3.氧化物表面酸性的测定酸性中心一般看作是氧化物催化剂表面的活性中心。在催化裂化、异构化、聚合等反应中烃类分子和表面酸性中心相互作用形成正碳离子,是反应的中间化合物。正碳离子理论可以成功地解释烃类在氧化物表面上的反应,也对酸性中心的存在提供了强有力的证明。为了进一步表征固体酸性催化剂的性质,需要测定表面酸性中心的类型(L酸、B酸)、强度和酸量。测定表面酸性的方法很多,如碱滴定法、碱性气体吸附法、热差法等。但这些方法都不能区别L酸中心和B酸中心。红外光谱方法被广泛用来研究固体表面酸性,可以有效地区分L酸和B酸。利用红外光谱研究表面酸性常常利用氨、吡啶、三甲基胺、正丁胺等碱性吸附质,其中应用比较广泛的是吡啶和氨。下面着重讨论利用吡啶吸附的红外光谱来研究固体酸。 Parry首先提出了利用C_5H_5N吸附测定氧化物 3. Determination of oxide surface acidity Acid center is generally regarded as the active center of the oxide catalyst surface. In the catalytic cracking, isomerization, polymerization and other reactions in the hydrocarbon molecules and the surface acid centers interact to form positive carbon ions, the reaction of the intermediate compounds. The theory of normal carbon ions can successfully explain the reaction of hydrocarbons on the oxide surface and also provide a strong proof of the existence of acidic sites. To further characterize the nature of the solid acidic catalyst, the type of acid sites (L acid, B acid), strength, and acid content of the surface need to be determined. There are many ways to determine the surface acidity, such as alkali titration, alkaline gas adsorption, thermal differential method. However, these methods do not distinguish between L acid sites and B acid sites. Infrared spectroscopy is widely used to study the surface acidity of solids, which can effectively distinguish between L acid and B acid. The use of infrared spectroscopy surface acidity often use ammonia, pyridine, trimethylamine, n-butylamine and other alkaline adsorbates, which are widely used pyridine and ammonia. The following focuses on the use of pyridine adsorption of infrared spectroscopy to study the solid acid. Parry first proposed the use of C_5H_5N adsorption determination of oxides