This study investigated the effects of ZSM-5 impregnation with boron on its catalytic properties in catalytic fast pyrolysis (CFP) of cellulose, low-density polyethylene (LDPE), and their mixtures. A series of boron-modified ZSM-5 zeolites were prepared by impregnating a conventional ZSM-5 with different boron loadings (0.5-3 wt.%). Due to boron deposition, the acidity and pore size of ZSM-5 decreased with increasing the boron loading. When impregnated with 1 wt.% boron, ZSM-5 preserved sufficient catalytic activity for the production of valuable monoaromatic hydrocarbons and decreased the formation of undesired polyaromatic hydrocarbons in CFP of cellulose. In addition, the pore narrowing of ZSM-5 by boron deposition greatly enhanced p-xylene production over m- and o-xylenes in CFP. This result indicates that slightly decreasing the pore size of ZSM-5 can improve aromatic distribution toward more valuable products in CFP. Co-feeding of cellulose with LDPE in CFP further improved the product distribution. As a result of boron modification and co-feeding, the monoaromatic yield increased from 20.0 C% for CFP of cellulose alone with the parent ZSM-5 to 24.6 C% for co-feed CFP of cellulose and LDPE mixture (mixing ratio of 4:1) with the boron-modified ZSM-5, while the polyaromatic yield decreased from 11.3 C% to 6.0 C%. The yield for p-xylene also increased from 2.23 C% to 5.57 C% while the selectivity increased from 47.9% to 75.2%. The results indicate that ZSM-5 modification with boron and co-feeding of plastics have a beneficial effect for improving aromatic product distribution in CFP of biomass. (C) 2014 Elsevier B.V. All rights reserved.