New bi-functional catalysts for a novel continuous production of propylene oxide with in-situ generated hydrogen peroxide

Abstract

Combined direct synthesis of hydrogen peroxide (DSHP) and epoxidation of propene to propylene oxide with hydrogen peroxide (HPPO) was carried out first time in a continuous laboratory-scale trickle bed reactor operating under mild conditions of 8 bar and 10°C. The reaction was performed with bimetallic gold–palladium catalysts supported on titanium silicalite 1 (TS-1). Three series of catalysts were synthesized from two different lots of TS-1 and different calcination heating rates. The catalysts were extensively examined using XRD, SEM-EDS, TEM-SAED, STEM-EDS, ICP-OES, XPS, UV–vis DRS, nitrogen-physisorption and ammonia-TPD. The metal-modification of TS-1 containing anatase impurities was shown first time, where the preferential deposition site for the bimetallic nanoparticles was on the minor anatase phase, found in different amounts in commercial TS-1 materials. In the first catalyst series, a higher anatase content was found, which led to a decrease of the AuPd nanoparticle size compared to the second and third series. Increasing the heating rate in calcination resulted in an additional reduction of the AuPd nanoparticle size. The propylene oxide selectivity was 55.7 % using catalysts of the third series, while the propylene oxide production rate was 0.17  mol·kg_cat^-1·h⁻¹ with 19.2 % propene conversion. The use of a palladium-poor alloy was found to be crucial for this reaction system to limit the hydrogenation of hydrogen peroxide and propene. The catalyst activity was investigated in the separate processes of DSHP and epoxidation to get a deeper insight into the reaction mechanism. In the switch experiments, DSHP followed by the combined reaction of DSHP and HPPO, the competing side reactions, hydrogenation of propene and hydrogen peroxide were confirmed. In another experiment, the dismutation of hydrogen peroxide was disproved.