This journal is c The Royal Society of Chemistry 2011 Catal. Sci. Technol., 2011, 1, 1383–1392 1383 Cite this: Catal. Sci. Technol., 2011, 1, 1383–1392 Catalytic properties of cobalt and nickel ferrites dispersed in mesoporous silicon oxide for ethylbenzene dehydrogenation with CO 2 Tiago Pinheiro Braga, a Ba´rbara Maria Campos Sales, a Antonio Narcisio Pinheiro, a W. T. Herrera, b E. Baggio-Saitovitch b and Antoninho Valentini* a Received 16th May 2011, Accepted 15th August 2011 DOI: 10.1039/c1cy00176k A polymeric precursor method was applied to synthesize catalysts of the general formula MFe 2 O 4 (M = Co and Ni) in order to contribute to studies on ethylbenzene dehydrogenation in the presence of CO 2 . The catalysts were characterized by TG, H 2 -TPR, XRD, Mossbauer spectroscopy (MS), N 2 adsorption/desorption isotherms and TPD-CO 2 . Investigations using XRD and MS revealed that the spinel structures of CoFe 2 O 4 and NiFe 2 O 4 phases were formed. The catalytic results suggested that materials with a spinel structure are particularly interesting for ethylbenzene dehydrogenation. Compared to the other catalysts synthesized the sample containing cobalt ferrite showed higher conversion and good styrene selectivity. The analysis of the spent catalyst (DRX) showed that the CoFe 2 O 4 phase was stable under the reaction conditions and that a coke (TG) deposit was more pronounced for the NiFeSi. 1. Introduction Catalytic ethylbenzene dehydrogenation in the presence of steam (reaction (1)) is a representative process for the produc- tion of styrene, an important monomer for synthetic polymers. 1–4 C 6 H 5 –CH 2 CH 3 (g) " C 6 H 5 –CH Q CH 2 (g) + H 2 (g) (1) The catalysts used in the above process are usually based on iron oxide, which can be further modified by the addition of promoters, such as potassium, chromium, calcium and cerium. 5 Due to relatively fast catalytic deactivation, many research groups have dedicated their efforts to synthesize catalysts with better stability. 6–8 Currently, researchers have studied the use of carbon dioxide (CO 2 ) as a co-feeder gas in ethylbenzene dehydrogen- ization (reaction (2)) with the aim of introducing an alternative route to the steam process. 7–10 C 6 H 5 –CH 2 CH 3 (g) + CO 2 (g) " C 6 H 5 –CH Q CH 2 (g) + CO(g) + H 2 O(g) (2) With this goal in mind, a large amount of catalysts with diverse composition have been tested in ethylbenzene dehydrogenization in the presence of CO 2 . 7–11 Nevertheless, the results observed point to the need for more research to improve catalytic stability and thus to decrease the process cost. Various publications have shown that, for catalysts containing hematite as the active phase, magnetite forms during the dehydrogenation reaction, which subsequently affects the conversion of ethylbenzene to styrene. 4,5,9,12 On the other hand, there are some publications pointing to materials with spinel structures, such as ferrites, as presenting remarkable catalytic activity and stability in this reaction. 13,14 In addition to their attractive redox and acid/base properties, spinel structures are versatile compounds offering structural stability. 15 Therefore, materials of the general type MFe 2 O 4 can be used in heterogeneous catalysis. 15–18 Specifically in the ethylbenzene dehydrogenization reaction, the ferrites of Co and/or Ni may be interesting due to their dehydrogenation ability. Additionally, these ions (Co 2+ or Ni 2+ ) may occupy different positions in the spinel structure, changing the interactions of CO 2 with the catalyst surface and the redox properties of the Fe 3+ , which is the main site for ethylbenzene adsorption. 19 The synthesis of ferrites of Co and Ni with nanometric size has already been described in the literature. 20–22 Nevertheless, in order to apply these materials (ferrites of Co and Ni with nanometric size) in heterogeneous catalysis, it is necessary to avoid the sintering process. In this context, we report the synthesis and characterization of MFe 2 O 4 (M = Ni or Co) compounds embedded in SiO 2 with the purpose of studying their catalytic performance for ethylbenzene dehydrogenation in the presence of carbon dioxide. a Langmuir - Laborato ´rio de Adsorc ¸a ˜o e Cata ´lise, Departamento de Quı´mica Analı´tica e Fı´sico-Quı´mica, Universidade Federal do Ceara ´, Campus do Pici, CEP 60455-970, Fortaleza CE, Brasil. E-mail: valent@ufc.br; Fax: +55 85 3366 9982; Tel: +55 85 3366 9951 b Departamento de Fı´sica Experimental, Centro Brasileiro de Pesquisas em Fı´sica, Rua Dr. Xavier Sigaud 150, CEP 22290-180, Rio de Janeiro RJ, Brasil Catalysis Science & Technology Dynamic Article Links www.rsc.org/catalysis PAPER Downloaded on 20 February 2013 Published on 06 September 2011 on http://pubs.rsc.org | doi:10.1039/C1CY00176K View Article Online / Journal Homepage / Table of Contents for this issue