Catalytic Kinetics of Different Types of Surface Atoms on Shaped Pd Nanocrystals

Unveiling the Dynamic Electrocatalytic Activity of Online Synthesized Bimetallic Nanocatalysts via Electrochemiluminescence Microscopy

Effective bimetallic nanoelectrocatalysis demands precise control of composition, structure, and understanding catalytic mechanisms. To address these challenges, we employ a two-in-one approach, integrating online synthesis with real-time imaging of bimetallic Au@Metal core-shell nanoparticles (Au@M NPs) via electrochemiluminescence microscopy (ECLM). Within 120 s, online electrodeposition and in situ catalytic activity screening alternate. ECLM captures transient faradaic processes during potential switches, visualizes electrochemical processes in real-time, and tracks catalytic activity dynamics at the single-particle level. Analysis using ECL photon flux density eliminates size effects and yields quantitative electrocatalytic activity results. Notably, a nonlinear activity trend corresponding to the shell metal to Au surface atomic ratio is discerned, quantifying the optimal surface component ratio of Au@M NPs. This approach offers a comprehensive understanding of catalytic behavior during the deposition process with high spatiotemporal resolution, which is crucial for tailoring efficient bimetallic nanocatalysts for diverse applications.

Dynamics of chemical reactions on single nanocatalysts with heterogeneous active sites

Modern chemical science and industries critically depend on the application of various catalytic methods. However, the underlying molecular mechanisms of these processes still remain not fully understood. Recent experimental advances that produced highly-efficient nanoparticle catalysts allowed researchers to obtain more quantitative descriptions, opening the way to clarify the microscopic picture of catalysis. Stimulated by these developments, we present a minimal theoretical model that investigates the effect of heterogeneity in catalytic processes at the single-particle level. Using a discrete-state stochastic framework that accounts for the most relevant chemical transitions, we explicitly evaluated the dynamics of chemical reactions on single heterogeneous nanocatalysts with different types of active sites. It is found that the degree of stochastic noise in nanoparticle catalytic systems depends on several factors that include the heterogeneity of catalytic efficiencies of active sites and distinctions between chemical mechanisms on different active sites. The proposed theoretical approach provides a single-molecule view of heterogeneous catalysis and also suggests possible quantitative routes to clarify some important molecular details of nanocatalysts.

Revealing the catalytic kinetics and dynamics of individual Pt atoms at the single-molecule level

Here, with single-molecule fluorescence microscopy, we study the catalytic behavior of individual Pt atoms at single-turnover resolution, and then reveal the unique catalytic properties of Pt single-atom catalyst and the difference in catalytic properties between individual Pt atoms and Pt nanoparticles. Further density functional theory calculation indicates that unique catalytic properties of Pt single-atom catalyst could be attributed intrinsically to the unique surface properties of Pt₁-based active sites.

Due to the importance of single-atom catalysts (SAC), here, the catalysis of Pt SAC was studied at the single-molecule single-atom level. Both static and dynamic activity heterogeneity are observed in Pt SAC. It reveals that the intrinsic catalytic activity of Pt SAC is higher than that of Pt nanoparticles (NPs), although they follow the same bimolecular competition mechanism. Significantly, Pt SAC presents no catalysis-induced surface restructuring, meaning that the dynamic activity fluctuation of Pt SAC can only be attributed to the spontaneous surface restructuring, and the catalysis process does not affect much of the structure of Pt₁-based active sites, all different from Pt NP catalysis, in which the surface restructuring and the catalysis can affect each other. Further, density functional theory (DFT) calculation indicates that the unique catalytic properties of Pt SAC or the different catalytic properties between Pt SAC and NPs could be attributed to the strong adsorptions of both reactant and product on Pt SAC, large surface energy of Pt SAC, and strong binding of Pt₁ on support. Knowledge revealed here provides fundamental insights into the catalysis of atomically dispersed catalyst.

Studies on the Morphology Effect on Catalytic Ability of a Single MnO2 Catalyst Particle with a Solid Nanopipette

Investigating the catalytic ability of an individual catalyst particle helps to understand heterogeneity and can provide new insights into the synthesis of high-efficiency catalysts. Solid-state nanopores have become a promising tool for detecting single molecules/particles due to their high temporal and spatial resolution. Here, we report a nanopore-based strategy for the evaluation and comparison of a single MnO₂ catalyst particle with different morphologies by monitoring the generated O₂ bubbles from the catalytic decomposition of H₂O₂. The finite element simulation was introduced to account for the flow velocity and bubble-induced current variation in the nanopore. In particular, the differences in catalytic ability of spherical and cubic MnO₂ have been studied by calculating the production rate and volume of O₂. It demonstrates that the shape of a single MnO₂ catalyst particle has a significant effect on its catalytic activity indeed.

Adsorption and desorption mechanisms on graphene oxide nanosheets: Kinetics and tuning

A knowledge of the adsorption and desorption behavior of sorbates on surface adsorptive site (SAS) is the key to optimizing the chemical reactivity of catalysts. However, direct identification of the chemical reactivity of SASs is still a challenge due to the limitations of characterization techniques. Here, we present a new pathway to determine the kinetics of adsorption/desorption on SASs of graphene oxide (GO) based on total internal reflectance fluorescence microscopy. The switching on and off of the fluorescent signal of SAS lit by carbon dots (CDs) was used to trace the adsorption process and desorption process. We find that sodium pyrophosphate (PPi) could increase the adsorption equilibrium of CDs thermodynamically and promote the substrate-assisted desorption pathway kinetically. At the single turnover level, it was disclosed that the species that can promote desorption may also be an adsorption promoter. Such discovery provides significant guidance for improving the chemical reactivity of the heterogeneous catalyst.

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The kinetics of adsorption and desorption process were revealed, respectively, by monitoring a fluorogenic process of carbon dots on the surface of graphene oxides at the single turnover level

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By regulating the equilibrium of adsorption and desorption, a mechanism for the simultaneous promotion of adsorption and desorption has been discovered

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A desorption accelerator could play a satisfactory double action, i.e., adsorption promoter on thermodynamics and desorption promoter on kinetics

Laser illumination-induced dramatic catalytic activity change on Au nanospheres

Understanding morphology dependent catalytic kinetics from a single nanoparticle plays a significant role in the development of robust nano-catalysts with high efficiency. Unfortunately, detailed knowledge of the morphology dependent catalytic properties of single nanoparticles after shape transitions is lacking. In this work, the distinct catalytic properties of a single gold nanoparticle (GNP) after symmetry breaking were disclosed at the single-particle level for the first time. The morphology of the spherical GNP was elongated into a rod shape (i.e., gold nanorod, GNR) with a tightly focused Gaussian laser beam based on the photothermal effect. By using the fluorogenic oxidation reaction (i.e., amplex red to resorufin) as a model reaction, noticeable variation in catalytic efficiency after the shape modulation process was found at the single-particle level. The GNP displays noticeably higher catalytic efficiency which might be ascribed to the heterogeneous lattice structure on the particle surface as confirmed by transmission electron microscopy (TEM) characterization. Rearrangement of surface atoms after shape modulation normally generates a more ordered crystal structure, resulting in a lower surface energy for catalytic reaction. However, both of these nanoparticles still exhibit dynamic activity fluctuation in a temporal dependent route, indicating a distinct spontaneous dynamic surface restructuring process. These kinetic evidences might facilitate the development nanoparticle-based heterogeneous catalysts, particularly based on the morphology effect.

Site-Resolved Cu2 O Catalysis in the Oxidation of CO

The identification of the contribution of different surface sites to the catalytic activity of a catalyst nanoparticle is one of the most challenging issues in the fundamental studies of heterogeneous catalysis. We herein demonstrate an effective strategy of using a series of uniform cubic Cu₂ O nanocrystals with different sizes to identify the intrinsic activity and contributions of face and edge sites in the catalysis of CO oxidation by a combination of reaction kinetics analysis and DFT calculations. Cu₂ O nanocrystals undergo in situ surface oxidation forming CuO thin films during CO oxidation. As the average size of the cubic Cu₂ O nanocrystals decreases from 1029 nm to 34 nm, the dominant active sites contributing to the catalytic activity switch from face sites to edge sites. These results reveal the interplay between the intrinsic catalytic activity and the density of individual types of surface sites on a catalyst nanoparticle in determining their contributions to the catalytic activity.

Size-dependent catalytic kinetics and dynamics of Pd nanocubes: a single-particle study

Due to the well-known significant effect of the size on the catalytic activity of nanocatalysts, here we use single-molecule fluorescence microscopy to study the size-dependent catalytic kinetics and dynamics of individual Pd nanocubes. A series of size-dependent catalytic properties were revealed in both product formation and product desorption processes. It was found that, due to the different adsorption mechanisms of substrate molecules on Pd nanocubes, H2 adsorption is independent of the size of Pd nanocubes, while the large flat resazurin molecules show stronger adsorption on larger sized Pd nanocubes. Apparently, the Pd nanocubes can be divided into three types: when the size of the Pd nanocube is small, substrate binding can prohibit product desorption and product desorption prefers the direct pathway; when the size is in an appropriate range, the product desorption process could be independent of substrate binding and shows no selectivity between two parallel desorption pathways; if the size is large enough, substrate binding can promote product desorption and product desorption prefers the indirect pathway. We also observed the surface-restructuring-induced dynamic heterogeneity of individual Pd nanocubes in both product formation and desorption processes with timescales of about tens to one hundred seconds. The activity fluctuation of individual Pd nanocubes was found to be mainly due to the spontaneous surface-restructuring rather than the catalysis. Furthermore, we estimated the size-dependent activation energies and time scales of spontaneous dynamic surface restructuring, which are fundamental to heterogeneous catalysis. The work presented here reveals new insight into nanocatalysis and exemplifies the advantages of the single-molecule approach in probing the catalytic properties of nanocatalysts.

Imaging the chemical activity of single nanoparticles with optical microscopy

Chemical activity of single nanoparticles can be imaged and determined by monitoring the optical signal of each individual during chemical reactions with advanced optical microscopes. It allows for clarifying the functional heterogeneity among individuals, and for uncovering the microscopic reaction mechanisms and kinetics that could otherwise be averaged out in ensemble measurements.

Recent progress on single-molecule nanocatalysis based on single-molecule fluorescence microscopy

Understanding the heterogeneous catalytic properties of nanoparticles is of great significance for the development of high efficient nanocatalysts, but the intrinsic heterogeneities of nanocatalysts were always covered in traditional ensemble studies. This issue can be overcome if one can follow the catalysis of individual nanoparticles in real time. This paper mainly summarizes recent developments in single-molecule nanocatalysis at single particle level in Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. These developments include the revealing of catalytic kinetics of different types (plane & edge) of surface atoms on individual Pd nanocubes, the observing of in situ deactivation of individual carbon-supported Pt nanoparticles during the electrocatalytic hydrogen-oxidation reaction, and the measurement of catalytic activation energies on single nanocatalysts for both product formation process and dissociation process, etc. These studies further indicate the advantages or unique abilities of single-molecule methods in the studies of nanocatalysis or even chemical reactions.

Tailoring Copper Nanocrystals towards C2 Products in Electrochemical CO2 Reduction

Favoring the CO2 reduction reaction (CO2RR) over the hydrogen evolution reaction and controlling the selectivity towards multicarbon products are currently major scientific challenges in sustainable energy research. It is known that the morphology of the catalyst can modulate catalytic activity and selectivity, yet this remains a relatively underexplored area in electrochemical CO2 reduction. Here, we exploit the material tunability afforded by colloidal chemistry to establish unambiguous structure/property relations between Cu nanocrystals and their behavior as electrocatalysts for CO2 reduction. Our study reveals a non-monotonic size-dependence of the selectivity in cube-shaped copper nanocrystals. Among 24 nm, 44 nm and 63 nm cubes tested, the cubes with 44 nm edge length exhibited the highest selectivity towards CO2RR (80 %) and faradaic efficiency for ethylene (41 %). Statistical analysis of the surface atom density suggests the key role played by edge sites in CO2RR.