PROMOTION EFFECT OF COATING ALUMINA-SUPPORTED PALLADIUM WITH SODIUM-HYDROXIDE ON THE CATALYTIC CONVERSION OF NITRIC-OXIDE

The catalytic conversion of NO into nitrogen and oxygen over different Pd/Al2O3 catalysts was studied in a flow reactor. The catalytic activ ity of the catalysts was profoundly promoted by pre-coating the alumin a support with NaOH before the palladium impregnation. Observed nitrog en yield was raised from 15% to 60% at a temperature of 900 K by coati ng a 4.8% Pd/Al2O3 catalyst with 13% NaOH. A simultaneous thermogravim etric-analysis and differential-scanning-calorimetry (TGA-DSC) charact erization on adsorptions of NO indicated that some NO molecules were s trongly adsorbed and possessed a higher enthalpy of adsorption (simila r to 140 kJ (mol NO)(-1)) than Pd/Al2O3 (similar to 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 obse rved increase in N-2 yield from NaOH promoted Pd/Al2O3 catalysts was t herefore attributed to the adsorption of NO on the strongly adsorbed s ites. (C) 1998 Elsevier Science B.V.