On the Behavior of O2− and O− Radicals over V2O5–SiO2 Catalyst

Abstract

The behavior of oxygen, O2− and O− radicals adsorbed on the partially reduced V2O5–SiO2 catalysts has been investigated. Oxygen is adsorbed mainly in a molecular state at room temperature, the sum of amounts of paramagnetic adsorbed species O2− and O− being less than 10% of total amount of adsorbed oxygen. High degree of reduction, high content of V2O5 and low pressure of oxygen at adsorption equilibrium are favorable for the formation of O− radical. It was confirmed by the quantitative analysis of reaction products and the adsorbed species that O2−, not O−, is the active species in the oxidation of propylene at room temperature. A mechanism involving an intermediate of an epoxide structure was proposed.

Reaction mechanism of photooxidation of propane over alkali-metal-ion-modified silica-supported vanadium pentaoxide under irradiation by visible light

“…2.5 wt.%) was prepared by impregnating the silica (V 2 O 5 with an aqueous solution of ammonium metavanadate. 14 The speciÐc surface area of VS was 465 m2 g~1. VS-m catalyst (Rb-VS) was prepared by impregnating VS with an aqueous solution of RbOH containing the desired amount of rubidium ion, followed by calcination in a dry air stream at 773 K for 5 h. The contents of rubidium ion are 4 wt.% as The Rb 2 O. speciÐc surface area of Rb-VS was 170 m2 g~1.…”

“…was supplied from Centre C 3 D 8 dÏEtudes de Saclay (purity 98%) and was used without further puriÐcation. Silica was prepared by hydrolysis of the distilled TEOS and calcination at 773 K for 5 h. 14 The speciÐc surface area of the silica was estimated to be 588 m2 g~1 by the BET method.…”

X-Ray absorption spectroscopy (EXAFS/XANES) evidence for the preferential formation of isolated VO4 species on highly photoactive V2O5/SiO2 catalysts

“…A V 0 4 unit in Na3V04 is considered to be very close to a regular tetrahedron because its XANES feature is similar to that of a regular tetrahedron V 0 4 in Pb5(V04)3C110 rather than that of the distorted V 0 4 units in NH4V03. 7 The XANES spectra of VSS catalysts are more like that of NH4V03 than Na3V04, suggesting that the V 0 4 tetrahedra in VSS are distorted from a regular tetrahedron.…”

Roles of Enhancement of C−H Activation and Diminution of C−O Formation Within M1‐Phase Pores in Propane Selective Oxidation

“…The formation of CH 3 CHO has been proposed to involve a surface epoxy‐like species, which suggests that C−O bond formation is required prior to C−C cleavage and C−O bond formations are also required to form CH 3 COCH 3 and CH 3 CH 2 CHO from C 3 H 6 [21c,40] . Thus, we conclude that undesired and desired reactions can be grouped as C−O formation and C−H activation limited reactions, respectively, which then allows a general framework for understanding how abstractor strength and pore confinement influences selectivity by differently influencing the two types of reactions.…”