Influence of dealumination and treatments on the chromium speciation in zeolite CrBEA Konstantin Hadjiivanov a, * , Anna Penkova a , Radoslav Kefirov a , Stanislaw Dzwigaj b,c, * , Michel Che b,c,d a Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria b UPMC Univ. Paris 6, UMR 7609, Laboratoire de Réactivité de Surface, 4 Place Jussieu, 75252 Paris Cedex 05, France c CNRS, UMR 7609, Laboratoire de Réactivité de Surface, 4 Place Jussieu, 75252 Paris Cedex 05, France d Institut Universitaire de France, France article info Article history: Received 4 March 2009 Received in revised form 21 April 2009 Accepted 28 April 2009 Available online 5 May 2009 Keywords: Adsorption BEA Carbon monoxide Chromium Dealumination, nitrogen monoxide Speciation TPR FTIR abstract Two samples of chromium-containing BEA zeolite, CrAlBEA and CrSiBEA prepared by different methods, are investigated by XRD, TPR and FTIR of CO adsorbed at 100 K and NO at ambient temperature. CrAlBEA is prepared by conventional ion exchange, and CrSiBEA, by a two-step post-synthesis method (dealumi- nation of TEABEA zeolite by treatment with nitric acid followed by incorporation of chromium into resulting SiBEA by impregnation with Cr(NO 3 ) 3 aqueous solution). In both calcined and activated sam- ples, the major part of chromium is in the form of Cr 6+ . A small amount of Cr 3+ is also detected in CrAlBEA by adsorption of CO (a Cr 3+ –CO band at 2189 cm 1 ) and NO (a Cr 3+ –NO band at 1875 cm 1 ). The TPR pattern of CrSiBEA exhibits a main peak at 726 K, while two main peaks, at 520 and 760 K are observed with CrAlBEA. All these peaks are due to reduction of Cr 6+ species. In line with the TPR results, the speciation of chromium in CrSiBEA does not change upon treatment of the sample at 573 K in H 2 . In contrast, the same treatment leads to the reduction of CrAlBEA with creation of Cr 3+ as shown by the appearance, after CO adsorption, of Cr 3+ –CO bands at 2208–2202 cm 1 . When CrAlBEA is treated with H 2 at 773 K, some Cr 2+ appear which can form tricarbonyls (as evidenced by IR bands at 2214, 2206 and 2179 cm 1 ). The treatment of CrSiBEA with H 2 at 773 K leads to the formation of similar Cr 2+ sites. However, with this sample, some Cr 3+ is also present, as shown by a Cr 3+ –CO band at 2198 cm 1 appear- ing after CO adsorption. In the presence of NO, Cr 2+ ions are slowly oxidized to Cr 3+ . These results dem- onstrate the important effect of dealumination of BEA zeolite and the treatment of Cr-containing BEA on the chromium speciation. Ó 2009 Elsevier Inc. All rights reserved. 1. Introduction Metal-containing zeolites have found wide applications in adsorption and catalysis. It is now well established that the zeolite matrix strongly affects the state and the properties of the metal cations. For instance, the cations exchanged in zeolites are charac- terized by a low coordination number with respect to the frame- work oxygen which allows coordination of more than one guest molecule [1–10]. However, the metal cation properties are deter- mined by many factors, such as the nature of the exchanged cation, its oxidation state, its radius and its position in the zeolite. The presence of aluminum in zeolites is a reason for their low hydrothermal stability, explaining why, in some cases, siliceous zeolites can be advantageous as compared to Al-containing zeolites. However, dealumination of the latter suppresses their ion-exchange capacity and the cations introduced in different ways are generally characterized by properties differing from those of exchanged cations. However, in some cases cations in siliceous zeolites can also be highly coordinatively unsaturated [11,12]. Moreover, cations introduced into siliceous zeolites can occupy framework positions and generate new properties of the zeolite [12–17]. We compared earlier the speciation of nickel and cobalt cations in two BEA zeolites: HAlBEA and dealuminated SiBEA [8,18]. It was found that the presence of aluminum strongly affected the cation speciation and, in consequence, also the properties of Ni- and Co- containing BEA zeolites. Chromium-containing zeolites have important application in catalysis [19–22]. For instance, it has been reported that Cr-ZSM- 5 is active in the elimination of chlorinated VOCs and oxidation of alcohols leading to a high yield of ketones [19,20]. Cr/SiO 2 cata- lysts are well known to be active in polymerization of ethylene and 1387-1811/$ - see front matter Ó 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2009.04.038 * Corresponding authors. Tel.: +359 2 9793598; fax: +359 2 8705024 (K. Hadjiivanov), tel.: +33 1 44275291; fax: +33 1 44276033 (S. Dzwigaj). E-mail addresses: kih@svr.igic.bas.bg (K. Hadjiivanov), stanislaw.dzwigaj@ upmc.fr (S. Dzwigaj). Microporous and Mesoporous Materials 124 (2009) 59–69 Contents lists available at ScienceDirect Microporous and Mesoporous Materials journal homepage: www.elsevier.com/locate/micromeso