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Abstract
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This study utilized citric acid to modify HZSM-5 zeolite and investigated the effects of calcination atmosphere (air and N2) on the catalyst support ’s pore structure and acidic sites. Different transition metals (Ni, Mn, Cu) were loaded onto the catalyst, and their effects on the catalytic cracking performance of biomass tar model compound (toluene) were compared. The results show that citric acid modification and calcination in air significantly enhance the mesopore average pore diameter, reduce molecular diffusion resistance, and improve catalytic activity. On the other hand, calcination in an N2 atmosphere increases the strong acidic sites of the catalyst, which enhances toluene catalytic activity. After loading metals such as Ni, Mn, and Cu, the catalytic activity was further enhanced, with Ni showing the best catalytic performance, achieving a toluene conversion efficiency of 75.50%. In air atmosphere, metals exist in the form of metal oxides (NiO, Cu2O, MnO2), while in nitrogen (N2) atmosphere, Ni and Cu exist in their metallic form, and Mn remains in the form of MnO2. The metal oxides of Ni and Cu participate in the reaction through lattice oxygen, which improves H2 yield. MnO2, due to its strong oxygen-carrying ability, increases the CH4 proportion. Additionally, the numerical model constructed using COMSOL Multiphysics accurately simulates the experimental process and reveals the effects of toluene mass flow rate and catalyst contact area on conversion efficiency. The results indicate that reducing toluene flow rate or increasing the contact area can improve conversion efficiency.
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