Catalytic behaviour of Mn2.94M0.06O4-δ (M=Pt, Ru and Pd) catalysts for low temperature water gas shift (WGS) and CO oxidation

Abstract

Noble metal (Pt, Ru and Pd) substituted Mn3O4 catalysts have been synthesized in this work by a sonochemical route. The catalysts were characterised by XRD, XPS, TEM, H2-TPR and BET surface area analyser and the activity of these catalysts was tested towards low temperature water gas shift reaction (WGS) and CO oxidation reaction. It was observed that these catalysts have the tetragonal crystalline structure of Mn3O4 and the average particle size was found in the range of 12 nm–22 nm. H2-TPR results show that the strong metal support interaction between substituted metal and Mn3O4 leads to high reducibility and makes these catalysts active for WGS and CO oxidation. Pt substituted Mn3O4 showed higher activity towards WGS compared to other synthesized catalysts and 99.9% conversion was observed at 260 °C without methane formation. The activation energy of Mn2.94Pt0.06O4-δ was found to be 59 ± 0.6 kJ/mol. DRIFTS analysis was carried out to propose the reaction mechanism for water gas shift and CO oxidation. Redox mechanism was hypothesized for WGS and used to correlate the experimental data over Pt substituted Mn3O4. Similarly, kinetic parameters were estimated based on Langmuir-Hinshelwood mechanism for CO oxidation over Pd substituted Mn3O4 which showed better activity compare to other synthesized catalysts and 99.9% conversion was observed at 175 °C. The activation energy was calculated from Arrhenius plot which was found to be 30 ± 0.4 kJ/mol.