Methoxycarbonylation of ethylene/ethane mixture to methyl propionate over Pd-phosphine system with H-Beta zeolite and sulfonic acid as acid promoters

A series of heterogeneous Pd-catalysts was prepared via a facile new method. • Use of zeolite on EMC in C 2 mixture greatly reduced the corrosiveness of system. • The H-Beta zeolite catalyst with SiO 2 /Al 2 O 3 ratio of 22 showed superior performance. • The cooperation of H-Beta and trace MSA in presence of H 2 O boosted C 2 H 4 conversion. • A possible reaction mechanism was proposed for heterogeneous Pd-based system. Ethylene methoxycarbonylation (EMC) is highly efficient route for converting ethylene to methyl propionate (MP) with 100% atom economy, which has been commercialized over homogeneous Pd-based catalyst in pure ethylene. However, concerns about severe corrosiveness of strong liquid acids have always existed. Herein, H-Beta zeolite for the first time was introduced to cooperate with trace methanesulfonic acid (MSA) in the presence of water, to catalyze EMC in C 2 mixture. Over WMB-22 catalyst (containing H-Beta zeolite with SiO 2 /Al 2 O 3 ratio of 22, 0.32 wt% H 2 O, 0.005 wt% MSA, palladium/1,2-bis(di- tert -butylphosphinomethyl) benzene (d t bpx) complex with Pd/d t bpx/MSA ratio of 1/2/0.5), a superior ethylene conversion of 97.9% and 100% product selectivity, were obtained with C 2 H 6 /C 2 H 4 /CO feeding ratio of 1/2/2. A good linear correlation between C 2 H 4 conversions and the total acid content of H-Beta zeolite and MSA revealed that the synergistic effect between H-Beta zeolite and MSA could enhance C 2 H 4 conversion. Compared with the homogeneous catalyst with Pd/d t bpx/MSA of 1/2/15, under similar C 2 H 4 conversion conditions, the MSA amount of heterogeneous system was 1/30 of homogeneous system, indicating the addition of zeolite could greatly reduce the corrosiveness of system. 31 P nuclear magnetic resonance (NMR) results indicated that the introduction of zeolite, water and MSA could promote the generation and stabilization of active species. 1 H magic angle spinning (MAS) NMR and isotope D-tracing experiments clarified the interaction among Brønsted acid of zeolite, water and methanol, confirming the proposed mechanism pathways. This work provides a facile new method for using H-Beta zeolite and MSA as potential high-performance acid promoters for EMC. Download: Download high-res image (136KB) Download: Download full-size image