Phyto-mediated Synthesis of CeO₂ Particles by Tea Residue Extract: Structure Characterization and Use for Diesel Soot Combustion

Abstract

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 F_2g 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.