Three biomass-to-liquid process steps (volatilization of cellulose, tar-cleaning of organic products, and water-gas-shift of the gaseous effluent) have been integrated into a single autothermal catalytic reactor for the production of high quality synthesis gas at millisecond residence times (∼30 ms). Particles of cellulose (∼300 μm) were directly impinged upon the hot, catalytic bed of Rh–Ce/γ-Al2O3 catalyst on 1.3 mm α-Al2O3 spheres in the presence of O2, N2, and steam in a continuous flow fixed-bed reactor at 500–1100 °C. Complete conversion to gases was observed for all experimental parameters including N2/O2, S/C, the total flow rate of cellulose, and the fuel-to-oxygen ratio (C/O). The addition of steam increased the selectivity to H2 and decreased the selectivity to CO in agreement with water-gas-shift equilibrium. Optimal conditions produced a clean gaseous effluent which exhibited ∼80% selectivity to H2 at a synthesis gas ratio of H2/CO = 2.3 with no dilution from N2 at a fuel efficiency of ∼75%. Carbon-free processing was explained by relating the domain of experimental parameters to the thermodynamic prediction for the formation of solid carbon, CS.