Characteristics of Dehydrogenation Catalysis at Solid-liquid Interface Kept with Any Temperature Gradient

在沸腾条件下，浸渍不足有机底物的碳载体金属催化剂(以下称为“液膜态”)的脱氢活性明显高于悬浮催化剂。在合适的催化剂用量与基质用量的比例下，观察到下列特征：(1)基质液体的蒸发速率降低。(2)催化剂层的温度高于沸腾液体的温度。(3)气泡不仅从液体本体中产生，而且从碳载体催化剂的粉末表面产生。(4)释放出的气泡可以通过气液平衡不充分的液膜，向气相提供富含产物的组分。(5)通过分步冷凝将产物氢从基质蒸汽中分离出来。底物在低温下缩合，直接提供给催化剂，具有良好的吸附性能和良好的覆盖性，在沸腾条件下，催化剂在液膜状态下进行动力学控制脱氢，反应速率高，单程转化率高。催化剂的产物脱附与固-液界面的温度梯度相耦合，这与“热扩散”的热力学特征是一致的(Prigogine，1947)。得到了异丙醇和环己烷催化脱氢的各种实验证据。

Carbon-supported metal catalysis dipped with insufficient amounts of organic substrates (hereafter termed as "liquid-film states") have been found to exhibit strikingly-enhanced activities of dehydrogenation under boiling conditions in comparison with those of suspended catalyst states. Following characteristics were observed at the adequate ratio of catalyst amounts to substrate amounts :(1) The rates of evaporation from the substrate liquid phase were decreased.(2) Temperatures of the catalyst layr were higher than that of the boiling liquid bulk.(3) Vigorous evolution of bubbles occurred not only from the liquid bulk but also from the powder surfaces of carbon-supported catalysts.(4) Evolved bubbles can pass through the liquid film with insufficient gas-liquid equilibration, supplying product-rich components to the gas phase.(5) Product hydrogen were separated from the substrate vapor by fractional condensation, which resulted in no possibility of hydrogen return to the boiling reaction solution.(6) The substrate was condensed at low temperatures and supplied directly to the catalyst, with advantageous adsorption and predominant coverage assured.Consequently, kinetically-controlled dehydrogenation with catalysts in liquid-film states under boiling conditions undergoes at high reaction rates and one-path conversions. Product desorption from the catalyst would be coupled with the temperature gradient at the solid-liquid interface, for which common thermodynamic features are pointed out with those of "thermal diffusion" (Prigogine, 1947). Various kinds of experimental evidence were obtained for catalytic dehydrogenation of 2-propanol as well as of cyclohexanes.