Factors limiting selectivity in C3 and C4 amm(oxidation) reactions

An extensive data-mining study of C3 and C4 selective oxidation and ammoxidation reactions occurring in the gas phase over solid catalysts has been conducted. The reactions include the amm(oxidation) of propane, propene, isobutane and isobutene to produce α,β-unsaturated mononitriles and unsaturated carboxylic acids. Selectivity-conversion plots were generated for each reaction from the patent and scientific literature. For each reaction there is a clear upper limit in terms of selectivity-conversion beyond which experimental studies have not advanced. The results show that for some reactions, such as the oxidation of isobutane to methacrylic acid, high product selectivities are never realised due to the production of by-products via parallel oxidation of reaction intermediates, and more importantly, via consecutive oxidation of the unstable product. However, for the reactions of propane amm(oxidation) to produce acrylonitrile and acrylic acid the situation appears to be different. For these reactions, the central problem resides in the inability of conventional catalysts to suppress the propensity of the propene intermediate to desorb and oxidise further to oxides of carbon, rather than the loss in acrylic acid or acrylonitrile selectivity via consecutive oxidation.