Application of One-Dimensional Nanomaterials in Catalysis at the Single-Molecule and Single-Particle Scale (original) (raw)
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Approaches to Single-Nanoparticle Catalysis
Annual Review of Physical Chemistry, 2014
Nanoparticles are among the most important industrial catalysts, with applications ranging from chemical manufacturing to energy conversion and storage. Heterogeneity is a general feature among these nanoparticles, with their individual differences in size, shape, and surface sites leading to variable, particle-specific catalytic activity. Assessing the activity of individual nanoparticles, preferably with subparticle resolution, is thus desired and vital to the development of efficient catalysts. It is challenging to measure the activity of single-nanoparticle catalysts, however. Several experimental approaches have been developed to monitor catalysis on single nanoparticles, including electrochemical methods, single-molecule fluorescence microscopy, surface plasmon resonance spectroscopy, X-ray microscopy, and surface-enhanced Raman spectroscopy. This review focuses on these experimental approaches, the associated methods and strategies, and selected applications in studying single-nanoparticle catalysis with chemical selectivity, sensitivity, or subparticle spatial resolution.
Novel In Situ Probes for Nanocatalysis
MRS Bulletin, 2007
During the past few years, substantial effort has been devoted to developing new experimental techniques capable of delivering atomic-scale information on surfaces and nanoparticles under catalytic reaction conditions. Since the advent of surface science, pioneering experiments under highly idealized conditions have been performed (at very low gas pressures, <10−6 mbar), and idealized model material systems (e.g., single crystals) have been investigated. However, understanding chemical reactions on singlecrystal surfaces close to ultrahigh vacuum does not always enable prediction of the performance of nanoparticles operating at gas pressures near or above atmospheric pressure. Therefore, this MRS Bulletin issue focuses on the capabilities of atomic-scaleresolution, high-gas-pressure- and high-temperature-compatible in situ probes sensitive to the structure, chemical composition, and dynamical properties of nanomaterials. It will be demonstrated how novel in situ techniques enable...
Single-molecule nanocatalysis reveals heterogeneous reaction pathways and catalytic dynamics
Nature Materials, 2008
Nanoparticles are important catalysts for many chemical transformations. However, owing to their structural dispersions, heterogeneous distribution of surface sites and surface restructuring dynamics, nanoparticles are intrinsically heterogeneous and challenging to characterize in ensemble measurements. Using a single-nanoparticle single-turnover approach, we study the redox catalysis of individual colloidal Au nanoparticles in solution, using single-molecule detection of fluorogenic reactions. We find that for product generation, all Au nanoparticles follow a Langmuir-Hinshelwood mechanism but with heterogeneous reactivity; and for product dissociation, three nanoparticle subpopulations are present that show heterogeneous reactivity between multiple dissociation pathways with distinct kinetics. Correlation analyses of single-turnover waiting times further reveal activity fluctuations of individual Au nanoparticles, attributable to both catalysis-induced and spontaneous dynamic surface restructuring that occurs at different timescales at the surface catalytic and product docking sites. The results exemplify the power of the single-molecule approach in revealing the interplay of catalysis, heterogeneous reactivity and surface structural dynamics in nanocatalysis.
Imaging the electrocatalytic activity of single nanoparticles
2012
The electrocatalytic properties of nanoparticles depend on 2 their size, shape and composition 1,2. These properties are 3 typically probed by measuring the total electrocatalytic 4 reaction current of a large number of nanoparticles, but this 5 approach is time-consuming and can only measure the 6 average catalytic activity of the nanoparticles under study. 7 However, the identification of new catalysts requires the 8 ability to rapidly measure the properties of nanoparticles 9 synthesized under various conditions and, ideally, to measure 10 the electrocatalytic activity of individual nanoparticles. Here, 11 we show that a plasmonic-based electrochemical current-12 imaging technique 3 can simultaneously image and quantify 13 the electrocatalytic reactions of an array of 1.6 3 10 5 platinum 14 nanoparticles printed on an electrode surface, which could 15 facilitate high-throughput screening of the catalytic activities 16 of nanoparticles. We also show that the approach can be used 17 to image the electrocatalytic reaction current and measure 18 the cyclic voltammograms of single nanoparticles. 19 Scanning electrochemical microscopy (SECM) can be used to 20 rapidly screen the electrocatalytic Q2 of nanoparticles 4. However, 21 SECM relies on mechanical scanning of a microelectrode across a 22 sample surface, which limits the imaging speed and can interfere 23 with the electrocatalytic reactions of the nanoparticles 5. Methods 24 that can probe the catalytic reactions of individual nanoparticles 25 have also been developed 6-9 , including nanoelectrodes 8 and super-26 resolution fluorescence microscopy 9. In particular, ultramicroelec-27 trodes have been used to monitor current spikes associated with 28 individual collision events of nanoparticles dissolved in an electro-29 lyte 6,7. However, this non-imaging method cannot assign spikes to a 30 specific nanoparticle and it is difficult to measure the entire cyclic 31 voltammogram (CV) of each nanoparticle. 32 Unlike conventional electrochemical techniques (including 33 SECM), which measure the electrical current associated with chemi-34 cal reactions taking place on an electrode surface, our plasmonic-35 based electrochemical current imaging (P-ECi) approach measures 36 the conversion between oxidized and reduced species near the elec-37 trode 3,10-12. We have shown 3 that the plasmonic signal in P-ECi is 38 directly related to the electrical current, allowing us to determine 39 the current optically and to image the local current density of the 40 entire electrode surface quickly (microsecond to millisecond) and 41 non-invasively. This capability allows us to image and measure 42 the electrocatalytic current of multiple individual nanoparticles 43 versus time or potential, simultaneously. 44 Platinum nanoparticles are well known for their electrocatalytic 45 activities. Q3 An important example is the electrocatalytic reduction 46 of protons to generate hydrogen. To demonstrate the capability of P-ECi for high-throughput screening of the electrocatalytic reactions of platinum nanoparticles, we synthesized nanoparticles and LETTERS
Bimetallic Effect of Single Nanocatalysts Visualized by Super-Resolution Catalysis Imaging
ACS central science, 2017
Compared with their monometallic counterparts, bimetallic nanoparticles often show enhanced catalytic activity associated with the bimetallic interface. Direct quantitation of catalytic activity at the bimetallic interface is important for understanding the enhancement mechanism, but challenging experimentally. Here using single-molecule super-resolution catalysis imaging in correlation with electron microscopy, we report the first quantitative visualization of enhanced bimetallic activity within single bimetallic nanoparticles. We focus on heteronuclear bimetallic PdAu nanoparticles that present a well-defined Pd-Au bimetallic interface in catalyzing a photodriven fluorogenic disproportionation reaction. Our approach also enables a direct comparison between the bimetallic and monometallic regions within the same nanoparticle. Theoretical calculations further provide insights into the electronic nature of N-O bond activation of the reactant (resazurin) adsorbed on bimetallic sites. ...
The Journal of Physical Chemistry C, 2009
The electrocatalytic properties of individual single Pt nanoparticles (NPs) can be studied electrochemically by measuring the current-time (i-t) responses during single NP collisions with a noncatalytic ultramicroelectrode (UME). The Pt NPs are capped with citrate ions or a self-assembled monolayer (SAM) of alkane thiols terminated with carboxylic acid that affect the observed it responses. By varying the length of the SAMs or the composition of a mixed monolayer, we have studied the effect of adsorbed molecules on the catalytic activity of Pt NPs at the single particle level through electrocatalytic amplification of single NP collisions. Collisions of single NPs were triggered and recorded as individual current steps whose amplitude represents the reactivity of single Pt NPs for the reaction of interest, here hydrazine oxidation, at a given electrode potential. The catalytic properties of Pt NPs are dependent not only on the nature of the interaction between the adsorbed monolayer and the catalytic NP surface, but also on the rate of electron transfer through the SAMs, governed by their length.
Chemical Physics Letters, 2014
Direct real time studies of reacting individual atoms in technologically important gold and platinum nanocatalysts in controlled reducing and oxidising gas environments and operating temperatures using novel environmental scanning transmission electron microscopy (ESTEM) with single atom sensitivity are presented. The direct in situ observations provide new insights into the dynamic behaviour of single atoms which may be important as catalytic active sites as well as migrating as part of deactivation mechanisms. The single atom dynamics reveal that the primary role of nanoparticles in the catalysts is to act as reservoir of ad-atoms or clusters. Possible reaction mechanisms are described briefly. .
Quantitative super-resolution imaging uncovers reactivity patterns on single nanocatalysts
Nature Nanotechnology, 2012
Metal nanoparticles are used as catalysts in a variety of important chemical reactions 1,2 , and can have a range of different shapes 3-8 , with facets and sites that differ in catalytic reactivity 1,2,9 . To develop better catalysts it is necessary to determine where catalysis occurs on such nanoparticles and what structures are more reactive. Surface science experiments or theory can be used to predict the reactivity of surfaces with a known structure 1,2,10 , and the reactivity of nanocatalysts can often be rationalized from a knowledge of their well-defined surface facets 3-5 . Here, we show that a knowledge of the surface facets of a gold nanorod catalyst is insufficient to predict its reactivity, and we must also consider defects on the surface of the nanorod. We use super-resolution fluorescence microscopy to quantify the catalysis of the nanorods at a temporal resolution of a single catalytic reaction and a spatial resolution of ∼40 nm. We find that within the same surface facets on the sides of a single nanorod, the reactivity is not constant and exhibits a gradient from the centre of the nanorod towards its two ends. Furthermore, the ratio of the reactivity at the ends of the nanorod to the reactivity at the sides varies significantly from nanorod to nanorod, even though they all have the same surface facets.
Highlights of the major progress in single-atom catalysis in 2015 and 2016
Chinese Journal of Catalysis, 2017
The idea that single metal atoms dispersed on a solid support can act as an efficient heterogeneous catalyst was raised in 2011 when single Pt atoms on an FeOx surface were reported to be active for CO oxidation and preferential oxidation of CO in H2. The last six years have witnessed tremendous progress in the field of single-atom catalysis. Here we introduce the major achievements on this topic in 2015 and 2016. Some particular aspects of single-atom catalysis are discussed in depth, including new approaches in single-atom catalyst (SAC) synthesis, stable gold SACs for various reactions, the high selectivity of Pt and Pd SACs in hydrogenation, and the superior performance of non-noble metal SACs in electrochemistry. These accomplishments will encourage more efforts by researchers to achieve the controllable fabrication of SACs and explore their potential applications.