A Comparison of Catalytic Properties of Cs x H3−x PW12O40 Salts of Various Cesium Contents in Gas Phase and Liquid Phase Reactions

Abstract

The cesium salts Cs x H 3-x PW 12 O 40 of Cs content x = 2 up to x = 3 were tested as the catalysts in the gas and liquid phase reactions. Dehydration of ethanol and transesterification of triglycerides with methanol were selected as the catalytic reactions. Apart from the standard preparation, the catalysts were prepared by two-stage procedure with methanol or water as a solvent. The Cs-salts were characterized by FT-IR, XRD, scanning electron microscopy and energy dispersive X-ray techniques. In turn, the influence of Cs-salts composition on the pH and conductivity of their aqueous colloidal solutions was investigated. The results obtained by the latter techniques were also characteristic for acidity of surface layer of colloidal particles because of surface layer-solution equilibrium. It has been shown that the secondary structure of acidic cesium salts existing in crystalline samples (solid solution of H 3 PW 12 O 40 in Cs 3 PW 12 O 40 ) changes after contacting with polar medium to the system consisting most probably of Cs 3 PW 12 O 40 core with epitaxial layer of heteropolyacid. This is result of the protons migration from bulk to surface layer of primary particles enhanced by polar medium. It strongly influences the surface acidity of primary particles as well as the activity of Cs-salts in transesterification of triglycerides with methanol. In such polar medium, Cs 2 HPW 12 O 40 salt becomes the most active catalyst, more active than Cs 2.5 H 0.5 PW 12 O 40 . An accumulation of partial glycerides and in particular glycerol on the surface of primary particles of Cs-salts resulted in relatively low maximum conversion of triglycerides, most probably due to partial blockage of the catalytic centers. This effect and the almost constant activity of Cs-salts under recycling use in the transesterification experiments are considered to be experimental evidences that methanolysis over Cs-salts was accomplished with the participation of surface protons.

Review on Biodiesel Production from Various Feedstocks Using 12-Tungstophosphoric Acid (TPA) as a Solid Acid Catalyst Precursor

“…Therefore, it was appropriate to assign flowpath 2 for SBA-15, MCM-41 and flowpath 3 for HZSM-5, H-β zeolites (column 3 of Supporting Information Table S.2). Most of the TPA salts reviewed in this study (case number 5, 18, 21, 22) were porous. ,,,, However, Ag, TPPS and TEAPS3 salts (case number 9, 10, 12, 13) were non porous. ,,, Thus, it was appropriate to assign flowpath 1 and 3 respectively for these (column 3 of Supporting Information Table S.2). In the case of various TPA salts (e.g., CsH 2 PW 12 O 40 ), the metal or organic cations (e.g., Cs for CsH 2 PW 12 O 40 ) were tagged by their molecular weight in that salt (e.g., molecular wt.…”

Heteropoly acids-catalyzed organic reactions in water: doubly green reactions

“…The problem of their acid strength determination in terms of pKa and the number of acid sites has constantly been a challenge to search for trustworthy experimental methods (24)(25)(26)(27)(28).…”

“…The secondary structures of heteropoly anion (heteropoly anion together with protons) are rather transferable on account of the interaction with polar molecules. For such systems, water as a polar organic molecule plays a key role which is absorbed into the bulk of crystallites of HPAs and protonated clusters and influences their acidity and absorption properties (13,27,28,40,41).…”

Catalytic Hydroxylation of Benzene to Phenol with Hydrogen Peroxide over Cesium Salts of Keggin-type Heteropoly Acids

“…[28] Compared with the application of cesium salts of heteropoly acids as catalyst in acid reactions and gaseous phase oxidation reactions, their application in liquid phase oxidation reaction as water-tolerant catalysts was rare. [29][30][31] From the synthetic point of view, the typical procedure for preparation of cesium salts of HPAs are generally proceeded through a solution method by titrating the controlled amount of an aqueous solution of Cs 2 CO 3 into the aqueous solution of HPA. [32,33] In the previous report we found that the solid synthesis method by ball milling of HPA with CsNO 3 at room temperature is much simpler than the solution method, which is convenient to control the cesium content and has great potential in large scale preparation.…”