Operando TEM study of working TiO₂ supported Au and Au-Cu catalysts during butadiene hydrogenation

Understanding the structural stability and chemical dynamics of supported metal nanoparticles under working conditions is essential for the rational design of selective hydrogenation catalysts. In this work, we investigate monometallic Au/TiO₂ and bimetallic Au-Cu/TiO₂ catalysts during the selective hydrogenation of 1,3-butadiene using operando environmental scanning transmission electron microscopy (STEM) combined with mass spectrometry. Real-time imaging under atmospheric pressure and at temperatures up to 400 °C reveals markedly different stability and sintering behaviors between the two catalysts, while simultaneous mass spectrometry measurements confirm butadiene conversion and butene formation under reaction conditions. Monometallic Au nanoparticles remain highly stable on TiO₂, showing negligible sintering and limited morphological evolution up to 400 °C. In contrast, Au-Cu nanoparticles undergo pronounced temperature-dependent restructuring, including Ostwald ripening at 300 °C and a distinct growth mechanism at 400 °C, attributed to the reduction and reincorporation of mobile copper species into the alloy. Atomic-scale STEM analyses demonstrate that both Au and Au-Cu nanoparticles preserve a face-centered cubic structure during the reaction, while copper enrichment within Au-Cu nanoparticles is evidenced by lattice contraction at elevated temperature. These observations highlight the critical role of copper mobility and alloying effects in governing nanoparticle dynamics, hydrogen activation, and catalytic performance under reaction conditions. This operando study provides direct insights into the structure-reactivity relationships of Au-based catalysts and underscores the necessity of characterizing bimetallic systems under realistic working environments.