Direct Observation of Atomistic Reaction Process between Pt Nanoparticles and TiO2 (110)

Tuning Adsorbate-Mediated Strong Metal-Support Interaction by Oxygen Vacancy: A Case Study in Ru/TiO2

The adsorbate-mediated strong metal-support interaction (A-SMSI) offers a reversible means of altering the selectivity of supported metal catalysts, thereby providing a powerful tool for facile modulation of catalytic performance. However, the fundamental understanding of A-SMSI remains inadequate and methods for tuning A-SMSI are still in their nascent stages, impeding its stabilization under reaction conditions. Here, we report that the initial concentration of oxygen vacancy in oxide supports plays a key role in tuning the A-SMSI between Ru nanoparticles and defected titania (TiO2-x). Based on this new understanding, we demonstrate the in situ formation of A-SMSI under reaction conditions, obviating the typically required CO2-rich pretreatment. The as-formed A-SMSI layer exhibits remarkable stability at various temperatures, enabling excellent activity, selectivity and long-term stability in catalyzing the reverse water gas-shift reaction. This study deepens the understanding of the A-SMSI and the ability to stabilize A-SMSI under reaction conditions represents a key step for practical catalytic applications.

Real-time tracking of three-dimensional atomic dynamics of Pt trimer on TiO2 (110)

Single and multi-atoms supported on oxide substrates ultimately increase the efficiency of noble metal atom use, and moreover, catalytic activity and selectivity are also improved substantially. However, single and multi-atoms are unstable under catalytic conditions, and these metal atoms spontaneously aggregate and grow into nanoparticles. Catalytic performance is strongly related to local atomic configurations, and hence, it is essential to determine the three-dimensional (3D) atomic structures of multi-atoms on the substrate and their structural dynamics. Here, we show the real-time tracking of the 3D structural evolution of a Pt trimer on TiO2 (110) substrate at a high temperature, using high-spatiotemporal-resolution scanning transmission electron microscopy, where sub-angstrom spatial resolution is maintained, while the temporal resolution reaches 40 milliseconds. With the aid of prior structural knowledge of a Pt trimer for 3D reconstruction, the present method could open the way to characterize in situ atomic-scale structural dynamics, especially meta-stable structural transition.

Photocatalytic Synthesis of Ultrafine Pt Electrocatalysts with High Stability Using TiO2 -Decorated N-Doped Carbon as Composite Support

Commercial Pt/C (Com. Pt/C) electrocatalysts are considered optimal for oxygen reduction and hydrogen evolution reactions (ORR and HER). However, their high Pt content and poor stability restrict their large-scale application. In this study, photocatalytic synthesis was used to reduce ultrafine Pt nanoparticles in-situ on a composite support of TiO2 -decorated nitrogen-doped carbon (TiO2 -NC). The nitrogen-doped carbon had a large surface area and electronic effects that ensured the uniform dispersion of TiO2 nanoparticles to form a highly photoactive and stable support. TiO2 -NC served as a composite support that enhanced the dispersibility and stability of ultrafine Pt electrocatalyst, owing to the presence of N sites and the strong metal-support interaction. Relative to Com. Pt/C, the as-obtained Pt/TiO2 -NC had positive shifts of 44 and 10 mV in the ORR half-wave potential and HER overpotential at -10 mA cm-2 , respectively. After an accelerated durability test, Pt/TiO2 -NC had lower losses in electrochemical specific area (0.7 %) and electrocatalytic activity (0 mV shift) than Com. Pt/C (25.6 %, 22 mV shift). These results indicate that the developed strategy enabled the facile synthesis and stabilization of ultrafine Pt nanoparticles, which improved the utilization efficiency and long-term stability of Pt-based electrocatalysts.

Pt modified NiMoO4-GO/NF nanorods withstrong metal-support interaction as efficient bifunctional catalysts for overall water splitting

Catalysts for the electrolysis of water are critical in the production of hydrogen for the energy industry. The use of strong metal-support interactions (SMSI) to modulate the dispersion, electron distribution, and geometry of active metals is an effective strategy for improving catalytic performance. However, in currently used catalysts, the supporting effect does not significantly contribute directly to catalytic activity. Consequently, the continued investigation of SMSI, using active metals to stimulate the supporting effect for catalytic activity, remains very challenging. Herein, the atomic layer deposition technique was employed to prepare an efficient catalyst composed of platinum nanoparticles (Pt NPs) deposited on nickel-molybdate (NiMoO₄) nanorods. Nickel-molybdate's oxygen vacancies (V_o) not only help anchor highly-dispersed Pt NPs with low loading but also strengthen the SMSI. The valuable electronic structure modulation between Pt NPs and V_o resulted in a low overpotential of the hydrogen and oxygen evolution reactions, returning results of 190 mV and 296 mV, respectively, at a current density of 100 mA cm^-2 in 1 M KOH. Ultimately, an ultralow potential (1.515 V) for the overall decomposition of water was achieved at 10 mA cm^-2, outperforming state-of-art catalysts based on the Pt/C || IrO₂ couple (1.668 V). This work aims to provide reference and a concept for the design of bifunctional catalysts that apply the SMSI effect to achieve a simultaneous catalytic effect from the metal and its support.

Metal-Metal Oxide Catalytic Interface Formation and Structural Evolution: A Discovery of Strong Metal-Support Bonding, Ordered Intermetallics, and Single Atoms

In-depth investigation of metal-metal oxide interactions and their corresponding evolution is of paramount importance to heterogeneous catalysis as it allows the understanding and maneuvering of the structure of catalytic motifs. Herein, using a series of core/shell metal/iron oxide (M/FeO_x, M = Pd, Pt, Au) nanoparticles and through a combination of in situ and ex situ electron and X-ray investigations, we revealed anomalous and dissimilar M-FeO_x interactions among different systems under reducing conditions. Pd interacts strongly with FeO_x after high-temperature reductive treatment, featured by the formation of Pd single atoms in the FeO_x matrix and increased Pd-Fe bonding, while Pt transforms into ordered PtFe intermetallics and Pt single atoms immediately upon the coating of FeO_x. In contrast, Au does not manifest strong bonding with FeO_x. As a proof of concept of tailoring metal-metal oxide interactions for catalysis, optimized Pd/FeO_x demonstrates 100% conversion and 86.5% selectivity at 60 °C for acetylene semihydrogenation.

Development of γ-Al2O3 with oxygen vacancies induced by amorphous structures for photocatalytic reduction of CO2

Inducing amorphous components into Al₂O₃ leads to elongation of the Al-O bond and the formation of oxygen vacancies, which makes Al₂O₃ an independent photocatalyst for CO₂ adsorption and reduction. The generation rate of CO can reach 36.5 μmol g^-1 h^-1, which is 6.5 times that of P25 TiO₂.