Ammoxidation of toluene on vanadyl polyphosphates-VO(PO3)2, 1. synthesis and characterization of the parent samples

Abstract

Vanadyl polyphosphates with a P/V ratio = 2 (crystalline (~-VO(PO3)2 and 13-VO(PO3)2 as well as amorphous VO(PO3)2) were synthesized, starting from Usually prepared precursor VO(H2PO4)2 but pursuing new methods using V2Os/H3PO4 as well as VOHPO4 9 1/2 H20/H3PO4, too. The products were characterized by chemical analysis and X-ray diffractometry. In situ ESR spectroscopy was used as a tool to predict their catalytic activity in the ammoxidation reaction.

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

“…The quotient of the 4th and the square of the 2nd moment of the ESR signal were used as a parameter to describe this interaction remaining nearly unaffected for the crystalline phases, while it decreased by about 7% for amorphous VP/2 in the presence of toluene at 723 K [18]. A stronger interaction has always been observed for (NHa)z(VO)3(P207)2-containing phases (e.g.…”

“…The synthesis of VHP, using V205 and H3PO4 in the presence of oxalic acid (aqueous route) is described elsewhere [20] as well as the generation of the (NH4)z(VO)3(P207)2 + 'VxOy' (AVPgen) catalyst by treatment of VHP in an air/NH3/1-IzO vapor flow [10]. Additionally, V(PO3)3 (VP/3) was obtained by melting of V205 and H3PO4 in air at 803 K (3h) [18]. This sample was included in the investigations to study a polyphosphate sample that only contains vanadium in the valence state +III.…”

“…To our knowledge, a comprehensive study on the catalytic properties of these materials during the ammoxidation of methylaromatics has never been done so far. Part 1 of these investigations dealt with the synthesis of different P/V = 2 polyphosphates (a-VO(PO3)2, 13-VO(PO3)z, mixtures of both modifications and amorphous VO(PO3)z) as well as their characterization and the prediction of their activity behavior in the ammoxidation of toluene by in situ ESR spectroscopy [18].…”

“…13-VO(PO3)2 (13-VP/2) and amorphous VO(PO3)z (VP/2) were synthesized by calcination of VO(HzPOa)z (VHP/2) in air at 1073 K (1 h) and 673 K(6 h), respectively [18]. A mixture of the o~-and 13-modification (~/13-VP/2) was obtained from VzOs/H3PO4 by heating in air at 693 K (5 h) [18]. As mentioned above, the VOHPOa.1/2H20 (VHP) precursor was used for comparison.…”

Crystal structure and thermal expansion studies of α-VO(PO3)2

“…Vanadium phosphate and their hydrate products remained in interest for chemists for a long time due to their interesting catalytic properties [8][9][10] as well as their interesting structural features in particular of vanadium oxygen polyhedral unit [11,12]. Recently, one-dimensional magnetic chain has been observed in several low valent vanadium phosphates which further add to the importance of fundamental research [13][14][15] in these systems.…”