Hydrogen production from biomass-derived oil over monolithic Pt- and Rh-based catalysts using steam reforming and sequential cracking processes

The conversion of biomass-derived crude oil towards H2 production was investigated using continuous catalytic steam reforming and sequential cracking/reforming processes. The performances of Pt/Ce0.5Zr0.5O2 and Rh/Ce0.5Zr0.5O2 catalysts deposited on cordierite monoliths were comparatively studied. The Pt-based catalyst showed better catalytic activity than Rh for steam reforming in the whole range of steam-to-carbon molar ratios (S/C) studied, the amount of added water determining the H2 yield for both noble metals. The best H2 yield (70%, corresponding to ∼49 mmol of H2/g of bio-oil) was obtained with the Pt catalyst at S/C ratio of 10 at 780 °C, with CH4 concentrations below 1%. In the case of sequential cracking, the process alternated cracking steps, during which the bio-oil is converted into H2, CO, CO2, CH4 and carbon stored on the catalyst, with regeneration steps where the deposited coke was burnt under O2. Comparison with thermal bio-oil cracking showed that the catalyst plays a major role in enhancing the H2 productivity up to 18 mmol of H2/g of bio-oil (∼50% of H2 in gaseous products stream) and lowering the CH4 formation. The steam reforming offers high yields towards H2 but is highly endothermic, whereas the sequential cracking, despite lower H2 yields, offers a better control of coke formation and catalyst stability, and due to lower energy input can theoretically run auto-thermally.