Green synthesis of <scp> MO ₂ </scp> and Ag/ <scp> MO ₂ </scp> (M = Ce and Ti) nanomaterials using Tulsi leaf extract and its application for <scp>CO</scp> oxidation: Insights into surface interaction

Abstract This study investigates the catalytic performance of MO 2 and Ag/MO 2 (M = Ce and Ti) nanoparticles using green synthesis route using Tulsi ( Ocimum sanctum ) leaf extract. The role of quercetin flavonoid was confirmed from the Fourier transform infrared (FTIR) analysis of leaf extract and the final samples. X‐ray diffraction (XRD) analysis confirms the pure phase of all the samples and with the addition of silver, the crystallite size increases and lattice strain decreases. Ag/TiO 2 exhibited pronounced structural deformation and phase transformation, likely due to the interaction between Ag and TiO 2 lattice sites. Brunauer–Emmett–Teller (BET) surface area demonstrates a drop in porosity and surface area with silver addition that attributes to the nanoparticle growth according to Ostwald ripening. Scanning electron microscopy (SEM) analysis confirms the increased particle agglomeration and morphological heterogeneity, further corroborating structural modifications induced by silver incorporation. X‐ray photoelectron spectroscopy (XPS) confirmed the presence of Ce, Ti, Ag, and O in varying oxidation states, with partial oxidation of Ag in Ag/TiO 2 contributing to lattice distortions and enhanced surface reactivity. Catalytic performance evaluations demonstrated enhanced CO oxidation activity in Ag/TiO 2 ( T 50% = 360°C) and Ag/CeO 2 ( T 50% = 264°C) systems, attributed to increased oxygen vacancy concentrations, improved electron transfer, and surface reactivity. The proposed reaction mechanism for the supported catalyst is the Mars–van Krevelen mechanism. These findings highlight the importance of Ag dispersion and structural integrity in enhancing the catalytic performance of metal oxide‐supported catalysts for CO oxidation. The insights offered pathways for designing efficient and sustainable catalysts for air purification and energy conversion technologies.