Effect of vanadium pentoxide (and other transition metal oxides) on gas‐phase combustion. III. The isobutene‐oxygen system

Abstract

AbstractThe slow combustion of isobutene at 320–360° in a static system, using vessels coated with vanadium pentoxide, molybdenum oxide and bismuthphosphomolybdate, has been studied. No pressure decrease and little autocatalysis was observed. The maximum rate of oxidation in a V2O5‐coated vessel was independent of isobutene pressure and of added inert gas pressure, but depended markedly on the oxygen pressure. The overall activation energy was about 28 kcal/mole. The main products were CO, CO2 and H2O and there was less acetone, methacrolein, isobutyraldehyde and formic acid. Packing the V2O5‐coated vessel reduced the rate of consumption of isobutene considerably. With a MoO3‐coating the yields of organic products were generally greater and those of carbon oxides were less. With a bismuthphosphomolybdate coating the yield of methacrolein was higher than with other surfaces and that of isobutyraldehyde was lower.Possible homogeneous and heterogeneous processes in the oxidation mechanism are discussed. It is concluded that most of the isobutene was consumed in the propagation steps of an unbranched chain reaction, initiation being homogeneous and termination heterogeneous. However, some direct heterogeneous oxidation of the olefin occurred, and the methacrolein was formed by oxidative dehydrogenation of the isobutyraldehyde at the surface.