Promotion effect of coating alumina supported palladium with sodium hydroxide on the catalytic conversion of nitric oxide

Abstract

The catalytic conversion of NO into nitrogen and oxygen over different Pd/Al 2O 3 catalysts was studied in a flow reactor. The catalytic activity of the catalysts was profoundly promoted by pre-coating the alumina support with NaOH before the palladium impregnation. Observed nitrogen yield was raised from 15% to 60% at a temperature of 900 K by coating a 4.8% Pd/Al 2O 3 catalyst with 13% NaOH. A simultaneous thermogravimetric-analysis and differential-scanning-calorimetry (TGA–DSC) characterization on adsorptions of NO indicated that some NO molecules were strongly adsorbed and possessed a higher enthalpy of adsorption (∼140 kJ (mol NO) −1) than Pd/Al 2O 3 (∼114 kJ (mol NO) −1). A temperature-programmed-desorption (TPD) study further indicated that some strongly adsorbed NO molecules may stay on the NaOH promoted catalysts till the system temperature was raised over 950 K. The observed increase in N 2 yield from NaOH promoted Pd/Al 2O 3 catalysts was therefore attributed to the adsorption of NO on the strongly adsorbed sites.