Speciation-controlled incipient wetness impregnation: A rational synthetic approach to prepare sub-nanosized and highly active ceria–zirconia supported gold catalysts

• Sub-nanosized Au supported CeZrOx can be prepared by incipient-wetness impregnation.
• The control in the speciation of the gold precursor by pH adjustment is crucial.
• Metal dispersion, loading and efficiency in gold precursor usage are maximized.
• Facile preparation and easy scaling-up of very active CO oxidation catalysts.

On the basis of calculated thermodynamic species distribution diagrams and by appropriately controlling the pH of aqueous HAuCl4 solutions, it has been possible to prepare, using a Speciation-controlled Incipient Wetness Impregnation (ScIWI) approach, Au catalysts supported on ceria–zirconia mixed oxides featuring both high gold loadings and excellent metal dispersions. This rational synthesis method is carried out at room temperature. It is both much simpler, in equipment terms, and less expensive than widely used Deposition–Precipitation (DP). Moreover, the use of ScIWI allows overcoming the severe limitations of previously assayed impregnation methods. With this procedure it is possible to prepare active catalysts in CO oxidation with high efficiency in terms of gold precursor usage, i.e. minimizing Au losses during synthesis. Therefore this, quite amenable, novel strategy for the facile preparation of highly dispersed supported gold catalysts gathers the necessary requirements for both its use at lab scale and an easy scaling-up to industrial levels.

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