Mesoporous Solid Acid Catalysts

Solid acids as cocatalysts in the chelation-assisted hydroacylation of alkenes and alkynes

The use of homogeneous Brønsted acid cocatalysts (such as benzoic acid) in hydroacylation reactions via imine intermediates has been extensively studied. However, the use of heterogeneous cocatalysts has been limited to montmorillonite K10. Thus, we can use other solid acids to increase the efficiency of the reaction. In this study, we describe the effects of sulfated zirconia, Al-MCM-41 or superacid modified montmorillonite on the hydroacylation of alkenes and alkynes with aldehydes via imine intermediates and in the presence of the Wilkinson complex. Furthermore, we addressed the dual role of montmorillonite, a redox reagent in the presence of TEMPO and an acid solid, allowing the direct use of benzyl alcohols as substrates to generate saturated or α,β-unsaturated ketones.

Versatile design and synthesis of mesoporous sulfonic acid catalysts

Mesoporous sulfonic acid catalysts (MSAC) are widely used in acid-catalyzed reactions, including biomass conversions with plenty of polar solvents and precursors. The catalytic efficiency of MSAC is greatly affected by the microenvironment around the sulfonic acid sites. In this review, the progress on modification of microenvironment of MSAC is reviewed over the past decade. Hydrophobic modification allows MSAC prevent the adhesion of water molecules onto sulfonic acid sites, to abate the risk of reduced acid strength and catalytic efficiency. In comparison, hydrophilic properties can bring positive effect on acid-catalyzed reactions with the aid of hydrophilic interaction between polar functional groups on MSAC and hydrophilic groups of specific substrates. Amphiphilic MSAC with tunable wettability for specific substrates and solvents tend to improve the efficiency in certain reactions with mixed solvents or reactants of different polarity, especially for biphasic systems of immiscible liquids. Furthermore, much attention has been attracted on modification of surface to simulate the microenvironment of homogeneous solvents and enzyme biocatalysts in recent research. New trends of this field are also highlighted.

Enzymatic Pretreatment Coupled with the Addition of p-Hydroxyanisole Increased Levulinic Acid Production from Steam-Exploded Rice Straw Short Fiber

Levulinic acid production, directly from lignocellulosic biomass, resulted in low yields due to the poor substrate accessibility and occurrence of side reactions. The effects of reaction conditions, enzymatic pretreatment, and inhibitor addition on the conversion of steam-exploded rice straw (SERS) short fiber to levulinic acid catalyzed by solid superacid were investigated systematically. The results indicated that the optimal reaction conditions were temperature, time, and solid superacid concentration combinations of 200 °C, 15 min, and 7.5 %. Enzymatic pretreatment improved the substrate accessibility to solid superacid catalyst, and p-hydroxyanisole inhibitor reduced the side reactions during reaction processes, which helped to increase levulinic acid yield. The levulinic acid yield reached 25.2 % under the optimal conditions, which was 61.5 % higher than that without enzymatic pretreatment and inhibitor addition. Therefore, enzymatic pretreatment coupled with the addition of p-hydroxyanisole increased levulinic acid production effectively, which contributed to the value-added utilization of lignocellulosic biomass.

ZSM-5 seed-grafted SBA-15 as a high performance support for cobalt Fischer–Tropsch synthesis catalysts

Strong bifunctional performance was observed on a ZSM-5 seed-grafted SBA-15 supported cobalt catalyst reacted at 260 °C in FTS.

Catalytic applications of mesoporous silica-based materials

Mesoporous materials featuring high surface areas (>600m2g−1), narrow pore size distribution and tuneable pores diameters (>2nm), have attracted a great deal of attention in recent years due to their promising properties and applications in various areas including adsorption, separation, drug delivery, sensing and catalysis. Catalytic applications of such materials have been extended to numerous processes and reactions which range from acid catalysis (alkylations, acylations, esterifications, biodiesel production, etc.) to redox chemistries (oxidation of alcohols, alkenes, sulfides and hydrogenations of acids, aldehydes and ketones and alkenes/alkynes). In this chapter, we aim to provide an overview on the utilisation of mesoporous materials in heterogeneous catalysis, with special emphasis on acid and redox catalysed processes.