PULSE REACTION STUDIES OF TRANSIENT NATURE OF ADSORBATES DURING NO-COREACTION OVER RH SIO2/

The transient nature of adsorbates for the reaction of NO with CO over a 4 wt % Rh/SiO2 catalyst has been studied by in situ infrared spectr oscopy combined with pulse transient techniques. Dynamic behavior of i nfrared-observable Rh-NO-, Rh-NO+, Rh+(CO)(2), and linear and bridged CO reveals that dissociation of Rh-NO- oxidizes Rh-0 to Rh+; Rh+ chemi sorbs CO and NO as Rh+(CO)(2) and Rh-NO+, respectively; and Rh+(CO)(2) can either undergo reductive agglomeration or react with adsorbed oxy gen to produce CO2 at 473-523 K. At 573 K, Rh is in the reduced state where linear CO and bridged CO react with the oxygen produced from dis sociation of Rh-NO- to produce CO2. The catalyst in the reduced surfac e state is more active for the formation of N2O and CO2 products, and the response of N2O formation leads that of CO2 formation at temperatu res below the light-off temperature. The rapid CO2 response during the pulse reaction studies indicates that the reaction can quickly reach steady state at temperatures above 473 K when the reaction conditions are altered.