Catalytic hydrogenation, hydrocracking and isomerization reactions of biomass tar model compound mixture over Ni-modified zeolite catalysts in packed bed reactor

Gas-phase conversion of a model mixture of biomass tar (5 wt% naphthalene and 95 wt% of 1-methylnaphthalene) into 2-methylnaphthalene liquid product and ethylene and propane gas mixture was carried out over different zeolites and metal promoted zeolites in a packed-bed reactor for the first time. In the present work, a series of MFI (H-ZSM-5), BEA (H-β), FAU (H-Y, H-USY), and MOR (H-Mordenite) zeolites were investigated. The effect of Ni metal addition on the promotion of parent zeolite catalysts was studied. The most successful catalysts were characterized by BET, ICP-AES, XRD, HRSEM, STEM-HAADF, and STEM-BF with EDXS, NH3-TPD, H2-TPR, TGA, and pyridine-DRIFT techniques. The superior performance in comparison to the other studied catalysts was established over the 5 wt%Ni/H-ZSM-5 (SiO2/Al2O3 = 30) with 96.2 mol% of selectivity to 2-methylnaphthalene in the liquid phase, 90 mol% total conversion with the highest part (82.9 wt%) of ethylene and propane in the gas phase after 24 h time-on-stream. This high catalytic performance of the 5 wt%Ni/H-ZSM-5 catalyst can be attributed to the presence of the high mesopore volume, pore diameter, and high mesopore surface area, the existence of the redox active sites, and the presence of strong Lewis acid sites due to synergetic interaction between Ni metal species and zeolite acid support. Based on the product distributions observed, the reaction scheme of the conversion of biomass tar model mixture of naphthalene and 1-methylnaphthalene over studied catalysts was proposed. Our catalytic results obtained over pristine and Ni-modified zeolite catalysts shed light on the potential use of these catalysts in the biomass tar valorization process under atmospheric pressure.