Synthesis and characterization of soluble alkali metal, alkaline earth metal and related Keggin-type [PMo12O40]3− salts for heterogeneous catalysis reactions

Comprehensive Study of Isobutane Selective Oxidation Over Group I and II Phosphomolybdates: Structural and Kinetic Factors

“…The phosphomolybdic acid and other reagents were obtained from Aldrich and used without purification; analysis determined that the phosphomolybdic acid was hydrated with 29 waters per Keggin unit. A typical preparation for Li 2 H[PMo 12 O 40 ] follows: 10.3196 g of phosphomolybdic acid was dissolved in *40 mL of water with stirring. 0.3273 g of Li 2 CO 3 was added with continued stirring (evolution of carbon dioxide).…”

“…The small pores of heteropoly compounds generally result in low surface areas [4,5]. XRD studies have identified several phases, including triclinic, primitive and body-centered cubic [6][7][8][9][10][11][12][13][14]. The degree of hydration heavily influences unit cell dimensions, whereby complete phase changes can occur [15].…”

“…The publication reported that the XRD data of the divalent compounds was ''largely featureless''. Silviani and Burns [12] have also investigated the diffraction spectra of the alkaline earth phosphomolybdates and observed only a cubic structure without evidence of any amorphous or other phases (including triclinic).…”

Structural and Activity Investigation into Al3+, La3+ and Ce3+ Addition to the Phosphomolybdate Heteropolyanion for Isobutane Selective Oxidation

“…Decomposition of phosphomolybdic acid occurs at temperatures above 400°C [32,[45][46][47], so the lower maximum temperature for the initial TPRS experiment allowed for elimination of water and other molecules from the phosphomolybdates, whilst ensuring thermal degradation of the Keggin framework does not occur before useful selective oxidation data can be obtained. It should be noted however, the addition of cations to the phosphomolybdate anion enhances thermal stability significantly [33,[48][49][50], so the termination of the first experiment at 400°C is a conservative precaution; indeed, kinetic investigation into the aluminum, lanthanum and cerium salts has shown no evidence of degradation with the later experiments with ca. 500°C maximums (vide infra).…”

“…Distinguishing between the primary and secondary structures is vital to understanding catalytic processes [26]. Many X-ray diffraction studies have been conducted and several phases have been identified with heteropoly compounds, including triclinic, and primitive and body-centered cubic [27][28][29][30][31][32][33][34][35]. The unit cell dimensions of heteropoly compounds are heavily dependent upon the degree of hydration, whereby complete phase changes can occur [36].…”