Catalysis Today 191 (2012) 25–31 Contents lists available at SciVerse ScienceDirect Catalysis Today jou rn al h om epage: www.elsevier.com/locate/cattod Acid-activated vermiculites as catalysts of the DeNO x process Lucjan Chmielarz a,∗ , Magdalena Wojciechowska a , Małgorzata Rutkowska a , Andrzej Adamski a , Agnieszka W˛ egrzyn a , Andrzej Kowalczyk a , Barbara Dudek a , Paweł Boro ´ n a , Marek Michalik b , Adam Matusiewicz c a Jagiellonian University, Faculty of Chemistry, Ingardena 3, 30-060 Kraków, Poland b Jagiellonian University, Institute of Geological Sciences, Oleandry 2a, 30-063 Kraków, Poland c The Institute of Ceramics and Building Materials, Glass and Building Materials Division, Cementowa 8, 31-983 Kraków, Poland a r t i c l e i n f o Article history: Received 31 August 2011 Received in revised form 20 February 2012 Accepted 19 March 2012 Available online 19 April 2012 Keywords: Vermiculite Acid-activation DeNOx SCR NO-process a b s t r a c t Vermiculite was treated with 0.8 M solutions of hydrochloric and sulphuric acids for 2, 8, and 24 h. The obtained materials were characterized with respect to their composition (XRF), structure (XRD, FTIR, UV–vis-DRS), texture (BET), surface acidity (NH 3 -TPD) and catalytic properties. Modification of vermi- culite with acids significantly increased its surface area and pore volume and led to partial leaching of iron, aluminium and magnesium ions from its octahedral sheets. Efficiency of the leaching process depended on its duration and the nature of acid used. Acid treatment strongly modified the vermiculite structure leading to a distinct increase of its catalytic activity in the selective catalytic reduction of nitric oxide (SCR NO) process. In a series of the studied samples the best catalytic performance was found for vermiculite treated with sulphuric acid for 8 h. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Cationic layered clays are excellent raw materials for the catalysts preparation [e.g. 1]. Various methods for the catalytic activation of clay minerals, including intercalation of metal oxides into their interlayer spaces [e.g. 2, 3], were proposed. One of the cheapest and most effective methods of the clay activation is based on their acid treatment [4]. For example, acid-activated montmorillonites were used as commercial catalysts for crack- ing process of heavy oil fractions [5]. More recently, also other important reactions based on acid treated clays, including alky- lation (e.g. alkylation of benzene with 1-dodecane), acylation (e.g. acylation of diisobutylene with acetic anhydride), dimer- ization (e.g. dimerization of -methylstyrene), oligomerization (e.g. oligomerization of 1,3-diisopropenylbenzene), izomerization (e.g. izomerization of -alkylnaphtalenes into -alkylnaphtalenes), etherification (e.g. synthesis of methyl-tert-butyl ether from tert- butanol and methanol), estrification (e.g. estrification of myristic acid with propylene) and condensation (e.g. aldol condensation of cyclohexanone) were reported [6]. Acid treated montmorillonites were reported to be the most often used clays in various catalytic processes [6] and their catalytic activation was related to the mod- ification of the surface acidic properties. The other cationic layered ∗ Corresponding author. Tel.: +48 126632006; fax: +48 126340515. E-mail address: chmielar@chemia.uj.edu.pl (L. Chmielarz). clays, especially in the form of acid treated minerals, were sig- nificantly less intensively studied as potential catalysts. However, there is a plethora of natural clay minerals which vary in their chemical composition, density of layer charge, texture, morphol- ogy, surface acidity and cation exchange capacity. Thus, such a broad variety of clays of different properties gives a rare possibility to produce catalysts for dedicated applications. Vermiculite is a cationic layered clay which contains a signif- icant amount of iron as natural component. On the other hand, iron was reported to be catalytically active in the SCR NO x reac- tion [e.g. 7, 8]. Unfortunately, iron ions are located mainly in the octahedral sheets of vermiculite and therefore, their accessibility is rather limited. Thus, as it was shown in our previous studies, the catalytic activity of raw vermiculite in the SCR NO x process is very low [4]. However, treatment of vermiculite with a solution of nitric acid effectively activated this clay in the SCR NO x reaction [4]. Acid treatment resulted in a partial leaching of cations, includ- ing Fe 3+ ions, from the octahedral sheets of vermiculite and their consecutive deposition in the form of both isolated cations or aggre- gated metal oxide clusters on the clay surface. Thus, acid treatment resulted in transfer of iron species into positions accessible for reac- tants. Additionally, acid treatment significantly increased surface area and porosity of vermiculite due to its partial transformation into amorphous silica and possibly also deposition of metal oxide clusters into interlayer space of this clay mineral. Therefore, such simple and cheap method used for the vermiculite modification resulted in a production of active, selective and non-toxic catalyst 0920-5861/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cattod.2012.03.042