Heteropoly acid supported on titania as solid acid catalyst in alkylation of p-cresol with tert-butanol

Abstract

Butylation of p-cresol with tert-butanol was investigated on titania modified with 12-tungstophosphoric acid (TPA/TiO 2) catalyst under vapor phase conditions. Catalysts with different TPA loadings (10–25 wt.%) and calcination temperatures (650–750 °C) were prepared by suspending titanium hydroxide in methanol solution of TPA followed by drying and calcination. These catalysts were characterized by surface area, XRD, 31P MAS NMR, XPS, NH 3-TPD, and FTIR pyridine adsorption. XRD results indicated that the presence of TPA retarded the crystallization of titania and stabilized TiO 2 in anatase phase. 31P MAS NMR indicated the presence of TPA in various forms (dispersed, highly fragmented and Keggin intact). These catalysts showed both Brönsted and Lewis acidity, and 20% TPA on TiO 2 calcined at 700 °C (from here after words 20% TT-700) had the highest Brönsted as well as total acidity. Further, the catalytic activities were examined in tert-butylation of p-cresol with tert-butanol. The catalytic activity depended on TPA coverage, and the highest activity corresponded to the monolayer of TPA on titania. The most active catalyst 20% TT-700 gave 82% conversion of p-cresol and 89.5% selectivity towards 2- tert-butyl cresol (TBC), 2,6-di- tert-butyl cresol (DTBC) 7.5% and cresol- tert-butyl ether (CTBE) 3% under optimized conditions. The activity was always higher than that of WO 3/ZrO 2, sulfated zirconia (SZ), USY, H-β zeolites and montmorillonite K-10 (K-10mont) under similar conditions.