Microstructural evolution and sintering of Pt nanoclusters on diatomite under CO oxidation conditions: An <em>operando</em> and 3D TEM study

In this work, we investigate the microstructural evolution and thermal stability of platinum (Pt) nanoparticles supported on natural diatomite bio-silica (SiO₂) during catalytic carbon monoxide (CO) oxidation using advanced transmission electron microscopy (TEM) techniques. Pt nanoparticles with an average size of ~1 nm were obtained by impregnating purified diatomite from Coscinodiscus sp. with a Pt(acac)₂ precursor and are preferentially located on the <em>cribrum/foramen</em> regions, where a native Fe/Al‑rich oxide layer promotes selective anchoring. <em>Operando</em> TEM combined with mass spectrometry reveals that the Pt-diatomite catalyst is active from room temperature up to 400 °C, exhibiting fast reaction kinetics between 25-100 °C and at 400 °C. Three‑dimensional electron tomography performed on the same Pt-diatomite grain before and after CO oxidation enables direct comparison of Pt nanoparticle positions and silica porosity, confirming the high structural stability of the catalyst under these conditions. The microstructural behavior was further examined up to 1000 °C under reactive atmosphere: the catalyst remains stable up to 600 °C, while at higher temperatures (600–800 °C) Pt nanoparticle sintering occurs as the Fe/Al‑oxide layer degrades, leading to enhanced CO conversion up to ~950 °C followed by partial deactivation at higher temperatures due to extensive sintering. These results provide direct nanoscale evidence of how a natural Fe/Al‑rich interfacial layer governs the stability, sintering pathways and performance of bio-silica‑supported Pt catalysts under severe CO oxidation conditions, outlining a general mechanism for the thermal stability and deactivation of bio‑derived hierarchical silica supports in high‑temperature oxidation catalysis.