Synthesis Of Immobilized Molybdenum Catalyst For Oxidation Processes

This research work reports a general concept in liquidphase oxidative catalysis which combined the advantages ofhomogeneous and heterogeneous catalysis, by the use of a resinimmobilized molybdenum catalyst.The immobilized molybdenum catalyst is prepared by asorption process, whereby the molybdenum ions are anchored onthe active sites of a polymer resin (Amberlite IRA-400 in CIform). Experimental observations suggest that the polymerresin probably has two active sites for sorption, and this ledto the development of a model equation for two parallel firstorderreactions with a common product for the sorption processas:[Mo] = 3.47 x iO -5(0.45e-0.081t + (1 - 0 .45 )e-0.026t )For comparison of the polymer immobilised catalystversus 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 concertwith ammonium molybdate. The rate of the epoxidationreactions was monitored by analysing the concentrations ofmaleic acid, hydrogen peroxide, and the volume of oxygenevolved due to the inevitable decomposition of hydrogenperoxide in aqueous solutions. A maximum obtainable yield ofthe epoxide was 84% at the conversion of 97% and selectivityof 87% based on H.202 consumed with the immobilized catalyst,while the corresponding values with homogeneous catalyst was56% at the conversion of 76% and selectivity of 74%.A detailed exploitation of the immobilized catalyst (inpseudo-homogeneous system) resulted in the proposition of amathematical expression for the rate of epoxidation (based onH202 consumed).

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