Gold nanoparticles (NPs) have attracted attention due to their superior catalytic performance in CO oxidation at low temperatures. Along with the size and shape of Au NPs, the catalytic function of Au-catalyzed CO oxidation can be further optimized by controlling the physicochemical properties of oxide-supporting materials. We applied a combinatorial approach of experimental analyses and theoretical interpretations to study the effect of a surface structure of supporting oxides and the corresponding CO oxidation activity of supported Au NPs. We synthesized Au NPs (average d ≈ 3 nm) supported on shape-controlled CeO2 nanocrystals, Au/CeO2 cubes, and Au/CeO2 octahedra for experimental analyses. The catalysts were modeled as Au/CeO2(100) and Au/CeO2(111) via density functional theory (DFT) calculations. The DFT calculations showed that the O–C–O type reaction intermediate could be spontaneously formed at the Au–CeO2(100) interface upon sequential multi-CO adsorption, accelerating CO oxidation via the Mars-van Krevelen mechanism. The additional kinetic process required for O–C–O formation at the Au–CeO2(111) interface slowed down the reaction. The experimental turnover frequency (TOF) of the Au/CeO2 cubes was 4 times greater than that of the Au/CeO2 octahedra (under 0.05 bar CO and 0.13 bar O2). The increasing TOF as a function of CO partial pressure and the positive correlation between the reducibility of CeO2 and the catalytic activity of Au/CeO2 catalysts confirmed the theoretical prediction that CO molecules occupy the surface of Au NPs and that the oxidation of Au-bound CO occurs at the Au–CeO2 interface. Through a comparative study of DFT calculations and in-depth experimental analyses, we provide insights into the catalytic function of CeO2-supported Au NPs toward CO oxidation depending on the shape of CeO2 and ratio of CO/O2.

Catalytic supremacy of Pt-single atoms achieved by CeOx–TiO2 interfaces.

No abstract

Direct graphene synthesis on substrates via chemical vapor deposition (CVD) is an attractive approach for manufacturing flexible electronic devices. The temperature for graphene synthesis must be below ∼200 °C to prevent substrate deformation while fabricating flexible devices on plastic substrates. Herein, we report a process whereby defect-free graphene is directly synthesized on a variety of substrates via the introduction of an ultrathin Ti catalytic layer, due to the strong affinity of Ti to carbon. Ti with a thickness of 10 nm was naturally oxidized by exposure to air before and after the graphene synthesis, and the various functions of neither the substrates nor the graphene were influenced. This report offers experimental evidence of high-quality graphene synthesis on Ti-coated substrates at 150 °C via CVD. The proposed methodology was applied to the fabrication of flexible and transparent thin-film capacitors with top electrodes of high-quality graphene.

The catalytic activity derived from the metal–support interaction at the Pt–CeO2 interface can be demonstrated by the two descriptors of Pt particle size and CeO2 morphology.

Utilization of carbon dioxide (CO2) molecules leads to increased interest in the sustainable synthesis of methane (CH4) or methanol (CH3OH). The representative reaction intermediate consisting of a carbonyl or formate group determines yields of the fuel source during catalytic reactions. However, their selective initial surface reaction processes have been assumed without a fundamental understanding at the molecular level. Here, we report direct observations of spontaneous CO2 dissociation over the model rhodium (Rh) catalyst at 0.1 mbar CO2. The linear geometry of CO2 gas molecules turns into a chemically active bent-structure at the interface, which allows non-uniform charge transfers between chemisorbed CO2 and surface Rh atoms. By combining scanning tunneling microscopy, X-ray photoelectron spectroscopy at near-ambient pressure, and computational calculations, we reveal strong evidence for chemical bond cleavage of O‒CO* with ordered intermediates structure formation of (2 × 2)-CO on an atomically flat Rh(111) surface at room temperature.

In this study, we report a facile synthetic pathway to three-dimensional (3D) Pd nanosponge-shaped networks wrapped by graphene dots (Pd@G-NSs), which show superior electrocatalytic activity toward the hydrogen evolution reaction (HER) and exhibited excellent long-term stability in acidic media. Pd@G-NSs were synthesized by simply mixing Pd precursors, reducing agent, carbon dots (Cdots), and Br– ion at 30 °C. Experimental results and density functional theory (DFT) calculations suggested that the Br– ions played an essential role in accelerating the exfoliation of Cdot, supplying graphene layers, which could wrap the nanosponge-shaped Pd and finally form Pd@G-NS. In the absence of the Br– ions, only aggregated Pd nanoparticles (NPs) were formed and randomly mixed with Cdots. The resultant Pd@G-NS exhibited a high electrochemically active surface area and accelerated charge transport characteristics, leading to its superior electrocatalytic activity toward the HER in acidic media. The HER overpotential of Pd@G-NS was 32 mV at 10 mA cm–2, and the Tafel slope was 33 mV dec–1. Furthermore, the unique Pd@G-NS catalyst showed long-term stability for over 3000 cycles in acidic media as well, owing to the protection of Pd nanosponges by graphene dot wrapping. The overall HER performance of the Pd@G-NS catalyst exceeded that of commercial Pt/C.

Platinum-based heterogeneous catalysts are mostly used in various commercial chemical processes because of their high catalytic activity, influenced by the metal/oxide interaction. To design rational catalysts with high performance, it is crucial to understand the relationship between the metal–oxide interface and the reaction pathway. Here, we investigate the role of oxygen defect sites in the reaction mechanism for CO oxidation using Pt nanoparticles supported on mesoporous TiO2 catalysts with oxygen defects. We show an intrinsic correlation between the catalytic reactivity and the local properties of titania with oxygen defects (i.e., Ti3+ sites). In situ infrared spectroscopy observations of the Pt/mesoporous TiO2−x catalyst indicate that an oxygen molecule bond can be activated at the perimeter between the Pt and an oxygen vacancy in TiO2 by neighboring CO molecules on the Pt surface before CO oxidation begins. The proposed reaction pathways for O2 activation at the Pt/TiO2−x interface based on density functional theory confirm our experimental findings. We suggest that this provides valuable insight into the intrinsic origin of the metal/support interaction influenced by the presence of oxygen vacancies, which clarifies the pivotal role played by the support.