(678e) Highly Active Atomically Dispersed Gold/Titania Methanol Steam Reforming Catalysts Stabilized By Sodium Ions
The gold-catalyzed reaction of steam reforming of methanol (SRM) has been studied on various oxide supports (e.g. CeO2, ZnO, and ZrO2) and demonstrated to achieve a wide temperature window for CO-free hydrogen production[1-3]. The apparent activation energy of the SRM reaction rate is 110±8 kJ/mol for all supported gold catalysts regardless of the support oxide employed, indicating a similar reaction mechanism, with Au-Ox as the active site. However, the overall activity of the catalyst relies on the capacity of the support oxide to anchor gold active center through Au-Ox-support linkages. In this work, Au/TiO2 was investigated for the first time as a low-temperature SRM catalyst. Applying gold by deposition-precipitation, the anatase TiO2 surface failed to preserve active gold species under the reaction conditions. Gold nanoparticles (~ 6.2 nm) were formed, resulting in poor SRM catalytic performance.
Inspired by the concept of the alkali stabilized Au-Ox- species for the WGS reaction on inert support oxides, we developed a one-step synthesis route to create exclusively single-gold-atom centric clusters stabilized by the –O-Na linkages in an alkaline solution, without the involvement of the TiO2 support. A simple incipient impregnation (IWI) of the new gold precursor on the TiO2 support achieved the atomic dispersion (100 %) of the cationic gold up to 1 wt.%. Without further treatment, the new Au-Na-TiO2 catalysts give high activity, H2-selectivity, and stability in the low-temperature SRM reaction (200-300˚C). The identified single-site Au(I)-O(OH)x- species serve as the catalytic centers for the reaction, showing similar intrinsic activity as other atomically dispersed gold anchored on CeO2 or composite oxides, such as Au-ZnZrOx. The present work opens a new practical route to prepare a new group of heterogeneous gold catalysts that may be active for other low-temperature fuel-gas processing reactions.