Broadening the Realm of Nanoporous Gold Catalysts: Preparation and Properties When Emanating from AuCu as Parent Alloy

Nanoporous gold (npAu) attracted increasing attention over the last 20 years as a highly active and selective oxidation catalyst in particular at low temperatures. Previous research mainly focused on npAu that was fabricated by corrosive dealloying of AuAg parent alloys. Yet, the use of other binary alloys, such as AuCu, promises interesting variations of the catalytic properties, when considering that residual amounts of the less noble metal were shown to be co-catalytically involved. Aiming at providing a platform for systematic studies in this direction for Cu, we not only dealt with strategies for a reliable and reproducible preparation of npAu(Cu) catalysts from AuCu, but also with their potential for CO oxidation in comparison to npAu(Ag). We were able to develop an approach based on thermally quenched Au0.3Cu0.7 alloys, providing distinct synthetic advantages as a starting material for the catalyst fabrication versus the thermodynamically more stable AuCu3 intermetallic compound. Using PCD (potentiostatically controlled dealloying), well-defined pore structures with ligament diameters of similar to 40 nm and variable residual Cu concentrations in the range between similar to 0.6 at % and similar to 1.2 at % could be straightforwardly obtained. After activating such catalysts at 150 degrees C, they reproducibly showed catalytic activity for aerobic CO oxidation in a broad temperature window between 40 degrees C and 250 degrees C. As opposed to npAu(Ag), the activity increased with decreasing residual Cu content, outperforming the former at temperatures above similar to 60 degrees C not only with respect to CO2 formation rates but also with respect to thermal stability. Based on X-ray photoelectron spectroscopic and transmission electron microscopic results, it was possible to conclude that Cu segregates to the surface and, with rising Cu bulk content, increasingly occurs in form of Cu2+ species at the surface. While the latter are expected to be catalytically inactive, Cu and Cu+ species are likely candidates for the activation of oxygen being not possible on pure Au. Nanoporous gold has emerged as a highly active oxidation catalyst, especially at low temperatures. While in the past it was predominantly synthesized from AuAg alloys, this study explores AuCu as starting material. Since residues of the less noble metal are co-catalytically involved, deviating properties are expected and were indeed observed. image