Experimental Microkinetic Approach of De-NOx by NH3 on V2O5/WO3/TiO2 Catalysts. 4. Individual Heats of Adsorption of Adsorbed H

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• 作者：Fran莽ois Giraud ; Julien Couble ; Christophe Geantet ; Nolven Guilhaume ; Eric Puzenat ; S茅bastien Gros ; Lynda Porcheron ; Mohamed Kanniche ; Daniel Bianchi
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：July 16, 2015
• 年：2015
• 卷：119
• 期：28
• 页码：16089-16105
• 全文大小：745K
• ISSN：1932-7455

文摘

The present study is a part of an experimental microkinetic approach of the removal of NO_x from coal-fired power plants by reduction with NH₃ on V₂O₅/WO₃/TiO₂ catalysts (NH₃-selective catalytic reduction, NH₃-SCR). It is dedicated to the characterization of the heats of adsorption of molecularly adsorbed H₂O_ads species formed on sulfate-free and sulfated TiO₂ supports. Water, which is always present during the NH₃-SCR, may be in competition and/or react (formation of NH₄⁺) with the adsorbed NH₃ species controlling the coverage of the adsorbed intermediate species of the reaction. Mainly, an original experimental procedure named adsorption equilibrium infrared spectroscopy (AEIR) previously used for the adsorption of NH₃ species on the same solids is adapted for the adsorption of H₂O. At T_a = 300 K and for P_H2O 鈮?1 kPa, three main H₂O_ads species are formed (associated with a minor amount of dissociated H₂O species) on the two TiO₂ solids. The species are identified by the positions of their IR bands in the 3750鈥?000 cm^鈥? range. Considering the decreasing order of stability, they are (a) coordinated to strong (L₂) and weak (L₁) Lewis sites and denoted H₂O_ads-L2 and H₂O_ads-L1, respectively, and (b) hydrogen bonded to the H₂O_ads-L species and on O^{2鈥?/sup>/OH sites of the solids (denoted H₂O_wads). The three species have a common well-defined 未_H2O IR band at a position in the range 1640鈥?610 cm鈥? according to the total coverage of the surface. According to the AEIR method, the evolution of the intensity of this IR band during the increase in the adsorption temperature T_a in isobaric condition provides the evolution of the average coverage of the three species and then to their individual heats of adsorption as a function of their coverage. It is shown that there are no significant differences on the two TiO₂ solids. In particular, the heat of adsorption of the H₂O_ads-L2 species varies from 鈭?14 to 61 kJ/mol at low and high coverages respectively, indicating that it can be present in the experimental conditions of the NH₃-SCR. In a forthcoming article, the competitive chemisorptions and reaction between adsorbed H₂O and NH₃ species are studied and modeled on the TiO₂ supports and model and commercial V₂O₅/WO₃/TiO₂ catalysts.}