Studies of Fundamental Factors Controlling Catalyzation of Reactions of Gases with Carbonaceous Solids. Final Report

摘要

Studies of the effects of catalyst particle size and composition and of reaction temperature on the gasification of graphite in H sub 2 + 2% H sub 2 O by dispersed metal catalysts have produced a fairly comprehensive understanding of the process. The experimental observations suggest that the role of catalysts is to effect dissociation of H sub 2 O. The absorbed H and O adatoms then transfer, that is, spill over, to the carbon surface and combine to form CO and CH sub 4 . Spill-over cannot occur if a thin insulating barrier is present between metal and graphite. Gasification is highly localized around each catalyst particle and results in the formation of surface channels and deep pits on single crystals of graphite due to anisotropy in carbon bonding. Similar, but extremely fine, terrace channeling occurs on the graphite microcrystalline aggregates compressed into planchets. Th rate of gasification by Fe over a wide range of particle size (approx. 10 nm to 1 mm) is determined by the total surface area. Thus the simple relation that reaction rate = wt % catalyst/particle size provides a useful guide to the activity of a particular catalyst powder. Transition metal alloys generally show a reduced level of catalytic activity. Ni-Cu alloys are of interest as they were found to produce a desirable increase in the CH sub 4 /CO ratio of the product gas. Several readily available forms of highly dispersed iron powder could be used as expendable catalyst additives for coal gasification, particularly to enhance in situ (underground) methods.