Two separate aspects of hot-gas conditioning for molten carbonate fuel cells (MCFC) were investigated under this contract: potential high temperature chloride sorbent materials were sreened and tested and carbon deposition on MCFC components was studied experimentally to determine guidelines for maximizing MCFC efficiency while avoiding carbon fouling. Natural minerals containing sodium carbonate were identified as the most promising candidates for economical removal of chlorides from coal gasifier effluents at temperatures of about 800 K (980/sup 0/F). The mineral Shortite was tested in a fixed bed and found to perform remarkably well with no calcination. Using Shortite we were able to achieve the program goal of less than 1 ppmV chlorides at 800 K. Shortite is an abundant mineral with no competing commercial demand, so it should provide an economical chloride cleanup sorbent. Measurements showed that carbon deposition can occur in the equilibrium carbon freee region because of the relative rates of the relevant reactions. On all surfaces tested, the Boudouard carbon formation reaction is much faster than the water-gas shift reaction which is much faster than the methanation reaction. This means that the normal practice of adding steam to prevent carbon formation will only succeed if flows are slow enough for the water shift reaction to go substantially to completion. More direct suppression of carbon formation can be achieved by CO/sub 2/ addition through anode recycle to force the Boudouard reaction backward. Addition of steam or CO/sub 2/ must be minimized to attain the highest possible MCFC efficiency. 28 references, 31 figures, 22 tables.