【摘要】 本文认为在一定反应条件下,醇类及其水溶液光催化脱氢其活性顺序主要取决于反应速率控制步骤。实验表明,可见光照机械混合Pt/CdS或化学沉积Pd/CdS的50℃醇水溶液的光催化脱氢活性顺序为异丙醇>乙醇>正丙醇>甲醇>>叔丁醇>丙烯醇>丙炔醇≈0。在认定本文之条件下的反应速率控制步骤是在烷氧负离子捕获光生空穴而后α-H脱落的前提下,从各种醇α碳上的结构效应结合能态的量化计算得出理论预测的活性顺序与实验结果完全一致,并对前人提出的不同活性顺序之可能原因作出解释。更多还原

【Abstract】 It is believed that under definite reaction conditions, the activity sequence of the photocatalytic dehydrogeriation of alcohol or its aqueous solution is mainly dependent on the rate determining step. Owing to the differences in semiconductor supporters, surface modification by different metals, and preparative methods of photocatalysts, and reaction conditions, rate determining step, probably, will be different, which resulted in the different photocataly tic dehydrogena-tion activity sequence. The experimentally determined activity squence of alcohols on mechanically mixed Pt/CdS or chemically deposited Pd/CdS under visible light irradiation at 50℃ is i-propanol>ethanol> n-propanol>methanol>>t-butanol>allyl alc. >propargyl alc.≈0. As it is supposed that the rate determining step of alcohol photocataly tic dehydrogenation under present conditions would be the capture of photoinduced hole by the alkoxy anion and then the scission of α-H, the indexes of the induction effect of substituents on the α-carbon of alcohols were calculated. Energy of the concerned energy states of n-propanol and ethanol, and relative energy needed for scission of α-H and β-H were calculated by quantum-chemical method. From the abo-vementioned calculation results the theoretical activity sequence of alcohols was obtained, which is in good agreement with the experimental results. The reasons for the lower dehydrogenation activity of unsaturated alcohols were analyzed theoretically. Possible causes for different activity sequences of the photocataly tic dehydrogenation of alcohols or their aqueous solutions reported in literatures were explained tentatively.更多还原