A Study on The Effect of Transition Metal Dopants In Ceria Praseodymium Catalyst for Soot Oxidation Activity and Its Kinetics

Abstract

The catalytic descriptors (lattice oxygen, metal-oxygen bond strength, host structure, redox capability, multi-functionality of active sites, site isolation, and phase cooperation) govern the heterogeneous oxidation reactions. The present study aims to explore the catalytic descriptors that govern the soot oxidation activity of transition metal doped Ceria-Praseodymium catalyst system and its kinetics thereof. The transition metal (0 to 20 mol %) doped Ceria-Praseodymium catalysts (Copper doped Ceria-Praseodymium, Cobalt doped Ceria-Praseodymium, Iron doped Ceria-Praseodymium, Manganese doped Ceria-Praseodymium and Chromium doped Ceria-Praseodymium) were successfully synthesized by Solution Combustion Method and characterized by X-Ray Diffraction, Raman Spectroscopy, Scanning Electron Microscopy, X-Ray Photoelectron Spectroscopy, BET & BJH surface area analysis, and tested for soot oxidation activity and its kinetic study using Thermo-gravimetric analysis. The 5 mol% Copper doped Ceria-Praseodymium catalyst system showed better soot oxidation activity which is attributed to the better reactive planes and chemisorbed oxygen species compared to other Copper-doped Ceria-Praseodymium catalyst system and Ceria-Praseodymium catalyst system. 5 mol% Cobalt doped Ceria-Praseodymium catalyst system showed better soot oxidation activity among the Co doped Ceria-Praseodymium catalysts, and the descriptors controlling the catalytic activity are phase cooperation (solid-solution formation) and better redox properties compared to Co-CP and CP catalyst systems. The descriptors controlling the soot oxidation activity of the Iron doped Ceria-Praseodymium catalyst system are (secondary phase formation and redox properties), and the 5 mol % Iron-doped Ceria-Praseodymium catalyst system showed better soot oxidation activity. In Manganese doped Ceria-Praseodymium catalyst system, the 5 mol% Manganese-doped Ceria-Praseodymium catalyst system showed better catalytic activity for the soot oxidation reaction. The descriptors controlling the soot oxidation activity are surface area, crystallite size, active surface adsorbed O- species, and Mn3+/Mn4+ surface concentration. The surface concentration of Cr3+ and Pr3+ played a significant descriptor role, and Chromium doped Ceria-Praseodymium catalyst system showed better soot oxidation activity than other Ceria-Praseodymium catalyst systems. As the Cr concentration increased, there was a decrease in the Cr3+ and Pr3+ concentrations in the Chromium-doped Ceria-Praseodymium catalyst system. Compared to all the transition metals doped Ceria-Praseodymium catalysts in the present study 5 mol % Cobalt doped Ceria-Praseodymium catalyst system showed better catalytic activity with lowest T50 of 349±1℃. ii In the transition metal (TM (5 mol%) = Cr, Mn, Fe, Co, and Cu) -doped Ceria-Praseodymium nanofiber catalysts 5 mol% Chromium doped Ceria-Praseodymium nanofiber showed better soot oxidation activity and is attributed to larger average pore size and pore volume and, the nano string diameter is smaller than all other nanofiber catalysts. The kinetic triplets namely activation energy, pre-exponential factor and the reaction models were evaluated.