ELSEVIER Applied Catalysis B: Environmental 14 (1997) 305-321 6. ENVIRONMENTAL Sulphur poisoning of nickel-based hot gas cleaning catalysts in synthetic gasification gas II. Chemisorption of hydrogen sulphide Jouko Hepola*, Pekka Simell VTT Energy, Energy Production Technologies, Espoo, Finland Received 4 September 1996; received in revised form 14 April 1997; accepted 20 April 1997 Abstract The effect of different components of gasification gas on sulphur poisoning of nickel catalysts were studied. In addition, the sulphur distribution and content of nickel catalyst beds were analysed to account the poisoning effect of sulphur on the activity of catalysts to decompose tar, ammonia and methane. The desorption behaviour of chemisorbed sulphur from the bed materials was monitored by temperature programmed hydrogenation (TPH). It was established that bulk nickel sulphide was active in decomposing ammonia in high-temperature gasification gas-cleaning conditions. The decomposing activity of methane was not affected by bulk nickel sulphide formation, but that of toluene was decreased. The activity of the catalyst regained rapidly when H2S was removed from the gas. However, the conversion of ammonia was not regained at as high a level as before sulphur addition, most probably due to irreversible sulphur adsorption on the catalyst. The temperature increase could also be used to regenerate the catalyst performance especially in respect to methane and toluene. Sulphur adsorbed on nickel catalysts in different chemical states depends on the process conditions applied. At >9Oo” C the sulphur adsorbed on the catalyst formed an irreversible monolayer on the catalyst surfaces, while at <9OO” C the adsorbed sulphur, probably composed of polysulphides (multilayer sulphur), was desorbed from the catalyst in sulphur-free hydrogen containing atmosphere. However, a monolayer of sulphur still remained on the catalyst after desorption. The enhanced effect of high total pressure on sulphur-poisoning of nickel catalysts could be accounted for the increased amount of sulphur, probably as a mode of polysulphides, adsorbed on the catalyst. 6 1997 Elsevier Science B.V. Keywords: Ammonia; Biomass; Gasification; Hot gas cleaning; Poisoning; Nickel catalyst; Sulfur; Tar 1. Introduction Nickel based catalysts have proved to be very efficient in decomposing tar, ammonia and methane in biomass gasification gas mixture at about 900°C. *Corresponding author. Tel.: +358 9 456 6590; fax: +358 9 460 493; e-mail: jouko.hepola@vtt.fi However, especially in pressurised conditions the effect of the catalyst is decreased due to sulphur adsorption on the nickel surfaces. On the other hand, ammonia conversion seemed to be enhanced by high H2S concentrations in gas [ 11. Due to the high number of gas components in the real gasification gas mixture, it is very difficult to separate the influence of different gas components on the sulphur poisoning of catalysts. 0926-860X/97/$17.00 c 1997 Elsevier Science B.V. All rights reserved. PII SO926-3373(97)00030-l