(58g) Improving Long Chain Hydrocarbon Formation in Dimethyl Ether Homologation over Mesoporous Hbea Supported Cu Catalysts

Methanol and/or dimethyl ether can be converted with high selectivity to a mixture of branched C₄ – C₇ alkanes under mild conditions (i.e., 180 – 220 °C and 60 – 250 kPa of DME) over HBEA catalyst. The addition of Cu to the BEA zeolite enables incorporation of gas phase H₂ into the desired products and leads to a 2-fold increase in the hydrocarbon productivity relative to unmodified HBEA. However, overcracking of long chain hydrocarbon is still considerable as indicated by high selectivity of butanes and lower alkanes. In this contribution, we propose the use of mesoporous zeolite supports to enhance diffusion of the hydrocarbon products, therefore limit the overcracking to light hydrocarbons and improve yield to long chain hydrocarbon products.

A series of mesoporous zeolites were prepared by post-synthetic treatment of commercially available HBEA (parent HBEA). Cu was added on zeolite support by incipient wetness impregnation, targeting 5wt% of Cu loading. ICP analysis confirmed the actual loading of Cu in the range of 4.5 – 5 wt%. All catalysts have similar total acid site density, as indicated by NH₃-TPD characterization. N₂ physisorption was performed to study textural properties of the catalysts. The parent HBEA catalyst possesses either micropores from the zeolite framework or mesopores larger than 4 nm in diameter. Post-synthetic treatment generated small mesopores in the range of 2 – 4 nm in diameter. And addition of Cu did not alter the textural properties of the catalysts.

Activity of the supported Cu catalysts were compared in the DME homologation reaction under mild condition (i.e. 200 ^oC and atmospheric pressure). The results showed that mesoporosity of the support not only enhances overall catalytic activity, but also improves product selectivity to heavy hydrocarbons (i.e. C5+ hydrocarbons). These results indicate the benefits of mesoporosity in the DME homologation reaction, which enhances diffusion of hydrocarbon products, reduce overcracking and coke formation.