The chemical origin and catalytic activity of coinage metals: from oxidation to dehydrogenation

Abstract

The high oxidation activity of coinage metals (Cu, Ag and Au) has been widely applied in various important reactions, such as oxidation of carbon monoxide, alkenes or alcohols. The catalytic behavior of those inert metals has mostly been attributable to their size effect, the physical effect. In the present study, the chemical effects on their high oxidation activity have been investigated. We mechanistically examine the direct and oxidative dehydrogenation (partial oxidation) reactions of ethanol to acetaldehyde on a series of transition metals (groups 9, 10 and 11) with identical physical characteristics and varied chemical origins using density functional theory (DFT) calculations and electronic structure analyses at the GGA-PW91 level. The energetic results show that coinage metals have much lower activation energies and higher exothermicities for the oxidative dehydrogenation steps although they have higher energy for the direct dehydrogenation reaction. In the electronic structure analyses, coinage metals with saturated d bands can efficiently donate electrons to O* and OH*, or other electronegative adspecies, and better promote their p bands to higher energy levels. The negatively charged O* and OH* with high-lying p bands are responsible for lowering the energies in oxidative steps. The mechanistic understanding well explains the better oxidation activity of coinage metals and provides valuable information on their utilization in other useful applications, for example, the dehydrogenation process.

Semiconductor–Metal Nanofloret Hybrid Structures by Self-Processing Synthesis

“…The coinage metals and Au in particular are well-known for their catalytic role in promoting the oxidation and dehydrogenation of alcohols. 35,36 Therefore, we further studied the NF synthesis for other metals, including Ag and Cu, which together with Au constitute the coinage metal elements, all showing NF structures with different morphologies as detailed in the sections below (see Figure 7). In contrast, Pd and even Pt salts did not yield such structures, although Pt provides a high driving force for the process, further supporting the role of the coinage metals in surface-catalyzed redox reactions that drive the NF synthesis process.…”

“…We further demonstrated the role of EtOH not only as solvent but also for promoting the redox reactions by employing several other reducing agents including glucose, phenol, and ascorbic acid, all resulted in NF structures with different morphologies while keeping similar overall dH and L dimensions (Figure S13, Supporting Information). The coinage metals and Au in particular are well-known for their catalytic role in promoting the oxidation and dehydrogenation of alcohols. , Therefore, we further studied the NF synthesis for other metals, including Ag and Cu, which together with Au constitute the coinage metal elements, all showing NF structures with different morphologies as detailed in the sections below (see Figure ). In contrast, Pd and even Pt salts did not yield such structures, although Pt provides a high driving force for the process, further supporting the role of the coinage metals in surface-catalyzed redox reactions that drive the NF synthesis process.…”

Reaction Mechanism of Ethanol on Model Cobalt Catalysts: DFT Calculations

“…The traditional Bronsted-Evans−Polanyi (BEP) correlation is used to examine the thermodynamical effect on reaction barriers. In previous studies, a good linear relationship has been identified in barrier and reaction energy for C−H, C−C, and O−H dissociation on vast metal surfaces including Co. 57,58 Whether the C−H and C−C cleavages on metal oxide states as Co 2+ and Co 3+ sites we emphases hold the BEP relation is not clear. Herein the relationship of the barrier and the reaction energy on Co 2+ and Co 3+ sites is plotted in Figure 3.…”

13 Atomlu Cu-Ag-Au Üçlü Nanoalaşımların Kimyasal Sıralama ve Yapısal Özelliklerinin İncelenmesi

“…Altın ise katalizör olarak, oksidasyon, hidrojenasyon ve diğer birçok dönüşüm için başarı ile kullanılmaktadır [7]. Bu sonuçlar ışığında, Grup 11 metalleri, oksidasyon aktivitelerinde önemli bir rol oynadığı için yakıt hücrelerindeki oksijen indirgeme reaksiyonu (ORR) için en iyi katalizörlerden biri olarak kabul edilmektedir [9][10][11]. Ayrıca, Cu-Ag-Au nanoalaşımları, yüzey ayrışmaları giderek daha fazla önem kazandığı için ve özellikleri iyi bilinen Grup 11 metallerinden oluştuğu için ilgi çekmektedirler [2,12].…”