Two methods of controlling byproducts of coal gasification processes were studied in laboratory-scale apparatus. Vapor phase cracking (VPC) was investigated as a means of eliminating heavy organics from the hot gasifier exit stream by catalytic cracking. Wet oxidation was investigated as a means of eliminating phenolic compounds from the quench water used to cool the gasifier exit stream by catalytic oxidation in the aqueous phase at elevated temperature and pressure. In the VPC studies the activities of various coal-derived materials and commercial catalysts towards cracking model coal pyrolysates (such as phenol, naphthalene, and phenanthrene) were measured in the presence of simulated coal gasifier gas at 3.35 MPa and 600 to 1073 K. The most promising catalyst was a presulfided cobalt-molybdate, which almost completely eliminated phenol at 450/sup 0/C in a space time of approximately 11 seconds. Steam present in large amounts in the simulated coal gas strongly inhibited the cracking activity of many catalysts evaluated. In the wet-oxidation studies, gasifier chars, supported metal-oxide catalysts, and homogeneous catalysts were tested at 3.55 MPa and 473 to 498 K. The supported copper-oxide catalysts were the best materials found for oxidation of phenol in water and in actual gasification wastewater. In the presence of 25 g/L of copper oxide on alumina catalysts, 92 percent of the phenolics, 64 percent of the chemical oxygen demand, and 58 percent of the total organic carbon were removed from slagging fixed-bed-gasifier wastewater 34-minute residence time.