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

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 (similar to1 bar) and the kinetics of the reaction compared with the conventional high surface area Pd/gamma-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 NOx removal is discussed.