Influence of Metallic Modification on Ethylbenzene Dealkylation over ZSM‐5 Zeolites

Abstract

A series of metal-modified HZSM-5 catalysts were prepared by impregnation and were used for ethylbenzene dealkylation of the mixed C8 aromatics (ethylbenzene, m-xylene and o-xylene). The effects of different supported metals (Pt, Pd, Ni, Mo) on catalytic performance, including reaction conditions, were investigated. The physicochemical properties of catalysts were characterized by means of XRD, BET, TEM and NH 3 -TPD. Experimental results showed that metallic modification obviously increased the ethylbenzene conversion and reduced the coke deposition, greatly improving the catalyst stability. The distinction of ethylbenzene conversion depended on the interaction between hydrogenation reactivity and acidic cracking of bifunctional metal-modified zeolites. Compared with Pt and Ni, Pd and Mo were easier to disperse into HZSM-5 micropores during loading metals. The acidic density of different metal-modified HZSM-5 declined in the following order: HZSM-5＞ Pt/HZSM-5＞Pd/HZSM-5＞Ni/HZSM-5＞Mo/HZSM-5. The activity of ethylene hydrogenation decreased with Pt/HZSM-5＞Pd/HZSM-5＞Ni/HZSM-5＞Mo/HZSM-5. In comparison, Pd/HZSM-5 showed the best catalytic performance with both high activity and high selectivity, with less cracking loss of m-xylene and o-xylene. Moreover, the following reaction conditions were found to be preferable for ethylbenzene dealkylation over Pd/HZSM-5: 340 ℃, 1.5 MPa H 2 , WHSV 4 h −1 , H 2 /C8 4 mol/mol.

Propylphenol to Phenol and Propylene over Acidic Zeolites: Role of Shape Selectivity and Presence of Steam

“…42 The process is attained in the presence of precious metals under H 2 atmosphere in order to prevent catalyst deactivation by coking. 41,42 As a consequence, low-value short alkanes are formed from the side chain rather than the more preferable short alkenes such as ethylene and propylene. 41,43 In contrast to that of alkylbenzenes, literature on alkylphenol dealkylation is scarce.…”

Shape selectivity vapor-phase conversion of lignin-derived 4-ethylphenol to phenol and ethylene over acidic aluminosilicates: Impact of acid properties and pore constraint

“…Catalytic hydrocracking can occur at milder temperature with a selectivity of 70%. Still, products from the alkyl side chain are alkanes, whereas formation of alkenes is more desirable [35]. Besides exploration of mature technologies, dealkylation was also studied in supercritical water, yielding a very low phenol selectivity (42%), having methane and CO 2 as main side products [36].…”

“…Therein, it was shown that the combination of a zeolite and steam is essential to obtain a stable catalytic performance. This zeolite-catalysed reaction with alkylphenols is fundamentally different from the classic ethylbenzene dealkylation transformation, for which H 2 and Pt are required to achieve stable catalysis, while lowvalue ethane is formed as by-product [35]. Yet, several aspects clearly deserve more attention, such as the exact nature of the active sites, the effect of acid strength and density, pore constraints, definition of primary and secondary reaction types and their relationship in a reaction network, thermodynamic vs. kinetic aspects, and mass transfer issues.…”

Hydroxymethylation of xylenol over micro/mesoporous TiO2‐containing bifunctional catalyst: Effect of the Y zeolite incorporation with MCM‐41

“…This is mainly owing to the secondary adsorption of intermediates on the acid sites in the microporous zeolite and the diffusion restriction in the micropores. 22,23 Inhibition of dealkylation selectivity under high conversion activity is a huge obstacle to the widespread use of microporous zeolites in alkylphenol hydrodealkylation. Al-MCM-41 mesoporous molecular sieve [24][25][26] has a large pore volume and pore size structure, which allows macromolecules to enter and exit freely in the pore channel and has wide applications in catalyzing macromolecular reactions.…”

“…It was found that side reactions of cracking and dehydroxylation occurred in the hydrodealkylation of alkylphenols. This is mainly owing to the secondary adsorption of intermediates on the acid sites in the microporous zeolite and the diffusion restriction in the micropores 22,23 . Inhibition of dealkylation selectivity under high conversion activity is a huge obstacle to the widespread use of microporous zeolites in alkylphenol hydrodealkylation.…”