SURFACE-CHEMISTRY OF V-SB-OXIDE IN RELATION TO THE MECHANISM OF ACRYLONITRILE SYNTHESIS FROM PROPANE .1. CHEMISORPTION AND TRANSFORMATION OF POSSIBLE INTERMEDIATES

The mechanism of propane ammoxidation to acrylonitrile on V-Sb-oxide i s analysed by IR spectroscopy in three papers dealing with the study o f (i) the reaction network in propane conversion, (ii) the relationshi p between ammonia chemisorbed species and catalytic behaviour and (iii ) the effect of ammonia chemisorption on the surface reactivity. This first part deals with the study of the nature of surface adspecies for med by chemisorption of acetone, isopropyl alcohol, acrylic acid, ally l alcohol, propene, propionic acid, acetic acid, propane and acrylonit rile on a vanadium antimonate catalyst (V/Sb=1.0) and subsequent therm al treatment. The results indicate that the catalyst is characterized by multifunctional properties (II-abstraction O-insertion and oxidativ e cleavage properties), the relevance of which for the mechanism and c atalytic behaviour in acrylonitrile synthesis from propane is discusse d. A surface reaction network in propane oxidation is also proposed in volving multiple possible pathways of transformation. The main route o f propane conversion is through the formation of propene as an interme diate, although a side reaction of acrylate formation via a propionate intermediate is possible. Propene may be oxidized according to two ro utes, the first leading to acetone which undergoes quick oxidative cle avage to an acetate species and a C-1 fragment, and the second to the formation of an allyl alcoholate adspecies which transforms to acrolei n which quickly further converts to an acrylate species. The acrylate species strongly interacts with the surface and is thermally stable up to relatively high temperatures.