Enhancing pyrolysis gas and bio-oil formation through transition metals as in situ catalysts

•Effectiveness of six transition metal catalysts on cellulose pyrolysis investigated.•Bio-oil and non-condensable gases analyzed to determine catalytic effect.•Copper and nickel produced higher hydrogen gas yields at lower temperatures.•Copper and nickel reduced tar compounds formed at high sweep-gas flow rates.•At lower temperatures copper enhances conversion but not to completion.