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© 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

International audience; A new type of acidic macrocellular and mesoporous silica-alumina foam is obtained via a one pot alkaline sol-gel route coupled with a concentrated emulsion-based templating technique. The mixed oxide monolith exhibits high surface acidity, translating in excellent performance in the acid-catalyzed dehydration of bioethanol to ethene.

Despite the enormous amount of research dedicated to this topic in the last 20 years or so, there is still a need for a general, cost-effective methodology allowing the synthesis of mesoporous mixed oxide catalysts. This review deals with the synthesis and catalytic applications of mixed oxides prepared by the nonhydrolytic sol–gel (NHSG) process based on the reaction of chloride precursors with ether or alkoxide oxygen donors. This NHSG process offers simple, one-step syntheses of mixed oxides with well-controlled compositions and non-ordered mesoporous textures, avoiding the use of supercritical drying or templates. Over the last decade, this process has been used to prepare various mesoporous mixed oxide catalysts, which showed real potential in major reactions such as partial and total oxidation, reduction of NOx, alkene metathesis, or alkylation. The main reactions involved in this NHSG process and the characteristics of the resulting mixed oxides are described in the first part of this review, underlining the decisive advantages in terms of simplicity and of control (in terms of composition, homogeneity or texture) offered by this process. In a second part, the literature dealing with mixed oxide catalysts prepared by this NHSG method is exhaustively reviewed and the catalytic performance of NHSG catalysts is compared, whenever possible, to that of catalysts with similar compositions prepared by other methods. The excellent catalytic performances of NHSG-catalysts (notably Si Ti, Ti V and Si Al Mo catalysts) compared to state-of-the art aerogels or ordered mesoporous materials evidences the potential of this sol–gel method, which should open the door to the synthesis of improved catalysts and to the discovery of new catalysts.

The catalytic performance of Cr-ZSM-5 catalysts prepared by solid-state reaction from different chromium salts (acetate, chloride, nitrate and ammonium dichromate) was evaluated in the selective ammoxidation of ethylene to produce acetonitrile. Cr-ZSM-5 catalyst characterization by chemical analysis, XRD, FTIR, N-2 physisorption, Al-27 MAS NMR, TEM/EDX, UV-visible DRS, XPS, Raman and DRIFT spectroscopies and H-2-TPR is reported. From textural analysis, it is obvious, after chromium exchange, that a decrease of S-BET and of porous volume is observed. On the other hand, FTIR. XRD and Al-27 MAS NMR results show that there is no collapse of the parent zeolite during thermal treatment. From H2-TPR, DRS, Raman and XPS spectroscopies, it is concluded that Cr ions and Cr(III) oxide coexist. TEM/EDX results confirmed that chromium oxide species are either heterogeneously or homogeneously dispersed on the support, depending on the nature of the precursor. DRIFT showed that chromium exchange leads strictly to the consumption of Si-O+H-Al groups. The catalyst prepared from chromium chloride showed higher activity and selectivity towards acetonitrile, being this catalytic modification probably due to the differentiated nature of chromium species formed using this precursor. A similarity with Fe-ZSM-5 system is underlined. In fact, higher oxidation states of chromium species are required for ethylene ammoxidation, while Cr2O3 clusters seem to enhance the hydrocarbon oxidation. (C) 2011 Elsevier B.V. All rights reserved.

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.

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).

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).

Oxides and mixed oxides have a tremendous importance in the field of heterogeneous catalysis, serving either as catalysts or as supports for active species. The performance of a catalyst depends directly on its composition, texture, structure and surface properties, which have to be precisely controlled and adapted to each application. In this context, the sol-gel process is a unique tool for the preparation and understanding of catalytic materials, owing to its exceptional versatility. In the last 10 years, the non-hydrolytic sol-gel (NHSG) or non-aqueous sol-gel process based on nonhydrolytic condensations in nonaqueous media has established itself as a simple and powerful method for the design of a wide range of oxide, mixed oxide and hybrid materials with controlled composition, morphology, texture and structure. NHSG proved particularly interesting for the preparation of catalytic materials, notably mesoporous xerogels, single site catalysts and highly crystalline nanoparticles. This critical review addresses the application of NHSG to the preparation of heterogeneous catalysts, emphasizing the specificities of this process, and giving a comprehensive overview of the literature (251 references).

MoO3-based materials are known to be appropriate catalysts for the heterogeneous metathesis of light olefins. Classical preparation methods involve the deposition of a Mo oxide phase on the surface of preformed support via impregnation, grafting or thermal spreading. An alternative sol–gel approach for the elaboration of Mo-based catalysts is presented in this article. Mesoporous ternary Si–Al–Mo mixed oxides are prepared in one step, via non-hydrolytic condensation of chloride precursors in non-aqueous media. After calcination, effective catalysts with very good textures and highly dispersed surface molybdenum species are obtained. The Si/Al ratio influences both the texture and the acidity of the materials, which significantly affects the propene self-metathesis activity. The activity also increases with the MoO3 content. The best catalysts with optimized composition significantly outperform the catalysts prepared by other methods.