Vibrational spectroscopic studies on CO adsorption, NO adsorption CO + NO reaction on Pd model catalysts

Abstract

CO adsorption, NO adsorption and CO + NO reaction on various Pd model catalysts have been studied using vibrational spectroscopy from ultrahigh vacuum (UHV) up to elevated pressures (∼1 bar) and the kinetics of the reaction compared with the conventional high surface area Pd/γ-Al₂O₃ catalysts. The structure sensitivity of the CO + NO reaction on different Pd surfaces is explained using Pd(111), Pd(100) single crystals and planar Pd/SiO₂/Mo(110), Pd/SiO₂/Mo(112), Pd/Al₂O₃/Ta(110) supported model catalysts by emphasizing the particle size/morphology effects and particle-support interactions. A reaction intermediate, isocyanate (–NCO), is detected via in situ vibrational spectroscopy at elevated pressures on Pd(111) single crystal surface and the significance of this reaction intermediate on the improvement of the catalytic NO_x removal is discussed.