Supported VPO Catalysts for Selective Oxidation of Butane. II. Characterization of VPO/SiO₂Catalysts

Abstract

SiO2-supported VPO catalysts with different P/V ratios were prepared, used in selective oxidation of butane, and characterized by X-ray diffraction (XRD), laser Raman spectroscopy (LRS), near-edge X-ray absorption spectroscopy (XANES), and 31P magic angle spinning NMR. Similar to the SiO2-supported catalysts of lower metal loadings studied previously, the maleic anhydride selectivity increased with increasing P/V ratio, to greater than 50 mol % for P/V = 2. XRD and LRS detected predominantly α1-VOPO4 or a phase that is structurally very similar for both P/V = 1 and P/V = 2 samples. However, within the detection limit of the XANES experiment, the P/V = 1 catalyst contained mostly V5+ under reaction conditions, whereas the P/V = 2 catalyst contained 100% V4+.

VPO catalyst for n-butane oxidation to maleic anhydride: A goal achieved, or a still open challenge?

“…The same procedure can be adopted to reduce the VOPO 4 AE 2- [72,73], to obtain a high-surface-area precursor and finally a VPP that is more active and selective than that one prepared by conventional procedures (60% conversion, 78% selectivity at 390°C) [71]. Dispersion of VPP inside or over high-surface-area silica was also tried by other researchers, but in general this procedure did not lead to active catalysts [74][75][76]. (d) Preparation of an amorphous, microspheroidal VPO catalyst using supercritical CO 2 as an antisolvent [77,78].…”

Vanadium phosphates on mesoporous supports: model catalysts for solid-state NMR studies of the selective oxidation of n-butane

“…Table 3 gives a survey on the chemical shift data of the different 31 P MAS NMR and 31 P spinecho NMR signals of VPO precursors and activated VPO materials [3,6,17,21,22]. Generally, phosphorus atoms in the neighborhood of V 4+ and V 3+ species cause very broad solid-state 31 P NMR signals in the range of ca.…”

“…It is the most complex selective oxidation reaction industrially practiced. Although it is widely assumed that vanadyl pyrophosphate is the main component of the bulk VPO catalysts, little is known about the detailed nature of the active phases and sites till date [2][3][4][5][6]. Therefore, recent research focuses on the improvement of the understanding of this catalyst system as an important prerequisite for enhancing its activity and selectivity.…”

The dilution of vanadyl pyrophosphate, catalyst for n-butane oxidation to maleic anhydride, with aluminum phosphate: unexpected reactivity due to the contribution of the diluting agent

“…Volta et al [13] postulated the formation of a solid solution, in which the Al 3+ cations dissolve in the VPP lattice. In the case of silica-supported V/P/O [4][5][6][7], both activity and selectivity to MA were worse than those of unsupported V/P/O. This was due to the fact that the presence of silica hindered the crystallization of VPP, and favored the formation of bulk VOPO 4 .…”

“…Several papers describe attempts to impregnate the active phase precursor, VO-HPO 4 AE 0.5H 2 O, on conventional supports such as titania, alumina or silica [4][5][6][7][8][9][10][11], or on less conventional ones, such as Al phosphate [12,13]. In most cases, however, the intrinsic characteristics of the VPP are worsened due to the chemical interaction, which develops between the active phase and the support.…”