Multifunctionality of Cu-ZnO-ZrO2/H-ZSM5 catalysts for the one-step CO2-to-DME hydrogenation reaction

A series of Cu-ZnO-ZrO2/H-ZSM5 multifunctional catalysts for the one-step CO2-to-DME hydrogenation reaction was prepared via coprecipitation of methanol catalyst precursors by means of different precipitating agents (i.e., sodium bicarbonate, ammonium carbonate, oxalic acid and urea) in a slurry containing dispersed zeolite particles. The samples were characterized by XRF, XRD, N-2 adsorption/desorption isotherms, SEM, N2O-titration, TPR and NH3/CO2 TPD techniques, while the catalytic testing was carried out in a fixed-bed reactor operating at 3.0 MPa, in the T-R range 473-513 K and space velocity of 10,000 h(-1) (CO2/H-2/N-2, 3/9/1). The experiments revealed that the preparation methodology significantly affects catalyst properties and hence catalyst activity. The multifunctional catalyst prepared via ammonium carbonate precipitation resulted to be the most active in CO2 conversion, also accomplishing high DME selectivity, with a maximum space-time yield of 0.225 kg(DME)/kg(cat)/h. Catalyst characterization disclosed that the strength of basic sites, the ratio between acid and basic sites along with the Cu particle sizes are crucial to achieve maximum catalytic performance, keeping CO selectivity to a minimum value. (C) 2014 Elsevier B.V. All rights reserved.