Reactive calcination route for synthesis of active Mn–Co3O4 spinel catalysts for abatement of CO–CH4 emissions from CNG vehicles

Abstract

The present paper described an exotic route of reactive calcination (RC) of a precursor (basic cobalt–manganese carbonate) for the synthesis of highly active Mn promoted Co3O4 spinel catalyst (Cat-R) for simultaneous oxidation of CO–CH4 emissions from CNG fuelled vehicles. The RC route involved feed of a low concentration of chemically reactive, 4.5% CO–air mixture over the precursor at low temperature in the beginning and finally increased to 400°C. The precursor was also calcined around 400°C following two other methods: (1) conventionally in stagnant air (Cat-S) and, (2) in flowing air (Cat-F). The catalysts were characterized by XRD, SEM, SEM-EDX, N2-sorption, XPS, TPR, Particle size, and FTIR techniques. The RC produced Mn promoted Co3O4 spinel (Cat-R) with the highest surface area, smallest nano-size crystallites and highly dispersed oxygen deficient structural defect morphology as compared to Cat-F and Cat-S. The Cat-R showed total oxidation of lean CO–CH4 mixture at the lowest temperature (340°C) in comparison to Cat-F (380°C) and Cat-S (420°C). A synergetic effect was observed that the temperature for total oxidation of CH4 in CO–CH4 mixture was 80°C less than when CH4 was oxidized separately over Cat-R. The remarkable activity of Cat-R over other catalysts in simultaneous oxidation of CO–CH4 was associated with the presence of its unusual textural and morphological characteristics. The activity order of the catalysts produced by various calcination strategies for CO–CH4 oxidation was as follows: Cat-R>Cat-F>Cat-S. Thus, RC route can be recommended for synthesis of highly active catalysts over conventional methods for control of CO–CH4 emissions from CNG vehicles.