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. © 2016 Published by Elsevier Ltd.