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用TPD和脉冲微型反应器分别测定了HZSM-5上CO_2和NH_3的吸附量及乙醇脱水反应的活性和选择性。HZSM-5吸附NH_3后的TPD谱图上出现两个峰,T_M值分别为 296和500℃。随着Na交换度的增大,NH_3吸附量增加;交换度40—50％时,开始出现第Ⅱ峰,以后渐增。CO吸附在HZSM-5上也有两个脱附峰即L-峰和H-峰,T_M值分别为126—156°和 380一460℃。随着交换度的增大,H-峰减小,而L-峰在交换度为20％时最大,交换度为40—50％时,乙醇脱水反应活性和生成乙烯的选择性最高。脱水反应主要在第Ⅰ峰对应的酸中心上进行。交换度约20％时,生成乙醚的量最大,所以脱水生成乙醚比生成乙烯需要较弱的酸性,脱水反应虽然主要在酸中心上进行,但碱中心也起一定作用。
The adsorption capacity of CO_2 and NH_3 on HZSM-5 and the activity and selectivity of ethanol dehydration reaction were measured by TPD and pulse microreactor respectively. HZSM-5 adsorption of NH_3 TPD spectra showed two peaks, T_M values were 296 and 500 ℃. With the increase of Na exchange rate, the adsorption amount of NH_3 increased; when the degree of exchange was 40-50%, the second peak began to appear, and then increased gradually. CO adsorbed on HZSM-5 also has two desorption peaks, L-peak and H-peak, with T_M values of 126-156 ° and 380-460 ° C, respectively. With the increase of exchange degree, the H-peak decreases, while the L-peak has the largest exchange degree of 20%. When the degree of exchange is 40-50%, the dehydration reaction of ethanol and the selectivity to ethylene are the highest. The dehydration reaction is mainly carried out on the acid center corresponding to the peak I. When the degree of exchange is about 20%, the amount of diethyl ether generated is the largest. Therefore, dehydration to form ether requires a weaker acidity than that to produce ethylene. Although the dehydration reaction mainly proceeds on the acid center, the alkali center also plays a role.