Amorphous V–P Mixed Oxide with P/V = 2.0 as Active Phase for Butane Oxidation

Abstract

V–P mixed oxide catalysts prepared by evaporation method was made up of a mixture of an amorphous phase with P/V = 2.0 and a crystalline phase of (VO)2P2O7. The amorphous phase, separated from the (VO)2P2O7 particles by dissolving the precursor in boiled water, was found to show essentially the same selectivity and activity per unit surface area for the maleic anhydride formation from butane as the unseparated catalyst.

Amorphous Vanadium Phosphate Catalysts Prepared Using Precipitation with Supercritical CO2 as an Antisolvent

“…Indeed, recently Coulston et al (12) have shown that the presence of V 5+ appears to be essential for the initial activation of n-butane, an observation that is essentially in agreement with earlier TAP pulse reactor experiments (13). To some extent, the debate concerning the involvement of specific VPO phases is complicated by the observation that many vanadium phosphate catalysts contain significant amounts of disordered material (5,6,(9)(10)(11)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29). Some studies suggest the amorphous material is an active component (5,6,15,18,19,(26)(27)(28)(29), whereas others consider this not to be the case (8)(9)(10)(11)22).…”

“…This indicates that Co promotes the catalytic performance of the amorphous material derived from this preparation method. It is interesting to note that Co does not have this effect for the amorphous vanadium phosphate catalysts prepared using supercritical CO 2 as an antisolvent (29), at least at the concentration investigated in this study; (e) oxidation of (VO) 2 P 2 O 7 has been shown to enhance the selectivity to maleic anhydride and oxidise the surface of the catalyst (22,28). This oxidation treatment also correlates with an increase in the depth of the amorphous overlayer as observed on edge-on the (VO) 2 P 2 O 7 crystallites viewed using very low illumination transmission electron microscopy (48).…”

“…Many studies have suggested that an amorphous overlayer on the crystalline VPO subsurface may be the active surface for this reaction (5,6,15,18,19,(26)(27)(28)(29). This has also been observed on related vanadium carbide catalysts for butane oxidation (21).…”

“…To some extent, the debate concerning the involvement of specific VPO phases is complicated by the observation that many vanadium phosphate catalysts contain significant amounts of disordered material (5,6,(9)(10)(11)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29). Some studies suggest the amorphous material is an active component (5,6,15,18,19,(26)(27)(28)(29), whereas others consider this not to be the case (8)(9)(10)(11)22). Amorphous VPO compounds have been used as one way to secure in situ regeneration in industrial reactors (30) by using a high temperature treatment with pure n-butane.…”

Ammoxidation of toluene on vanadyl polyphosphates-VO(PO3)2, 2. Catalytic properties

“…polyphosphates) as catalysts [14][15][16] were the subject of some studies, both related to the partial oxidation of n-butane. The use of P/V = 2 catalysts in the ammoxidation of methylaromatics is restricted to the application of (NHn)2VOP2O7; which is mainly transformed during this reaction into NI--IaVP2O 7 [4,17].…”