Preparation Of Unsupported Nanoporous Gold/Metallic Oxide Catalysts And Study Of Their Catalytic Performance For CO Oxidation

Au catalysts is represents an interesting class of heterogeneous catalysts. Currently, supported gold nanoparticle catalysts prepared by chemical methods have been most extensively investigated. It is noted that the apparent catalytic activity of supported gold nanocatalysts is considered to be a result of interplay among many factors, including particle size, nature of the support, etc. Therefore, the study on the catalytic activity of the catalyst becomes complicated. In contrast to supported gold catalyst systems, unsupported systems have attracted more and more attention. Moreover, unsupported gold catalysts allow the relevant catalytic mechanisms to be more easily understood due to the exclusion of the effect of the supports.The role of metallic oxide is a topic of continuous debate for the CO oxidation. At present, dealloying has proven to be a powerful and versatile method in producing bicontinuous interconnected nanoporous materials. Considering that the dealloying process is a competition between reactive metal-dissolution-induced surface roughening and Au-diffusion-induced surface smoothing, the dissertation focuses on the preparation of nanoporous gold?NPG? catalysts with similar ligament size and active or inert oxide residues by a simple electrochemical dealloying method. The microstructure and morphology of NPG catalysts were characterized in detail by means of SEM, BET, and XPS etc. Then, we explore the catalytic performances of the unsupported NPG catalysts for low-temperature CO catalytic oxidation.Firstly, we carefully analyzed the phase diagram between Au and Cu, Al, Mn atoms. The AuM?Mn, Cu, Al? alloy foils with 15:85 at.% were selected. The corresponding high-purity metals?>99.99%? Mn, Cu, Al, and Au were mixed and refined. Then, we mainly investigated the effect of different applied voltages, different electrolyte solutions, and the concentration of solution on the structure and ligament size of NPG catalysts during the process of electrochemical dealloying. The NPG catalysts with the so-called “active CuO” and “inert Al₂O₃” residues were successfully fabricated under the optimized corrosion condition, characterized by a bicontinuous interconnected network architecture with narrow ligament size distribution less than 10 nm.Next, we systematically explored the CO catalytic activity over the two unsupported NPG catalysts. By comparison, NPG_?Cu? and NPG_?Al? catalysts showed similar reaction rates, turnover frequency, and reaction kinetics, which demonstrate that different types of residual surface oxides have almost no effect on the catalytic activity of NPG toward CO oxidation. It can be concluded that it is metallic gold that plays the catalytic role in this unsupported NPG system, this would never exclude the possibility that higher content of residual metallic Cu or Al could also contribute to the enhancement of the catalytic performance.In addition, the NPG catalysts with different ligament sizes were successfully fabricated by the electrochemical dealloying of AuMn alloy. We systematically explored the catalytic activity of unsupported NPG_?Mn? catalysts for low temperature CO oxidation at 303 K. The results showed that the catalytic activity toward CO gradually decreased with the increase of ligament size while the long-term catalytic stability of NPG increased. NPG_?Mn? with narrow ligament size?15 nm? shows a conversion of 48.0% at 303 K. By comparison, NPG with larger ligament size showed a poor catalytic activity for CO oxidation than NPG with smaller ligament size?15 nm?. This can be attributed to a sharp decrease of low-coordinated gold atoms existing on the NPG surface, which leads to the decrease of catalytic activity of gold for CO oxidation.