Fabrication and catalytic performance of meso-ZSM-5 zeolite encapsulated ferric oxide nanoparticles for phenol hydroxyla
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RESEARCH ARTICLE
Fabrication and catalytic performance of meso-ZSM-5 zeolite encapsulated ferric oxide nanoparticles for phenol hydroxylation Zhenheng Diao (✉), Lushi Cheng, Wen Guo, Xu Hou, Pengfei Zheng, Qiuyueming Zhou School of Chemical Engineering, Advanced Institute of Materials Science, Changchun University of Technology, Changchun 130012, China
© Higher Education Press 2020
Abstract An encapsulation-structured Fe2O3@mesoZSM-5 (Fe@MZ5) was fabricated by confining Fe2O3 nanoparticles (ca. 4 nm) within the ordered mesopores of hierarchical ZSM-5 zeolite (meso-ZSM-5), with ferric oleate and amphiphilic organosilane as the iron source and meso-porogen, respectively. For comparison, catalysts with Fe2O3 (ca. 12 nm) encapsulated in intra-crystal holes of meso-ZSM-5 and with MCM-41 or ZSM-5 phase as the shell were also prepared via sequential desilication and recrystallization at different pH values and temperatures. Catalytic phenol hydroxylation performance of the as-prepared catalysts using H2O2 as oxidant was compared. Among the encapsulation-structured catalysts, Fe@MZ5 showed the highest phenol conversion and hydroquinone selectivity, which were enhanced by two times compared to the Fe-oxide impregnated ZSM-5 (Fe/ Z5). Moreover, the Fe-leaching amount of Fe@MZ5 was only 3% of that for Fe/Z5. The influence of reaction parameters, reusability, and $OH scavenging ability of the catalysts were also investigated. Based on the above results, the structure-performance relationship of these new catalysts was preliminarily described. Keywords phenol hydroxylation, encapsulation structure, structure-performance relationship, meso-ZSM-5, ferric oxide
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Introduction
Dihydroxybenzenes (DHB) are significant intermediates in organic synthesis, which have been widely used in the Received February 23, 2020; accepted June 11, 2020 E-mail: [email protected]
fields of chemical pesticides, synthetic perfume, photographic chemical, polymerization inhibitor, pharmaceutical and dyestuffs [1]. During the past decades, several processes have been proposed for the production of DHB, especially hydroquinone (HQ). Among these methods, phenol hydroxylation via Fenton-like reactions with H2O2 as oxidant is considered as a green, clean and promising process because of its economic and eco-friendly characteristics [2]. For these Fenton-like reactions, homogeneous and heterogeneous catalysts have been extensively investigated. Heterogeneous catalysts are preferable due to their reusability and excellent catalytic selectivity [3]. Iron oxide has been widely employed as a heterogeneous catalyst for Fenton-like reactions due to its lowcost and environmental friendliness. Ding et al. [4] and Yang et al. [5] prepared Fe2O3 catalysts via calcination method and illuminated the relationship between the calcination temperature and catalytic activity. Monolithic iron oxides can be easily prepared. However, their low surface area would lead to a low accessibility of active sites and thus an unsatisfactory activity. To solve this problem, zeoli
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