Innovative Sol‐Gel Routes for the Bottom‐Up Preparation of Heterogeneous Catalysts

Abstract

Heterogeneous catalysts can be prepared by different methods offering various levels of control on the final properties of the solid. In this account, we exemplify bottom-up preparation routes that are based on the sol-gel chemistry and allow to tailor some decisive properties of solid catalysts. First, an emulsion templating strategy is shown to lead to macrocellular self-standing monoliths with a macroscopic 3D structure. The latter can be used as catalyst or catalyst supports in flow chemistry, without requiring any subsequent shaping step. Second, the aerosol-assisted sol-gel process allows for the one-step and continuous production of porous mixed oxides. Tailored textural properties can be obtained together with an excellent control on composition and homogeneity. Third, the application of non-hydrolytic sol-gel routes, in the absence of water, leads to mixed oxides with outstanding textural properties and with peculiar surface chemistry. In all cases, the resulting catalytic performance can be correlated with the specificities of the preparation routes presented. This is exemplified in catalytic reactions in the fields of biomass conversion, petro chemistry, enantioselective organic synthesis, and air pollution mitigation.

Ag- and Cu-Promoted Mesoporous Ta-SiO2 Catalysts Prepared by Non-Hydrolytic Sol-Gel for the Conversion of Ethanol to Butadiene

“…Sol-gel processes have emerged as promising routes for the preparation of advanced heterogeneous catalysts [23,24]. In classical sol-gel methods, molecular precursors undergo hydrolysis and inorganic polycondensation reactions to form, in a bottom-up fashion, a solid material with the desired properties.…”

Macrocellular Titanosilicate Monoliths as Highly Efficient Structured Olefin Epoxidation Catalysts

“…These issues triggered intensive research on the incorporation of titanium in silica‐based materials with larger pores in order to broaden the range of applications for titanosilicates . New strategies in this field are flourishing, taking benefits of bottom‐up sol‐gel routes involving templating methods – possibly combined to supercritical, or aerosol, drying strategies – or realized under non‐aqueous conditions …”

NaAlO2‐Promoted Mesoporous Catalysts for Room temperature Knoevenagel Condensation Reaction

“…In order to improve their catalytic performance, active species are incorporated into the pores and it can be done by various ways, such as impregnation, ion exchange, chemical vapor deposition, sol‐gel processing and in‐situ impregnation . Among these methods, the introduction of active species into the mesoporous framework by impregnation method makes it possible to form uniform base sites distribution . Such composite materials are therefore attracting attention for application as effective heterogeneous solid base catalysts for various organic transformations.…”

“…[2,13] Among these methods, the introduction of active species into the mesoporous framework by impregnation method makes it possible to form uniform base sites distribution. [14] Such composite materials are therefore attracting attention for application as effective heterogeneous solid base catalysts for various organic transformations. Much attention has been given to generate basic sites on mesoporous supports by various methods [15,16] Amino group functionalized silica, [17] alkali metal doped carbon, [18] MnO 2 doped hexagonal mesoporous silica have been reported as solid mesoporous base catalysts recently.…”