Phosphotungstic acid

About: Phosphotungstic acid is a research topic. Over the lifetime, 1925 publications have been published within this topic receiving 38059 citations. The topic is also known as: Phosphowolframic acid.

Effect of calcination temperature on the catalytic activity of zirconia-supported heteropoly acids

Abstract: Zirconia-supported silicotungstic acid (15% STA) catalyst with different calcination temperatures (600–850 °C) was prepared by suspending zirconium oxyhydroxide in methanol solution of STA followed by drying and calcination. These catalysts were characterized by XRD, FTIR pyridine adsorption and DRUV–vis spectroscopy. The catalysts showed both Bronsted as well as Lewis acidity and 15% STA on zirconia calcined at 750 °C (15 SZ-750) had the highest Bronsted acidity. Characterization of 15 SZ-750 catalyst by Raman spectroscopy showed the presence of zirconia-anchored mono-oxotungstate as the major tungsten species present in this catalyst. These catalysts were used in benzoylation of veratrole with benzoic anhydride and 15 SZ-750 catalyst showed the highest activity. For catalyst with support calcined at different temperatures before HPA impregnation, catalytic activity decreases as the support calcination temperature increases due to the decrease in Bronsted acidity. Comparison of the catalytic activity of 15 SZ-750 with that of zirconia-supported phosphotungstic acid (15%, calcined at 750 °C, 15 PZ-750) in benzoylation of veratrole with benzoic anhydride, acylation of anisole with acetic anhydride and in alkylation of diphenylether with 1-dodecene showed that 15 SZ-750 catalyst has higher activity and deactivation resistance due to its higher Bronsted acidity. The deactivated catalyst could be regenerated by calcination without appreciable loss in activity.

Heterogeneous Fenton-like degradation of 4-chlorophenol using a novel FeIII-containing polyoxometalate as the catalyst

Abstract: Fenton-like degradation of 4-chlorophenol (4-CP) in aqueous solution was studied over a novel Fe III -containing polyoxometalate (POM) as heterogeneous catalyst. The POM, assigned as Fe III AspPW 12 , was synthesized via precipitation reaction of phosphotungstic acid (PW 12 ) with the complex of ferric ion and aspartic acid (Asp) in aqueous solution. The catalyst displays high activity and good reusability for oxidation of 4-CP by hydrogen peroxide in the range from acidic to circumneutral pH values. The enhanced oxidation of 4-CP was observed when the reaction system was irradiated by a high pressure mercury lamp. Under the conditions of H 2 O 2 20 mM, Fe III AspPW 12 0.2 g/L, temperature 25 ± 2 °C and pH 6.5, the complete total organic carbon (TOC) removal for 100 mg/L 4-CP solution could be achieved in both dark and irradiation systems within 120 and 60 min, with H 2 O 2 utilization of 77% and 83% respectively. It is speculated that the catalysis may possibly undergo the redox cycles of Fe III ⇌ Fe II and POM ⇌ POM − on the surface of Fe III AspPW 12 , accompanied by hydroxyl radical formation from H 2 O 2 , and the oxidation of 4-CP consequently.