Silver Surface Enrichment on ZSM-5 Zeolites for the Catalytic Cracking of n-Pentane to Produce Light Olefins

Abstract

The effects of Ag-incorporation on the catalytic performance of ZSM-5 zeolites have been investigated. Since Ag-incorporation can promote the formation of light olefins and significantly enhance catalytic performance in n-pentane catalytic cracking. However, the Ag-incorporated ZSM-5 zeolite was rapidly deactivated in npentane catalytic cracking. Thus, CLD and sulfation methods were introduced to improve catalytic activity and stability of Ag-incorporated ZSM-5 zeolites. The Agincorporated ZSM-5 zeolites have been prepared by the incipient wetness impregnation and CLD methods. Moreover, the sulfated catalyst was prepared by the sequential CLD and sulfation of commercial HZSM-5 zeolite. The catalytic activity and stability of Ag-incorporated ZSM-5 zeolites have been evaluated and compared using n-pentane catalytic cracking. The effects of the modification methods on the Ag-incorporated ZSM-5 zeolites have been investigated via the characterizations including XRD, TEM, surface area analyzer (BET), XRF and XPS. The catalyst characterizations confirmed that the characteristic ZSM-5 zeolite structure was well preserved after the Ag-incorporation by impregnation, CLD, and sulfation methods. Compared with the Ag-impregnation, the Ag-CLD method forced the introduced Ag concentrating on the external surface by generating a porous overlayer. In addition, the sulfation treatment further generated a surface sulfate phase over the porous overlayer and promoted the diffusion process of n-pentane in the ZSM-5 zeolite. Thus, CLD-Ag-Z5 and S-CLD-Ag-Z5 achieved higher light olefins production, and more efficient to maintain catalytic activity in n-pentane catalytic cracking in comparison to the parent HZSM-5 and Ag-Z5.