Reactive Calcination Route for Synthesis of Highly Active NiCo2O4 Catalyst for Abatement of Cold-Start CO–HC Emissions from LPG Vehicles

Abstract

An idea of an exotic route of reactive calcination (RC) of a precursor (co-precipitated basic carbonates of nickel and cobalt) for the synthesis of highly active NiCo2O4−δ spinel catalyst (Cat-R) for oxidation of CO and HCs emissions from LPG fueled vehicles is reported in the present paper. The route involved feed of a low concentration of chemically reactive 4.5% CO–air mixture over the precursor at low temperature of 433 K in the beginning and finally increased to 573 K. The precursor was also calcined around 573 K following two other methods: (1) conventionally in stagnant air (Cat-S) and (2) in flowing air (Cat-F) for comparative studies. The catalysts were characterized by XRD, N2 sorption techniques, TPR, SEMEDX and XPS. The formation of spinel structure is confirmed in all the catalysts. The activity measurement showed that total oxidation of lean mixture of CO–LPG occurred at the lowest temperature of 433 K over Cat-R in comparison to Cat-F (451 K) and Cat-S (458 K). The total combustion of the CO–LPG mixture at such low temperature of 433 K was never reported earlier. The remarkable activity of Cat-R over Cat-F and Cat-S in oxidation of CO–LPG mixture is due to the formation of partially reduced NiCo2O4−δ (Cat-R) oxygen deficient structure having the highest surface area smallest crystallites and highly dispersed homogeneous morphology when produced following the RC-route. The activity order of the catalysts produced by various calcination strategies for CO and LPG oxidation was as follows: RC > flowing-air > stagnant-air. Cat-R was also compared with noble metal and the catalytic activity order in the decreasing sequence was as follows: Cat-R > Cat-F > Cat-S > Cat-Pt. Stability test of the catalyst showed that the Cat-R has satisfactory catalytic stability. Thus the Cat-R is the most suitable for abatement of cold-start emissions of CO and HCs from LPG fuelled vehicles.