Nanotubular titanate supported palladium catalysts: The influence of structure and morphology on phenol hydrogenation activity

Nanotubular titanates were synthesized by a simple methodology using a commercial TiO2 (Degussa P25 containing anatase and rutile phases) and a base (KOH) solution. Prior to the removal of KOH, the samples of TiO2 were aged for three different time intervals (0, 2, 61 days). The freshly prepared synthetic samples were characterized for their structural and morphological properties by BET, XRD, Raman, TEM, HRTEM, EDX and SEM. Both TEM and SEM analysis revealed that ageing time influenced the tubular structure and morphology of the new materials. Raman and surface analysis data also showed that ageing time affected both the structural and surface properties of TiO2. The XRD results indicated that the crystallinity of the TiO2 decreased with increasing ageing time. Energy dispersive X-ray spectroscopy (EDX) showed that the tubes derived from TiO2 are comprised of potassium, titanium and oxygen. Catalysts A, B and C were prepared by the addition of 1 wt% Pd (wet impregnation) to the titanate formed by ageing TiO2 in KOH for 0, 2 and 61 days, respectively and revealed Pd particle sizes of < 1 nm for catalyst B. The catalysts were tested for the vapour phase hydrogenation of phenol in a fixed-bed micro-reactor within the temperature range of 165-300 degrees C under atmospheric pressure. Of the three catalysts, catalyst B showed the best activity (conversion 97%) and total selectivity to cyclohexanone (99%). In contrast, catalyst C, which showed a moderate activity favoured selectivity to cyclohexanol. These results are attributed to differences in surface morphologies between the two catalysts B and C, associated with a change in the surface properties. Catalyst B also showed a higher resistance towards deactivation and maintained a higher total selectivity to cyclohexanone than did catalyst C. (C) 2007 Elsevier B.V. All rights reserved.