Applied Catalysis A: General 263 (2004) 33–38 Preparation of phenol from benzene by one-step reaction B. Liptáková ∗ , M. Báhidský, M. Hronec Department of Petroleum Technology and Petrochemistry, Slovak University of Technology in Bratislava, Radlinskeho 9, 812 37 Bratislava, Slovak Republic Received in revised form 20 November 2003; accepted 2 December 2003 Abstract The direct gas-phase oxidation of benzene to phenol with a mixture of oxygen–ammonia–water vapors was studied over mixed calcium- copper-hydroxyapatite catalysts. The effect of various reaction parameters on the transformation of benzene to phenol was tested. About 3% conversion of benzene and 97% phenol selectivity was achieved at atmospheric pressure and the temperature of 450 ◦ C in the first 3 h of reaction, when deactivation of the catalyst was not so significant. However, after this period the deactivation of the catalyst was pronounced and probably caused by destruction of an active hydroxyapatite structure of the catalyst. © 2003 Elsevier B.V. All rights reserved. Keywords: Benzene; Oxidation; Phenol; Hydroxyapatite 1. Introduction Phenol is an important intermediate for the production of antioxidants, agrochemicals and polymers. More than 90% of the world production of phenol is obtained by the multi-step cumene process, while the direct hydroxylation of benzene has long remained highly desirable. Many attempts to accomplish one-step direct oxidation of benzene by molecular oxygen have not been successful. Interaction of benzene with oxygen is accompanied by the destruction of the aromatic ring and results in low phenol selectivity [1,2]. Better results have been obtained in the hydroxylation of benzene with hydrogen peroxide or with an oxygen/hydrogen mixture, using zeolites modified with metals as catalysts [3,4]. More promising results seem to derive from the use of alternative oxidants as nitrous oxide. The most active and selective catalyst for this reaction is Fe-ZSM-5 [5–7]. The mechanism of this reaction is the mat- ter of discussions. Some authors [8] have proposed that the Brönsted acid sites (AS) take part in the reaction. Others [9] consider the extra framework aluminium to be important for the reaction. Panov et al. [10–12] have proposed that N 2 O decomposes on the iron present in zeolite giving rise to the so called -oxygen responsible for the reaction. ∗ Corresponding author. Tel.: +42-12-5932-5403; fax: +42-12-5249-3198. E-mail address: lipo@chelin.chtf.stuba.sk (B. Lipt´ akov´ a). We have studied the gas-phase hydroxylation of benzene to phenol with in situ produced nitrous oxide, which is formed by the reaction of air and aqueous ammonium hy- droxide over mixed hydroxyapatites [13]. Hydroxyapatite catalysts containing calcium and copper are suitable for this synthesis. The aim of this work was to study the calcium-copper- hydroxyapatite catalysts for the hydroxylation of benzene under various reaction parameters. 2. Experimental The oxidation of benzene to phenol was carried out in an electrically heated stainless steel reactor (10 mm i.d., 750 mm length) filled with 2 g of solid catalyst with a par- ticle size 0.6–1.0 mm. The temperature was measured in the catalyst bed with a thermocouple. Both benzene and an aqueous ammonium solution were pumped into the reactor with linear sample injectors. The flow rates of air and nitro- gen were controlled and measured by mass flowmeters. The reaction products were collected in a cooled flask. 2.1. Catalyst preparation The mixed calcium-copper-hydroxyapatite catalysts were prepared by direct precipitation. Aqueous solution of Ca(NO 3 ) 2 and Cu(NO 3 ) 2 with an aqueous solution of 0926-860X/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2003.12.002