Phyto-mediated Synthesis of CeO<sub>2</sub> Particles by Tea Residue Extract: Structure Characterization and Use for Diesel Soot Combustion

This study presents the synthesis and characterization of CeO2 particles using tea residue extract as a phytomediated approach. The synthesized CeO2 sample was conducted to test its application in the catalytic combustion of diesel soot. The thermal behavior of the as-prepared sample was evaluated by TGA/DTG. Two main weight-loss steps were identified due to the evaporation of adsorbed water and the elimination of residual organic materials. The XRD pattern showed high-intensity peaks consistent with the fluorite-type structure of CeO2 (JCPDS 34-0394) and a crystallite size was determined to be 9.51 ± 0.06 nm. Raman spectroscopy provided the main F2g mode at 463 cm−1 with a defect-induced mode at 600 cm−1, confirming the Ce-O8 vibration and tetrahedral symmetry. A signal of EPR spectra (g = 2.003) at room temperature indicated the presence of oxygen vacancy in the sample. XPS investigation further confirmed the coexistence of Ce4+ and Ce3+ ions and the oxygen vacancies presence on the synthesized CeO2 samples, demonstrating the oxygen vacancies presence and Ce3+ species, which are crucial for catalytic activity. The synthesized CeO2 exhibited superior soot catalytic combustion performance in the tight contact operation, with T50 and T90 at 440°C and 485°C, respectively. The higher catalytic activity was contributed to the larger surface area and higher concentration of oxygen vacancies. Activation energy analysis revealed lower energy barriers for soot conversion with the synthesized CeO2 compared to commercial and direct combustion (DC) samples, highlighting its potential for diesel soot control applications.