ROLES OF ZEOLITE SUPPORT AND NOBLE METAL IN SULFUR-TOLERANT CATALYST FOR LOW TEMPERATURE HYDROGENATION OF AROMATICS
Open Access
- Author:
- Kim, Hyun Jae
- Graduate Program:
- Energy and Geo-Environmental Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- July 06, 2011
- Committee Members:
- Chunshan Song, Dissertation Advisor/Co-Advisor
Chunshan Song, Committee Chair/Co-Chair
Yaw D Yeboah, Committee Member
Yongsheng Chen, Committee Member
Adrianus C Van Duin, Committee Member - Keywords:
- hydrogenation
sulfur tolerance
catalyst - Abstract:
- This dissertation focuses on fundamental understanding of the roles of supports and noble metals in the sulfur-tolerant catalysts for low-temperature hydrogenation of aromatics in the presence of sulfur. Emphasis was placed on investigating the effect of supports and supported metals for high sulfur tolerance and verifying a catalyst design concept for the sulfur-tolerant noble metal catalyst based on shape selective exclusion of sulfur and hydrogen spillover for low- temperature hydrogenation of aromatics [C.S. Song, Chemtech, 29 (1999) 26-30]. The hybrid zeolite-supported Pd catalyst was prepared to improve sulfur tolerance, based on the proposed catalyst design concept. The hybrid catalyst consists of Pd supported on Y and A type zeolites. For further investigation on small pore system in hybrid catalyst, surface metal passivation by silica coating and pore size control by potassium ion exchange were employed to zeolite A-supported Pd catalyst. Although Pd on Zeolite A showed no catalytic activity for hydrogenation of tetralin, adding the small-pore catalyst to Pd/Y significantly enhanced sulfur tolerance of the catalyst for both naphthalene and tetralin hydrogenation in the presence of sulfur in the form of benzothiophene. Sulfur tolerance of the hybrid catalyst is mainly attributed to the small pore system, inducing size-selective exclusion of bulky sulfur compounds as well as hydrogen spillover from metal inside small pore component. Hydrogen spillover plays two roles in maintaining high sulfur tolerance of the hybrid catalyst: first, regeneration of sulfur-poisoned metal active sites in the large pores of Pd/Y as well as hydrodesulfurization of aromatic sulfur compounds over the zeolite Y support. On the basis of the above results and discussion focusing on the importance of the supports and metal types for improving sulfur tolerance, the hybrid catalyst system based on the new design concept of sulfur tolerant catalyst is effective in the development of sulfur tolerant catalysts for low-temperature hydrogenation of aromatics.