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The promoting impact of alkali metals (i.e., Li, Na, K, Rb, Cs) on the carburization rate of Fe in Fe/Si catalysts was investigated by X-ray absorption spectroscopy. A multisample holder was used, allowing nearly simultaneous examination of the catalysts during activation in a CO/He mixture. With the white line intensity and shape as a fingerprint for oxidation state, TPR/XANES analysis enabled us to measure the relative composition of the different compounds as a function of the carburization time, temperature, and atomic number of the group 1 promoter. At the same time, TPR/EXAFS provided information on the changes in local atomic structure that accompanied the oxidation state changes. The rate of carburization increased in the following order: unpromoted < Li < Na < K = Rb = Cs. After 10 h of treatment the samples containing K, Rb, and Cs were completely carburized, and residual quantities of iron oxides were detected in both unpromoted and Li-promoted samples. The EXAFS spectra after carburization could be fitted well by considering a model containing Hägg carbide and Fe3O4. After 10 h of CO/He treatment at 290 °C, the main component observed was Hägg carbide. A model containing Hägg and ε-carbides, and Fe3O4, was also investigated. However, the r-factor was not significantly impacted by including ε-carbide in the fitting, and the resulting contribution of ε-carbide in each catalyst from the model was virtually negligible. Selectivity differences are thus not likely due to changes in the carbide distribution. Rather, the alkali promoter increases the CO dissociative adsorption rate, resulting in an increase in the surface coverage of dissociated CO and an inhibition in the olefin readsorption rate. This in turn results in higher olefin selectivities, in agreement with previous catalytic tests.

A series of hydrogen transfer reactions has been done using model compounds (donors and acceptors) at reaction conditions consistent with coal liquefaction. Emphasis was placed upon acceptors having C-C linkages and oxygen compounds with functionality likely to be present in coal. The cracking of dibenzyl was shown to be faster than that of diphenylbutane, diphenylmethane, and I-phenylhexane at 400-450 O C . With oxygen-containing compounds, the relative order of reactivity was: furans < phenols < ketones < aldehydes < chain ethers. A study of hydrogen transfer using either a deuterium atmosphere or deuterium-tagged donors was undertaken with the oxygen-containing compounds. It was shown that much of the hydrogen necessary to stabilize free radicals comes from the donor solvent or intramolecular rearrangement and not from dissolved gas.A simplified transient model of diffusion and reaction is considered in the stagnant boundary layer that surrounds a carbon particle during combustion. The model is used to develop local asymptotic stability criteria for analysis of the multiple steady states. A special case arises when carbon monoxide burns outside the boundary layer as the linearized conservation equations are then solvable by a finite Fourier transform. In the more general case, results are obtained by Galerkin's method. Regions of instability created by variation of the particle size and ambient oxygen concentration are presented.

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