Selective Oxidation of n-Butane over Vanadium Phosphate Based Catalysts: Reaction Network and Kinetic Analysis

The reaction network of n-butane selective oxidation was comparatively analyzed over a novel αII-V0.8W0.2OPO4 orthophosphate and a reference vanadyl pyrophosphate (VPP) based catalyst via parameter field studies (T = 360–420 °C, x(n-butane) = 0.5–2.0%, x(O2) = 10–20%) as well as cofeed and pulse experiments with presumed reaction intermediates. For VPP the selectivity to the target product maleic anhydride (MAN) is particularly sensitive to the reaction temperature, the n-butane concentration, and the amount of cofed H2O, whereas the selectivity to MAN over the W-containing catalyst is almost independent of all reaction parameters. The roles of 1-butene, acetylene, furan, acetaldehyde, water, and 2,5-dihydrofuran are discussed. Pulsing of possible C4 intermediates indicates that their desorption from the catalyst surface is detrimental to MAN selectivity. Ethylene and acetylene may be formed from MAN. The consecutive reaction of acetylene with H2O can lead to acetic acid, whereas all other byproducts are ...