Synthesis of dimethyl ether from methanol over aluminium phosphate and silica–titania catalysts F. Yaripour a, * , F. Baghaei * ,a , I. Schmidt b , J. Perregaard b a Catalysis Research Group, Arak Center, Petrochemical Research and Technology Company NPC, P.O.Box 1435, Arak, Iran b Haldor Topsøe A/S Research Laboratories, Nymøllevej 55, DK-2800, Lyngby, Denmark Received 18 December 2004; accepted 11 May 2005 Available online 24 June 2005 Abstract A series of solid–acid catalysts with different content of components were prepared by co-precipitation (sol–gel) method. These samples comprised silica–titania and modified c-Al 2 O 3 with phosphorus. To determination of optimum ones, the effects of various contents of phosphorus have been investigated. Dehydration of methanol to dimethyl ether (DME) on solid–acid catalysts was stud- ied in a fixed-bed reactor at a temperature of 300 °C under atmospheric pressure and a GHSV of 15,600 h 1 . The catalysts have been characterized using BET, XRD, FT-IR, NH 3 –TPD and elemental analysis techniques and also the results were reported. According to the experimental results, silica–titania catalysts have exhibited low activity for DME synthesis. Phosphorus-modified catalysts have shown better performance compared to the untreated c-Al 2 O 3 . It was found that surface areas increase with increasing in the molar ratio of aluminium-to-phosphorus at aluminium phosphate catalysts. Also, by modifying alumina with phosphorus, it was observed that the surface acidity of aluminium phosphate catalysts decrease with increasing in the molar ratio of Al/P at alu- minium phosphate catalysts. The sample of non-stoichiometric aluminium phosphate (molar ratio of Al/P = 2) have exhibited the best conversion without any by-product. Ó 2005 Elsevier B.V. All rights reserved. Keywords: Methanol; Dehydration; Dimethyl ether; Solid–acid catalysts 1. Introduction Catalytic dehydration of methanol is commercially important for the production of dimethyl ether (DME). During the last few years, with increasingly stringent environmental regulations, DME has received global attention due to its potential use as a clean alter- native fuel for diesel engines [1]. It is also used as an intermediate for producing many valuable chemicals such as lower olefins, methyl acetate, dimethyl sulfate, LPG alternative and power generation [2–6]. Several solid–acid catalysts have been studied for this reaction [2,7–11]. Although c-Al 2 O 3 is an excellent catalyst for the methanol dehydration, but this sample undergo a fairly rapid, irreversible deactivation. The deactivation of solid–acid catalysts used in hydrocar- bon transformation is mainly due to the deposite of heavy secondary products (HCs) inside the pores gen- erally known as coke [12,13]. It is known that HCs are formed on the strong acid-sites on the surface of the catalyst. In order to avoid the formation of coke and to increase the DME selectivity to 100%, the strength of the acid-sites must be reduced. It has been found that if the reaction of methanol dehydration take place on the modified-alumina catalysts with phosphorus, can be caused to reduce the amounts of coking and by-products [1,14]. 1566-7367/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.catcom.2005.05.003 * Corresponding author. Tel.: +98 861 228 77014; fax: +98 861 228 7705. E-mail addresses: f.yaripour@npc-rt.ir, Fereydoon_Yaripour@ yahoo.com (F. Yaripour). www.elsevier.com/locate/catcom Catalysis Communications 6 (2005) 542–549