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

Butylation of p-cresol with tert-butanol was investigated on titania modified with 12-tungstophosphoric acid (TPA/TiO2) 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, NH3-TPD, and FTIR pyridine adsorption. XRD results indicated that the presence of TPA retarded the crystallization of titania and stabilized TiO2 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 TiO2 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 WO3/ZrO2, sulfated zirconia (SZ), USY, H-β zeolites and montmorillonite K-10 (K-10mont) under similar conditions.

Graphical abstractThe catalytic activity of 12-tungstophosphoric acid (TPA) supported on titania was investigated in butylation of p-cresol with tert-butanol. The catalyst with 20% TPA/TiO2 calcined at 700 °C has shown higher activitiy than WO3/ZrO2, sulfated zirconia, H-beta catalyst in the above reaction. Figure optionsDownload full-size imageDownload as PowerPoint slide