Homogeneous Catalysts for Redox Processes Based on Heteropolyacids Solutions. V. Developing Two-Stage Process for Oxidation of Propylene to Acetone

Abstract

Investigations on the development of homogeneous chloride-free two-stage process (1st stage – target reaction, 2nd stage – catalyst regeneration) for oxidizing С3Н6 to acetone with oxygen in the presence of catalyst \({\text{Pd}}_{{{\text{aq}}}}^{{{\text{2 + }}}}\) + Mo-V-Р heteropoly acid (HPA-х, х is the number of V atoms) have been presented. The kinetic equation of the target reaction has been obtained, and its mechanism has been proposed. It has been shown that catalysts based on high-vanadium modified (non-Keggin) compositions HPA-xm are the most efficient. The kinetics of C3H6 oxidation in the presence of Keggin HPA-x and HPA-xm solutions has been the same, but only the \({\text{Pd}}_{{{\text{aq}}}}^{{{\text{2 + }}}}\) + HPA-xm catalysts have turned out to be technologically feasible. These have a high thermal stability (up to 180°C), which allows the catalyst to be rapidly regenerated with oxygen. This favorably distinguishes the catalysts based on HPA-xm from Keggin HPA-x, the thermal stability of which is limited to 140°C. The possibility of rapid regeneration of the catalyst has made it possible to close the 2-stage catalytic cycle of C3H6 oxidation to acetone with oxygen and has opened up prospects for the practical use of the process in the presence of \({\text{Pd}}_{{{\text{aq}}}}^{{{\text{2 + }}}}\) + HPA-xm. The catalyst has been successfully tested for stability.