Experimental Microkinetic Approach of De-NOx by NH3 on V2O5/WO3/TiO2 Catalysts. 1. Individual Heats of Adsorption of Adsorbed N

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• 作者：Fran莽ois Giraud ; Christophe Geantet ; Nolven Guilhaume ; S茅bastien Gros ; Lynda Porcheron ; Mohamed Kanniche ; Daniel Bianchi
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：July 24, 2014
• 年：2014
• 卷：118
• 期：29
• 页码：15664-15676
• 全文大小：525K
• ISSN：1932-7455

文摘

The present study is dedicated to the development of experimental procedures allowing the measurement of the individual heats of adsorption of adsorbed NH₃ species on a sulfate-free TiO₂ solid (P25 from Degussa). This solid has been selected because it is frequently used as support of V₂O₅鈥?or/and WO₃鈥揟iO₂ model catalysts for the understanding of the surface processes implicated in the selective catalytic reduction of NO_x by NH₃ (NH₃-SCR). Two original analytical procedures denoted adsorption equilibrium infrared spectroscopy (AEIR) and temperature-programmed adsorption equilibrium (TPAE) (developed in previous works) were applied. These methods are based on (a) the experimental measurement of the change in the adsorption equilibrium coverage of the individual adsorbed species in isobar conditions and (b) the comparison of the experimental data to an adsorption model. It is shown that in the ranges of the ammonia partial pressures and reaction temperatures of the NH₃-SCR process, only two adsorbed NH₃ species on Lewis sites (Ti^+未) are detected on the solid dehydrated at 673 K. These species noted NH_3ads-L1 and NH_3ads-L2 are differentiated by their 未_s NH₃ IR bands at 300 K (1149 and 1228 cm^鈥?, respectively), whereas their 未_as IR bands are at the same position (1596 cm^鈥?). The AEIR and TPAE methods indicate that the heats of adsorption of the NH_3ads-L1 and NH_3ads-L2 species (noted E_L1(胃) and E_L2(胃) accuracy 卤 5 kJ/mol) vary linearly with their respective coverages 胃 from E_L1(1) = 56 kJ/mol to E_L1(0) = 105 kJ/mol and from E_L2(1) = 105 kJ/mol to E_L2(0) = 160 kJ/mol. These values are compared to (a) isosteric heat of adsorption provided by the Clausius鈥揅lapeyron method and (b) literature data using temperature-programmed desorption, microcalorimetry, and DFT calculations. Forthcoming articles show that the simplicity of the analytical procedures allows studying the impact of the presence of sulfate and VO_x/WO_y depositions over TiO₂ on the nature and heats of adsorption of adsorbed NH₃ species.