Abstract
The calcium phosphate tungsten bronze (Ca-PWB) has been synthesized and characterized (TGA, DSC, XRPD, FTIR, SEM). The influence of solid insoluble materials Ca- PWB, as well as lithium doped (Li-PWB) and cation free phosphate tungsten (PWB) bronzes on the oscillatory Briggs-Rauscher (BR) reaction dynamics, is compared. The results show that doping with Li and Ca reduces sensitivity of the BR reaction towards bronzes addition. These findings suggest the usage of the BR reaction as an innovative method for testing of different properties of bronze material. The behavior of PWB in the BR reaction is significantly changed with divalent cation (Ca2+) doping. The reasons for the different bronzes behavior were found in their calculated unit cell volumes. Namely, the compressed Ca-PWB unit cell volume indicates the difficult availability of the active site for heterogeneous catalysis. Hence, the linear correlation (slope) of the BR oscillogram?s length (?osc) vs. mass of bronze in BR reaction might be considered as a new parameter for the evaluation of the bronzes catalytic activity.
Highlights
IntroductionThe ability of bronze cavities to accommodate guest ions [5, 10,11,12] is employed in this work for synthesis and characterization of novel Ca-doped phosphate tungsten bronze (CaPWB) obtained in the process of high-temperature transformation of 12-tungstophosphoric acid calcium salt (Ca-PWA)
Acids (HPAs) of Keggin’s type having general formula H(8-x)XM12O40×nH2O (Xx+ = P5+, Si4+, As5+, Ge4+, Ce4+, Th4+ where x is oxidation number of X, M = Mo, W, V, Nb and n = 6-31) are principally interesting because of their high protonic conductivity at room temperature [1,2,3]
The linear correlation of the BR oscillogram’s length vs. mass of bronze in BR reaction might be considered as a new parameter for the evaluation of the bronzes catalytic activity
Summary
The ability of bronze cavities to accommodate guest ions [5, 10,11,12] is employed in this work for synthesis and characterization of novel Ca-doped phosphate tungsten bronze (CaPWB) obtained in the process of high-temperature transformation of 12-tungstophosphoric acid calcium salt (Ca-PWA). This work further investigates the potential of the BR system to distinguish doped and undoped (cation free) phosphate tungsten bronzes and correlates their catalytic activity in the BR reaction with their structural properties. The obtained acidic salt CaHPW12O40×6H2O (Ca-PWA) is heated in a furnace (the velocity of heating is 10 °C min-1), in temperature range from room temperature to 590 oC, whereby the light-green crystals of calcium doped phosphate tungsten bronze are formed. The Ca-PWA and Ca-PWB samples were gold-coated for SEM study
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