Study of Ag/MO2 (M═Ce, Zr, Sn, and Ti) Nanomaterials Synthesized via Surfactant-Free One-Pot Hydrothermal Method for CO Oxidation

In this study, Ag/MO₂ (M═Ce, Zr, Sn, and Ti) nanomaterials were synthesized via a surfactant-free one-step hydrothermal process followed by calcination at 500 °C for 5 h and investigated the impact of different metal oxides on Ag-based nanomaterials as catalysts for CO oxidation. Comprehensive characterization analysis using various techniques including XRD, BET, FE-SEM with EDS and elemental mapping, TEM, HR-TEM with SAED and XPS, provided insights into the physicochemical properties of the Ag/MO₂ nanomaterials. Depending on the variation in the redox (Ag/CeO₂ and Ag/TiO₂) and nonredox (Ag/ZrO₂ and Ag/SnO₂) nature of metal oxides, Ag metallic state, crystallite sizes, surface area, morphology, and adsorbed surface oxygen are affected. The catalytic activity towards the CO oxidation was in the order: Ag/CeO₂> Ag/ZrO₂> Ag/TiO₂>> Ag/SnO₂. This enhanced performance can be attributed to the presence of metallic Ag, abundant surface oxygen (46.46%), improved interaction between metallic Ag and CeO₂ due to rice-ball structure. Ag/CeO₂ exhibited better catalytic activity even after 3 consecutive cycles toward CO oxidation (T_50% = 150 °C). This resilience can be linked to the stable spherical morphology and intact rice-ball structure. The findings demonstrate the impact of metal oxides on Ag-based nanomaterials physicochemical properties and thus CO oxidation activity.