ABSTRACT
In situ monitoring of electrocatalytic processes at solid-liquid interfaces is essential for the fundamental understanding of reaction mechanisms, yet quite challenging. Herein, Pt-on-Au nanocatalysts with a Au-core Pt-satellite superstructure have been fabricated. In such Pt-on-Au nanocatalysts, the Au cores can greatly amplify the Raman signals of the species adsorbed on Pt, allowing the in situ surface-enhanced Raman spectroscopy (SERS) study of the electrocatalytic reactions on Pt. Using the combination of an electrochemical method and in situ SERS, size effects of Pt on the catalytic performance of the core-satellite nanocomposites towards CO and methanol electrooxidation are revealed. It is found that such Pt-on-Au nanocomposites show improved activity and long-term stability for the electrooxidation of CO and methanol with a decrease in the Pt size. This work demonstrates an effective strategy to achieve the in situ monitoring of electrocatalytic processes and to simultaneously boost their catalytic performance towards electrooxidation.
ABSTRACT
Insightful understanding of how interfacial structures and properties affect catalytic processes is one of the most challenging issues in heterogeneous catalysis. Here, the essential roles of Pt-Au and Pt-oxide-Au interfaces on the activation of H2 and the hydrogenation of para-nitrothiophenol (pNTP) were studied at molecular level by in situ surface-enhanced Raman spectroscopy (SERS) and shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS). Pt-Au and Pt-oxide-Au interfaces were fabricated through the synthesis of Pt-on-Au and Pt-on-SHINs nanocomposites. Direct spectroscopic evidence demonstrates that the atomic hydrogen species generated on the Pt nanocatalysts can spill over from Pt to Au via the Pt-Au and Pt-TiO2-Au interfaces, but would be blocked at the Pt-SiO2-Au interfaces, leading to the different reaction pathways and product selectivity on Pt-on-Au and Pt-on-SHINs nanocomposites. Such findings have also been verified by the density functional theory calculation. In addition, it is found that nanocatalysts assembled on pinhole-free shell-isolated nanoparticles (Pt-on-pinhole-free-SHINs) can override the influence of the Au core on the reaction and can be applied as promising platforms for the in situ study of heterogeneous catalysis. This work offers a concrete example of how SERS/SHINERS elucidate details about in situ reaction and helps to dig out the fundamental role of interfaces in catalysis.
ABSTRACT
Surface molecular information acquired in situ from a catalytic process can greatly promote the rational design of highly efficient catalysts by revealing structure-activity relationships and reaction mechanisms. Raman spectroscopy can provide this rich structural information, but normal Raman is not sensitive enough to detect trace active species adsorbed on the surface of catalysts. Here we develop a general method for in situ monitoring of heterogeneous catalytic processes through shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) satellite nanocomposites (Au-core silica-shell nanocatalyst-satellite structures), which are stable and have extremely high surface Raman sensitivity. By combining operando SHINERS with density functional theory calculations, we identify the working mechanisms for CO oxidation over PtFe and Pd nanocatalysts, which are typical low- and high-temperature catalysts, respectively. Active species, such as surface oxides, superoxide/peroxide species and Pd-C/Pt-C bonds are directly observed during the reactions. We demonstrate that in situ SHINERS can provide a deep understanding of the fundamental concepts of catalysis.
