Methanol reforming over oxide supported transition metal catalysts.

Methanol steam (MSR) and autothermal (ATR) reforming reactions have emerged as leading candidates for H2 production to power portable fuel cells. The ATR combines steam reforming and partial oxidation reactions to produce H2 via a thermally neutral reaction. The primary focus of work described in this dissertation was to develop novel transition metal based catalysts for MSR and ATR and characterize key physical and chemical properties of the most promising materials. The Pd/ZnO and Pd/CeO2 catalysts were highly active for MSR. The Pd/ZnO catalysts had lower rates but were more selective for CO2 production than the Pd/CeO2 catalysts. The CH3OH conversion rates were proportional to the H2 chemisorption uptakes suggesting that the rate determining step was catalyzed by Pd. Results from examination of the reaction pathways, and characterization using in-situ infra-red spectroscopy and temperature programmed desorption helped explain the selectivities and isolate the surface intermediate as a formate. The CO2 selectivity depended on the acid-base properties of the catalyst with acid sites favoring CO2 production and base sites favoring CO formation. A series of Mo2C and Mo2N supported catalysts were also evaluated for MSR. The Pt/Mo2N catalyst was 50% more active than a commercial Cu/Zn/Al catalyst; however, the CO2 selectivity was substantially lower. Results from varying the reaction conditions suggested that the H2O adsorption/reaction rate on the Mo2N surface was lower than that on the Cu/Zn/Al catalyst. Additionally, CH3OH and CO competed for adsorption sites on the Pt/Mo2N catalyst. A series of ZnO supported copper-noble metal bimetallic catalysts were evaluated for ATR. The Cu/ZnO catalysts were inactive below 200°C while the noble metal based catalysts were active even at 110°C. The addition of Cu to the noble metal based catalysts significantly enhanced the activity presumably due to a synergistic interaction between Cu and the noble metal. Results from H2 chemisorption, temperature programmed reduction and N2O titration indicated that Cu did not act as a textural promoter. In fact, Cu was the dominant active site for the reaction. The noble metals facilitated the reduction of Cu at temperatures below 150°C and enabled them to participate in the reaction.Ph.D.Applied SciencesChemical engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/125865/2/3224729.pd