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Intermetallic compounds (IMCs) are interesting materials in the field of heterogeneous catalysis due to their ordered structure and tunable electronic properties. These IMCs can act as precursor to synthesize metal/metal oxide composite catalysts that are more active than just the starting IMCs. In this work, Sm2Co7 and SmCo5 IMCs were used as precursors to prepare highly active and stable Co_SmO, Co_Sm2O3 and Co3O4_Sm2O3 catalysts via controlled modification. Transmission electron microscopy (TEM) demonstrated that Co and Sm2O3 Nano crystallites were formed after the modification of the IMC. IMCs derived Co_SmO and Co_Sm2O3 were stable and active in NH3 synthesis with very low activation energy of 55 and 77 kJ mol−1 respectively. The structural, morphological and surface characterization revealed that a strong metal support interaction existed between Co and Sm2O3 (electronic effect) along with the presence of surface steps and edges of Co nano crystallites (structural effect) that activate the N2 at low temperature (360 °C). Similarly, Co3O4_Sm2O3 derived from the IMC were found to exhibit high CO2 and butane conversion in butane dry reforming at low temperature (550 °C) with excellent stability. The study revealed that the presence of Co3O4 and Sm2O3 active sites in close proximity (geometrical effect) promoted the simultaneous adsorption or activation of butane and CO2. The Co_Sm2O3 and Co3O4_Sm2O3 derived from IMCs exhibited superior catalytic performance in both NH3 synthesis and butane dry reforming compared to similar compositional catalyst synthesized by hydrothermal route. These studies pave the way to potential uses of IMCs as precursors to derive composite metal/metal oxide catalysts that are highly stable and active despite their low surface areas.

TiO2 pillared clay was prepared by intercalation of titan polyoxocation into interlamelar space of an Algerian montmorillonite and used for the photocatalytic degradation of the linuron herbicide as a target pollutant in aqueous solution. The TiO2 pillared montmorillonite (Mont-TiO2) was characterized by X-ray photoelectron spectroscopy (XPS), X-Ray diffraction (XRD), X-Ray fluorescence (XRF), scanning electronic microscopy (SEM), thermogravimetry and differential thermal analysis (TG-DTA), Fourier transformed infra-red (FT-IR), specific area and porosity determinations. This physicochemical characterization pointed to successful TiO2 pillaring of the clay. The prepared material has porous structure and exhibit a good thermal stability as indicated by its surface area after calcination by microwave. The effects of operating parameters such as catalyst loading, initial pH of the solution and the pollutant concentration on the photocatalytic efficiency and COD removal were evaluated. Under initial pH of the solution around seven, pollutant concentration of 10 mg/L and 2.5 g/L of catalyst at room temperature, the degradation efficiency and COD removal of linuron was best then the other operating conditions. It was observed that operational parameters play a major role in the photocatalytic degradation process. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

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, N2 physisorption TEM and XPS. Using NaIO4 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.

Pyrite reactivity with nitrate and nitrite was assessed in long-term batch tests to assess its possible oxidation in anoxic conditions at pH 8.5, at room temperature and atmospheric pressure. This was done in the frame of compatibility studies of nitrate-containing radioactive waste with a pyrite-containing clay host rock for geological disposal. Abiotic pyrite suspensions were prepared under inert atmosphere in 15 mM bicarbonate medium, as this simulates the inorganic carbon and pH conditions in the pore water of Boom Clay, which is a potential host rock for geological disposal in Belgium. Two forms of pyrite powder were used, formed via different genetic pathways and exhibiting a different morphology, namely pyrite obtained by crushing a large crystal cluster and pyrite extracted from Boom Clay by flotation. The reactivity of these two pyrite forms with nitrate and nitrite is reported and compared. Overall, after 2–2.5 years under abiotic conditions and inert atmosphere, no significant reaction between crushed pyrite and nitrate was detected, while a very limited reaction was observed between Boom Clay pyrite and nitrate. Between pyrite and nitrite, which is known to be more reactive than nitrate, a slow reaction took place for both forms of pyrite, with no significantly higher reactivity with the Boom Blay pyrite. The variability between the replicates of Boom Clay pyrite were also larger than for crushed pyrite. Overall, nitrate and nitrite induced a very limited, if any, oxidation reaction of the pyrite powders. These observations are important in assessing the safety of geological disposal of nitrate-containing radioactive waste.

Titanosilicates (Ti-SiO2) are well-known catalysts for the epoxidation of olefins. Isolated Ti inserted in the silica framework in tetrahedral coordination are the active species. Recently, adjusting the hydrophobic/hydrophilic balance of such catalysts’ surfaces has appeared as a promising tool to further boost their performance. However, adjusting the hydrophobic/hydrophilic balance via a one-pot classical sol-gel generally leads to a decrease in the Ti dispersion and/or collapse of the pore network. To overcome this limitation, hydrophobic mesoporous Ti-SiO2 were here synthesized by aerosol-assisted one-pot sol–gel, which allowed the simultaneous control of their Ti loading, degree of methyl-functionalization, and textural properties. Methyl-functionalization was achieved by a partial substitution of tetraethoxy silane (TEOS) by methyltriethoxy silane (MTES) in different ratios. Solid-state29Si-NMR, FTIR, TGA, and vapor-phase water adsorption showed that methyl moieties were effectively incorporated, conferring a hydrophobic property to the Ti-SiO2 catalysts. ICP-AES, DRUV, XPS, and N2 physisorption demonstrated that Ti dispersion and textural properties were both successfully preserved upon the incorporation of the methyl moieties. In the epoxidation of cyclooctene with tert-butyl hydroperoxide as oxidant, the hydrophobic Ti-SiO2 showed higher catalytic performance than pristine Ti-SiO2 prepared without MTES. In addition to disentangling the positive effect of adjusting the hydrophobic/hydrophilic balance of epoxidation catalysts on their performance, this contribution highlights the advantages of the aerosol procedure to synthesize mesoporous functionalized catalysts with very high dispersion of active sites.

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.

Mesoporous Ti–SiO2 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.

In the field of heterogeneous catalysis, the successful integration of enzymes and inorganic catalysts could pave the way to multifunctional materials which are able to perform advanced cascade reactions. However, such combination is not straightforward, for example in the case of zeolite catalysts for which enzyme immobilization is restricted to the external surface. Herein, this challenge is overcome by developing a new kind of hybrid catalyst based on hollow zeolite microspheres obtained by the aerosol-assisted assembly of zeolite nanocrystals. The latter spheres possess open entry-ways for enzymes, which are then loaded and cross-linked to form cross-linked enzyme aggregates (CLEAs), securing their entrapment. This controlled design allows the combination of all the decisive features of the zeolite with a high enzyme loading. A chemo-enzymatic reaction is demonstrated, where the structured zeolite material is used both as a nest for the enzyme and as an efficient inorganic catalyst. Glucose oxidase (GOx) ensures the in situ production of H2O2 subsequently utilized by the TS-1 zeolite to catalyze the epoxidation of allylic alcohol toward glycidol. The strategy can also be used to entrap other enzymes or combination of enzymes, as demonstrated here with combi-CLEAs of horseradish peroxidase (HRP) and glucose oxidase. We anticipate that this strategy will open up new perspectives, leveraging on the spray-drying (aerosol) technique to shape microparticles from various nano-building blocks and on the entrapment of biological macromolecules to obtain new multifunctional hybrid microstructures., A spray drying technique is used to prepare hollow zeolite microparticles into which an enzyme can be entrapped. Via this “Lego-like” strategy, we create hybrid heterogeneous catalysts that can run multistep chemo-enzymatic cascade reactions.

AlSBA-15 catalysts possessing Bronsted acid and Lewis acid–base bifunctionalities catalyze the direct arylation of benzyl alcohols to diarylmethanes with an 85% product yield through C–O bond activation. 2 and 4wt%AlSBA-15 catalysts have been synthesised by adopting a simple and efficient post-synthetic metal implantation route. The synthesised catalysts were characterized using XRD, N2 adsorption and desorption, 27Al MAS NMR, XPS, HR-TEM, NH3 and CO2-temperature-programmed desorption (TPD) and pyridine-transmission-FTIR spectroscopy techniques to confirm the existence of Bronsted acid and Lewis acid–base bifunctionalities. Through various control experiments, it is verified that Bronsted acid sites activate the benzyl alcohol and Lewis base sites interact with phenylboronic acid concurrently to accomplish the coupling reaction. In the recyclability study, 4wt%AlSBA-15 preserves its activity and stability up to 5 cycles. The 4wt%AlSBA-15 catalyst unlike homogeneous catalysts does not require additives, long reaction time and expensive metals.

This work presents the synthesis of Me2+ (Co, Mg, Ni and Zn)/Al layered double hydroxides (LDH) with a 3:1 M ratio by the co-precipitation method. Structural characterization and comparison of the series has been achieved using powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), nitrogen physisorption at 77 K, thermogravimetry measurements (TGA), temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), ammonia temperature-programmed desorption (NH3-TPD) and point of zero charge (pHpzc). Batch experiments were performed to analyze the adsorption capacity of the different LDH on diclofenac and salicylic acid, as example of emergent pollutants. The pH, mass of adsorbent, contact time and concentration of pollutant were the parameters used to compare the adsorption performance of the synthesized materials. Samples showed different behavior and the equilibrium was reached at different times, Mg6Al2 and Zn6Al2 showed lower equilibrium times but had higher adsorption capacity. Various adsorption and isotherm equation models were employed to study both the kinetic and equilibrium results and, in general, the removal of diclofenac was greater than that of salicylic acid. 1-Butanol conversion was also used as a means of acidity and basicity characterization and the results were compared with the adsorption performance of the samples in order to explain the results found. A relationship between the amount of pollutants adsorbed and the butenes formed in the dehydrogenation reaction of 1-butanol was found. This work was funded by the Spanish Ministry of Economy, Industry and Competitiveness (AEI/MINECO) , and the European Regional Development Fund (ERDF) through project MAT2016-78863-C2-R and the Government of Navarra through projects PI017-PI039 CORRAL. LS thanks Universidad Pública de Navarra for a pre-doctoral grant. AG also thanks Santander Bank for funding through the Research Intensification Program.

In 1-butanol dehydration (gas phase) on a Keggin heteropolyacid (HPA) catalyst, the large size of 1-butanol and its significant hydrophobicity make the bulk-type (also called pseudo liquid-type) catalytic mechanism impossible. This drastically limits the catalytic effect on the surface of the HPA, with an activity lower than what it could be. To overcome this limitation, partially substituted ammonium Keggin acid salts with the formula (NH4)xH3−xPW12O40 were here synthesized. Still maintaining enough acidity for the dehydration reaction, the replacement of some protons of H3PW12O40 with NH4+ increases the hydrophobicity of the crystal matrix and allows 1-butanol to enter the bulk of the salt. This consequently makes the protons inside the solid able to catalyse the reaction. The penetration of 1-butanol in the bulk is demonstrated by a combination of in situ methods (Raman, FTIR and XRD) applied during the pre-treatment of the catalyst and the catalytic reaction. When properly activated the pseudo liquid-type mechanism taking place in (NH4)xH3−xPW12O40 leads to a markedly higher 1-butanol conversion in comparison to the surface-type mechanism which is the only one achieved with the non-modified pristine HPA.

A complex kinetics of the photocatalytic decomposition of gaseous ethylene on nanoparticulate Fe(III) doped anatase TiO2 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.

© 2019 American Chemical Society. Herein, we present the aerosol-assisted sol-gel preparation of hierarchically porous TiO 2 -SiO 2 catalysts having a spherelike shell morphology and a high Ti dispersion. In order to control the porosity at the micro-, meso-, and macrolevels, we use the evaporation-induced self-assembly (EISA) of a surfactant, possibly combined with polymer beads as hard templates. These catalysts are tested for the epoxidation of cyclohexene with cumene hydroperoxide as the oxidant, and their performance is compared to the reference TS-1 zeolite. The high catalytic performance observed with the catalysts prepared by aerosol stems from their high specific surface area, but also from the short diffusion path length generated by the meso-/macropore architecture which provides entryways for bulky reactants and products. Besides, these materials can incorporate a higher Ti loading than TS-1 zeolite, while ensuring a good control over the Ti speciation. Thus, the unique features of the aerosol process - which is also known to be scalable - allow us to prepare catalytic materials with high epoxidation activity, also for bulky olefins. ispartof: Chemistry of Materials vol:31 issue:5 pages:1610-1619 status: published

Titania-silica (TiO2-SiO2) 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 TiO2-SiO2 mixed oxides in the epoxidation of cyclooctene with hydrogen peroxide by introducing hydrophobic organic moieties at their surface. Hydrophobic TiO2-SiO2 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 TiO2-SiO2 performed better in the epoxidation reaction than a fully inorganic more hydrophilic TiO2-SiO2 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.

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.

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 SiO2 and Al2O3 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.

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.

Supported NiO nanocluster catalysts were synthesized by using Ni colloid as a precursor and applied to the aerobic oxidation of 1-phenylethanol. Obtained catalysts were characterized through X-ray absorption fine structure (XAFS), X-ray photoelectron spectroscopy (XPS) and in situ X-ray diffraction (XRD). Activated carbon (AC) supported NiO nanocluster catalyst showed the catalytic activity to the aerobic oxidation of 1-phenylethanol without any additives. Only the AC support allowed the NiO catalyst to be active although the other supports did not. XAFS and in situ XRD revealed that NiO nanocluster was fixed on the supports successfully. XAFS and XPS gave the information about a difference in the local structure, chemical state and electronic state of Ni among the different supports. The obtained catalyst showed the activity more effectively compared to conventional nickel-based catalysts.

This paper examines the effect of the preparation method of sulfated and unsulfated V2O5/TiO2 catalysts on chlorobenzene total oxidation. In particular, the method of incorporation of vanadium, either by impregnation or by direct introduction of V during the preparation of TiO2 or TiO2–SO42− aerogel supports, is discussed. The obtained catalysts have been characterized by means of ICP-AES, N2 adsorption–desorption at 77 K, XRD, Raman spectroscopy, DRIFTS, XPS, H2-TPR and NH3-TPD. Without sulfate, the impregnated catalyst exhibits a higher V dispersion and performs better than the sol–gel catalyst. The beneficial effect of sulfate groups is clearly demonstrated as both the impregnated and one-pot sol–gel samples with sulfate markedly outperform the corresponding samples without sulfate. The sulfated one-pot sol–gel catalyst exhibits the best performance at high temperature, probably thanks to its sulfate-rich surface.

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, we present 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. We precisely take advantage of the CuAAC-formed triazole link 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. ispartof: Chemistry vol:25 issue:27 pages:6753-6762 ispartof: location:Germany status: Published online

Operando Raman spectroscopy is used here to enlighten crucial and yet unconsidered aspects of the catalytic behavior of Keggin heteropolyacids (HPAs) in the gas phase dehydration of methanol to dimethylether (DME). On one hand, HPAs are since a long time claimed as being able to absorb methanol into their bulk, but on the other hand this feature is not yet really exploited when it comes to develop/use HPA-based catalysts for the methanol-to-DME process. Actually, the conditions in which the bulk is simultaneously accessible and catalytically active are not yet clearly reported. Clarifying this is precisely the aim of our work, for which we have used H3PW12O40 and H4SiW12O40. We precisely operando-follow the νs(W[double bond, length as m-dash]Ot) band reflecting whether methanol penetrates or not in the HPAs' bulk. We show that, when the HPAs are used without having been beforehand completely dehydrated, methanol penetrates into their bulk. However, the conversion remains low (

Due to its superacidity and ability of its bulk to react following a pseudoliquid mechanism, the Keggin H3PW12O40 heteropolyacid attracts more and more attention as a catalyst for the gas phase methanol-to-DME reaction. However, in its pure state, H3PW12O40 has a very low surface area (typically 5−10 m2/g), which limits the accessibility of its inner protons due to diffusional constraints and explains why teams investigate H3PW12O40in its supported form. In the present work, we highlight the interest of using hexagonal boron nitride (BN) as a support. We show that, in contrast to commonly used supports such as TiO2, BN is able to increase the accessibility of H3PW12O40’s acid sites (i.e., stabilizing small enough crystallites) while preserving their strong acidity (i.e., not interacting too much with the Keggin units). At low loadings(typically around 16% of one ideal Keggin monolayer), BN leads H3PW12O40 to reach an almost 2 times higher methanol conversion than obtained with the adequately activated pure bulk sample, and an almost 10 times higher conversion than an optimized TiO2-supported H3PW12O40catalyst. At higher H3PW12O40 loadings, the BN-supported catalysts are still much more active than the optimized TiO2-supported one, but less active than the pure bulk-activated H3PW12O40,which we attribute to the partial intercalation of H3PW12O40 within the interlayers of BN.

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.

Single catalysts containing 3, 5 and 7 wt.% of Ru (Ru3/Al2O3, Ru5/Al2O3 and Ru7/Al2O3) were prepared via impregnation of alumina with RuO2 colloidal suspensions. Two mechanical mixtures, containing Ru3/Al2O3 + Ru5/Al2O3 and Ru3/Al2O3 + Ru7/Al2O3, were also prepared. Catalytic activity was measured during low-temperature ammonia synthesis reaction. Three different tests were performed after reduction pretreatment of the catalysts: 1) Standard test, the catalytic activity of ammonia synthesis; 2) Test under NH3 + He treatment, following ammonia decomposition; 3) Test under NH3 + He + H2 treatment, following ammonia decomposition in presence of hydrogen. Standard tests were additionally used to study the effect of the different treatments (NH3 + He and NH3 + He + H2) on the catalytic activity of ammonia synthesis. Catalysts were characterized by N2 physisorption, XRD and XPS spectroscopy. The size of Ru nanoparticles influences their performance during ammonia synthesis. The important role of the average size and size distribution of Ru nanoparticles in their activity for ammonia synthesis has been confirmed. Catalysts having a broad size distribution of Ru nanoparticles are more active than those having a narrow size distribution of Ru nanoparticles. Ammonia treatment has a negative effect in ammonia synthesis: results suggest that NHx intermediates remaining strongly adsorbed on the surface inhibit the activity of catalysts during ammonia synthesis. The presence of hydrogen during NH3 treatment inhibits ammonia decomposition and induces weaker adsorption of NHx intermediates. The presence of large particles is necessary to reach and maintain a high catalytic activity during ammonia synthesis. Taking into account previous studies, it could be suggested that large Ru nanoparticles activates mobile hydrogen atoms that migrate towards small Ru nanoparticles, promoting NHx hydrogenation. When mixing two catalysts having different mean Ru sizes, there is a significant synergistic effect in the catalytic activity, due to a more effective hydrogenation of NHx intermediates.

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.

The hybridization of polyoxometalates (POMs) through an organic–inorganic association offers several processing advantages in the design of heterogeneous catalysts. A clear understanding of the organization of these hybrid materials on solid surfaces is necessary to optimise their properties. Herein, we report for the first time the organization of Keggin phosphotungstic [PW12O40]3− and Wells–Dawson (WD) phosphomolybdic [P2Mo18O62]6− anions deposited on mica (hydrophilic), and highly oriented pyrolytic graphite (HOPG) (hydrophobic) surfaces. Next, the supramolecular organization of the organic–inorganic hybrid materials formed from the association of POM anions and dimethyldioctadecylammonium bromide (DODA) is investigated as a function of the hydrophilic or hydrophobic nature of the surfaces. The height of the Keggin-POM anions, measured with tapping mode (TM-AFM) is always in good agreement with the molecular dimension of symmetric Keggin-POM anions (ca. 1 nm). However, the asymmetric WD-POM anions form monolayer assemblies on the surfaces with the orientation of their long molecular axis (ca. 1.6 nm) depending on the hydrophilic or hydrophobic properties of the substrate. Namely, the long axis is parallel on mica, and perpendicular on HOPG. When hybridized with DODA, the organization of the hybrid material is dictated by the interaction of the alkyl side chains of DODA with the substrate surface. On HOPG, the DODA–POM hybrid forms small domains of epitaxially arranged straight nanorod structures with their orientation parallel to each other. Conversely, randomly distributed nanospheres are formed when the hybrid material is deposited on freshly cleaved mica. Finally, a UV–ozone treatment of the hybrid material allows one to obtain highly dispersed isolated POM entities on both hydrophilic and hydrophobic surfaces. The hybridization strategy to prevent the clustering of POMs on various supports would enable to develop highly dispersed POM-based heterogeneous catalysts with enhanced functionalities.

Pd nanoparticles supported on γ-Fe2O3 (2 wt.%) were synthesized using the water-in-oil microemulsion method (using hydrazine as a reductant agent). Materials were characterized by N2-BET at low temperature, XRD, XPS, Raman, and FTIR and tested in the gas phase reaction of oxidation of methanol. The direct formation of methyl formate (MF) from methanol was observed. Supported palladium catalysts produced methyl formate at low temperature (+2/Fe+3 ratio (2:1, 1:1, 1:2) used for the preparation of the supports. Methyl formate is already formed at 50 °C with the maximum at about 80 °C. At higher temperature, methyl formate is no longer formed and the oxidation to CO2 and CO occurs. Raman studies indicated the changes in the structure of the Fe2O3 support in the case of the 1:2 sample after chemical reduction with hydrazine.

CdS quantum dots were grown on mesoporous TiO2 films by successive ionic layer adsorption and reaction processes in order to obtain CdS particles of various sizes. AFM analysis shows that the growth of the CdS particles is a two-step process. The first step is the formation of new crystallites at each deposition cycle. In the next step the pre-deposited crystallites grow to form larger aggregates. Special attention is paid to the estimation of the CdS particle size by X-ray photoelectron spectroscopy (XPS). Among the classical methods of characterization the XPS model is described in detail. In order to make an attempt to validate the XPS model, the results are compared to those obtained from AFM analysis and to the evolution of the band gap energy of the CdS nanoparticles as obtained by UV–vis spectroscopy. The results showed that XPS technique is a powerful tool in the estimation of the CdS particle size. In conjunction with these results, a very good correlation has been found between the number of deposition cycles and the particle size.

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.

A functional 1D photonic crystal system built from a mesoporous mixed oxide multilayer is proposed that is able to switch from transparent to Bragg reflector states (characterized by a photonic stop band in the visible range) and vice versa by means of adsorption/desorption of liquid in/from the system. One-pot co-condensation of two different precursors enables tailoring of the optical refractive index of inorganic layers by a strict control of pore fraction and the ratio of mixed oxides. Using various templates, 1-hexadecyl trimethylammonium bromide for the low-refractive-index layers and Pluronic P123 for the high-refractive-index layers, an adequate distribution of the pore fraction was obtained. Mixing two oxides with high and low bulk refractive indexes enables tuning of the refractive index contrast between the adjacent layers. When the pores of the system are empty, the light passes through the medium with no reflection thanks to index matching between the layers, which confers to the mesoporous Bragg stack the ability to appear as an effective homogenous medium. The mesoporous Bragg stack has the ability to switch to colored when the pores are filled with water as a result of increasing the refractive index contrast between the layers. This functional multilayer system opens a new range of promising applications of inorganic mesoporous 1D photonic crystals, e.g. as smart coatings for privacy glass windows.

Mesoporous dielectric multilayer films exhibit an optical response (Bragg resonance) that is highly sensitive to the chemical environment. Using sol–gel preparation and spin-coating deposition method, titania/silica mesoporous layers were alternatively deposited and consolidated to form a Bragg stack on a glass substrate. Tuning of the effective refractive index of titania layers through the control of their porosity allowed us to tailor the optical response of the multilayer film, and in particular its color, to infiltrate liquids and/or molecules dissolved in a solvent. Selective grafting of hydrophobic molecules on the pore surfaces of titania mesoporous layers was likely to be at the origin of unusual behavior of the Bragg resonance spectral shift and intensity variation. The pore accessibility of the different layers forming the stack was investigated through the infiltration of Rhodamine 6G fluorescent dye. Confocal microscopy revealed a homogeneous distribution of the dye across all the layers of the stack. Capillary attraction induced by adequate pore size distribution between adjacent layers was found to play a key role in liquid infiltration throughout the entire mesoporous dielectric structure.

Methyl formate (MF) is a valuable platform molecule, the industrial production of which is far from being green. In this contribution, TiO2-supported Pd(z)Pt(1−z) catalysts were found to be effective in the green synthesis of methyl formate (MF)—at T=323 K and ambient pressure—through methanol (MeOH) oxidation. Two series of catalysts with similar bulk Pd/(Pd+Pt) molar ratios, z, were prepared; one by a water-in-oil microemulsion (MicE) method and the other by an incipient wetness impregnation (IWI). The MicE method led to more efficient catalysts owing to a weak influence of z on particle size distributions and nanoparticles composition. Pd(z)Pt(1−z)-MicE catalysts exhibited strong synergistic effects for MF production but weak synergistic effects for MeOH conversion. The catalytic performance of Pd(z)Pt(1−z)-MicE was superior to that of Pd(z)Pt(1−z)-IWI catalysts despite the latter displaying synergetic effects during the reaction. The catalytic behavior of TiO2-supported Pd(z)Pt(1−z) catalysts was explained from correlations between XRD, TEM, and X-ray photoelectron spectroscopy characterizations.

A spraymethod is proposed to improve the catalytic properties of ceramic papers to be used as catalytic lters 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 lter, are efciently and homogeneously deposited. On the contrary, the application of the conventional dripmethod results in bigger particlesmainly agglomerated at the crossings between the bers of the ceramic paper. As a result, catalytic papers prepared by the spraymethod exhibitmuch higher performance with soot combustion temperatures decreased by ~30 °C. Fil: Tuler, Fernando Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentina Fil: Gaigneaux, Eric M.. Université Catholique de Louvain; Bélgica Fil: Miro, Eduardo Ernesto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentina Fil: Milt, Viviana Guadalupe. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentina Fil: Debecker, Damien P.. Université Catholique de Louvain; Bélgica

International audience; tMagnetic nanoparticles based on Fe3O4(MNP) were coated with a silica (with thin or thick layers) priorto grafting with (3-aminopropyl) triethoxysilane (APTES) and octyltriethoxysilane (OTES) to increasetheir hydrophobicity and their pH stability. The synthetic conditions for the APTES grafting were chosento achieve either mono- or polylayers of chemically attached silane on the surface. The synthesizedFe3O4@SiO2- APTES and Fe3O4@SiO2-OTES core-shell particles were characterized by different methodsincluding XRD, TEM, FTIR-ATR, N2physisorption, ICP AES and XPS. The stability tests showed that coatingwith silica shell and grafting with organosilanes considerably improve the stability of MNP at pH 3; thethicker the silica layer the less iron oxide dissolved. The MNP-based materials showed catalytic activity inthe esterifications of propionic acid (PA) with n-butanol and of oleic acid (OA) with trimethylolpropane.In the PA containing medium the particles partly leach into a liquid medium contrary to the OA containingmedium where they seemed to be resistant to leaching.

The solution combustion method (SCS) is demonstrated as an easy and fast alternative method allowing the synthesis of mixed oxides with thermally sensitive metals, still keeping a good control on their stoichiometry and phase composition. Bismuth molybdates with different theoretical Bi/Mo atomic ratios, namely α-Bi2Mo3O12, β-Bi2Mo2O9, and γ-Bi2MoO6 were synthesized by the SCS, fully characterized by XRD, Raman, SEM/EDX, BET and XPS analyses, and tested in the partial oxidation of propene to acrolein. The SCS method allowed obtaining crystalline catalysts with Bi/Mo atomic ratios close to the theoretical values and very good catalytic properties namely high propene conversion (from 13.4 to 23.4%) and acrolein selectivity (from 71.5 to 80.0%) at 425 °C. A high purity of the SCS prepared bismuth molybdates was obtained by means of a subsequent calcination treatment. Such treatment did not alter the high catalytic activity of the catalysts, which slightly increased (from 12.3 to 25.5%), but induced a marked loss of acrolein selectivity (from 66.2 to 48.4%) at 425 °C. This effect is due to a strong increase of the oxidation states of Mo and Bi and reduction of the specific surface area during the calcination.

International audience; Four cation-exchange resins (Dowex 50wx2, Amberlyst 36, Purolite CT482 and Purolite CT275DR) wereinvestigated as catalysts in the esterification of oleic acid (OA) with trimethylolpropane (TMP). All fourresins accelerated the reaction kinetics. The results showed that in a solvent-free system, the gel-typeresin 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. Recyclabilitytests showed that the resins slightly lose their activity after the first use but retain stable activity duringthe further uses. The activity decay of the recycled resins is referred to the partial blocking of the activesites by the co-produced water. Additional studies confirmed the high stability of the chosen resinstoward leaching in polar medium. Overall, both high stability and possibility of reusing through stillhigh catalytic activity make the resins attractive candidates as heterogeneous catalysts for such complexindustrial process.

International audience; 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 ofmono- 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).

International audience; A new method of chemical immobilization of Keggin heteropolyacids (HPAs) was suggested. H3PW12O40, H4SiW12O40, and H3PMo12O40 were immobilized on the silica which was previously grafted with zirconium butoxide. The immobilization method promoted strong interaction HPA-support and yielded 25 wt.% of well-dispersed HPAs, so increasing the density of acid sites. The catalysts were active in the reaction of transesterification of methyl stearate with n-butanol and esterification of oleic acid with trimethylolpropane. We demonstrate that, contrary to the immobilized H3PMo12O40, the H3PW12O40and H4SiW12O40-based catalysts are stable toward leaching in a non-polar oleic acid medium. A discussion on circumventing the leaching in non-polar versus polar media is proposed in terms of interaction strength HPA-support. The stronger interaction (i.e., better resistance for leaching) between the support and H3PW12O40 (or H4SiW12O40) is referred to the lower difference of electronegativity between Zr andW and the lower polarizability of the bonds Zr–O–W compared to Zr–O–Mo.

Various characterization techniques, including UV-Vis, FTIR, EPR and XPS, were used for the description of structural changes in Fe-silicalite with low concentration of iron, which was activated using different methods (by conventional hydrothermal pretreatment at 600 °C and by treatment in the diluted flow of ammonia and propane in helium at 540 °C). Activated Fe-silicalite was subsequently used as a catalyst for the direct ammoxidation of propane. It has been shown that the studied methods of activation lead to materials with different catalytic behavior (activation in the flow of ammonia and propane resulting in the more active and selective catalytic materials). Results from the catalytic test are further discussed together with the results from the characterization of activated samples.

Mesoporous Re–Si–Al, Re–Al, and Re–Si mixed oxides were obtained via a one-step non-hydrolytic sol–gel route followed by calcination. The texture and surface properties of the resulting catalysts were characterized by a combination of EDX, XRD, N2-physisorption, XPS, ToF-SIMS, and NH3-TPD. The loss of rhenium during calcination, the texture and the acidity of the catalysts depended on their composition. Migration of rhenium toward the surface occurred during the calcination treatment, as evidenced by XPS and ToF-SIMS. After calcination, ToF-SIMS showed the presence of well-dispersed ReOx surface species. The influence of the composition of Re–Si–Al catalysts on their performances in the cross-metathesis of ethene and butene to propene was investigated. The specific activity of the Re–Si–Al catalysts was much higher than that of Re–Al catalysts, whereas the Re–Si sample was not active. The best Re–Si–Al catalysts displayed excellent specific activities (up to 45 mmol g−1 h−1) and apparent TOF values (98 × 10−3 s−1).

Novel modified “chemisorption–hydrolysis” technique and conventional “incipient wetness impregnation” procedure were compared for loading of cobalt species on mesoporous silica supports. Effect of cobalt amount, pH of the precursor solution, duration of the “chemisorption” procedure and pre-treatment medium, as well as topological characteristics of the mesoporous silica support were investigated. The state of the loaded cobalt species was studied by XRD, FTIR, FTIR of adsorbed pyridine, UV–vis, XPS and TPR methods and their catalytic properties were elucidated in methanol decomposition to hydrogen and carbon monoxide. The “incipient wetness impregnation” technique facilitates the formation of finely dispersed spinel cobalt oxide species. Their catalytic activity could be significantly increased by hydrogen pretreatment, but the effect is more pronounced when mesoporous silica with ordered pseudo 1D pore structure (SBA-15) is used as a support. The modified “chemisorption–hydrolysis” procedure facilitates the formation of strongly interacting with the support cobalt species, which are stable under the reduction conditions. Their properties could be regulated during the modification procedure, by varying the cobalt content and pH of the impregnated solution as well as by the duration of the “chemisorption” procedure.