Cesium Heteropolyacid Salts: Synthesis, Characterization and Activity of the Solid and Versatile Heterogeneous Catalysts

Abstract

Keggin-type heteropolyacid cesium salts have been regarded as potential candidates for heterogeneous catalytic reactions. This review describes the success of Keggin-type heteropolyacids cesium salts (Cs-HPA salts) as efficient catalysts in various synthesis processes. The Cs-HPA catalysts can be synthesized as solid salts through the metathesis of a solution containing precursor HPA and another solution containing soluble Cs salt, which will give Cs-HPA salt as a solid precipitate. Alternatively, they can be also obtained from the commercial precursor HPA. In this review, all the routes to prepare the different cesium salts (i.e., saturated, lacunar, metal-doped) were described. These salts can be used in acid-catalyzed reactions (i.e., esterification, etherification, acetalization, dehydration) or oxidative transformations (oxidative esterification, oxidation, epoxidation). All of these reactions were addressed herein. Aspects related to the synthesis and characterization of these catalyst salts were discussed. This review aims to discuss the most pertinent heterogeneous catalytic systems based on Keggin HPA Cs salts. The focus was to correlate the physicochemical properties of these salts with their catalytic activity. Ultimately, the most recent advances achieved in the applications of these Cs-HPA salts as catalysts in the synthesis of industrial interest compounds were discussed. Cesium heteropoly salts are an alternative to the traditional soluble mineral acids as well as to solid-supported catalysts.

Cesium salt of tungstophosphoric acid/mesoporous (zirconia–silica) composite for highly efficient synthesis of 7-hydroxy-4-methyl coumarin and removal of methylene blue

“…The total acidity of the surface of the prepared samples was calculated by using the potentiometric titration by 0.1 g of each sample dispersed in 10 mL of acetonitrile for 30 minutes and stirred for three hours. 22,23 Aerward, by using an Orion 420 digital A model electrode, the dispersion was titrated against 0.025 N n-butylamine mixed with acetonitrile (0.005 mL min −1 ) to obtain the related potentials. Pyridine was adsorbed onto the catalyst surface, and its FT-IR spectra were acquired to investigate its Lewis and Brønsted acid sites.…”

“…20 Cesium-exchanged Keggin heteropolyacid salts with their various ratios (Cs x H 3− x PW 12 O 40 ) have been the most used catalysts due to their low solubility in aqueous and polar solvents compared with the Keggin structure of tungstophosphoric acid. 21,22…”

“…20 Cesium-exchanged Keggin heteropolyacid salts with their various ratios (Cs x H 3−x PW 12 O 40 ) have been the most used catalysts due to their low solubility in aqueous and polar solvents compared with the Keggin structure of tungstophosphoric acid. 21,22 Water treatment has become a highly important subject in terms of environmental protection in recent years. 2 Dye contamination is an increasing environmental hazard and efficient removal from water bodies is critical.…”

Liquid Phase Calorimetric Method as a Tool for Acid Strength Measurements and Application to a Variety of Sustainable Catalysts

“…However, unlike HPW, Cs x H 3−x PW salts have very limited solubility in water or organic solvents and are used exclusively as heterogeneous catalysts. While cesium derivatives show greater thermal stability, some of them have greater catalytic activity in certain reactions than HPW [126][127][128]. Salts in the Cs x H 3−x PW 12 O 40 series (x = 1; 2; 2.5; and 3) are prepared and characterized by structure and acidity using the Cal-Ad method.…”

Furfural and Levulinic Acid: Synthesis of Platform Molecules from Keggin Heteropolyacid-Catalyzed Biomass Conversion Reactions

“…However, solid-supported HPA catalysts can undergo leaching due to the high polarity of the reaction medium. To overcome this drawback, an alternative is to convert HPAs to insoluble salts, exchanging their protons with large ionic radius cations such as cesium [23][24][25][26]. It makes them solids with a high surface area and resistant to leaching.…”