Issue 10, 1999

Solid-state reactions of vanadium(V) phosphates in the presence of ammonia

Abstract

The structural transformation of vanadyl(V) phosphate dihydrate (V V OPO 4 ·2H 2 O, V/P = 1) and a Ga-containing vanadyl(V) phosphate dihydrate ([Ga(H 2 O)] x (V V O) 1–x PO 4 ·2H 2 O, V/P = 1 – x) in the presence of ammonia have been investigated. V V OPO 4 ·2H 2 O was transformed in the presence of an NH 3 –air–water vapour flow at temperatures of ca. 670 K mainly into distorted (NH 4 ) 2 (V IV O) 3 (P 2 O 7 ) 2 (V/P = 0.75). Additionally, the generation of crystalline V 2 O 5 (up to 10%) was observed, mainly representing the remainder of the vanadium of the precursor compound. [Ga(H 2 O)] x (V V O) 1–x PO 4 ·2H 2 O was synthesised by the replacement of a number of the (V V O) 3+ groups of the parent V V OPO 4 ·2H 2 O by [Ga(H 2 O)] 3+ . A similar solid-state transformation was observed when this material was treated under the same gas flow but, besides crystalline V 2 O 5 , a significant proportion of GaPO 4 was also formed. The heterogeneous catalytic ammoxidation of toluene to benzonitrile was applied as a test reaction in the temperature range 570–625 K for the evaluation of catalytic performance. The V V OPO 4 ·2H 2 O derived catalyst revealed an improved catalytic activity in comparison to similar catalysts obtained by the transformation of V(IV)-containing precursor compounds. It seems very likely that this is due to the existence of a proportion of crystalline V 2 O 5 . The catalytic activity of the Ga-containing material is much lower, but is still in the range of the V(IV)-derived catalysts. Characterisation of the parent samples and the generated products (after equilibration as well as catalytic runs) carried out by means of XRD, XPS and FTIR spectroscopy.

Article information

Article type
Paper

J. Mater. Chem., 1999,9, 2523-2527

Solid-state reactions of vanadium(V) phosphates in the presence of ammonia

A. Martin, U. Steinike, K. Melánová and V. Zima, J. Mater. Chem., 1999, 9, 2523 DOI: 10.1039/A903491I

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