3.2 Catalytic performance of methanol dehydrogenation in CMNR
The conversion efficiencies of methanol dehydrogenation under the reaction temperature 340 ℃, the gas flux 8 m3·m-2·h-1 through the membrane, and only one sheet of membrane of thickness 1 mm, are shown in Figure 8. It can be seen that Ti membrane substrate is almost inactive for methanol dehydrogenation. There is a slight increase of conversion efficiency of methanol after the reactant gas permeating through the Cu/Ti membrane and ZnO/Ti membrane. On the contrary, the conversion efficiency of methanol can be increased significantly after the reactant gas permeating through the Cu/ZnO/Ti CMNR, with its value being one order of magnitude higher than the Cu/Ti membrane. The higher conversion efficiency of methanol in the Cu/ZnO/Ti CMNR can be attributed to several factors. Higher Cu immobilization in Cu/ZnO/Ti CMNR could increase contact probability between the catalyst and reactant. Besides, ZnO as Cu carrier can improve the utilization of Cu atom, promote the dispersion of Cu nanoparticles and more catalysis active site can be exposed during the process of methanol crack. Furthermore, Cu and ZnO nanoparticles could synergistic methanol dehydrogenation34. It has been reported that the presence of Lewis acid sites on the surface of metal oxides can improve the first step of methanol dehydrogenation-the formation of methoxy35. Besides, ZnO also can enhance the spillover of H atoms, which is attributed to the interaction between methanol and O anions of ZnO36.