The surface chemistry of supported chromium catalysts (Cr/SiO, -AI , O, ) has been systematically investigated as a function of the support composition (Si : Al ratio) and the Cr oxide loading by a combination of diffuse reflectance spectroscopy (DRS), Raman spectroscopy (RS), X-ray Absorption spectroscopy (EXAFS-XANES) and temperature-programmed reduction (TPR). Combination of all the obtained results by these characterization techniques leads to a uniform interpretation and general picture of surface Cr. On hydrated surfaces, the molecular structure of the Cr oxide species depends on the isoelectric point of the oxide support and the Cr loading : more polymerized Cr oxide species correspond to higher Cr loading and silica content of the support. After calcination, the Cr oxide species are anchored onto the surface by reaction with surface hydroxy groups of the supports. On alumina the reaction starts with the most basic OH groups on alumina. This suggests that the anchoring process is an acid-base reaction. On calcined surfaces, the polymerization of the anchored Cr oxide species and the amount of Cr, O, clusters increases with silica content and Cr loading. Reduced Cr samples possess both Cr2+ and Cr3+, the relative concentrations of which are support and loading dependent: lower Cr2+ : Cr3+ ratios correspond to higher Cr loading and alumina content of the support.

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Inhibiting and deactivating effects of water on the selective catalytic reduction (SCR) of NO with NH3 over MnOx/Al2O3 Kijlstra, W.S.; Daamen, J.C.M.L.; van de Graaf, J.M.; van der Linden, B.; Poels, E.K.; Bliek, A. Published in:Applied Catalysis B-Environmental DOI:10.1016/0926-3373(95) Link to publication Citation for published version (APA):Kijlstra, W. S., Daamen, J. C. M. L., van de Graaf, J. M., van der Linden, B., Poels, E. K., & Bliek, A. (1995). Inhibiting and deactivating effects of water on the selective catalytic reduction (SCR) of NO with NH3 over MnOx/Al2O3. Applied Catalysis B-Environmental, 7(3/4), 337-357. DOI: 10.1016/0926-3373(95)00052-6 General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. AbstractThe effect of water on the selective catalytic reduction (SCR) of nitric oxide with ammonia over alumina supported with 2-l 5 wt.-% manganese oxide was investigated in the temperature range 385-600 K, with the emphasis on the low side of this temperature window. Studies on the effect of l-5 vol.-% water vapour on the SCR reaction rate and selectivity were combined with TPD experiments to reveal the influence of water on the adsorption of the single SCR reactants. It turned out that the activity decrease due to water addition can be divided into a reversible inhibition and an irreversible deactivation. Inhibition is caused by molecular adsorption of water. TPD studies showed that water can adsorb competitively with both ammonia and nitric oxide. Additional kinetic experiments revealed that adsorbed ammonia is present in excess on the catalyst surface, even in the presence of water. Reduced nitric oxide adsorption is responsible for the observed reversible decrease in the reaction rate; the fractional reaction order changes from 0.79 in the absence of water to 1.07 in its presence. Deactivation is probably due to the dissociative adsorption of water, resulting in the formation of additional surface hydroxyls. As the amount of surface hydroxyls formed is limited to a saturation level, the deactivating effect on the catalyst is limited too. The additional hydroxyls condense and desorb in the temperature range 525-775 K, resulting in a lower degree of deactivation at higher temperature. A high temperature treatment at 775 K results in a complete regeneration....