Conversion of Dimethyl Ether to 2,2,3-Trimethylbutane over a Cu/BEA Catalyst: Role of Cu Sites in Hydrogen Incorporation

Recently, it has been demonstrated that methanol and/or dimethyl ether can be converted into branched alkanes at low temperatures and pressures over large pore acidic zeolites such as H-BEA. This process achieves high selectivity to branched C-4 (e g, isobutane) and C-7 (e g, 2,2,3-trimethylbutane) hydrocarbons. However, the direct homologation of methanol or dimethyl ether into alkanes and water is hydrogen deficient, resulting in the formation of unsaturated alkylated aromatic residues, which reduce yield and can contribute to catalyst deactivation. In this paper we describe a Cu modified H-BE,A catalyst that is able to incorporate hydrogen from gas phase H-2 cofed with dimethyl ether into the desired branched alkane products while maintaining the high C-4 and C-7 carbon selectivity of the parent H-BEA. This hydrogen incorporation is achieved through the combination of metallic Cu nanoparticles present on the external surface of the zeolite, which perform H-2 activation and olefin hydrogenation, and Lewis acidic ion exchanged cationic Cu present within the H-BEA pores, which promotes hydrogen transfer. With cofed H-2, this multifunctional catalyst achieved a 2-fold increase in hydrocarbon productivity in comparison to H-BEA and shifted selectivity toward products favored by the olefin catalytic cycle over the aromatic catalytic cycle.