Synthesis and characterization of tungstophosphoric acid-modified mesoporous silica nanoparticles with tuneable diameter and pore size distribution

Abstract

H 3−X PW 12 O 40 ] (3−X)− species interacting electrostatically with the ≡Si-OH 2 + groups, and by potentiometric titration the solids presented very strong acid sites. In summary, they are good candidates to be used in reactions catalyzed by acids, especially to obtain quinoxaline derivatives.

Iron (III) Silicotungstate: An Efficient and Recyclable Catalyst for Converting Glycerol to Solketal

“…The lowest pH value triggered by the metal cation may be assigned to the highest Lewis acidity, which favors their reaction with residual water present in the system, releasing H 3 O + ions. 31,47,52 When we compared these data with the values of initial electrode potential (Ei; Table 2), obtained in potentiometric titration measurements with n-butylamine in CH 3 CN, which indicate the strength of acidity of the salt catalysts, 34,47 we verified that the strongest acid catalyst was Fe 4/3 SiW 12 O 40 (Ei = 645 mV), while the weakest acid catalyst was Ni 2 SiW 12 O 40 (Ei = 240 mV).…”

“…The strength of acidity of the catalysts was estimated by measuring the initial electrode potential (i.e., Bel, model W3B) of an acetonitrile solution containing soluble salt. The number of acidic sites was determined by potentiometric titration as described by Pizzio et al 34 Typically, 50 mg of salt was dissolved in CH 3 CN, magnetically stirred for 3 h, and then titrated with n-butylamine solution in toluene (ca. 0.025 mol L −1 ).…”

“…29−32 Keggin HPAs are soluble in polar solvents; therefore, to facilitate their recovery and allows their reuse in the acetalization reactions of glycerol, they have been supported or immobilized on the matrixes that have a high surface area. 33,34 Nonetheless, besides the laborious synthesis, solid-supported catalysts can also undergo leaching and deactivation.…”

An alternative route for the preparation of phenol: Decomposition of cyclohexylbenzene‐1‐hydroperoxide

“…Therefore, phosphotungstic acid loaded on zeolites as a carrier has excellent catalytic potential benefiting from the catalytic properties of HPW and the pore structure of zeolites. [27][28][29][30][31] The acidic decomposition reaction of cyclohexylbenzene-1-hydroperoxide (CHBHP) is similar to that of cumene hydroperoxide. Selvin et al 9 compared the catalytic activity in the presence of various carriers (montmorillonite K-10, SiO 2 , TiO 2 , MCM-41, metal ion exchange montmorillonite) loaded with phosphotungstic acid for the catalytic decomposition of cumene hydroperoxide.…”

Reusable Heterogeneous Tungstophosphoric Acid-Derived Catalyst for Green Esterification of Carboxylic Acids

“…The HPAs are environmentally friendly alternatives to the use of mineral acids (H 2 SO 4 , HCl, or HF) . However, they show very high solubility in a range of polar solvents being studied as a homogeneous catalyst; , albeit usually, this type of catalyst exhibited good catalytic activity and recovery, and further reuse is costly. ,, Therefore, to facilitate recovery and easily reuse, a heterogeneous version has been prepared by supporting or immobilizing the HPAs. Different studies have been performed using immobilized HPAs on materials such as silica , and oxides − for esterification reactions.…”