Hydrocracking, hydrogenation and isomerization of model biomass tar in a packed bed reactor over bimetallic NiMo zeolite catalysts: Tailoring structure/acidity

Abstract

In this experimental study, various NiMo-promoted (as follows: H-beta, H-mordenite, H-USY, H-Y, and H-ZSM-5) catalysts were prepared, tested, and compared with pristine zeolites for the purpose of the gas phase hydrocracking, hydrogenation, and isomerization in a packed bed reactor at 370 °C under atmospheric relative pressure. 5 wt.% naphthalene/95 wt.% 1-methylnaphthalene were selected as biomass tar model molecule compounds, based on real chemical compositions. A series of material characterization techniques were applied to determine the physical structural, morphological, textural, redox, and acidic properties of synthesized catalysts. An outstanding catalytic activity and stability were found over the 2.5 wt.% Ni–2.5 wt.% Mo/ZSM-5 with high carbon deposition resistance, 2-methylnaphthalene selectivity (96.0 mol.%) in the liquid with the products with a yielded total conversion of 96.3 mol.% after an 18 h time on stream, where ethylene/propane were main (94.2 wt.%). The latter can be attributed to the presence of mesopore volume/surface area, existing boundary interface, the amount of medium/strong acid sites, and the synergetic interaction phenomena between metal atom species/supports. Attention should be paid to particle size dimensions, diameters and acidity, which facilitated poly-aromatic hydrocarbon removal. Considering particular obtained distributions, intermediates reaction pathway was proposed. Cracking, synthetic ring opening, alkylation, condensation and disproportionation were additionally involved. Results were consistent with the occurrence of two competing mechanisms, a monomolecular, as well as a bimolecular one.