Bimetallic AuPd catalysts have been extensively studied for many liquid-phase oxidation reactions in recent years and are often reported to be active and stable in these applications. However, reports on the use of these catalysts for low-temperature gas-phase reactions such as CO oxidation and water-gas shift are scarce. Here we initially established the presence of a synergistic effect in a range of AuPd/CeZrO4 catalysts by measuring their activity for the selective oxidation of benzyl alcohol. The catalysts were then evaluated for WGS, CO oxidation and formic acid decomposition (Fig. 1), all of which are believed to be mechanistically related. The introduction of Pd to a mono-metallic Au catalyst significantly reduced the catalytic activity for the gas-phase reactions. Furthermore, mono-metallic Pd was more active than Pd-rich bimetallic catalysts. This effect was characterized as anti-synergy between Au and Pd. The nature of this effect was probed by several techniques that all indicated nano-particle growth occurred upon Pd addition. In situ CO-DRIFTS (Fig. 2a) revealed that the molar ratio of the metals was related to the number of interfacial adsorption sites and this could be correlated with catalytic activity. XPS analysis showed a similar correlation whereby the presence of Au0* was correlated with catalytic activity. (Fig. 2b). It was therefore proposed that peripheral Au0* species form part of the active centers in the most active catalysts for the three gas-phase reactions.

Synergy and anti-synergy between palladium and gold in nano-particles dispersed on a reducible support

253rd National Meeting (2017)

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