Sulfur poisoning of nickel-based hot gas cleaning catalysts in synthetic gasification gas

The sulfur distribution and content of nickel catalyst beds were analyzed to account for poisoning effects of sulfur on the activities of catalysts which decompose tar, ammonia and methane in synthetic gasification gas. The desorption behavior of chemisorbed sulfur from the bed materials was monitored by temperature programmed hydrogenation (TPH). Sulfur adsorbs on nickel catalysts in different chemical states depending on the process conditions. At > 900 degrees C the sulfur adsorbs on the catalyst forming an irreversible monolayer on catalyst surfaces, while at < 900 degrees C adsorbed sulfur, probably composed of polysulfides (multilayer sulfur), is desorbed from the catalyst in a sulfur-free hydrogen-containing atmosphere. However, a monolayer of sulfur still remains on the catalyst after desorption. The enhanced effect of high pressure on sulfur-poisoning of nickel catalysts can be attributed to an increased amount of adsorbed sulfur, probably in the form of polysulfides. In addition, it was established that bulk nickel sulfide is active in decomposing ammonia in high-temperature gasification gas-cleaning conditions. The activity for decomposing methane is not affected by bulk nickel sulfide formation, but that of toluene is decreased.