Enhancement of biphenyl hydrogenation over gold catalysts supported on Fe-, Ce- and Ti-modified mesoporous silica (HMS)

Mesoporous metallosilicates (HMS-M; M = Ce, Fe, Ti) were used as supports for the preparation of Au catalysts, and were tested in the liquid-phase hydrogenation of biphenyl at 5 MPa and 488 K. Irrespective of the support, uniformly dispersed Au nanoparticles in range 3.2-6.5 nm were obtained. The highest turn over frequency (TOF), expressed per surface Au atom, was achieved on the Au/HMS-Fe, furthermore this catalyst gave the highest selectivity to the most saturated compound (bicyclohexyl with the highest cetane number) by means of enhancing the second aromatic-ring hydrogenation. From the catalyst activity-structure correlation, the highest activity of the Au/HMS-Fe catalyst is linked with: (i) the higher ratio of positively charged metallic gold Au delta+/Si (XPS), and (ii) the higher stability of Au nanoparticles (HRTEM). A linear correlation between the activity (per gram of metal) of the catalysts and their ratio Au delta+/Si is observed; however, Au/HMS-Ce catalyst displays a different behaviour in terms of activity per gram of metal exposed caused by the fact that ceria is not incorporated in the framework. (C) 2009 Elsevier Inc. All rights reserved.