Redox Properties and Catalytic Oxidation Activities of Polyatom-Substituted H n PW11M1O40 (M = V, Nb, Ta, and W) Keggin Heteropolyacid Catalysts

Abstract

Redox properties and catalytic oxidation activities of polyatom-substituted H n PW 11 M 1 O 40 (M = V, Nb, Ta, and W) Keggin heteropolyacids (HPAs) were examined. Reduction potentials and UV-visible absorption edge energies of H n PW 11 M 1 O 40 (M = V, Nb, Ta, and W) HPA catalysts in solution were determined by an electrochemical method and UV-visible spectroscopy measurements, respectively. It was observed that reduction potentials of H n PW 11 M 1 O 40 (M = V, Nb, Ta, and W) HPA catalysts increased and UV-visible absorption edge energies of the HPA catalysts decreased with decreasing electronegativity of substituted polyatom. It was also found that the lower absorption edge energy corresponded to the higher reduction potential of the HPA catalyst. Vapor-phase oxidation of benzyl alcohol was carried out as a model reaction to probe the redox properties of H n PW 11 M 1 O 40 (M = V, Nb, Ta, and W) HPA catalysts. Yield for benzaldehyde increased with increasing reduction potential and with decreasing absorption edge energy of the HPA catalyst, and in turn, with decreasing electronegativity of substituted polyatom. Reduction potential of H n PW 11 M 1 O 40 (M = V, Nb, Ta, and W) HPA catalysts measured by an electrochemical method and absorption edge energy of the HPA catalysts measured by UV-visible spectroscopy could be utilized as a probe of oxidation catalysis of the HPA catalysts.

UV–H2O2degradation of methyl orange catalysed by H3PW12O40/activated clay

“…Moreover, two little peaks emerged at 29.6 • and 29.9 • in the XRD patterns of H 3 PW 12 O 40 /activated clay, which might be attributed to the crystalline phase of H 3 PW 12 O 40 [17]. The FT-IR spectra (1500-600 cm −1 ) of samples were presented in Figure 1b [18,19]. Compared with the W-O b -W peak reported by [20], the change in peak shape and position might be caused by peak interaction from activated clay.…”

The role of niobia location on the acidic and catalytic functionalities of heteropoly tungstate

“…The resultant mixture was stirred for 3 h. Excess water was evaporated on a water bath and the dried catalyst mass was kept for further drying in an air oven for overnight. Finally the sample was calcined at 300 • C for 2 h. TPANb 1 catalyst was prepared according to the procedure reported in the literature [7]. In a typical procedure, 10 g of niobium oxalate was dissolved in 100 ml of 0.1 M oxalic acid solution and 6 g of Na 2 HPO 4 was dissolved in 100 ml of distilled water.…”

“…The catalytic properties of heteropoly acids (HPAs) can be tuned in a systematic way by exchanging counter-cations and hetero atoms [3][4][5][6]. Park et al studied the acidic and oxidation properties of HPA catalysts by exchanging the identity of addenda atom with group-V metal ions such as V 5+ , Nb 5+ and Ta 5+ [7][8][9].…”

“…HPAs with incorporation of V into its primary structure were reported [7,10]. This modification resulted in the increase of the redox nature of HPAs particularly heteropoly molybdate for different oxidation reactions [11][12][13].…”

Vanadium‐Substituted Tungstophosphoric Acids as Efficient Catalysts for Visible‐Light‐Driven Oxygenation of Cyclohexane by Dioxygen

“…[44,45] There are af ew catalytic applications reportedo nt he vanadium-substituted tungstophosphoric (PWV) acids such as oxidation of alcohols [46,47] and benzylamine, [48] bromination of olefins, [49] nitration of phenol, [50] and photooxidative degradation of various organic pollutantsi n water. [51][52][53] To the best of our knowledge,h owever,t he PWVacids-catalyzed selectiveo xidation of inactivated hydrocarbons by O 2 under visible light has rarely been reported so far.I ti s also of interest to learn interesting how to mediate the photocatalytic oxidation performance of PWV acids.…”