Characterization of Cu−Mn/Zeolite-Y Catalyst for One-Step Synthesis of Dimethyl Ether from CO−H2

Cu−Mn/zeolite-Y catalysts prepared using a coprecipitation impregnation procedure have been investigated to develop active Cu-based catalysts for the dimethyl ether synthesis from syngas. A great enhancement of CO conversion and DME selectivity is observed on Mn-containing catalysts compared to its Mn-free counterpart. However, an excess addition of manganese suppresses the syngas−dimethyl ether (STD) activity. Manganese has been found to be interacting with copper to form copper manganese mixed oxides phase (Cu1+xMn2−xO4) upon calcinations, and the excess addition of copper or manganese will induce the segregation of copper or manganese as the isolated CuO or Mn2O3 phase, respectively. The segregates CuO phases enhanced the reducibility of the Cu1+xMn2−xO4 phase and the Mn2O3 phase by reducing spill-over species. Harder reduction of the mixed oxides leads to the formation of much smaller metallic Cu particles, and MnO remaines closely associated with copper particles after reduction treatment, acting as a site for stability against CO2 oxidation of the surface copper. Furthermore, it is found that addition of Mn to Cu/zeolite-Y catalyst decreases the average crystalline size of copper to the same extent. Combining the TPR and XRD analysis, it suggests that catalysts with the excess CuO phases in conjunction with copper manganese mixed oxides are much more active than that with excess Mn2O3 phases together with copper manganese mixed oxides in the hydrogenation of CO to DME.