Temporal Analysis of Products Study of HCl Oxidation on Copper- and Ruthenium-Based Catalysts

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• 作者：Amol P. Amrute ; Cecilia Mondelli ; Miguel A. G. Hevia ; Javier Pe虂rez-Rami虂rez
• 刊名：Journal of Physical Chemistry C
• 出版年：2011
• 出版时间：February 3, 2011
• 年：2011
• 卷：115
• 期：4
• 页码：1056-1063
• 全文大小：295K
• 年卷期：v.115,no.4(February 3, 2011)
• ISSN：1932-7455

文摘

The use of in situ approaches to study mechanisms of experimentally demanding and complex reactions under conditions of practical relevance opens doorways to discover new or improved heterogeneous catalysts. A representative example within this category of reactions is the gas-phase oxidation of HCl to Cl₂ (Deacon process). Studies in the temporal analysis of products (TAP) reactor complemented by flow experiments at ambient pressure evidenced pronounced mechanistic differences between copper catalysts (CuO, CuCl, and CuCl₂, that is, Deacon-like catalysts) and RuO₂ (the basis of the recent Sumitomo鈥檚 catalyst for large-scale Cl₂ production). RuO₂ is 1 order of magnitude more active than the copper-based materials. HCl oxidation on RuO₂ obeys a Langmuir鈭扝inshelwood mechanism in the presence of adsorbed species over a partially chlorinated surface. HCl oxidation on the copper catalysts is more complex: all the samples experience bulk changes, namely, chlorination, resulting in multiphase materials. Besides, lattice species also participate in the reaction. In particular, fresh CuO follows a Mars鈭抳an Krevelen mechanism, in which lattice oxygen is active for Cl₂ and H₂O production, leading to bulk chlorination, whereas for copper chlorides activated upon exposure to the Deacon mixture and used CuO, a combination of Mars鈭抳an Krevelen and Langmuir鈭扝inshelwood mechanisms seems to be a better description. Investigations over the copper-based phases and characterization of the fresh and used samples by X-ray diffraction indicate that a copper (hydr)oxychloride is the main active phase. Our mechanistic study suggests that a more active and particularly stable copper catalyst can be achieved by controlling the degree of surface chlorination. This is more or less a self-regulated process on the ruthenium-based catalyst.