Waste ashes as catalysts for the pyrolysis–catalytic steam reforming of biomass for hydrogen-rich gas production

Combustion ashes from coal, refuse-derived fuel (RDF) and waste tyres have been investigated as potential catalysts for the production of a hydrogen-rich gas from waste biomass. The process used a two-stage reactor involving pyrolysis of the biomass followed by catalytic steam reforming of the evolved pyrolysis gases using the ash catalysts. The ashes were also impregnated with 10 wt% nickel to determine the influence on hydrogen production. In the presence of the ash samples, the total gas yield and hydrogen yield significantly increased, particularly for the refuse-derived ash. The ash samples contained a high metal content, including Al, Ca, Mg, Cu and Fe, K, Na and Zn. All such metals have been reported to act as catalysts for hydrogen production. In the absence of catalyst, the total gas yield from the biomass was 39.9 wt% which increased to 52.7 wt% with the tyre rubber ash, to 50.3 wt% with coal ash and 59.5 wt% with RDF ash. The highest hydrogen yield of 7.90 mmol g−1biomass was produced in the presence of the RDF-derived ash, representing 29.73 vol% H2. Addition of nickel to the combustion ash samples showed a further significant increase of ~ 20% in the yield of hydrogen.