Catalytic upgrading of Kraft lignin derived bio-oil in supercritical ethanol over different crystal size hierarchical nano-HZSM5

•Reduction in HZSM5 crystal size enhanced the catalytic performance.•Alkylated guaiacols were the major compounds obtained upon bio-oil upgrading.•HHV value increased from 27.03 to 30.85 MJ/Kg upon bio-oil upgrading over HZSM5-375.•Tetrahedral Al atoms were lost from the zeolite framework after bio-oil upgrading.•Decline in the Al content reduced the catalytic performance of HZSM5-375.