Variability of surface components in gold catalysts - The role of hydroxyls and state of gold on activity and selectivity of Au-Nb2O5 and Au-ZnNb2O6 in methanol oxidation

- As made Au-Nb2O5 and Au-ZnNb2O6 contain (Au0)δ− and acidic hydroxyls.
- Dehydroxylation of catalysts leads to oxygen defects, Au0 and nucleophilic oxygen.
- Rehydroxylation during MeOH oxidation generates basic hydroxyls and rebuilds (Au0)δ−.
- Rehydroxylated gold catalysts present much higher activity than dehydroxylated ones.
- Activity jump is faster on Au-ZnNb2O6 than on Au-Nb2O5 due to easier e− transfer.

The aim of this study was to use gold catalysts supported on niobium(V) oxide and mixed niobium-zinc oxide in methanol oxidation and to characterize step by step changes in the surface of catalysts that were caused by the activation of the catalyst and methanol oxidation. The purpose was to identify the species important for the activity and selectivity of the reaction. The following surface species were identified by XPS in as prepared catalysts: (i) highly nucleophilic oxygen with the excessive negative charge; (ii) lattice oxygen O2− in the metal oxide; (iii) oxygen in surface hydroxyls; (iv) negatively charged gold NPs (Au0)δ−; and (v) metal cations (niobium, zinc and gold). Activation of catalysts resulted in dehydroxylation accompanied by the formation of highly nucleophilic oxygen and metallic gold showing low activity in selective methanol oxidation. The interaction of the reaction products changed surface species towards basic hydroxyls and next to (Au0)δ− inducing the activity jump and total oxidation of methanol.

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