The objective of this program is to screen catalysts and determine operating conditions for maximizing gas and char production from the pyrolysis of coal gasification tars. The product yields from cracking a bituminous coal tar in a fixed-bed reactor were determined at various temperatures in the presence and absence of some packing materials. Synthetic zeolites, Linde LZ-Y82, Norton Zeolon 900-H (mordenite), Davison 13-X, and ultra-stable faujasite (H-Y), as well as a natural zeolite, chabazite, showed strong catalytic activity. In contrast, molecular sieves 5-A and natural erionite having smaller pore diameters were found to be much less active. Clay minerals such as kaolinite, montmorillonite and Kieselguhr exhibited catalytic activities which were similar to those of the zeolites with small pore sizes, but they were still far more effective than quartz particles. Based on the assumption of first-order kinetics, the activation energies for the tar conversion were evaluated for several packing materials. It was found that the zeolite LZ-Y82 was remarkably effective in converting tar to chars and gases in the temperature range of 350 to 500/sup 0/C, although this effectiveness decreased very rapidly with a continuous tar feed carried by an inert gas. Among the factors involved for catalytic effectiveness are (1) the effective pore size greater than about 0.7 nm (or 7A), (2) large internal surface area accessible to the tar vapor, and (3) large number of strongly acidic sites. 22 references, 6 figures, 22 tables.