presents the mass balance of the products in the presence and absence of catalysts. Herein, the proportion of each pyrolysis products is presented in percentage with respect to the initial amount of biomass (dry ash free base). One can see that the yields of CO slightly increase to some extent for Cu-modified-zeolites, indicating that Cu-modified -zeolite can further pro-mote decarbonylation reactions. It should be noted that less heavy oil is remained when using Cu-modified -zeolite, suggesting that they have better cracking activity. Especially, considering the higher gaseous products and hydrocarbons selectivity, 0.5 wt%Cu-modified -zeolite possesses better performance for deoxygenation of bio-oil. One can see that less heavy oil remains in the upgraded bio-oil when using 1.00 wt% Cu-modified -zeolite,however, as shown in Fig. 4, its selectivity is lower than 0.5 wt% Cu-modified. It is possible that some of the cracked products could not be further deoxygenized but deposited on the catalyst surface. For 3.00 wt% Cu-modified -zeolite, more CO2and less CH4and H2 are obtained. The increased CO2 could be generated from the reduction of CuO by the reductive pyrolysis gas because more agglomerated CuO exists on the outer surface of -zeolite at high Cu loading, as proved from XRD and H2-TPR observations. In this case, more Cu species could appear on the catalyst, which will be also benefit for the cracking of hydrocarbons and result in more coke deposit on the catalyst surface. Similar finding about this has been reported before[23]. In addition, the water-gas shift reaction (WGSR) should also contribute for the increase of CO2 yield.