Hualei Hu,Jinghui Lyu,Jiayao Rui,Jie Cen,Qunfeng Zhang,Qingtao Wang,Wenwen Han,Xiaonian Li
Ethylbenzene is the major side product in benzene alkylation with methanol and it is difficult to be suppressed over hierarchical porous ZSM-5. Moreover, the separation of ethylbenzene from xylene still remains a great challenge. Our research indicated that ethylbenzene formation could be highly suppressed by changing the Si/Al ratio of the catalyst. Hierarchical porous ZSM-5 catalysts with different Si/Al ratios were prepared via reducing the amount of Al in the solvent evaporation assisted dry gel conversion method. In this method, tetra-n-propylammonium hydroxide was used as the direct agent to create micropores, and hexadecyltrimethoxysilane was added to create additional porosities by forming organic assemblies which occupied a certain space between zeolitic walls. The catalyst with a Si/Al ratio of 1800 could achieve high benzene conversion (59.5%) and high xylene selectivity (39.0%) as well as excellent suppression of ethylbenzene formation (<0.1%).
Phenol is an important intermediate for high value chemicals. Current phenol production via a three-step cumene process causes severe energy-waste and environmental problems. The conversion of benzene to phenol under mild condition can be achieved by oxidation with Cu-based zeolites. However, conventional microporous zeolite suffers from severe diffusion limitation, especially when bulky molecules are involved, such as benzene. In this work, we used a hierarchically macro-meso-microporous ZSM-5 single crystal (Hier-ZSM-5) as substrate for Cu species (Cu@Hier-ZSM-5). Irregular morphology of opal-like Hier-ZSM-5 exhibits abundant surface Si-OH groups and provides a platform for stabilizing Cu2+ sites. Meanwhile, hierarchical porosity provides significantly improved diffusion ability of bulky molecules. As a result, excellent selective oxidation performance of benzene was obtained with the Cu@Hier-ZSM-5, achieving a conversion of 77% and a phenol selectivity of 73%, which is 1.5 times and 2 times of these obtained with a catalyst based on a microporous ZSM-5, respectively. Species of CuOOH were identified as an important intermediate for benzene oxidation. This hierarchical zeolite system with a synergistic effect of site anchoring and molecular diffusion presents an excellent platform for catalyst design.
Ke Yang,Gang Wu,Bo Zhang,Liangyuan Jia,Huiyan Zhang
Catalytic fast pyrolysis (CFP) is one of the most efficient methods for directly converting biomass into green aromatics. Although ZSM-5 catalyst is efficient at producing aromatics, the catalyst deactivation brings challenge to industrial applications. Constructing additional mesoporous structure in ZSM-5 catalyst can overcome this drawback. In this study, two solid wastes are used as raw materials to synthesize hierarchically porous ZSM-5 catalyst based on solvent-free method, aligning with the target of “green chemistry”. Comparing with the commercial ZSM-5 catalyst, the synthesized catalyst achieves a higher BTX yield (benzene, toluene, and xylene), with increases of approximately 44 %, 7 %, and 12 %, respectively. The mesopore-to-micropore volume ratio is a key factor in determining catalytic efficiency. Moreover, PI-MS is used to monitor the deactivation behavior of catalyst online during the CFP process, showing that the synthesized catalyst has a slower deactivation rate. The hierarchically porous structure plays a crucial role in slowing the transformation of oxygenated coke into graphite-like coke, which is a major contributor to catalyst deactivation. This work can provide a green and convenient method for producing hierarchically porous ZSM-5 catalyst and be useful for improving the selectivity of aromatic compounds, offering a promising alternative to conventional ZSM-5 catalyst in industrial applications.
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