Genesis and Stability of Silicomolybdic Acid on Silica-Supported Molybdenum Oxide Catalysts: In-Situ Structural-Selectivity Study on Selective Oxidation Reactions

UV/Vis/near-IR spectroscopic characteristics of H4–xCsxPVMo11O40 (x = 0, 2) catalyst under different temperatures and gas atmospheres

“…Unfortunately, however, the title compound in particular with x = 0, is thermally unstable, which makes it especially difficult to determine the catalytically active center. Many efforts have been made to investigate the thermally unstable state, for example, by XRD [2,4], TG-DTA coupled with IMR-MS and DSC [2,5], IR [4,[6][7][8], EPR [9,10] and Raman [11][12][13]. To improve the stability and catalytic activity of such compounds, cations were introduced in the secondary structure [14,15].…”

Spectroscopic Study on Mo Species of Mo-SBA-15 Synthesized Hydrothermally from H₂MoO₄ and Tetraethylorthosilicate

“…All spectra have similar profile with shoulder at around 950 and peak at 997 cm -1 . Those are of surface polymolybdate or MoO3 oligomer 21), 22) . The typical peaks assigned to MoO3 phase were not observed, indicating no formation of MoO3 crystallized after the calcination.…”

Raman Observation of Silicomolybdic Acid Formation Derived from H₂MoO₄ and Excess Tetraethylorthosilicate Using Hydrothermal Sol-gel Method

“…The existence of both α-and β-SMA in solution was reported by M. S. Kasprzak et al 8) , C. R. Deltcheff et al 9) and J. D. H. Strickland 10) . In 1995, M. A. Bañares et al 4) observed the formation of β-SMA on SiO2 by in-situ Raman spectroscopy when the calcined 5 wt% MoO3/ Silica derived from ammonium heptamolybdate ((NH4)6Mo7O24) was exposed to the oxygen saturated with water vapor for 24 h at room temperature. It is also reported that β-SMA is a meta-stable phase of SMA and the phase transition to the alpha form is favorable even at room temperature 10) .…”

“…α-and β-MoO3, however, are common crystalline MoO3 species which can be detected by both Raman spectroscopy and X-ray diffraction (XRD). It is well accepted that thermally decomposed SMA is restored by a reversible reaction in the presence of water vapor: 4) carried out in-situ Raman spectroscopy to prove that isolated surface molybdate species and SMA were the reversible transformation, each other. While A. Kido et al 3) proposed a scheme for SMA thermal decomposition and regeneration; at high heating rate (i.e.…”