A comparison of the selective catalytic reduction of NOx over Al2O3 and sulphated Al2O3 using CH3OH and C3H8 as reductants

Commercial Al2O3 has been used in the selective reduction of NOx reaction using both C3H8 and CH3OH as reductants. The CH3OH was seen to be more active at lower temperatures, converting 100% of the NOx in the reaction stream to N-2 at 350 degrees C, while the C3H8 was more active at higher temperatures. Presulphation of the Al2O3 resulted in a small decrease in the % conversion to N-2 when CH3OH was used as a reductant but resulted in the almost total quenching of N-2 formation when C3H8 was used. Individually NO, NO2 and CH3OH all adsorb on Al2O3 at ambient temperature while C3H8 was only seen to adsorb at higher temperature in the presence of adsorbed NOx and in the absence of sulphur on the surface. Gaseous O-2 increases the amount of NO which can adsorb at room temperature while preadsorbed sulphur reduces the number of 'strong' chemisorption sites for NOx. The decrease in the NOx adsorption capacity of the Al2O3 upon sulphation is cited as the primary reason for the quenching of the deNOx reaction when C3H8 is used as a reductant while the ability of both NOx and CH3OH to strongly adsorb is thought to yield a stronger resistance to sulphation in the case of the reaction when CH3OH is the reductant. (C) 1998 Elsevier Science B.V.