The dry reforming of methane was systematically studied over a series (2-30 wt%) of Co (~5nm in size) loaded CeO2 catalysts, with an effort to elucidate the behavior of Co and ceria in the catalytic process using in-situ methods. For the systems under study, the reaction activity scaled with increasing Co loading, and a 10 wt% Co-CeO2 catalyst exhibiting the best catalytic activity and good stability at 500 °C with little evidence for carbon accumulation. The phase transitions and the nature of active components in the catalyst were investigated during pretreatment and under reaction conditions by ex-situ/in-situ techniques including X-ray diffraction (XRD) and ambient-pressure X-ray photoelectron spectroscopy (AP-XPS). These studies showed a dynamical evolution in the chemical composition of the catalysts under reaction conditions. A clear transition of Co3O4 → CoO → Co, and Ce 4+ to Ce 3+ , was observed during the temperature programmed reduction under H2 and CH4. However, introduction of CO2, led to partial re-oxidation of all components at low temperatures, followed by reduction at high temperatures. Under optimum CO and H2 producing conditions both XRD and AP-XPS indicated that the active phase involved a majority of metallic Co with a small amount of CoO both supported on a partially reduced ceria (Ce 3+ /Ce 4+). We identified the importance of dispersing Co, anchoring it onto ceria surface sites, and then utilizing the redox properties of ceria for activating and then oxidatively converting methane while inhibiting coke formation. Furthermore, a synergistic effect between cobalt and ceria and the interfacial site are essential to successfully close the catalytic cycle.

Research to demonstrate in situ laser-absorption-based sensing of H2O, CH4, CO2, and CO mole fraction is reported for the product gas line of a biomass gasifier. Spectral simulations were used to select candidate sensor wavelengths that optimize sensitive monitoring of the target species while minimizing interference from other species in the gas stream. A prototype sensor was constructed and measurements performed in the laboratory at Stanford to validate performance. Field measurements then were demonstrated in a pilot scale biomass gasifier at West Biofuels in Woodland, CA. The performance of a prototype sensor was compared for two sensor strategies: wavelength-scanned direct absorption (DA) and wavelength-scanned wavelength modulation spectroscopy (WMS). The lasers used had markedly different wavelength tuning response to injection current, and modern distributed feedback lasers (DFB) with nearly linear tuning response to injection current were shown to be superior, leading to guidelines for laser selection for sensor fabrication. Non-absorption loss in the transmitted laser intensity from particulate scattering and window fouling encouraged the use of normalized WMS measurement schemes. The complications of using normalized WMS for relatively large values of absorbance and its mitigation are discussed. A method for reducing adverse sensor performance effects of a time-varying WMS background signal is also presented. The laser absorption sensor provided measurements with the sub-second time resolution needed for gasifier control and more importantly provided precise measurements of H2O in the gasification products, which can be problematic for the typical gas chromatography sensors used by industry.

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Copper doped ceria (CuCeria) has been shown to catalyze the water gas shift (WGS) reaction (H2O + CO → H2 + CO2). The Cu+2 ion replaces Ce+4 ion in the fluorite lattice at a shifted position that allows the Cu ion to have square planar oxygen coordination. The CuCeria has been shown to be active when the Cu atom leaves the fluorite lattice [1]. In order to better understand the transformation from CuCeria to Cu particles on ceria, we have made in situ measurements of CuCeria while cycling pulses of O2 and CO. These measurements were made with a combined Diffuse reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). XRD and PDF instrument at beamline 11ID-B at the Advanced Photon Source [2]. The changes in the series of PDF data (top Figure) during the transformation appear to be minor, but can be clearly seen when data from the cyclic series of PDF measurements are demodulated by the Phase Sensitive Detection (PSD) technique (bottom Figure) [3]. The data from the oxidized portion of the PSD (blue line) show the Cu-O of the Cu in the ceria lattice and the Ce-O resolved from each other. The plot from the data in the reduced region (red line) shows the appearance of the shortest Cu-Cu contact in the Cu metal formed on the surface of the ceria. The Ce-Ce distance peak in the oxidized region is 3.75Å and increases to 3.99Å in the reduced region. The "local" structure change in nearest Ce-Ce distance is much larger than the average structure value determined from the crystalline powder pattern; however is consistent with the expected short range changes. The PSD of the simultaneous DRIFTS measurement shows several spectral features that can be correlated with the PSD of the PDF changes. The advantage of PSD analysis of the time resolved (TR) series of PDF's shows only changes to the amount of each PDF distance and the relative time that the change occurs. In this case, the changes during oxidizing and reducing conditions are resolved.