Experimental Microkinetic Approach of De-NOx by NH3 on V2O5/WO3/TiO2 Catalysts. 3. Impact of Superficial WOz

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• 作者：Fran莽ois Giraud ; Christophe Geantet ; Nolven Guilhaume ; St茅phane Loridant ; 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 9, 2015
• 年：2015
• 卷：119
• 期：27
• 页码：15401-15413
• 全文大小：639K
• ISSN：1932-7455

文摘

The present article is dedicated to the measurement of the individual heats of adsorption of adsorbed NH₃ species on WO₃/TiO₂ and V₂O₅/WO₃/TiO₂ (a catalyst for the selective catalytic reduction of NO_x by NH₃ on stationary sources, briefly NH₃-SCR) model and commercial solids by using an original experimental procedure (adsorption equilibrium infrared spectroscopy, AEIR) developed in parts 1 [Giraud et al. J. Phys. Chem. C 2014, 118, 15664] and 2 [Giraud et al. J. Phys. Chem. C 2014, 118, 15677] for the adsorbed NH₃ species on TiO₂ and V₂O₅/TiO₂ solids. In agreement with the literature, Raman and Fourier transform infrared spectra indicate the presence of well-dispersed V_xO_y and WO_z entities on the different solids. For NH₃ adsorption at pressure P_a < 0.5 kPa and temperature T_a in the range 300鈥?73 K, the modifications of the V鈺怬 and W鈺怬 overtone IR bands indicate that these entities are involved in the adsorption of NH₃, forming NH_3ads-L and NH₄⁺ species on Lewis and Br酶nsted sites, respectively. For T_a = 300 K, it is shown that four adsorbed NH₃ species are formed on the WO_z-containing catalysts: two are adsorbed on Lewis sites, named NH_3ads-L1 and NH_3ads-L2, and two are adsorbed on Br酶nsted sites, named NH₄⁺-1 and NH₄⁺-2 (鈥?鈥?and 鈥?鈥?indicate the increasing order of stability of the different species). Using the 未_as IR band characteristic of the NH_3ads-L (鈭?600 cm^鈥?) and NH₄⁺ (鈭?445 cm^鈥?) species, it is shown that the AEIR method provides the individual heats of adsorption of the four adsorbed species at low and high coverages of their adsorption sites. For instance, on a model 0.5% V₂O₅/6% WO₃/TiO₂ catalyst the heats of adsorption of the two more stable species (which slightly change with the exact composition of the solid) at low and high coverages of the sites are 105 and 148 kJ/mol for NH_3ads-L2 and 78 and 135 kJ/mol for the NH₄⁺-2 species, respectively. These values indicate that the presence of WO_z increases significantly the heat of adsorption of the NH₄⁺ species, as compared to TiO₂ and V₂O₅/TiO₂, explaining that both NH_3ads-L2 and NH₄⁺-2 species can be present in the experimental conditions of NH₃-SCR.