Catalytic Activities and Product Selectivities of Noble Metal-supported ZSM-5 Hydrodesulfurization Catalysts

Abstract

Hydrodesulfurization (HDS) of thiophene was performed over noble metals (Pt, Rh, Pd, Ru)-supported HZSM-5 and NaZSM-5. Among the tested catalysts, Pt/HZSM-5 exhibited the highest HDS activity. Butane was the dominant product in HDS of thiophene over Pt/HZSM-5. Selectivity of aromatics was high on Rh/HZSM-5, Pd/HZSM-5 and Ru/HZSM-5, and remarkable deactivation was observed on these catalysts. Products of consecutive reaction, mainly aromatics, were thought to be the sources of carbon deposit. Because deactivation was remarkable in HDS over the catalysts which produced aromatics.
The IR s pectra of acidic hydroxy groups and adsorbed pyridine, and the NH₃-TPD spectra show that the amount of acid site of HZSM-5 impregnated with noble metals were almost the same as that of original HZSM-5. The dispersion of Pt determined by XRD was lower than those of Rh and Pd. However, Pt was stable against hydrogen sulfide. It was indicated that HDS activity depended on the hydrogen activation ability of metals in the presence of hydrogen sulfide.
Moreover, HDS activity depended on the dispersio n of Pt, and the acidity of zeolite affected on dispersion of Pt.
These results indicate that a highly active catalyst for HDS can be prepared by the use of zeolite which has a large amount of acid sites and Pt which shows anti-sulfur ability.