Homogeneous Redox Catalysts Based on Heteropoly Acid Solutions VI: Development of a Process for Low-Temperature CO Oxidation with Oxygen

Abstract

Studies on the development of a homogeneous process for the low-temperature oxidation of carbon monoxide in the presence of a platinum group metal + vanadium-containing heteropoly acid (HPA) catalyst system have been described. Optimum reaction conditions to provide the maximum rate of CO oxidation to CO₂ have been determined, features of reaction kinetics have been found, and a mechanism has been proposed. It has been shown that systems based on a Pd^II aqua complex exhibit high activity and productivity; however, they have low stability and are used on stream only at a pH below 1.5. The stability of the catalyst can be increased by the simultaneous introduction of σ- and π-donor ligands into the system; however, the use of a Pt^IV complex in the presence of catalytic amounts of palladium salt in a ratio of 100/1 is more effective. Switching from HPA solutions with a low vanadium atom content (H₇PMo₈V₄O₄₀) to high-vanadium solutions of modified compositions (H₁₀P₃Mo₁₈V₇O₈₄) provides an increase in the activity and productivity of the system, while the shapes of the kinetic curves and the general laws governing CO oxidation are preserved. The combined homogeneous Pt^IV + Pd^II + H₁₀P₃Mo₁₈V₇O₈₄ catalyst remains stable during multicycle use without loss of activity, does not have an induction period in on-stream performance, and can be used at a pH of 0.7−2.5, which simplifies the hardware support of the process.