Non-hydrolytic sol–gel routes to heterogeneous catalysts

Abstract

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).

The Power of Non-Hydrolytic Sol-Gel Chemistry: A Review

“…Neither ligand exchange nor homocondensation were observed in the reaction mixtures and high homogeneity at the atomic scale was attained. This was proved mainly by early crystallization of silicon phosphates and the 29 Si CPMAS NMR spectroscopy where a strong resonance assigned to Si(OP) 6 moieties was observed, with no evidence of Si-O-Si or P-O-P bond formation detected [39]. and Hampden-Smith were followed.…”

Controlled deposition of titanium oxide overcoats by non-hydrolytic sol gel for improved catalyst selectivity and stability

“…Non-hydrolytic sol-gel (NHSG) chemistry is a well-known technique for material synthesis and has been previously used for catalyst synthesis [28,29]. However, we have found limited use of sol-gel chemistry for the deposition of thin oxide films and its effect on catalysis.…”

Preparation and characterization of EPDM/silica composites prepared through non-hydrolytic sol-gel method in the absence and presence of a coupling agent

“…An alternative method to prepare organic-inorganic material is the non-hydrolytic sol-gel (NHSG) process, which can be used to produce metal oxides of high purity and crystallinity. Moreover, the NHSG route features different reactions and reaction conditions, which significantly affect the texture, homogeneity and surface chemistry of the resulting oxide [4][5][6]. In the past 20 years, several non-hydrolytic synthesis methods of oxides and mixed oxides have been described, involving the reaction of precursors (alkoxides, chlorides, acetylacetonates) with oxygen donors (ethers, alcohols, ketones) [4][5][6][7][8][9][10].…”

“…Moreover, the NHSG route features different reactions and reaction conditions, which significantly affect the texture, homogeneity and surface chemistry of the resulting oxide [4][5][6]. In the past 20 years, several non-hydrolytic synthesis methods of oxides and mixed oxides have been described, involving the reaction of precursors (alkoxides, chlorides, acetylacetonates) with oxygen donors (ethers, alcohols, ketones) [4][5][6][7][8][9][10]. The main non-hydrolytic routes involve the reaction of a metal chloride with either a metal alkoxide or organic ether, acting as oxygen donors [7][8][9] as described in Figure 1.…”