Effect of different acidity modifications on the activity and selectivity on H-ZSM5 zeolites in n-butene isomerization

Abstract

H-ZSM-5 was modified by silylation [tetraethylorthosilicate (TEOS) and triaminopropyltriethoxysilane], alkali (NaOH), acid (HCl) and ammoniumhexafluorosilicate (AHFS) treatments. The parent and modified zeolite forms were tested in n-butene isomerization. Modifications affected total acidities, the strength of the acid sites, pore sizes and surface areas of the H-ZSM-5 differently. The modifications decreased the conversion obtained by the parent catalyst. TEOS and alkali modifications did not promote formation of isobutene. Pre-alkali treatment before acid treatment increased selectivity to isobutene from 56.0 to 66.7 %, while conversion changed a little, it dropped from 52 to 50 %. AHFS modification provided the highest enhancement in selectivity to isobutene (87.5 %) for which n-butene conversion was dropped by about 10 % compared to H-ZSM-5. This was attributed to a slight modification of the pore size and to the reduction in strong and weak acid sites and generation of new Lewis acid sites.

Preparation and Performances of Hierarchical Structured HZSM‐5 Washcoating on Stainless‐Steel Substrates

“…, Table ). The desorption peaks centered at a low temperature (240°C) and a high temperature (450°C) are referred as weak and strong acid sites, respectively . There were no large differences between the total acidity of parent and modified zeolites especially for ZM‐P and ZM‐AT1.…”

Effect of surface silicon modification of H-beta zeolites for alkylation of benzene with 1-dodecene

“…Chemical silicon deposition is a common method for passivating the acid sites on the external surface of zeolites. [27][28][29][30][31][32][33] Shang et al investigated HMCM-22 zeolite silylated with silicon tetrachloride (SiCl 4 ), tetraethoxysilane (TEOS) and 8-hydroxyquinoline (C 9 H 7 NO) to passivate the external surface acidity, which sharply increased the selectivity of isobutene. 34 Li et al reported that silanization modication of HZSM-5 zeolites by CLD not only passivated the acidity of the external surface, but also gave narrower pore opening and promoted shape-selectivity.…”

Distribution of Effective Ferrierite Active Sites for Skeletal Isomerization of n‐Butene to Isobutene

“…Conversely, at low (NH 4 ) 2 SiF 6 concentration, the HF and NH 4 F produced by hydrolysis can effectively eliminate the non‐framework aluminum deposited in the FER channels. In this case, orthosilicate can fill the structural defect, resulting in a slight increase in relative crystallinity . In addition, the results of 27 Al magic angle spinning nuclear magnetic resonance ( 27 Al MAS NMR) shown that compared with the proportion of framework aluminum in FER−P, that in FER‐0.2 increases, while those in FER‐0.5 and FER‐0.8 decrease, which is consistent with the results of XRD (Figure and Table ).…”

“…In this case, orthosilicate can fill the structural defect, resulting in a slight increase in relative crystallinity. [19][20] In addition, the results of 27 Al magic angle spinning nuclear magnetic resonance ( 27 Al MAS NMR)…”