FIGURE 8 Conversion efficiency of methanol dehydrogenation with different CMNRs. (Reaction temperature 340 ℃, gas flux 8 m3.m-2.h-1 through the membrane, one sheet of membrane of thickness 1 mm)
The stability of the Cu/ZnO Ti CMNR was shown in Figure 9. It can be seen that the conversion efficiency of methanol did not decrease significantly and the selectivity of formaldehyde can be kept over 95% after continuous reaction for 18 h, which indicated the Cu/ZnO nanoparticles was not deactivated. In general, carbon deposited produced by side reactions and catalyst sintering caused by local temperature overheating were the common problems for catalyst deactivation during methanol dehydrogenation. In our developed Cu/ZnO/Ti CMNR, the catalyst nanoparticles were immobilized in membrane pores, the uniform distribution and size of membrane pores promote the temperature, methanol concentration and residence time being distributed uniformly. These properties of the CMNR can prevent side reactions and local temperature overheating at the scale of catalytic bed layer. Therefore, high stability of the catalysis performance can be achieved in CMNR for methanol dehydrogenation.