Preparation, characterization and reactivity of V- and/or Co-containing AlPO-18 materials (VCoAPO-18) in the oxidative dehydrogenation of ethane Patricia Concepci  on a , Teresa Blasco a , Jos  e M. L opez Nieto a, * , Alejandro Vidal-Moya a , Arturo Mart  ınez-Arias b a Instituto de Tecnolog  ıa Qu  ımica, Univ. Politecnica de Valencia UPV-CSIC, Avenida de los Naranjos s/n, 46022 Valencia, Spain b Instituto de Cat alisis y Petroleoqu  ımica, c/ Marie Curie, Campus Cantoblanco, 28049 Madrid, Spain Received 22 May 2003; received in revised form 6 November 2003; accepted 9 November 2003 Abstract V- and/or Co-containing aluminophosphates with AEI structure (CoAPO-18, VAPO-18 and VCoAPO-18) have been prepared by hydrothermal synthesis, characterized by several physicochemical techniques (S BET , thermogravimetric analysis, XRD, solid state MAS NMR, UV–vis, EPR, TPD), and tested in the oxidative dehydrogenation of ethane. The results obtained by the spectroscopic techniques employed here suggest that V (V 5þ and VO 2þ ) and Co 2þ atoms are isomorphically incorporated into the alumino- phosphate framework, although some vanadium is involved in an extraframework oxide, especially at high contents. Upon calci- nation in air of the V, Co-containing samples with the AEI structure, most vanadium and cobalt oxidate to V 5þ and Co 3þ and present redox activity, while only Co-containing materials posses acid properties. Comparison with Co-containing AlPO-5 evidences that the strength of acid sites depends on the framework structure. VCoAPO-18 catalysts are active and selective in the oxidative dehydrogenation of ethane with selectivities to ethylene higher than the corresponding VAPO-18 or CoAPO-18. The catalytic results give evidence of the incorporation of V and Co into the AlPO-18 structure, and the segregation of an oxide phase in V-rich samples. The V- and/or Co-containing AlPO-18 are more selective in the ODH of ethane than the corresponding materials with AFI structure (i.e. VCoAPO-5, VAPO-5 or CoAPO-5). Ó 2003 Elsevier Inc. All rights reserved. Keywords: Vanadium and/or cobalt containing aluminophosphate; AEI microporous material; Catalyst characterization (XRD, 31 P and 27 Al MAS NMR, EPR, Diffuse reflectance, TPD-NH 3 ); Oxidation catalysts; Oxidative dehydrogenation of ethane to ethylene 1. Introduction A strong research effort has been devoted in the last two decades to develop active and selective catalysts for the oxidative dehydrogenation (ODH) of short chain alkanes to the corresponding olefins [1–6]. A key factor in the design of efficient catalysts in the ODH reactions is the site isolation [4–6]. Besides this, the reducibility of the active sites and the acid–base properties of the cat- alysts are also important factors in the enhancement of the catalytic performance by modifying the rate of the alkane conversion and the desorption rate of the reac- tion intermediates [1–6]. Isomorphous substitution of active metal species into microporous and mesoporous materials is an attractive strategy to design new effective catalysts for gas phase selective oxidation reactions [6]. This is the case of V- silicalite [7,8] and VAPO-5 [9,10], which possess isolated vanadium species, active and selective in the ODH of propane to propylene. More recently, other V-contain- ing microporous and mesoporous catalysts have been reported to be selective in the oxydehydrogenation (ODH) of short chain alkanes [11–16]. However, the results indicate that the catalytic activity of vanadium is strongly influenced by its local environment and by the co-existence of acid sites in the host material [9–16]. An inert matrix seem to be required to achieve high selec- tivities in the ODH of propane [7–10], while acid materials are preferred for the ODH of ethane [14–18]. In the latter reaction, the selectivity to ethylene is * Corresponding author. Tel.: +34-96-387-7808; fax: +34-96-387- 7809. E-mail address: jmlopez@itq.upv.es (J.M. L opez Nieto). 1387-1811/$ - see front matter Ó 2003 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2003.11.005 www.elsevier.com/locate/micromeso Microporous and Mesoporous Materials 67 (2004) 215–227