SO 2 deactivation in NO reduction by NH 3: III. Auger studies of deactivated catalysts

Abstract

Deactivation of the supported metal catalysts by SO 2 in the reduction of NO by NH 3 was studied in a differential, packed-bed flow reactor. Foils of the same metals as the catalyst were placed in the reactor with the catalysts. Auger electron spectroscopy was used to study the metal foils subsequent to reaction. At 200 °C, 50 ppm SO 2 reduced activity of Ru Al 2O 3 by only fourfold as compared with three to five orders of magnitude activity reduction for Pt Al 2O 3 , Pd Al 2O 3 , and Ni Al 2O 3 . For Pt Al 2O 3 , Pd Al 2O 3 , and Ni Al 2O 3 , the surface of the metal foils was covered with approximately a monolayer of sulfur, and there was considerable incorporation of sulfur into the bulk of the metal. The Ru foil had a very small concentration of sulfur on the surface, and no sulfur was present in the subsurface layers. All of the sulfur present was in the form of sulfide; no sulfate was observed.