Energy & Fuels 1988,2, 289-292
fouling rates, and actual as well as simulated turbine deDosit comDositions.
This work was funded by the Advanced Research Department Of and Technology Development Program. J.S.R. acknowledges funding through the Oak Ridge Associated Univ-
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ersities Postdoctoral Training Program. We appreciate the assistance of Dale W. Wilson, Jr., in construction of the apparatus, David. R. Goff in the design of the two-color optical pyrometer, and Cindy J. Romanowski for the collection of some of the experimental data. Registry No. Sodium, 7440-23-5.
NO Reduction by A1203-SupportedRhodium, Palladium, and Platinum. 2. Effects of SO2 Poisoning Jeffrey S. Hepburn and Harvey G. Stenger, Jr.* Department of Chemical Engineering, Lehigh University, Bethlehem, Pennsylvania 18015 Received March 12, 1987. Revised Manuscript Received December 3, 1987
The effects of SO2 poisoning on nitric oxide reduction using alumina-supported Pt, Pd, and Rh catalysts are reported. The reduction conditions were at typical stack gas temperatures (less than 200 "C), with hydrogen used as the reducing gas. In this work, reversible and irreversible modes of SO2 poisoning are identified. For the conditions studied in this paper, Pt is irreversibly poisoned by small pulses of SOz, while poisoning of Rh and Pd with pulses of SOz is reversible. When treated with a feed stream containing 850 ppm of SOz, all three catalysts were poisoned irreversibly and could not be regenerated by hydrogen or air at 300 "C. During poisoning, reaction selectivity decreases for N2 and increases for N20 with Pd and Rh but does not change with Pt.
Background There is a strong and continued interest to control emissions of man-made oxides of nitrogen.' Current technology accomplishes this control by selective catalytic reduction using supported metal oxide catalysts at temperatures above 400 0C.2 Future applications require a low temperature catalyst capable of reducing NO, at temperatures below 200 "C. This is desired since pending legislation would require retrofitting existing combustion facilities with NO, control. The simplest and probably most cost effective location for the catalyst unit, in retrofit installations, will be at or near the flue gas stack. Excellent NO, removal can be achieved by catalytic reduction using noble metals at stack gas temperatures.lp3 However, it is uncertain what/effect SOz will have on noble metals at these lower temperatures. The effects of SOz on the performance of noble-metal catalysts have been studied extensively for automobile c a t a l ~ s t s . ~ Summers ' and Baron4 report significant loss of NO reduction activity when Pt/AlZO3,Rh/AlZO3,and Pt-Rh/Alz03 are poisoned with 20 ppm of SO2 at 475 "C. Their work shows Rh to be most resistant to poisoning while Pt is severely inhibited. SO2 also decreases NO conversion a t 200 "C for their Pt-Rh catalyst; however, (1) Harrison, B.;Diwell, A. F,; Wyatt, M. Platinum Met. Rev. 1985, 29,50.
(2) Kiovsky, J. R.;Koradia, P. B.; Lim, R. C. Ind. Eng. Chem. Prod. Res. Deu. 1980, 19, 218. ( 3 ) Stenger, H. G., Jr.; Hepburn, J. S. Energy Fuels 1987, 1, 412. (4) Summers, J. C.; Baron, K.J. Catal. 1979, 57, 380. (5) Williamson, W. B.; Stepien, H. K.; Gandhi, H. S. Enuiron. Sci. Technol. 1980, 14, 319. (6) Kummer, J. T.J. Catal. 1975, 38, 166. (7) Jone, J. H.; Kummer, J. R.; Otto, K.; Shelef, M.; Weaver, E. E. Enurron. Sci. Technol. 1971, 5, 790.
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ita activity recovers when SO2 is removed from the feed gas if oxygen is present and does not recover if oxygen is absent. They do not address the issue of reversibility with the single-metal catalyst, nor do they present selectivity changes during poisoning. Williamson et report similar findings. Their work shows Rh to be less inhibited by SO2 than Pt at 550 OC. However, they do not report results at lower temperatures, nor do they discuss changes in selectivity for the NO reduction reactions. Although helpful in understanding SO2 poisoning effects, the results from automotive catalysts have limited applicability to the present work for two reasons. First, automotive catalysts operate at temperatures much higher than stack gases (>500"C versus
