Thermal Behavior of 12-Molybdophosphoric Acid Supported on Zirconium-Loaded Silica

Abstract

The thermal behavior of 12-molybdophosphoric acid (HPMo) supported on silica and Zrloaded silica (Zr content from 1.6 to 17.0 wt %) was studied by X-ray diffraction, Fouriertransform infrared, in situ Raman, and X-ray photoelectron spectroscopic techniques. A silica support stabilizes the Keggin unit of HPMo up to 773 K, which is ca. 100 K higher than the unsupported one. For the Zr(1.6)SiO 2 support at 773 K, the thermal stability of HPMo is similar to that of the silica-supported counterpart. For Zr contents above 5.6 wt %, decomposition of HPMo occurs at lower temperatures, and this is accompanied by the formation of structure analogues of Zr(MoO 4 ) 2 . While Zr(x)SiO 2 supports stabilize surface molybdenum oxide species, silica is unable to spread molybdena, which segregates like bulk MoO 3 . The interactions of the Mo-Zr oxide species appear to be responsible for the activity enhancement in methanol oxidation. The marked decrease of the dimethyl ether/ formaldehyde selectivity ratio with increasing zirconium content on the samples calcined at 723 K indicates that the redox function of the interaction of Mo-Zr species increases formaldehyde selectivity.

Functionalized Graphene–Polyoxometalate Nanodots Assembly as “Organic–Inorganic” Hybrid Supercapacitors and Insights into Electrode/Electrolyte Interfacial Processes

“…Figure 1A-C displays the deposition scheme and representative scanning electron microscopy (SEM) images of POM 20 , POW 20 and a series of composites with rGO (rGO-POM 20,60,80 and rGO-POW 20,60,80 ) revealing uniform surface morphology. The rGO exhibits porous architecture composed of ultrathin nanosheets conformed to electrically conductive framework beneficial for electron transfer and ion transport while maintaining electrical conductivity with substantial accessible specific surface area for ion sorption.…”

“…The optical (UV-Vis absorption and fluorescence) spectroscopy measurements are carried out in solutions of POM 20,60 and POW 20,60 by themselves and their suspensions with rGO (rGO-POM 10,60,80 and rGO-POW 10,60,80 ) to investigate the electronic structure of rGO supported HPAs, the representative spectra are shown in Figure S2. In general, all absorption spectral bands arising in UV-Vis range of the electronic spectra of heteropoly compounds containing Keggin polyanion [ [55,56].…”

“…In total, fourteen different powders were prepared. In addition, it is emphasized that methanol was also used to wet the graphene surface and that the stability of HPAs is significantly improved in water-alcohol mixtures [80]. Finally, the pH in aqueous film dropped as water evaporated.…”

Molecular structures of supported metal oxide catalysts under different environments

“…Bulk HPMo decomposes at 673 K intǒ -MoO 3 , as shown by Raman bands at 851 and 775 cm 1 . 72 At 773 K, the˛-andˇ-MoO 3 phases co-exist and˛-MoO 3 dominates at 823 K. 72 On heating silica-supported HPMo, a progressive degradation of the HPMo phase is evident and at 823 K the Raman bands at 993, 861, 818 and 280 cm 1 reveal that a mixture of˛-andˇ-MoO 3 co-exist [ Fig. 10(A-f)].…”

Phytochemical and Biological Studies of Natural Egyptian Recipe with Anticancer Effect

“…The agar plate method was used to determine the MIC of tested samples reported by Damyanova et al 2000 [11] . The MIC was considered to be the lowest concentration that completely inhibits against inoculums comparing with the control, disregarding a single colony or a faint haze caused by the inoculums.…”