ABSTRACT
This research work reports a general concept in liquid phase oxidative catalysis which combined the advantages of homogeneous and heterogeneous catalysis, by the use of a resin immobilized molybdenum catalyst. The immobilized molybdenum catalyst is prepared by a sorption process, whereby the molybdenum ions are anchored on the active sites of a polymer resin (Amberlite IRA-400 in CI form). Experimental observations suggest that the polymer resin probably has two active sites for sorption, and this led to the development of a model equation for two parallel firstorder reactions with a common product for the sorption process as: [Mo] = 3.47 x iO -5(0.45e-0.081t + (1 - 0 .45 )e-0.026t ) For comparison of the polymer immobilised catalyst versus the unsupported (homogeneous) catalyst, maleic acid (pK. = 1,83, pK, = 6.50) was selected as the model substrate, because it can be smoothly oxidized to cis-epoxysuccinic acid (pK1, = 1.98, pK2., = 3.92), using hydrogen peroxide in concert with ammonium molybdate. The rate of the epoxidation reactions was monitored by analysing the concentrations of maleic acid, hydrogen peroxide, and the volume of oxygen evolved due to the inevitable decomposition of hydrogen peroxide in aqueous solutions. A maximum obtainable yield of the epoxide was 84% at the conversion of 97% and selectivity of 87% based on H.202 consumed with the immobilized catalyst, while the corresponding values with homogeneous catalyst was 56% at the conversion of 76% and selectivity of 74%. A detailed exploitation of the immobilized catalyst (in pseudo-homogeneous system) resulted in the proposition of a mathematical expression for the rate of epoxidation (based on H202 consumed).