The catalytic oxidation of 1-butene over bismuth molybdate : V. The kinetics of the oxidation: B. Experiments with continuous flow and recirculation; reduction and reoxidation of Bi---Mo

The kinetics of the oxidation of 1-butene over the Bi2O3 · MoO3 (koechlinite) catalyst were investigated in continuous flow experiments and in experiments with recirculation of the feed. The reaction was strongly inhibited by the product butadiene especially at lower temperatures and is zero-order in the oxygen pressure. The order of the butene partial pressure could not be determined because of the predominance of the inhibition by the product. The initial rate of reduction of the catalyst by 1-butene is approximately equal to that of the catalytic reaction: it is also strongly inhibited by butadiene and the rate appears to be determined by the combined influences of inhibition and progressive oxygen depletion. Contrary to reduction by hydrogen, that follows the usual parabolic law, it does not progress further than Mo5+ and Bi3+. Reoxidation of catalyst once reduced is fast and not inhibited by butadiene. Therefore, the diene inhibition has to be viewed as a competition between butene and butadiene for the same oxidized site. It is concluded that the absence of diene inhibition in pulse experiments is caused by the diene adsorption being slow in comparison to the residence time in pulse technics. By combining the data the conclusion can be drawn that the curved log k vs.1/T relation observed is caused by the interference of the diene inhibition. The diene inhibited reaction has an activation energy of 36 kcal mole-1, the noninhibited reaction, of 11 kcal mole-1