431055 Highly Active Atomically Dispersed Gold/Titania Methanol Steam Reforming Catalysts Stabilized By Sodium Ions

Thursday, November 12, 2015: 1:50 PM
355C (Salt Palace Convention Center)
Chongyang Wang1, Ming Yang1, Jilei Liu1, Sungsik Lee2, Lawrence Allard3 and Maria Flytzani-Stephanopoulos1, (1)Department of Chemical and Biological Engineering, Tufts University, Medford, MA, (2)X-ray Science Division, Advanced Photonic Source, Argonne National Laboratory, Lemont, IL, (3)Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN

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[4]. 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[5], 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[2] or composite oxides, such as Au-ZnZrOx[1]. 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.

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See more of this Session: Atomically Dispersed Supported Metal Catalysts
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