Applied Catalysis A: General 193 (2000) 123–128 Aromatization of isophorone to 3,5-xylenol over Cr 2 O 3 /SiO 2 catalysts B. David Raju, K.S. Rama Rao, G.S. Salvapathi, P.S. Sai Prasad 1 , P. Kanta Rao ∗ Catalysis and Physical Chemistry Division, Indian Institute of Chemical Technology, Hyderabad – 500 007, India Received 16 July 1999; accepted 1 September 1999 Abstract SiO 2 supported Cr 2 O 3 catalysts with varying Cr content have been prepared and are characterized by nitrogen adsorption, low temperature oxygen chemisorption (LTOC), X-ray diffraction (XRD) and electron spin resonance (ESR) techniques. Aromatization of isophorone is carried out on these catalysts. A good correlation obtained between the oxygen uptake and aromatization yield helped to identify the nature of the active species. ©2000 Elsevier Science B.V. All rights reserved. Keywords: Aromatization; Isophorone; 3,5-xylenol; Cr 2 O 3 /SiO 2 catalysts 1. Introduction With the ever increasing concern for environmental protection, the quality aspect of the catalyst (selec- tivity, which in turn improves the yield) attains more and more importance compared to its quantity aspect (activity); more so in case of complex reactions that exhibit several reaction pathways. Under these circum- stances, it becomes imperative to look into the actual active site that drives the reaction towards the specified product. An attempt in this direction is the study on the aromatization of isophorone to produce 3,5-xylenol. 3,5-xylenol (the main component of the aromatiza- tion products) is an important intermediate in the pro- duction of Vitamin E, anti-oxidants, anti-microbial agents, laminating paper adhesives etc [1–7]. Alky- lation of phenol, the conventional route to synthesiz- ing 3,5-xylenol, gives very low selectivity. Catalytic aromatization of isophorone has subsequently been ∗ Corresponding author. E-mail address: saiprasad@iict.ap.nic.in (P.S. Sai Prasad). 1 Co-corresponding author. proved to be promising as an economically viable al- ternative for the above route. The reaction, which pro- ceeds by the dienone–phenol re-arrangement on the catalyst surface, leads to the formation of less num- ber of by-products [8,9]. Thus, identification of the active species is an important and challenging task to improve product selectivity. Aromatizaion of isophorone proceeds by the forma- tion of several side products, as illustrated in Fig. 1. Earlier work, from our laboratory, on this reaction has revealed some interesting results. The reaction carried out on V 2 O 5 /Al 2 O 3 and MoO 3 /Al 2 O 3 has resulted in the production of large quantities of isoxylitones, the decomposition products of isophorone [10]. This has been explained as due to the presence of polymeric oxide species of catalysts possessing strong acidity. Reaction of isophorone on -Al 2 O 3 alone has revealed that acid centres on the surface of the catalyst acti- vate decomposition of isophorone [11] and also lead to coke formation. Once coke formation starts cover- ing the acid centres, selectivity towards 3,5-xylenol is enhanced. These observations have been confirmed by using carbon-covered alumina (CCA) as the support 0926-860X/00/$ – see front matter ©2000 Elsevier Science B.V. All rights reserved. PII:S0926-860X(99)00418-4