Aromatics Reduction over Supported Platinum Catalysts. 3. Effects of Catalyst Precursors and Pretreatment Conditions on the Performance of Palladium-Promoted Platinum Catalysts

Fast Fourier transformation infrared spectroscopy was used to characterize the formation of bimetallic interactions of γ-Al2O3-supported Pd−Pt catalysts. The effects of bimetallic interactions on catalyst performance were examined in long-term stability tests, carried out with a pilot plant under the same operating conditions and feed as those of a commercial diesel hydrotreating process. These tests are the hydrotreating of straight run distillate diesel at 340 °C, 580 psig, and H2/oil (mol) = 2.5 over a 25 day period. The characterization results indicate that Pd precursors and pretreatment conditions affect Pd−Pt bimetallic interactions in the H2-reduced catalysts and the catalyst performance. The Pd−Pt catalysts made from palladium(II) acetate without calcination pretreatment presented a significant Pd−Pt bimetallic interaction, as evidenced by a shift in the infrared absorption peak characteristic of terminal CO ligands adsorbed on the Pt clusters to higher energy, bridging CO on the Pd to lower energy, and a catalytic reduction of palladium(II) acetate by Pt. In contrast, no significant bimetallic interactions were observed for both catalysts made from palladium(II) acetate with a calcination at 450 °C in air and from palladium amine. The long-term stability tests further indicate that the Pd−Pt catalysts with bimetallic interactions have a relatively high selectivity for aromatics reduction and hydrodenitrogenation (HDN), whereas they have a relatively low selectivity for hydrodesulfurization (HDS).