Reactivity of Pd/Al2O3, Pd/La2O3-Al2O3 and Pd/LaAlO3 catalysts for the reduction of NO by CO: CO and NO adsorption

Industrially manufactured Pd catalysts supported on Al2O3, La2O3-Al2O3, and LaAlO3 were prepared to contain different amounts of PdO. The effect of the chemical state of Pd on adsorption and thermal properties of CO and NO were investigated by temperature-programmed desorption (TPD) and Fourier transform infrared spectroscopy (FT-IR). CO adsorbed molecularly on all Pd catalysts forming linear and bridged CO species. The presence of PdO was found to strongly decrease the CO binding energy on Al3O3-supported Pd catalysts, as indicated by the subsequent lowering of the temperature of the TPD peak maximum. The destabilization of CO bonding was even further enhanced on Pd catalysts supported on LaAlO3 and La2O3-Al2O3. The interaction of CO with the Al2O3, La2O3-Al2O3, and LaAlO3 supports was negligible. In contrast to the behavior of CO, NO was observed to adsorb molecularly on Al2O3, La2O3-Al2O3, and LaAlO3 supports with high efficiency. Strong absorption bands of NO in the range of 1600-1200 cm(-1) were detected. The dissociation of NO, followed by the formation of N-2 and N2O during the temperature programmed reaction, was seen on all the Pd catalysts. The importance of the chemical state of Pd and the La-induced effects on the reactivity of CO and NO are discussed. (C) 1996 Academic Press, Inc.