AuOx/Ce0.6Zr0.3Y0.1O2 nano-sized catalysts active for the oxidation of methane

The nano-sized polycrystalline Ce0.6Zr0.3Y0.1O2 (CZY) support was fabricated adopting the cetyltrimethyl ammonium bromide (CTAB)-assisted hydrothermal treatment method and the CZY-supported nano-sized gold catalysts, y% AuOx/CZY (y% represents the Au weight percentage, y = 0.2–10.0), were prepared using an in situ reduction procedure with HAuCl4 as Au source, NaBH4 as reducing agent, and poly(N-vinyl-2-pyrrolidone) (PVP) as surfactant. We characterized the physicochemical properties of these materials by means of the XRD, Brunauer-Emmett-Teller (BET), high-resolution scanning electron microscopic (HRSEM), high-resolution transmission electron microscopic (HRTEM)/selected area electron diffraction (SAED), XPS, and hydrogen temperature-programmed reduction (H2-TPR) techniques, and examined their catalytic activities for the combustion of methane. It is observed that the CZY and gold were nanoparticles with the diameter of 5–50 and 2–20 nm, respectively. At a lower gold loading (y ≤ 0.6), the gold mainly existed in a highly dispersed AuOx (Au3+) domain on the CZY surfaces; at a higher gold loading (y ≥ 1.0), the gold were present in the form of metallic Au0 cluster as well as dispersed AuOx domains. With the introduction of gold, the reducibility of the y% AuOx/CZY catalysts was improved significantly, possibly due to the synergistic action between the nano-sized gold and the nanocrystalline CZY. Among the y% AuOx/CZY catalysts, the one at y = 0.2 showed the best activity for methane combustion. It is suggested that the good catalytic performance of CZY-supported gold materials with a lower gold loading (<1.0%) is associated with the high dispersion of AuOx domains, high atomic ratio of Au3+/Au0, nano-sized Au and CZY particles, and good reducibility.