CATALYTIC REDUCTION OF NITRIC-OXIDE OVER COPPER .2. INFLUENCE OF SULFUR-DIOXIDE

The influence of sulfur dioxide on the reduction of nitric oxide over copper, in the presence of isobutene and oxygen, has been examined und er reducing conditions in the 720 to 820 K temperature range. The cata lytic activity of NO conversion was drastically decreased by the prese nce of a few ppm of SO2 in the gas phase, and the toxicity of sulfur w as reduced when the temperature was increased. The Cu sample was chara cterized by X-ray photoelectron spectroscopy, at different stages of t he reaction. It was demonstrated that sulfur dioxide poisoned NO conve rsion by hindering the partial oxidation of the hydrocarbon and by occ upying the active sites, both factors contributing to a decrease in th e surface concentration of the active intermediate (oxygenated product ). Two kinds of adsorbed sulfided species, SO42- and S2-, were identif ied on the Cu surface. At the end of the reaction, the catalyst surfac e was poisoned both by carbon and sulfur species.