Influence of the precipitation agent in the deposition-precipitation on the formation and properties of Au nanoparticles supported on Al2O3.

Au nanoparticles supported on Al2O3 were prepared by deposition-precipitation of HAuCl4 with different precipitation agents NaOH and urea. The samples were investigated by means of different characterization techniques such as X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and transmission electron microscopy (TEM). The results show that depending on the precipitation agent, the Au particles have a different Au-Au coordination number and size after calcination at 523 K. Whereas the use of NaOH leads to the formation of Au nanoparticles with a Au-Au coordination number of 6.7 and a mean diameter below 2 nm, those prepared with urea have a mean size of 3.1 nm. The Au-Au coordination number could be determined as 8.6. At the smaller particles obtained with NaOH, hints for Au-O interactions were found. For these particles TEM results advise a rather flat lenticular morphology. Different deposition mechanisms depending on the precipitation agent are discussed as the reason for the formation of nanoparticles with different shapes, sizes, and valence states.

Development of highly active and selective novel Pd based acetoxylation catalysts and prevention of catalyst deactivation by Bi modification.

A first approach to successful prevention of catalyst deactivation while simultaneously achieving extremely high selectivity of benzyl acetate (> or = 95%) at significantly high toluene conversion (> 70%) by gas phase acetoxylation over novel Pd-Sb-Bi/TiO2 catalysts.