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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.