Hydrogenation of Aromatic Hydrocarbons over Supported Pt Catalysts .III. Reaction Models for Metal Surfaces and Acidic Sites on Oxide Supports
Hydrogenation of Aromatic Hydrocarbons over Supported Pt Catalysts .III. Reaction Models for Metal Surfaces and Acidic Sites on Oxide Supports
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DOI：
10.1006/jcat.1993.1299
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发表时间：
1993-10
影响因子：
7.3
通讯作者：
S. Lin;M. Vannice
中科院分区：
文献类型：
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作者：
S. Lin;M. Vannice
在317 ~ 364 K温度范围内，对一系列负载型铂催化剂上苯和甲苯加氢反应的16种不同反应模型进行了评价。对于苯加氢的Pt表面上，只有一个模型是一致的所有的数据调用的第一个H原子的芳香环的速率决定步骤（RDS），以及同时形成一个主要的H-缺乏表面物种。该模型还描述了甲苯在Pt上的加氢反应。缺氢物种为苯基（或甲苯基）。为了解释与酸性载体获得的较高的速率，一个类似的模型，涉及溢出的氢和芳香族分子吸附在酸性网站被认为是，它准确地拟合归因于支持表面的速率数据。然而，另一个模型提出的第二个H原子作为RDS在这些酸网站上，没有任何H-缺乏物种的抑制不能被忽视。苯的活化能为12 ± 2 kcal/mol。甲苯和二甲苯在Pt和Pd表面以及酸性位点上的氢化归因于例如环己二烯中间体的形成。1.3-环己二烯具有12.4千卡/摩尔的正生成自由能。这个模型似乎是一般性的，足以描述氢化的许多芳香族分子超过第VIII族金属。
Abstract Sixteen different reaction models were evaluated for benzene and toluene hydrogenation between 317 and 364 K over a family of supported Pt catalysts. For benzene hydrogenation on the Pt surface, only one model was consistent with all the data-that which invoked the addition of the first H atom to the aromatic ring as the rate-determining step (RDS) as well as the concurrent formation of a predominant H-deficient surface species. This model also described toluene hydrogenation on Pt. and the H-deficient species was indicated to be the phenyl (Or tolyl) group. To explain the higher rates obtained with acidic supports, a similar model involving spilled-over hydrogen and aromatic molecules adsorbed on acid sites was considered, and it accurately fit the rate data attributed to the support surface. However, another model proposing addition of the second H atom as the RDS on these acid sites and no inhibition by any H-deficient species could not be discounted. The similar activation energies of 12 ± 2 kcal/mol for benzene. toluene, and xylene hydrogenation on Pt and Pd surfaces as well as on acid sites is attributed to the formation of a cyclohexadiene intermediate; for example. 1.3-cyclohexadiene has a positive free energy of formation of 12.4 kcal/mol. This model appears to be general enough to describe the hydrogenation of numerous aromatic molecules over Group VIII metals.