Hydrogen-transfer catalytic activity of minerals common to coal

The hydrogenation/dehydrogenation catalytic activity of minerals commonly present in coal was investigated. The extent of reaction undergone by the model hydrogen-transfer system tetralin/1,2-dihydronaphthalene/naphthalene at 400 °C in the presence of these minerals was used to measure the catalytic activity. For the four most active minerals, the order of catalytic activity per gram of mineral, for a given range of particle size, is limonites > pyrites > diaspore > magnetites. The pure chemical analog of the limonites, Fe₂O₃, was found to have catalytic activity similar to that of the limonites. Heating the minerals at 400 °C before running the reaction was found to decrease these catalytic activities, despite the surface-area increases resulting from the annealing process. The catalytic activity per unit area of mineral was determined and used as an index of the catalytic activity of the reactive sites for these heterogeneous systems. The order of decreasing site catalytic activity for the more active minerals is pyrites > magnetites > diaspore > limonites. The observed mineral/ chemical compound catalytic activities indicate that the more reactive mineral hydrogenation/ dehydrogenation catalytic sites are composed of iron compounds.