Per Tunå

Catalytic Abatement of NH3 Using NOx in Reducing Environment

Removal of ammonia from synthesis gas is an important step in gas purification to prevent poisoning of downstream catalyst or formation of nitrogen oxides on combustion. This publication proposes that ammonia can be removed by using selective catalytic abatement with NOx, not unlike the selective catalytic reduction of NOx but under reducing environment. Two different catalysts have been used for the experiments; V2O5/WO3/TiO2 and H-mordenite. The conducted experiments were performed on a model synthesis gas and served to investigate the selectivity and to some extent the longevity of these catalysts under reducing atmosphere, and also the effect of water on the catalyst performance. A number of catalyst characterisation methods have been used to obtain a better understanding of the catalyst morphology and surface. The methods that have been used are Raman spectroscopy, Brunauer–Emmett–Teller nitrogen adsorption, X-ray diffraction and temperature programmed desorption using ammonia. The initial performance with respect to conversion and selectivity is good for the vanadia-based catalyst, but it is not chemically stable. This is manifested by a change in the catalyst crystal structure suggesting an oxygen depletion of the titania support and decreased activity with time-on-stream. The mordenite catalyst is stable but the activity and selectivity, especially to avoid the formation of N2O, needs to be improved before implementation. Based on the experimental work performed, none of the catalysts in their present state are suitable for the proposed operating conditions.