A comparison of the selective catalytic reduction of NOx over Al 2O 3 and sulphated Al 2O 3 using CH 3OH and C 3H 8 as reductants

Abstract

Commercial Al 2O 3 has been used in the selective reduction of NOx reaction using both C 3H 8 and CH 3OH as reductants. The CH 3OH was seen to be more active at lower temperatures, converting 100% of the NOx in the reaction stream to N 2 at 350°C, while the C 3H 8 was more active at higher temperatures. Presulphation of the Al 2O 3 resulted in a small decrease in the % conversion to N 2 when CH 3OH was used as a reductant but resulted in the almost total quenching of N 2 formation when C 3H 8 was used. Individually NO, NO 2 and CH 3OH all adsorb on Al 2O 3 at ambient temperature while C 3H 8 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 Al 2O 3 upon sulphation is cited as the primary reason for the quenching of the deNOx reaction when C 3H 8 is used as a reductant while the ability of both NOx and CH 3OH to strongly adsorb is thought to yield a stronger resistance to sulphation in the case of the reaction when CH 3OH is the reductant.