Elucidation of Catalysis by Molecular Hydrogen-Originated Protonic Acid Site

本研究旨在提出“分子氢源质子酸位点”的新概念，阐明由分子氢形成的表面质子所引起的催化特性。为了阐明氢与Pt/SO_4^<2->- zro_2表面相互作用的影响因素，对不同类型的Pt/SO_4^<2->- zro_2表面酸度进行了控制，测定了氢的吸附速率和酸性位点的生成。结果表明，吸附速率和吸氢量随表面酸度的增加而增加。首次证明了在氢存在的条件下，Pt/WO_3-ZrO_2和WO_3-ZrO_2在加热时表面会形成质子酸位。Pt/WO_3-ZrO_2比WO_3-ZrO_2更容易形成质子。从WO_3-ZrO_2的表面结构分析了质子在WO_3-ZrO_2上形成的机理。氢吸附动力学分析表明，Pt/WO3-ZrO2的缓慢吸附步骤为溢出步骤，WO_3-ZrO_2的缓慢吸附步骤为表面扩散步骤。测定了Pt/SO_4^<2->- zro_2和Pt/WO_3-ZrO_2对庚烷异构化的催化活性，以确定影响其选择性的因素。Pt/WO_3-ZrO_2的选择性高于Pt/SO_4^<2->- zro_2, Pt/SO_4^<2->- zro_2的转化率更高。结果表明，选择性与酸强度和氢的表面扩散速率有关。阐明了外溢氢参与异构化的机理。

The research aims at developing the new concept of "Molecular hydrogen-originated protonic acid site" and elucidating the catalytic features caused by the surface protons formed from molecular hydrogen.To elucidate the factors determining the interaction of hydrogen with the surface of Pt/SO_4^<2->-ZrO_2, the rate of hydrogen adsorption and generation of acidic sites were measured for different types of Pt/SO_4^<2->-ZrO_2 whose surface acidities were controlled. It was revealed that the rate and hydrogen uptake increases with an increase in the surface acidity.It was also proven fro the first time that the formation of protonic acid sites occurs on the surfaces of Pt/WO_3-ZrO_2 and WO_3-ZrO_2 on heating in the presence of hydrogen. The formation of the protons was much easy for Pt/WO_3-ZrO_2 than for WO_3-ZrO_2. The mechanism for the formation of the protons on WO_3-ZrO_2 was elucidated in relation with the surface structure. The kinetic analysis of the hydrogen adsorption revealed that the slow steps were spillover step for Pt/WO3-ZrO2 and and the surface diffusion step for WO_3-ZrO_2.The catalytic activities of Pt/SO_4^<2->-ZrO_2 and Pt/WO_3-ZrO_2 for heptane isomerization were measured to determine the factors governing the selectivity. Pt/WO_3-ZrO_2 exhibited higher selectivity than Pt/SO_4^<2->-ZrO_2 while the conversion rate was higher for Pt/SO_4^<2->-ZrO_2. It was concluded that the selectivity is governed by the acid strength and the rate of surface diffusion of hydrogen. The participation of the spiltover hydrogen in the isomerization mechanisms is clarified.