Adsorption and reduction of NO on tin(IV) oxide doped with chromium(III) oxide

Abstract

Rates for NO chemisorption were measured on SnO 2 containing small amounts of Cr 2O 3. Evaluation of the NO chemisorption rate was done by the Elovich equation. Very large increases in the rate and amount of adsorbed NO were obtained by adding 1% Cr 2O 3 to SnO 2. It was found that preadsorbed NO promotes the adsorption of CO. Analyses of the gas-phase during the adsorption and thermal desorption measurements indicated that the extent of the dissociative adsorption of NO was greatly enhanced by adding Cr 2O 3 to SnO 2. The catalytic reduction of NO with CO on pure SnO 2 proceeded with reproducible rates and complete conversion only above 360 °C. Catalytic reaction was detected below 200 °C as well. The conversion of NO, however, was much less and the surface very soon became poisoned by CO. A marked increase in the efficiency of the catalyst was experienced when a small amount of Cr 2O 3 was incorporated into the SnO 2. The reduction of NO with CO occurred with a complete conversion and well-measurable rates at 150–220 °C. CO exerted no poisoning effect at all. The high activity of SnO 2 containing Cr 2O 3 is attributed to the chromium ions located in the surface layer of SnO 2, which can easily be oxidized by NO and rapidly reduced by CO. A possible mechanism of the catalytic reduction of NO is discussed.