Guofu Xia

Strong effect of transitional metals on the sulfur resistance of Pd/HY-Al2O3 catalysts for aromatic hydrogenation

In order to improve the sulfur resistance of noble metal catalysts in the aromatic hydrogenation of diesel fuel, the alloying effect of non-noble metals with Pd was studied. Toluene hydrogenation over Pd and Pd-M bimetallic catalysts (M = Cr, W,La, Mn, Mo, Ag) on a mixed HY-Al2O3 support was investigated in the presence of 3000 ppm sulfur as thiophene in the feedstock. The results showed that the addition of the second metals strongly affected the activity of toluene hydrogenation, which suggests that the sulfur resistibility of Pd-M bimetallic catalysts is much different from single Pd. La, Mn, Mo and Ag decreased the sulfur resistance of the palladium catalysts. For example, the toluene conversion at 553 K was observed to decrease sharply from 39.4 wt.% on Pd to 1.6 wt.% on Pd-Ag, which is by a factor of 25. One of the important findings in this article is that Cr and W increase hydrogenation activity of Pd catalysts. The reactions occurring on these catalysts include hydrogenation, isomerization and hydrocracking, The addition of the second metals has no noticeable effects on the hydrogenation and isomerization selectivity, but it slightly suppresses hydrocracking reactions. The four typical catalysts, Pd-Cr, Pd-W, Pd-Ag and Pd were characterized by infrared (IR) spectroscopy of pyridine and CO. LR spectra of CO revealed the strong interaction between Pd and the second metal as Cr, W and Ag (or their oxide), indicating that the improvement in sulfur resistance originates from electron-deficient Pd with the addition of second metals

Hydroisomerization of long chain n-paraffins: the role of the acidity of the zeolite

The transformation of n-hexadecane (n-C16) was tested by two series of experiments over bifunctional catalysts with noble metal Pt and a one dimensional ZSM-22 zeolite to investigate the role of the acidity of the zeolite during the hydroisomerization of long chain n-paraffins. In series 1, varying the Si/Al ratio of the zeolite but fixing the zeolite content, reveals that the high acid strength of the zeolite can deteriorate the selectivity of the corresponding catalyst even at an initial conversion and that the low concentration of acid sites on the zeolite is beneficial to the improvement of the maximal value of the isomer yield. In series 2, varying the zeolite content but fixing the Si/Al ratio, reveals that the change of the zeolite content could not affect the selectivity of the catalyst. Both series 1 and series 2 revealed that the activity of the catalyst linearly increases with the acid strength, the concentration of acid sites and the content of the employed zeolite.

Selective ring opening of methylcyclopentane over surface-decorated Ir–Co bimetallic catalysts synthesized by galvanic replacement reaction

Surface-decorated Ir–Co bimetallic catalysts were synthesized by a modified galvanic replacement reaction and evaluated by the selective ring opening (SRO) of methylcyclopentane (MCP). Inductively coupled plasma atomic emission spectroscopy (ICP-AES) was utilized to characterize the catalyst synthesis process, and H2-temperature-programmed reduction (H2-TPR) was performed to characterize the reduction behavior of the calcined catalysts and oxidation resistance of the reduced catalysts. Transmission electron microscopy (TEM) analysis was used to characterize metallic particle size distribution. The reactor evaluation results show quite different behaviors in conversion and product selectivity of the surface-decorated Ir–Co/SiO2 and monometallic Ir/SiO2. At optimized Ir content, MCP conversion and mass-specific rate of SRO are significantly higher when catalyzed by surface-decorated Ir–Co/SiO2 than by monometallic Ir/SiO2. Moreover, compared with Ir/SiO2, Ir–Co/SiO2 has decreased 2-methylpentane selectivity but improved n-hexane selectivity. These catalytic behaviors were found to correlate with the surface-decorated bimetallic structure consisting of Co/SiO2 decorated with surface Ir atoms.