Graduation Year

2012

Document Type

Thesis

Degree

M.S.C.H.

Degree Granting Department

Chemical Engineering

Major Professor

John N. Kuhn

Keywords

ceria, cobalt, molybdenum doping, spinel, WGS

Abstract

As traditional sources of energy become depleted, significant research interest has gone into conversion of biomass into renewable fuels. Biomass-derived synthesis gas typically contains concentrations of approximately 30 to 600 ppm H2S in stream. H2S is a catalyst poison which adversely affects downstream processing of hydrogen for gas to liquid plants. The water-gas shift reaction is an integral part of converting CO and steam to H2 and CO2. Currently, all known water-gas shift catalysts deactivate in sulfur concentrations typical of biomass-derived synthesis gas. Novel catalysts are needed to remain active in the presence of sulfur concentrations in order to boost efficiency and mitigate costs. Previous studies have shown molybdenum to be active in concentrations of sulfur greater than 300 ppm. Cobalt has been shown to be active as a spinel in concentrations of sulfur less than 240 ppm. Ceria has received attention as a WGS catalyst due to its oxygen donating properties. These elements were synthesized via Pechini's method into various blends of spinel metal oxide solutions. Initial activity testing at lower steam to gas ratios produced near equilibrium conversions for a Ce-Co spinel which remained active in 500 ppm H2S over a temperature range of 350 °C to 400 °C. The catalysts became poisoned and deactivated in higher concentrations of sulfur. Addition of molybdenum to the Ce-Co base had little effect on sulfur tolerance, but it did lead to a reduction in selectivity for methanation. Surface area increased due to adsorbed H2S, and X-Ray Diffraction confirmed that bulk sulfiding did not occur. Incorporation of Ce and Co into a Fe spinel hindered conversion at lower temperatures and deactivated in higher levels of sulfur.

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