3.3 Effect of operation parameters on methanol dehydrogenation
Methanol dehydrogenation was an endothermic process and the increase of reaction temperature could promote the reaction37. From Figure 10A, it can be seen that the conversion efficiency of methanol was increased exponentially with reaction temperature. The conversion efficiency of methanol at 360 ℃ was two orders of magnitude higher than that at 260 ℃. The effect of reaction temperature on the selectivity of products was shown in Figure 10B. The production of formaldehyde and methyl formate performed monotonous tradeoff in the reaction temperature range of 260 ℃ and 360 ℃, which was consistent with the published reports44. The selectivity of formaldehyde can be increased from 10% to 98% with the reaction temperature increased from 260 ℃ to 360 ℃, and could be kept over than 90%, when the reaction temperature was over 320 ℃. This implied that the selectivity of formaldehyde was insensitive to temperature changes, if the reaction temperature was higher. During the process of methanol dehydrogenation for formaldehyde production, the produced formaldehyde would convert into methyl formate through hemiacetal reaction if the formaldehyde couldn’t desorb from the active sites in time45. In the general fixed bed reactor, the residence time was several seconds46. However, the residence time was only 0.2 s with uniform distribution in the developed Cu/ZnO/Ti CMNR. Therefore, the side reaction with methyl formate generation can be inhibited significantly.