Applied Catalysis A: General 208 (2001) 125–133 Continuous epoxidation of propylene with oxygen and hydrogen on a Pd–Pt/TS-1 catalyst Gregor Jenzer, Tamas Mallat, Marek Maciejewski, Florian Eigenmann, Alfons Baiker ∗ Laboratory of Technical Chemistry, Swiss Federal Institute of Technology, ETH-Zentrum, CH-8092 Zürich, Switzerland Received 29 March 2000; received in revised form 16 June 2000; accepted 19 June 2000 Abstract Propylene epoxidation over a Pd–Pt/TS-1 catalyst with in situ formed hydrogen peroxide was carried out in a fixed bed reactor under high pressure conditions. The continuous operation allowed the study of catalyst deactivation and changes in product distribution with time-on-stream. The initial propylene oxide selectivity was very high, 99% at 3.5% conversion, but the catalyst deactivated rapidly with time-on-stream and successively the formation of methyl formate became the prevalent reaction. Using carbon dioxide, instead of nitrogen, had a beneficial effect on the formation of propylene oxide, and even higher yields were obtained when increasing the pressure from 50 to 120 bar (supercritical fluid phase). Thermal analysis (TA-MS and TA-FTIR) indicated that catalyst regeneration requires oxidation at elevated temperature; washing with an organic solvent is less efficient. The serious catalyst deactivation and the striking shift in the selectivity pattern of the catalyst is traced to competing alcohol oxidation on platinum metal. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Epoxidation; Propylene; Propylene oxide; Palladium–platinum/titanium silicalite; Fixed bed reactor; Catalyst deactivation; Side reactions; Methanol oxidation; Supercritical CO 2 1. Introduction A considerable effort has been made in the past decades to develop heterogeneous catalytic pro- cesses for the economic production of propylene oxide from propylene [1,2]. The two main commer- cial epoxidation routes are the chlorohydrin and the hydroperoxide processes, both in the liquid phase. Examples on oxidation with hydroperoxides include the Halcon-ARCO and Shell processes using organic hydroperoxides [3,4], and the Enichem technology based on TS-1 and hydrogen peroxide [5–7]. For the latter process the best selectivity to propylene oxide ∗ Corresponding author. Tel.: +41-1632-3153; fax: +41-1632-1163. E-mail address: baiker@tech.chem.ethz.ch (A. Baiker). (97% at 90% hydrogen peroxide conversion) was achieved by Clerici et al. after hydrophobization of the Ti-substituted molecular sieve [6]. Direct oxidation in the gas phase with molecular oxygen is catalyzed by silver supported on carbonates and titanates (ARCO Chemical Technology [8,9]), and gold on titania [10–15]. The latter catalyst is highly selective (>99%) and up to 9.6% yield to propylene oxide has been attained [16]. Epoxidation of propylene by Pd–Pt/TS-1 is a par- ticularly interesting approach as the in situ formation of hydrogen peroxide from a mixture of oxygen and hydrogen over the noble metals and epoxidation of propylene by TS-1 are combined in the same catalyst [1,17–25]. In a comparative study TS-1 alone afforded 39% propylene oxide yield (based on propylene) us- ing hydrogen peroxide as oxidant, while no epoxida- 0926-860X/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0926-860X(00)00689-X