Soot oxidation activity and kinetics of Ce0.9M0.1O2-δ (M = Cs, Mg, Ca) catalysts: Impact of Cs doping in ceria and impact of nanorods on catalytic activity

Abstract

Solution combustion method is used to synthesize Ce<inf>0.9</inf>M<inf>0.1</inf>O<inf>2-δ</inf> (M = Cs, Mg, Ca) catalysts and calcined at 600 °C/5 h. XRD and Raman Spectroscopy Analyses the chemical structure, the phases observed, and the oxygen defects in the synthesized catalysts. A cubic fluorite structure of CeO<inf>2</inf> has been noticed for all the catalysts from XRD and Raman Spectroscopy analyses. FE-SEM micrographs are used to analyze the morphology of the Ce<inf>0.9</inf>M<inf>0.1</inf>O<inf>2-δ</inf> (M = Cs, Mg, Ca) catalysts. Ce<inf>0.9</inf>Cs<inf>0.1</inf>O<inf>2-δ</inf> catalyst shows the presence of nanorods (diameter: 63 nm), which are not seen in the other catalysts. The redox and surface properties of the synthesized catalysts are tested by H<inf>2</inf>-Temperature Programmed Reduction (H<inf>2</inf>-TPR) and O<inf>2</inf>-Temperature Programmed Desorption (O<inf>2</inf>-TPD), respectively. The Ce<inf>0.9</inf>Cs<inf>0.1</inf>O<inf>2-δ</inf> catalyst shows the greatest degree of reducibility from TPR studies and for the Ce<inf>0.9</inf>Cs<inf>0.1</inf>O<inf>2-δ</inf> catalyst, the oxygen species evolved from the O<inf>2</inf>-TPD studies are also the highest. Thermogravimetric Analysis (TGA) has been used to carry the soot oxidation activity of the developed catalysts. Soot oxidation kinetic studies have been conducted at different heating rates (5, 10, and 15 °C/min) for the catalysts. The kinetic triplets for the developed catalysts have been obtained, and rate plots ([Formula presented] vs. temperature) and Arrhenius plots (ln(k) vs. [Formula presented]) have been developed for the catalysts. From the soot oxidation and kinetic studies for the developed catalysts, Ce<inf>0.9</inf>Cs<inf>0.1</inf>O<inf>2-δ</inf> shows better soot oxidation activity (T<inf>50</inf> = 372 °C) than the other two catalysts, while Ce<inf>0.9</inf>Mg<inf>0.1</inf>O<inf>2-δ</inf> (T<inf>50</inf> = 556 °C) shows the lowest soot oxidation activity. All the catalysts follow a non-integral exponential model for soot oxidation, and the Ce<inf>0.9</inf>Cs<inf>0.1</inf>O<inf>2-δ</inf> catalyst has the lowest activation energy. © 2024 Institution of Chemical Engineers