear correlation between palladium particle size and methanol conversion was observed. Conversion and selectivity were correlated with the acidity of the catalysts. Very small particles were more active but less selective. A mechanism was proposed to explain the formation of methyl formate from methanol. [ABSTRACT FROM AUTHOR]

Abstract: CoMo catalysts supported on sodium-doped amorphous aluminosilicates (ASA) with different Si/(Si+Al) ratios were prepared. The catalytic performance of these catalysts in the HDT of synthetic FCC naphtha was compared with the one of a CoMo catalyst supported on pure alumina, as well as with another one supported on sodium-modified alumina. The catalysts results were also compared with the ones of CoMo catalyst supported on ASA without sodium. The catalysts were characterized by XRF, XRD, Raman, as well as their textural and acid properties. The sodium introduction simultaneously with the variation of the Si/(Si+Al) ratio conducts to obtain a catalyst (15% Si/(Si+Al), 3wt.% Na) with, on the one hand, an Mo oxide species distribution with an important participation of β-CoMoO4 crystalline species and, on the other hand, a selective formation of weak Brönsted acid sites. As a consequence of this especial balance between the acid properties and the oxidic Mo-surface-species distribution, this catalyst presented an activity similar to the one of the CoMo/Al2O3, but with improvements in the selectivity to HDS. Additionally, it was also encountered that when CoMo catalysts supported on materials of predominantly acidic nature are used, the linear olefins inhibit more the HDS activity than the branched ones, whereas the contrary effect was encountered when supports of a predominantly basic nature are used. [Copyright &y& Elsevier]

The article presents a study which suggests that palladium nanoparticles can be considered highly active catalysts when it comes to gas-phase reaction of methanol oxidation. It observes the formation of methyl formate from methanol. The reaction takes place at very low temperature with a high selectivity.

Abstract: CoMo catalysts supported on amorphous aluminosilicates (ASA) with different Si/(Si+Al) ratios (0, 0.15, 0.25, 0.33, 0.5, and 0.75) were prepared and evaluated in the hydrotreatment of synthetic FCC naphtha. 2-Methylthiophene was used as the sulfur compound, and a mixture of 2,4,4-trimethyl-1-pentene and 2,4,4-trimethyl-2-pentene (approximately 3:1) was used as olefin. With the increase of Si/(Si+Al) ratio, the activity of hydrodesulfurization (HDS) and hydrogenation of olefin (HYDO) reactions performed in the CUS sites of Mo promoted by Co was inhibited. Meanwhile, increments in the acid-type reactions (alkylation of 2-MT with olefins and olefin isomerization and cracking) were observed. These changes were not gradual; a kind of transition zone with huge changes in product distribution between catalysts with 15 and 25% Si/(Si+Al) was observed. This was explained by an increment in the density and strength of Brönsted sites. These Brönsted sites compete with the CUS sites of Mo promoted by Co for reactant adsorption. Moreover, it was shown that skeletal isomerization could aid to control HYDO and cracking reactions. In general, it was demonstrated that by modifying the support composition, it is possible to modify the hydrodesulfurization, hydrogenation of olefins, and acid-type reaction activities. [ABSTRACT FROM AUTHOR]

Hydration of manganese sulfate at a low reaction temperature (150 °C) induces high heterogeneous catalytic activity and stability in the oxidation of methanethiol. The temperature of the reaction controls the reversible change of structure, i.e., hydration/dehydration processes as well as the associated changes of activity and selectivity. [Copyright &y& Elsevier]

The catalytic performance of various zeolites such as H-ZSM-5, H-Y, H-beta, H-Mordenite in resorcinol alkylation with tertiary butanol demonstrated that pore characteristics have major influence on product selectivity, whereas acid strength and number of acid sites influenced resorcinol conversion. The passivation of external surface of H-beta zeolite by silylation and amine poisoning produced shape selectively O-alkylated resorcinol methyl tert butyl ether (RMTBE) and 4-tert butyl resorcinol (4-TBR). We propose that 4-TBR formation goes over external acid sites through RMTBE isomerization, whereas formation of 4-TBR takes place inside the pores through direct C-alkylation mechanism. Unlabelled Image • H-Beta and H-Y zeolite exhibited higher catalytic activity than H-ZSM-5 and H-MOR. • Pore characteristics of zeolites play a major role on the product selectivity. • 4-TBR forms on the external surface of H-Beta zeolite by RMTBE isomerization. • 4-TBR is also formed inside the pore of H-Beta zeolite by direct C-alkylation. • Di-tert-butyl dicarbonate is an excellent alkylating agent compared TBA and MTBE. [ABSTRACT FROM AUTHOR]

Mesoporous Ti–SiO 2 nanoparticles were prepared under alkaline conditions in the presence of a surfactant and were subsequently converted into a hierarchical micro-/macroporous TS-1 zeolite with large crystal size using steam assisted crystallization. In this procedure, the precursor nanoparticles were used both as macroporous hard template and as Si and Ti sources. The secondary macroporosity is a reminiscence of the nanoparticles which undergo dissolution and recrystallization upon steaming. The obtained catalyst has structural properties comparable to benchmark TS-1. We show that the successful conversion of the amorphous material into a fully crystalline catalyst stands for its excellent catalytic performance in aqueous media. Besides, the combination of large crystal size with a hierarchical pore structure ensures easy catalyst handling and processing without compromising on the catalytic activity. Image 1 • Calibrated Ti–SiO 2 nanoparticles are used as gel precursor and as macropore templates. • Steam assisted crystallization produces large microporous TS-1 zeolite crystals with macropores. • The large hierarchical TS-1 crystals maintain high external surface area thanks to macropores. • New materials are as active as TS-1 nano-crystal colloids but easier to recover. [ABSTRACT FROM AUTHOR]

Gliding arc plasma is an innovative method for synthesizing heterogeneous catalysts. All the hypothetical reactions from the literature currently attempting to explain the catalyst formation (usually metal (hydr)oxide), when precursors (metal salts) are exposed to plasma, only involve OH° and NO° radicals. Yet, these reactions remain unverified, and other reactive plasma species generated have never been considered to exert an influence on the precipitation of (hydr)oxide particles. In this context, this contribution investigates which species are responsible for the oxidoreduction of precursors exposed to the glidarc, with a specific focus on the role of NO° and OH° in the oxidoreduction of iron salts. To investigate the role of OH° radicals, radical scavenger (coumarin) was used. Similar solids precipitated whenever coumarin was used or not, suggesting that other plasma-generated species might contribute to the oxidation process, such as long-lived species. To challenge this hypothesis, the behaviour of metal precursors in demineralized water pre-exposed to plasma was studied. Similar precipitates were formed for both FeSO 4 and KMnO 4 when exposed to this "activated" water and when directly exposed to the discharge, showing that the predominant initiators of the precipitation are the long-lived species, that we identified in our system to be NO 3 - and HNO 2 /NO 2 -. We demonstrate that HNO 2 /NO 2 - species play a prominent role in the plasma precipitation process which has never been reported before. Yet slight differences in the composition of the precipitates formed when no short-lived species were present suggests that HNO 2 /NO 2 - may not be the sole agent responsible for initiating the precipitation. [Display omitted] • OH° are not the primary agent initiating glidarc plasma metal precursor precipitation. • The long-lived species are able to trigger the precipitation of catalysts. • Long-lived species mostly created in humid air glidarc plasma are NO 3 - and HNO 2 /NO 2 -. • HNO 2 /NO 2 - are the main species responsible for the catalyst precipitation process. • A single type of plasma species is not solely responsible of precursors precipitation. [ABSTRACT FROM AUTHOR]

The effect of adding secondary additives for tableting vanadium‑aluminum mixed-oxides, VAlO, on key physicochemical properties and on the catalytic performance in propane oxidation was investigated. Graphite was used as the primary shaping agent. The secondary additives were MgO, silica, BN, sepiolite, and ZnO. The hardness, fracture strength, and particle shape of the secondary additives were associated to the changes of the mechanical strength and porosity of the tablets. There was a compromise between mechanical strength and loss of mesoporosity and surface area. Meanwhile, the additives did not establish a chemical interaction with the VAlO material. Therefore, the secondary additives may act as co-catalysts during propane oxidation. BN and sepiolite were best for promoting both the reactivity of the catalytic formulations and the production of propene. This promotion may be due to the combination of a redox mechanism over the VAlO phase and to a surface radical mechanism occurring over the active moieties of BN and sepiolite. [Display omitted] • Tablets of vanadium-aluminum mixed oxide were manufactured using graphite as primary additive. • The effect of secondary tableting additives was investigated. • Secondary additives change mechanical resistance according to their hardness, fracture toughness, and shape. • A compromise between mechanical strength and loss in mesoporosity and surface area must be made. • Boron nitride and sepiolite act as co-catalysts in propane oxidation. [ABSTRACT FROM AUTHOR]

• The process for producing technical catalysts; tablets and extrudates, based on γ-MnO 2 is described. • Bench and pilot plant scale testing of technical catalysts for aromatics combustion is presented. • Technical catalysts able to eliminate styrene and benzene with high selectivity to carbon dioxide were prepared. • Insight into the reaction pathways of styrene combustion was obtained from the analysis of pilot plant results. Shaping is a crucial step to produce technical catalysts that remains as some sort of dark art for catalytic researchers in academia. This contribution discusses aspects concerning the fabrication of technical catalysts based on MnO 2 powders aimed for the combustion of hazardous aromatic compounds; namely, benzene and styrene. Both laboratory and pilot plant scale catalytic tests were done over tablets and extrudates of MnO 2. Key physicochemical properties of these materials; namely, surface area, porosity, crystallinity, and mechanical resistance, were assessed and correlated to the catalytic behaviour. On the one hand, the paper describes the hurdles to be overcome when formulating and testing a technical catalyst whose characteristics must be a good compromise between its physicochemical properties and catalytic behaviour at the pilot plant scale. Furthermore, the importance of adopting adequate security and waste management protocols for testing technical catalysts is highlighted. On the other hand, the following conclusions were drawn from the analysis of results: (i) Between tableting and extrusion, only the latter was found to produce shaped bodies with suitable mechanical resistance for pilot plant scale tests. (ii) Calcination of the fabricated extrudates at temperatures from 500 °C leads to a crystallographic transformation of the MnO 2 that had a positive impact on the intrinsic activity of the technical catalyst while favouring its mechanical resistance owing to densification at the expense of a decrease in surface area and enlargement of pore size distribution. (iii) Thanks to pilot plant testing of the catalysts, it was possible to identify a detailed reaction scheme for styrene combustion in which besides the occurrence of oxidation, reactions of hydrogenation, dehydrogenation, ring opening, and isomerization take place by a combination of both surface and free radical mechanisms. [ABSTRACT FROM AUTHOR]

Friedel–Crafts alkylation of resorcinol with methyl tertiary butyl ether was carried out over sulfated zirconia (SZ) catalysts in the liquid phase. The SZ catalysts were synthesized by an impregnation method with different sulfur amounts and characterized by XRD, FT-IR, nitrogen sorption, XPS, SEM, pyridine-FTIR, and NH3-TPD. The effect of the sulfur loading on the total acidity and catalytic activity was investigated. The influence of the nature of the solvents on the alkylation reaction was inspected in terms of their acceptor and donor numbers. The sulfur loading, amount of solvent, temperature, catalyst amount, mole ratio and reusability of the catalyst were examined. The SZ catalyst synthesized by impregnating 1 N sulfuric acid was found to be highly selective for the monoalkylation to 4-tertiary butyl resorcinol (72%) with a resorcinol conversion of ∼70%. The catalyst was recycled thrice with a negligible decrease in the yield for 4-tertiary butylresorcinol. The SZ exhibited the best performance at low temperature (60 °C) among the different types of solid acid catalysts studied so far. [ABSTRACT FROM AUTHOR]

• In situ IR upon pyridine adsorption allows quantitatively assessing the dispersion of supported H 3 PW 12 O 40 ("HPW12") catalysts. • The splitting of the IR band associated to the ν 19b pyridinium ring stretch mode is a fingerprint of agglomerated HPW12. • Thanks to a simple spectra treatment, the ν 19b pyridinium band allows assessing the fractions of dispersed vs. agglomerated HPW12. • The approach can be applied to any supported HPW12 catalyst, whatever the nature of the support. • The approach facilitates the proper selection of samples to be used as catalysts, whatever the reaction. Pyridine is since a long time used as an infrared (IR) molecular probe to characterize the acidity of solids, in particular of heteropolyacids (HPAs). The latter are metal-oxygen-clusters nowadays widely used in acid catalysis. Indeed, thanks to their exceptionally strong Brönsted acidity, they allow operating chemical reactions under significantly milder conditions than required by conventional catalysts. In the case of H 3 PW 12 O 40 , the most acidic Keggin-type HPA, it is well-known that the exposure to pyridine leads to an unusual IR spectrum. Indeed, the band at about 1540 cm−1 associated to the ν 19b pyridinium ring stretch mode is split in two. Up to now, this phenomenon was studied with the only aim of understanding its origin, which was proposed to be a tunneling effect related to a frustrated rotation of the pyridinium cation within the solid bulk of H 3 PW 12 O 40. Here, we demonstrate for the first time that it can actually be used as an analytical tool, namely to probe the degree of dispersion of supported H 3 PW 12 O 40 units, a key parameter dictating their catalytic performance. We support H 3 PW 12 O 40 on TiO 2 P25 (hydrophilic) and TiO 2 T805 (hydrophobic), so yielding samples with different degrees of dispersion, as qualitatively assessed through X-ray photoelectron spectroscopy. Through in situ Fourier-transform IR spectroscopy upon pyridine adsorption, we show that the ν 19b pyridinium vibration band only and systematically splits in the presence of agglomerated Keggin units. More precisely, the higher the fraction of agglomerated Keggin units, the more marked the band splitting. So, the latter appears as a fingerprint of agglomerated H 3 PW 12 O 40. Furthermore, following an easy treatment, the IR spectra allow quantitatively evaluating the fractions of dispersed vs. agglomerated Keggin units within the samples, which is very difficult to achieve through any other technique. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Impurities in pyrolytic graphite were found by XPS analysis. • Flood Gun manipulation led to impurities identification. • O 1s splitting between conductive and isolating moieties. Abstract This work reports differential charging effects in samples of pyrolytic graphite. Despite being considered a nuisance in XPS analyses, differential charging effects can be exploited for the identification and quantification of chemical species in heterogeneous materials. In this case, charging effects were useful to identify impurities at the surface of pyrolytic graphite. For these impurities, the analysis of the O 1s, Si 2p, and Al 2p core levels allowed distinguishing the contributions of SiO 2 and Al 2 O 3 from those of silicone/alumino-silicate oxides. Though both groups of compounds are insulators, a splitting of the above peaks was induced by the use of the flood gun device of the spectrometer when the samples were mounted on a conductive metallic sample holder. The shape and relative concentration of the chemical species ascribed to the split peaks served as a basis for the decomposition of the corresponding O 1s, Si 2p, and Al 2p peaks registered over a ceramic sample holder. The latter allowed for inducing a well controlled differential charging of the samples that led to the identification of true chemical shifts, i.e. those ascribed to variations on the chemical environment of the elements. A qualitative model for describing the observed charging effects was postulated. The model was based on an analogy between electrical circuits and the geometrical configuration of the impurity particles intercalated within the graphite particles. [ABSTRACT FROM AUTHOR]

The development of electrocatalysts for the oxygen evolution reaction (OER) especially in acidic media remains the major challenge that still requires significant advances, both in material design and mechanistic exploration. In this study, the incorporation of cobalt in Y2‐xCoxRu2O7−δ results in an ultrahigh OER activity because of the charge redistribution at eg orbitals between Ru and Co atoms. The Y1.75Co0.25Ru2O7−δ electrocatalyst exhibits an extremely small overpotential of 275 mV in 0.5 m H2SO4 at the current density of 10 mA cm−2, which is smaller than that of parent Y2Ru2O7−δ (360 mV) and commercial RuO2 (286 mV) catalysts. The systematic investigation of the composition related to OER activity shows that the Co substitution will also bring other effective changes, such as reducing the bandgap, and creating oxygen vacancies, which result in fast OER charge transfer. Meanwhile, the strengthening of the bond hybridization between the d orbitals of metal (Y and Ru) and the 2p orbitals of O will intrinsically enhance the chemical stability. Finally, theoretical calculations indicate that cobalt substitution reduces the theoretical overpotential both through an adsorbate evolution mechanism and a lattice oxygen‐mediated mechanism. [ABSTRACT FROM AUTHOR]

Nanostructured hybrid materials made of guest ions and a self-assembled copolymer were used as precursors for the preparation of NiMo-based catalysts. The hybrids were calcined in air and the recovered materials were characterized and tested in propane oxidative dehydrogenation. A 6-fold improvement of the yield to propene is obtained as compared with classically prepared catalysts. The exothermic degradation profile of the copolymer is the key point of our approach as it allows to prepare a porous β-NiMoO 4 , namely the phase particularly desired for its superior propene selectivity. More precisely, the polar backbone and the aliphatic side chains of the copolymer burn at different temperatures. The former ignites at moderate temperatures and initiates the early crystallization of β-NiMoO 4 . Occurring at higher temperature, the decomposition of the aliphatic part then induces the formation of mesopores. A β-NiMoO 4 can thus be prepared at moderate temperatures whereas elevated calcination temperatures (>650 °C) are usually required. This peculiar behavior enables to prevent the texture of NiMoO 4 from sintering and to maintain at high levels its mesoporosity, specific area and thus catalytic activity. At the end, the use of our tailor designed copolymer template allows reaching the remarkably high propene yields obtained. [ABSTRACT FROM AUTHOR]

Relevant findings on hydrogen adsorption and mobility are provided in this work to elucidate the mechanism of low-temperature ammonia synthesis, catalyzed by polydispersed Ru nanoparticles supported on alumina. H/D isotopic exchange technique, complemented by DRIFTS analysis, was applied to study the kinetics of hydrogen adsorption/desorption on metallic Ru and hydrogen diffusivity on alumina, for catalysts presenting different size distributions of Ru nanoparticles. H atoms adsorbed on large Ru nanoparticles present higher mobility and they migrate on alumina via exchange with OH groups. A broad size distribution of Ru nanoparticles leads to synergy in the rate of ammonia synthesis, and also in hydrogen mobility. The mechanism of catalytic cooperation involves transfer of H atoms from large to small nanoparticles, where the reaction rate is promoted. Considering dynamic catalytic processes in the formulation of kinetic models is crucial for a more accurate description of processes and the development of large-scale processes. [ABSTRACT FROM AUTHOR]

• Ru-carbon catalysts active and selective for the oxidative cleavage of oleic acid. • Macroporous carbon black provides high conversion (>99%) and yields (∼75%). • CBO-Ru(2%) maintains its activity up to 3 recycling tests. • Microporous materials not suitable for the oxidative cleavage of large alkenes. Microporous oxidized activated carbon (ACO) and macroporous oxidized carbon black (CBO) were assessed in the complexation of Ru for the oxidative cleavage of oleic acid. This reaction breaks carbon-carbon double bond to produce azelaic and pelargonic acids (highly demanded in pharmacology). Both carbon materials were treated with HNO 3 prior Ru deposition by wet impregnation method. Carbon supports were characterized by FTIR, Boehm's titration and N 2 physisorption, while Ru complexation was determined by ICP and XPS spectroscopy. Activated carbon catalyst displayed a low conversion (∼53%) in comparison to carbon black catalyst (>99%). The reason is related to the molecular length of oleic acid (2.2 nm), estimated by ab initio Hartree-Fock calculation, which is larger than micropores from activated carbon (∼0.7 nm). Despite Ru losses during the catalytic tests, CBO was more active and stable than ACO, confirming that a macroporous support is more suitable to perform the oxidative cleavage of oleic acid. [Display omitted] [ABSTRACT FROM AUTHOR]

Hybrid mesoporous silica films were prepared in acid-catalysed medium using a one-pot self-assembly method. A gradual content of methyl groups was introduced into the inorganic framework by co-condensation of tetraethyl orthosilicate and methyltriethoxysilane. To better understand how the ordered and disordered transition occurs in mesoporous hybrid organosilica sytem as function of the MTES molar ratio in the starting solution, textural, chemical and optical properties of the films were studied by transmission electronic microscopy (TEM), grazing-incident small angle X-ray scattering (GISAXS), transmission Fourier transformed infrared (FTIR) and UV–visible spectroscopy. Increasing the loading of the incorporated organic groups (up to 40% in the starting solution) led simultaneously to a disorganization of the pore mesostructure and a reduction in the pore diameter. Concomitantly, a disordered domain of the silica rings in the walls was observed, which created bond strains in the silica wall contributing also to the disorganization of the pore mesostructure. Furthermore, an optimal MTES content was identified in order to obtain antireflection coatings, exhibiting low reflection in the visible range. [ABSTRACT FROM AUTHOR]

Four cation-exchange resins (Dowex 50wx2, Amberlyst 36, Purolite CT482 and Purolite CT275DR) were investigated as catalysts in the esterification of oleic acid (OA) with trimethylolpropane (TMP). All four resins accelerated the reaction kinetics. The results showed that in a solvent-free system, the gel-type resin Dowex 50wx2 must be pre-swollen prior the reaction to achieve high catalytic performance. Contrary, the macro-reticular Amberlyst 36, Purolite CT482 and Purolite CT275DR do not need any pre-treatment to be active. The latter is due to the high crosslinking degree of these resins. Recyclability tests showed that the resins slightly lose their activity after the first use but retain stable activity during the further uses. The activity decay of the recycled resins is referred to the partial blocking of the active sites by the co-produced water. Additional studies confirmed the high stability of the chosen resins toward leaching in polar medium. Overall, both high stability and possibility of reusing through still high catalytic activity make the resins attractive candidates as heterogeneous catalysts for such complex industrial process. [ABSTRACT FROM AUTHOR]

According to our previous results, a broad size distribution of Ru-supported nanoparticles is required for a high activity in ammonia synthesis under mild reaction conditions, since a synergy in the catalytic activity was observed between particles of different sizes. In this work we reach a more controlled heterogeneity of sizes by mixing different ruthenia colloidal suspensions, before impregnation on alumina, which improves the catalytic activity. Kinetic studies, ‘in situ’ characterizations and H/D isotopic exchange experiments were separately performed on catalysts containing small Ru nanoparticles and catalysts containing larger particles, in order to elucidate the mechanism of catalytic cooperation. Clear evidence is presented of a mechanism involving the migration of H atoms from large to small Ru nanoparticles, which is expected to improve the catalytic performance by promoting the hydrogenation of adsorbed NH x species and the release of active sites. [ABSTRACT FROM AUTHOR]

A series of tetrabutyl ammonium (TBA) salts of V-included Keggin-type polyoxoanions with W (TBA4PW11V1O40 and TBA5PW10V2O40) and Mo (TBA4PMo11V1O40 and TBA5PMo10V2O40) as addenda atoms were prepared using a hydrothermal method. These synthesized materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), UV-Vis diffuse reflectance (DRS UV-Vis), thermogravimetric analysis (TGA), CHN elemental analysis (EA), inductively coupled plasma spectrometry (ICP-MS), and N2 physisorption techniques to assess their physicochemical/textural properties and correlate them with their catalytic performances. According to FT-IR and DRS UV-Vis, (PVXW(Mo)12−XO40)(3+X)− anions are the main species present in the TBA salts. Additionally, CHN-EA and ICP-MS revealed that the desired stoichiometry was obtained. Their catalytic activities in the liquid-phase aerobic oxidation of benzyl alcohol to benzaldehyde were studied at 5 bar of O2 at 170 °C. Independently of the addenda atom nature, the catalytic activity increased with the number of V in the Keggin anion structure. For both series of catalysts, TBA salts of polyoxometalates with the highest V-substitution degree (TBA5PMo10V2O40 and TBA5PW10V2O40) showed higher activity. The maximum benzyl alcohol conversions obtained were 93% and 97% using (TBA)5PMo10V2O40 and (TBA)5PW10V2O40 as catalysts, respectively. In all the cases, the selectivity toward benzaldehyde was higher than 99%. [ABSTRACT FROM AUTHOR]

Hypothesis The environmental mobility and bioavailability of Picloram (PCM) are determined by the amine and carboxylate chemical groups interaction with the soils mineral phases. Clay particles, such as montmorillonite (Mt), and the pH value of the media could play an important role in adsorption processes. Thus, the study of the role of soil components other than organic matter deserves further investigation for a more accurate assessment of the risk of groundwater contamination. Experiments Samples with PCM adsorbed on Mt dispersions were prepared at pH 3–9. Subsequently, the dispersions were separated, washed, centrifuged and stored at room temperature. Picloram (PCM) herbicide interaction with surface groups of montmorillonite (Mt) was studied using XRD, DTA, FTIR and XPS techniques. Findings The entrance of PCM into the Mt basal space, in two different arrangements, perpendicular and planar, is proposed and the final arrangement depends on PCM concentration. The interaction of PCM with Mt surface sites through the nitrogen of the pyridine ring and carboxylic group of PCM, forming bidentate and bridge inner-sphere complexes was confirmed by FTIR and XPS analysis. The acidity constant of the PCM adsorbed on the Mt surface was calculated. [ABSTRACT FROM AUTHOR]

This work investigates the effect of Amberlyst 36, Purolite CT482 and Purolite CT275DR on the esterification of oleic acid with trimethylolpropane for production of the triester. The results assess that, while the three resins catalyze heterogeneously the formation of mono- and diesters, the final triester is generated thanks to the acidity of residual oleic acid. This cooperative scenario between heterogeneous and homogeneous catalysis is of first importance, as to complete the reaction over conventional heterogeneous catalyst was not feasible because of the strong steric hindrance of the intermediate product (diester) and the final product (triester). [ABSTRACT FROM AUTHOR]

Highlights: [•] TiO2 supported RuO2 nanoparticles prepared by a green colloidal method. [•] Nano-RuO2/TiO2 catalyst highly efficient in propane total oxidation. [•] Activity higher if the catalyst is not calcined. [•] Migration of RuO2 towards rutile titania followed by sintering. [ABSTRACT FROM AUTHOR]

A Periodic Mesoporous Organosilica (PMO) functionalized with sulfonic acid groups has been successfully synthesized via a sequence of post-synthetic modification steps of a trans-ethenylene bridged PMO material. The double bond is functionalized via a bromination and subsequent substitution obtaining a thiol functionality. This is followed by an oxidation towards a sulfonic acid group. After full characterization, the solid acid catalyst is used in the acetylation of glycerol. The catalytic reactivity and reusability of the sulfonic acid modified PMO material is investigated. The catalyst showed a catalytic activity and kinetics that are comparable with the commercially available resin, Amberlyst-15, and furthermore our catalyst can be recycled for several subsequent catalytic runs and retains its catalytic activity. [ABSTRACT FROM AUTHOR]

[Display omitted] • CBO-PDA-Ru composite reaches around 95% of conversion and selectivity after 3 h. • Polydopamine can complex Ru species towards oxidative cleavage of oleic acid. • CBO-PDA-Ru catalyst maintains its catalytic activity even after 5 recyles. A new composite heterogeneous catalytic system is proposed for the transformation of cheap unsaturated fatty acids into value-added molecules through their oxidative cleavage. The valorization of oleic acid to azelaic and pelargonic ones (which are demanded in pharmacology) is specifically studied. The reaction is efficiently performed with a novel composite catalyst inspired from metal recovery technology, namely Ru species supported on a carbon black that was previously oxidized and then functionalized with polydopamine. Being a polymer with hydroxyl and amine groups polydopamine provides moieties acting as tweezers able to complex Ru species. A representation of this novel composite catalyst is built from its characterization by FTIR, TGA, N 2 physisorption TEM and XPS. Using NaIO 4 as oxidizing agent in a biphasic system at room temperature the conversion of oleic acid, and selectivity towards pelargonic and azelaic acids, reached around 95% after 3 h. The reaction mechanism is explored by UV–Vis spectrophotometry, ICP elementary analysis and NMR spectroscopy, together with recyclability and hot centrifugation tests. The occurrence of a boomerang mechanism is demonstrated. The solid catalyst is indeed recyclable at least 5 times without activity loss, but at the same time Ru species are shown performing the reaction in homogeneous phase namely in a dissolved state. Actually, polydopamine is confirmed to recover Ru species once the reaction ends, guarantying the recyclability of the catalyst. The composite catalyst therefore combines the advantages of homogeneous and heterogeneous catalysis in the investigated reaction. [ABSTRACT FROM AUTHOR]

Mesoporous titanium silica-coated cobalt ferrite core-shell structures were synthesized as catalysts for styrene oxidation by hydrothermal and sol-gel methods. The catalysts were characterized by XRD, AA, SEM, TEM, FTIR spectroscopy, N 2 physisorption, ICP-OES and XPS. XRD patterns indicated that the magnetic core was composed of cobalt ferrite. SEM and TEM micrographs along with the IR spectra confirmed the presence as desired of a dense SiO 2 layer on the core. XPS revealed that the outest layer of the structure was made of a mesoporous Ti-SiO 2 layer. The successful incorporation of Ti active oxidation sites (framework Ti, FW Ti) in the mesoporous layer was verified by XPS Ti 2p spectra decomposition. The post-grafting method for the Ti insertion proved to be better than the one-pot to obtain a higher number of active Ti sites on the surface. All the synthesized catalysts were active in styrene oxidation with dilute aqueous H 2 O 2. The highest styrene conversion (37%) was obtained with the catalyst synthesized by post-grafting of Ti on a preformed mesoporous SiO 2 layer with a high specific surface area. This catalyst was the one with the highest fraction of surface FW Ti (XPS). The major products of the reaction were benzaldehyde and phenyl acetaldehyde. The catalyst was easily recovered from the reaction medium using an external magnet, and no significant loss of activity was observed after four catalytic cycles. [Display omitted] ● Successful synthesis of core-shell catalysts by hydrothermal and sol-gel methods. ● Titanium was inserted in the mesoporous layer mainly as isolated framework Ti. ● Ti-SiO 2 @CF and Ti/SiO 2 @CF catalysts are active in styrene oxidation. ● Benzaldehyde and phenyl acetaldehyde are the main oxidation products. ● Easy recovery of Ti/SiO 2 @CF from the reaction medium due to magnetic properties. [ABSTRACT FROM AUTHOR]

Nanoreactors encapsulating homogeneous catalysts behave as heterogeneous catalysts at the macroscopic scale, enabling the homogeneous catalyst to be easily recovered. One way to synthesize such nanoreactors is by inserting the homogeneous catalyst (or synthesizing it in situ) in the porosity of an inorganic oxide material, followed by a silylation reaction to narrow the pore entrance, preventing the outwards diffusion of the jailed homogeneous catalyst during the reaction. This way, the often-superior activity of homogeneous catalysts is combined with the robustness and the easy recovery of heterogeneous ones. Hereunder, we report for the first time the implementation of such a strategy towards the synthesis of a deoxydehydration (DODH) catalyst, namely a bis-amino phenol Re-complex. 1,2-hexanediol was used as the DODH vicinal diol model substrate. The encapsulation of the homogeneous catalyst in SBA-1 was demonstrated. It proved active in the DODH test reaction although not sustainably; the deactivation mechanism was therefore elucidated. [Display omitted] ● Encapsulation of a DODH precatalyst in silylated SBA-1. ● Stability of the encapsulated catalyst is assessed in the DODH of 1,2-hexanediol. ● The deactivation mechanism of the encapsulated catalyst is pointed out. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this study is to evaluate the efficiency of benzimidazole removal using raw, thermally and mechanically treated montmorillonite surfaces. The comparison of benzimidazole adsorption curves on these montmorillonite surfaces was made. A two step sorption mechanism that describes the data was corroborated by X-ray diffraction (XRD) results. The removal efficiency for the different sorbents at pH 6 follows the sequence raw montmorillonite>thermally treated montmorillonite>mechanically treated montmorillonite. The external and the interlayer surfaces were proposed as adsorption sites. On the latter, benzimidazole adsorbs in a planar monolayer arrangement with a consequent reduced water uptake. Two different foms of benzimidazole nitrogen surface coordination were indicated by X-ray photoelectron spectroscopy (XPS) results and isoelectric point (IEP) values. Protonated and deprotonated nitrogen were equally coordinated to the surface for raw and thermally treated samples at low temperature (350°C). Stronger coordination of deprotonated nitrogen was found for samples treated at higher temperature (550°C), while only a cationic exchange and no coordination to the surface was observed for the mechanically treated sample. [Copyright &y& Elsevier]

Abstract: CoMo catalysts supported on a commercial γ-Al2O3 modified with B, Na or K were prepared in order to analyze the effect of acid–base characteristics on the FCC naphtha hydrotreatment. Catalysts were characterized by NH3 TPD, IR of pre-adsorbed pyridine and CO2, XPS, Raman, and XRD. In general, with either boron or alkaline metal modification the HDS/HYDO selectivity did not significantly improve. However, it is remarkable that when the alumina was modified to be either more acidic (B) or more basic (K, Na), improvements in the ratio between the HDS and the conversion of the internal branched olefin as well as in the ratio double-bond isomerization to HYD of linear olefins were observed. For both modifications, this fact was related to the promotion of the double-bond isomerization reaction from external to internal positions. For alkaline-doped catalysts, it was found that the double-bond isomerization was related to the existence of basic sites. For the boron, there is a range of boria content (2–3wt.%) where the double-bond isomerization was promoted selectively over the cracking and alkylation reactions because only weak Brönsted acid sites are present. Additionally, both modifications (Boron or alkaline metals) of alumina led to a decrease in the HDS activity, which was found to be related to changes in the distribution of Co and Mo species in the oxide state. Alkaline metal introduction led to the formation of alkaline metal molybdates, whereas boron introduction increased the proportion of octahedral polymeric Mo species, consequently, decreasing the dispersion of the Mo phase. [ABSTRACT FROM AUTHOR]

This contribution reports on the preparation, physicochemical characterization and catalytic performances of nitrided zeolites in the Knoevenagel condensation reaction. These basic materials were prepared by subjecting one Y zeolite (Si/Al ratio of 2.6) and two ultrastable Y zeolites (Si/Al ratio of 13 and 37) to nitridation, i.e., treatment with ammonia at high temperature. Both the amount and the chemical nature of incorporated nitrogen species were controlled by the nitridation temperature. Namely, an increase of the temperature induces an increase of the nitrogen content and the appearance of nitrogenous species in the following order of increasing temperature: NH4 +, adsorbed NH3, –NH2, >NH and >N–. The nitridation occurred practically in the same manner whatever the Si/Al ratio of the starting material. However, from a catalytic point of view different behavior was observed. No direct correlation was found with the nitrogen content of the samples. Nitrided zeolites were found to exhibit catalytic activity as long as the zeolitic framework was maintained. [ABSTRACT FROM AUTHOR]

Abstract: Thin films of α-MoO3 were efficiently deposited on Si (100) by spin-coating of various precursor solutions i.e. ammonium heptamolybdate (HMA), citrate (CIT) and oxalate (OXA) complexes of Mo6+, and peroxo-polymolybdic (PER) solutions. The effect of the nature and concentration of the precursor and of the spin-coating rate were studied by X-ray diffraction, Raman spectroscopy and scanning electron microscopy. The nature of the precursor used for the deposition influences the morphology of the crystals. For films obtained from CIT precursor solutions, an anisotropic morphology of MoO3 crystals with predominant basal faces is obtained, while MoO3 crystals spin-coated from PER precursor solutions possess a more isotropic morphology. Films deposition from OXA and HMA precursors possess an intermediate morphology. Homogeneity and thickness of the films can be adjusted by tuning the concentration of the precursor solution and the spin-coating rate. Whatever the precursor used, the larger the crystals formed, the more developed were the basal faces obtained. [Copyright &y& Elsevier]

Abstract: The aim of this work is to explore the applicability of the sol–gel method for the preparation of Ag/SiO2, Cu/SiO2 and Pd/SiO2 catalysts and to see whether such a method can yield silver, copper and palladium species stabilized by the carrier in the case of benzene oxidation. So Ag/SiO2, Cu/SiO2 and Pd/SiO2 xerogel catalysts were synthesized by cogelation of tetraethoxysilane (TEOS) and chelates of Ag, Cu and Pd with 3-(2-aminoethylamino)-propyltrimethoxysilane (EDAS). The resulting catalysts are composed of completely accessible metallic crystallites with a diameter of about 3nm located inside silica particles. [Copyright &y& Elsevier]

Abstract: Heteropoly catalysts based on the mixed PMoV heteropoly compounds (HPC) with Keggin structure were prepared. The behaviors of the samples (in bulk and in titania-supported form) as a function of temperature treatment in the range of 343–923K and the number of introduced V atoms into the heteropoly anions were studied. The catalytic activity of titania-supported catalysts was evaluated in the reaction of total oxidation of Cl-benzene at 473K. The samples were characterized by S BET method, thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The XRD, IR and Raman results provided clear evidence that V indeed is incorporated into the Keggin unit. Introduction of one V atom into heteropolyanion leads to a significant increase of its thermal stability. On the other hand, the presence of the vanadium centers appears to be responsible for the increased activity of the titania-supported samples in the reaction of total oxidation of chlorobenzene. [Copyright &y& Elsevier]

Abstract: This work investigates the reactivity of a molybdenum suboxide in the deoxygenation of benzoic acid in the presence of hydrogen or propylene. Major differences are highlighted with Mo8O23 as the active phase. When the reaction is performed in the presence of hydrogen as the reductant, benzoic acid is converted to benzaldehyde, toluene and benzene. If molecular hydrogen is replaced by propylene as a weaker reductant, the only product formed during the reaction is benzaldehyde. It is demonstrated that, in absence of molecular hydrogen in the reaction mixture, a large amount of benzoic acid remains irreversibly adsorbed on the catalyst surface. The comparison of the two series of catalytic tests allows to somehow discriminate how the nature and the mobility of the hydrogen atoms involved in the reaction dictate the behaviour of the catalyst. [Copyright &y& Elsevier]

Scanning electrochemical microscopy (SECM) is a powerful scanning probe technique for measuring the in situ electrochemical reactions occurring at various sample interfaces, such as the liquid-liquid, solid-liquid, and liquid-gas. The tip/probe of SECM is usually an ultramicroelectrode (UME) or a nanoelectrode that can move towards or over the sample of interest controlled by a precise motor positioning system. Remarkably, electrocatalysts play a crucial role in addressing the surge in global energy consumption by providing sustainable alternative energy sources. Therefore, the precise measurement of catalytic reactions offers profound insights for designing novel catalysts as well as for enhancing their performance. SECM proves to be an excellent tool for characterization and screening catalysts as the probe can rapidly scan along one direction over the sample array containing a large number of different compositions. These features make SECM more appealing than other conventional methodologies for assessing bulk solutions. SECM can be employed for investigating numerous catalytic reactions including the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), water oxidation, glucose oxidation reaction (GOR), and CO2 reduction reaction (CO2RR) with high spatial resolution. Moreover, for improving the catalyst design, several SECM modes can be applied based on the catalytic reactions under evaluation. This review aims to present a brief overview of the recent applications of electrocatalysts and their kinetics as well as catalytic sites in electrochemical reactions, such as oxygen reduction, water oxidation, and methanol oxidation. [ABSTRACT FROM AUTHOR]

• Successful synthesis of hydrophobic TiO 2 -SiO 2 catalysts by one-pot sol-gel procedure. • Hydrophobic TiO 2 -SiO 2 catalysts contain framework Ti species. • Hydrophobic TiO 2 -SiO 2 catalysts performed better than hydrophilic TiO 2 -SiO 2. • An optimal methyl-functionalization degree improves the catalyst performance. Titania-silica (TiO 2 -SiO 2) mixed oxides are known catalysts for the epoxidation of olefins. It has been demonstrated that their active sites consist in isolated framework Ti atoms. However, the latter species are only obtained when Ti loading is low, limiting the number of active sites and the catalytic performances. Thus, the need to search other approaches to boost them. We succeeded improving the catalytic activity of TiO 2 -SiO 2 mixed oxides in the epoxidation of cyclooctene with hydrogen peroxide by introducing hydrophobic organic moieties at their surface. Hydrophobic TiO 2 -SiO 2 mixed oxides were prepared through a one-pot sol-gel method. Titanium butoxide (TiBut) and tetraethoxy silane (TEOS) were used as the Ti and Si precursors respectively. Hydrophobization was achieved by substituting a fraction of TEOS in the synthesis by methyltriethoxy silane (MTES). The characterization of the Ti species was performed by FTIR, DRUV, and XPS, confirming the presence of significant amount of the active framework Ti. The methylation degree was evaluated by Solid State 29Si-NMR and TGA-MS. Hydrophobic TiO 2 -SiO 2 performed better in the epoxidation reaction than a fully inorganic more hydrophilic TiO 2 -SiO 2 prepared without MTES. A too high methylation degree of the catalysts is however detrimental. Our contribution allows elucidating the debate in literature about the consequence of hydrophobization of epoxidation catalysts on their performance. [ABSTRACT FROM AUTHOR]

• Non-porous mayenite was directly obtained after combustion reaction using a fuels mixture. • Calcination temperature for mayenite formation was reduced from 1300 °C to 250 °C. • Porous mayenite was obtained from 275 °C by an assisted solution combustion method. • Mayenite crystallinity and texture were tuned by varying the calcination temperature. • Porous mayenite exhibited an enhanced catalytic performance in the soot oxidation. Mayenite (Ca₁₂Al₁₄O₃₃) is an attractive, non-expensive material, conventionally prepared over 1300 °C via solid-state reaction, producing a solid with low specific surface area (1 m²/g). Although a recent alternative allowed mayenite formation from 400 °C using hydrothermal method, it still requires a ball-milling step to increase the specific surface area (≥20 m²/g), which is costly and energy-consuming, involving specialized equipment. Herein, we report a new, cost-effective and simple way to produce porous mayenite with enhanced textural properties at lower temperatures (˜275 °C). Initially, non-porous mayenite was directly produced from 250 °C via a self-combustion reaction of nitrates with a double-fuel mixture. Furthermore, the addition of oxalic acid was implemented, obtaining porous mayenite after calcination of a preformed precursor and boosting its specific surface area and pore volume up to 74 m²/g and 0.3 cm³/g, respectively. Such textural enhancement notably increased mayenite catalytic properties in the soot oxidation reaction. [ABSTRACT FROM AUTHOR]

Nanostructured metal oxides are good candidates for applications in heterogeneous catalysis. Recently our consortium has developed the preparation of such materials by exploiting the redox properties of the non-thermal gliding arc plasma (glidarc) in humid air. This contribution aims at sharing with the community active in the field of heterogeneous catalysis that the glidarc technique is an easy and accessible, but powerful technique with a very bright future that can be used for producing heterogeneous oxide catalysts. Therefore, we present here our most recent achievements in the preparation of titanium, iron and manganese oxide catalysts using glidarc. TiO 2 nanorods containing both rutile and anatase phases with improved photocatalytic activity under visible light were obtained by oxidizing Ti3+ ions in aqueous solution with the plasma species. Fe2+ ions exposed to the plasma discharge were transformed into sea-urchin-like porous goethite (α-FeOOH) nanostructures via the consecutive oxidation-hydrolysis processes. The synthesized goethite was mesoporous with a high surface area. Clay supported catalysts were also prepared by depositing the goethite particles on kaolinite. Those catalysts (and their calcination products) were active in heterogeneous Fenton degradation of organic dyes. α-MnO 2 nanorods were obtained by a rapid reduction of MnO 4 − ions after exposing an aqueous solution of potassium permanganate to the plasma discharge. [ABSTRACT FROM AUTHOR]

• LDH derived NiMgAl and NiMgAlFe oxides prepared by three methods. • Ultrasound-assisted (US) improves textural properties and decreases particle size. • NiMgAl US allows CO 2 methanation at lower temperature without deactivation for 40 h. • NiMgAl US offers great potential to be employed in the industrial CO 2 methanation. Within the idea to catalyze CO 2 methanation NiMgAl and NiMgAlFe oxides were synthesized by the layered double hydroxide route using co-precipitation and ultrasound-assisted co-precipitation. MgAl and MgAlFe oxides-supported Ni materials prepared by the impregnation method were used as references. Inductively-coupled plasma optical emission spectroscopy, X-ray diffraction, thermal decomposition, H 2 -temperature programmed reduction, N 2 physisorption, and transmission electron microscopy were used to characterize the catalysts. NiMgAl prepared using ultrasound-assisted co-precipitation showed the best activity with no deactivation for 40 h under stream. This was attributed mainly to the lower particle size, the higher specific surface area and pore volume as well as the better dispersion of nickel active species at the surface of the concerned materials. In our case, the ultrasound method saves a lot of time during the synthesis process since the maturation phase lasts only 30 min instead of 18 h required for the traditional co-precipitation. [ABSTRACT FROM AUTHOR]

• Transitory stage of photocatalytic degradation of ethylene was observed. • Non-volatile species of ethylene oxidation were observed. • Non-volatile by-products were assigned to furan and furfural oligomers (N < 10). • Theoretical model was proposed explaining the reaction kinetics. A complex kinetics of the photocatalytic decomposition of gaseous ethylene on nanoparticulate Fe(III) doped anatase TiO 2 was analyzed in a continuous-flow fixed-bed reactor. The analysis evidenced the production of non-volatile intermediate reaction products, which cover the photocatalyst surface and delay the time of attaining the stationary reactor performance. As a result, the reaction yield slowly increases during the long-lasted (∼3 h) intermediate stage. Based on Raman, FTIR and thermal post-treatment analyses, we assigned the major non-volatile reaction product to polymeric oxidized hydrocarbons: furan and furfural oligomers. A theoretical model is proposed explaining the observed kinetics. [ABSTRACT FROM AUTHOR]

Solid acid catalysts are central in our chemical industry and are major players in the valorization of bioresources. However, there is still a need to develop solid acid catalysts with enhanced acid strength and improved, or tunable, physicochemical profile to enhance the efficiency and sustainability of chemical processes. Here, a modular approach to tune the acid strength and surface polarity of silica‐supported sulfonic acid catalysts, based on a versatile copper‐catalyzed azide–alkyne cycloaddition (CuAAC)‐based anchoring scheme, is presented. The CuAAC‐formed triazole link was used to enhance the activity of the grafted sulfonic acids and to pair the acid sites with secondary hydrophobic functions. The beneficial effects of both the triazolium link and the paired hydrophobic site, as well as the optimal positioning of the sulfonic moiety on the triazole ring, are discussed in model esterification reactions. [ABSTRACT FROM AUTHOR]