Bifunctional hydroformylation on heterogeneous Rh-WOx pair site catalysts.

Metal-catalysed reactions are often hypothesized to proceed on bifunctional active sites, whereby colocalized reactive species facilitate distinct elementary steps in a catalytic cycle1-8. Bifunctional active sites have been established on homogeneous binuclear organometallic catalysts9-11. Empirical evidence exists for bifunctional active sites on supported metal catalysts, for example, at metal-oxide support interfaces2,6,7,12. However, elucidating bifunctional reaction mechanisms on supported metal catalysts is challenging due to the distribution of potential active-site structures, their dynamic reconstruction and required non-mean-field kinetic descriptions7,12,13. We overcome these limitations by synthesizing supported, atomically dispersed rhodium-tungsten oxide (Rh-WOx) pair site catalysts. The relative simplicity of the pair site structure and sufficient description by mean-field modelling enable correlation of the experimental kinetics with first principles-based microkinetic simulations. The Rh-WOx pair sites catalyse ethylene hydroformylation through a bifunctional mechanism involving Rh-assisted WOx reduction, transfer of ethylene from WOx to Rh and H2 dissociation at the Rh-WOx interface. The pair sites exhibited >95% selectivity at a product formation rate of 0.1 gpropanal cm-3 h-1 in gas-phase ethylene hydroformylation. Our results demonstrate that oxide-supported pair sites can enable bifunctional reaction mechanisms with high activity and selectivity for reactions that are performed in industry using homogeneous catalysts.

Effect of Dynamic and Preferential Decoration of Pt Catalyst Surfaces by WOx on Hydrodeoxygenation Reactions.

Catalysts containing Pt nanoparticles and reducible transition-metal oxides (WOx, NbOx, TiOx) exhibit remarkable selectivity to aromatic products in hydrodeoxygenation (HDO) reactions for biomass valorization, contrasting the undesired aromatic hydrogenation typically observed for metal catalysts. However, the active site(s) responsible for the high selectivity remains elusive. Here, theoretical and experimental analyses are combined to explain the observed HDO reactivity by interrogating the organization of reduced WOx domains on Pt surfaces at sub-monolayer coverage. The SurfGraph algorithm is used to develop model structures that capture the configurational space (∼1000 configurations) for density functional theory (DFT) calculations of a W3O7 trimer on stepped Pt surfaces. Machine-learning models trained on the DFT calculations identify the preferential occupation of well-coordinated Pt sites (≥8 Pt coordination number) by WOx and structural features governing WOx-Pt stability. WOx/Pt/SiO2 catalysts are synthesized with varying W loadings to test the theoretical predictions and relate them to HDO reactivity. Spectroscopy- and microscopy-based catalyst characterizations identify the dynamic and preferential decoration of well-coordinated sites on Pt nanoparticles by reduced WOx species, consistent with theoretical predictions. The catalytic consequences of this preferential decoration on the HDO of a lignin model compound, dihydroeugenol, are clarified. The effect of WOx decoration on Pt nanoparticles for HDO involves WOx inhibition of aromatic ring hydrogenation by preferentially blocking well-coordinated Pt sites. The identification of preferential decoration on specific sites of late-transition-metal surfaces by reducible metal oxides provides a new perspective for understanding and controlling metal-support interactions in heterogeneous catalysis.

Bond Selective Photochemistry at Metal Nanoparticle Surfaces: CO Desorption from Pt and Pd.

The use of visible photon fluxes to influence catalytic reactions on metal nanoparticle surfaces has attracted attention based on observations of reaction mechanisms and selectivity not observed under equilibrium heating. These observations suggest that photon fluxes can selectively impact the rates of certain elementary steps, creating nonequilibrium energy distributions among various reaction pathways. However, quantitative studies validating these hypotheses on metal nanoparticle surfaces are lacking. We examine the influence of continuous wave visible photon fluxes on the CO desorption rates from 1 to 2 nm diameter Pt and Pd nanoparticle surfaces supported on γ-Al2O3. Temperature-programmed desorption measurements quantified via diffuse reflectance infrared Fourier transform spectroscopy demonstrate that visible photon fluxes significantly enhanced the rate of CO desorption from Pt nanoparticles in a wavelength-dependent manner. 440 nm photons most efficiently promoted CO desorption from Pt nanoparticle surfaces, aligning with the excitation energy for the interfacial electronic transition within the Pt-CO bond. Conversely, visible photon fluxes had no measurable influence on CO desorption rates from Pd nanoparticle surfaces after accounting for photon-induced heating. Density functional theory calculations demonstrate that the Pt-CO bond exhibits a narrower LUMO resonance, stronger coupling between the photoexcitation and forces induced on the metal-C bond, and vibrational energy dissipation that more effectively couples to desorption as compared to Pd-CO. These results demonstrate the specificity photons provide in facilitating chemical reactions on metal nanoparticle surfaces and substantiate the idea that photon fluxes can steer processes and outcomes of catalytic reactions in ways not achievable by equilibrium heating.

Directly Probing the Local Coordination, Charge State, and Stability of Single Atom Catalysts by Advanced Electron Microscopy: A Review.

The drive for atom efficient catalysts with carefully controlled properties has motivated the development of single atom catalysts (SACs), aided by a variety of synthetic methods, characterization techniques, and computational modeling. The distinct capabilities of SACs for oxidation, hydrogenation, and electrocatalytic reactions have led to the optimization of activity and selectivity through composition variation. However, characterization methods such as infrared and X-ray spectroscopy are incapable of direct observations at atomic scale. Advances in transmission electron microscopy (TEM) including aberration correction, monochromators, environmental TEM, and micro-electro-mechanical system based in situ holders have improved catalysis study, allowing researchers to peer into regimes previously unavailable, observing critical structural and chemical information at atomic scale. This review presents recent development and applications of TEM techniques to garner information about the location, bonding characteristics, homogeneity, and stability of SACs. Aberration corrected TEM imaging routinely achieves sub-Ångstrom resolution to reveal the atomic structure of materials. TEM spectroscopy provides complementary information about local composition, chemical bonding, electronic properties, and atomic/molecular vibration with superior spatial resolution. In situ/operando TEM directly observe the evolution of SACs under reaction conditions. This review concludes with remarks on the challenges and opportunities for further development of TEM to study SACs.

Selective Methanol Carbonylation to Acetic Acid on Heterogeneous Atomically Dispersed ReO4/SiO2 Catalysts.

Methanol carbonylation to acetic acid (AA) is a large-scale commodity chemical production process that requires homogeneous liquid-phase organometallic catalysts with corrosive halide-based cocatalysts to achieve high selectivity and activity. Here, we demonstrate a heterogeneous catalyst based on atomically dispersed rhenium (ReO4) active sites on an inert support (SiO2) for the halide-free, gas phase carbonylation of methanol to AA. Atomically dispersed ReO4 species and nanometer sized ReOx clusters were deposited on a high surface area (700 m2/g) inert SiO2 using triethanolamine as a dispersion promoter and characterized using aberration corrected scanning transmission electron microscopy (AC-STEM), UV-vis spectroscopy, and X-ray absorption spectroscopy (XAS). Reactivity measurements at atmospheric pressure with 30 mbar of methanol and CO (1:1 molar ratio) showed that bulk Re2O7 and ReOx clusters on SiO2 (formed at >10 wt %) were selective for dimethyl ether formation, while atomically dispersed ReO4 on SiO2 (formed at <10 wt %) exhibited stable (for 60 h) > 93% selectivity to AA with single pass conversion >60%. Kinetic analysis, in situ FTIR, and in situ XAS measurements suggest that the AA formation mechanism involves methanol activation on ReO4, followed by CO insertion into the terminal methyl species. Further, the introduction of ∼0.2 wt % of atomically dispersed Rh to 10 wt % atomically dispersed ReO4 on SiO2 resulted in >96% selectivity toward AA production at volumetric reaction rates comparable to homogeneous processes. This work introduces a new class of promising heterogeneous catalysts based on atomically dispersed ReO4 on inert supports for alcohol carbonylation.

Uniformity Is Key in Defining Structure-Function Relationships for Atomically Dispersed Metal Catalysts: The Case of Pt/CeO2.

Catalysts consisting of atomically dispersed Pt (Ptiso) species on CeO2 supports have received recent interest due to their potential for efficient metal utilization in catalytic convertors. However, discrepancies exist between the behavior (reducibility, interaction strength with adsorbates) of high surface area Ptiso/CeO2 systems and of well-defined surface science and computational model systems, suggesting differences in Pt local coordination in the two classes of materials. Here, we reconcile these differences by demonstrating that high surface area Ptiso/CeO2 synthesized at low Pt loadings (<0.1% weight) exhibit resistance to reduction and sintering up to 500 °C in 0.05 bar H2 and minimal interactions with CO-properties previously seen only for model system studies. Alternatively, Pt loadings >0.1 weight % produce a distribution of sub-nanometer Pt structures, which are difficult to distinguish using common characterization techniques, and exhibit strong interactions with CO and weak resistance to sintering, even in 0.05 bar H2 at 50 °C-properties previously seen for high surface area materials. This work demonstrates that low metal loadings can be used to selectively populate the most thermodynamically stable adsorption sites on high surface area supports with atomically dispersed metals. Further, the site uniformity afforded by this synthetic approach is critical for the development of relationships between atomic scale local coordination and functional properties. Comparisons to recent studies of Ptiso/TiO2 suggest a general compromise between the stability of atomically dispersed metal catalysts and their ability to interact with and activate molecular species.

Structural evolution of atomically dispersed Pt catalysts dictates reactivity.

The use of oxide-supported isolated Pt-group metal atoms as catalytic active sites is of interest due to their unique reactivity and efficient metal utilization. However, relationships between the structure of these active sites, their dynamic response to environments and catalytic functionality have proved difficult to experimentally establish. Here, sinter-resistant catalysts where Pt was deposited uniformly as isolated atoms in well-defined locations on anatase TiO2 nanoparticle supports were used to develop such relationships. Through a combination of in situ atomic-resolution microscopy- and spectroscopy-based characterization supported by first-principles calculations it was demonstrated that isolated Pt species can adopt a range of local coordination environments and oxidation states, which evolve in response to varied environmental conditions. The variation in local coordination showed a strong influence on the chemical reactivity and could be exploited to control the catalytic performance.

Impact of chemical interface damping on surface plasmon dephasing.

The excellent light harvesting ability of plasmonic nanoparticles makes them promising materials for a variety of technologies that rely on the conversion of photons to energetic charge carriers. In such applications, including photovoltaics and photocatalysis, the excitation of surface plasmons must induce charge transfer across the metal-adsorbate or metal-semiconductor interface. However, there is currently a lack of molecular level understanding of how the presence of a chemical interface impacts surface plasmon dephasing pathways. Here, we report an approach to quantitatively measure the influence of molecular adsorption on the spectral shape and intensity of the extinction, scattering, and absorption cross-sections for nanostructured plasmonic surfaces. This is demonstrated for the case of thiophenol adsorption on lithographically patterned gold nanodisk arrays. The results show that the formation of a chemical interface between thiophenol and Au causes surface plasmons to decay more prominently through photon absorption rather than photon scattering, as compared to the bare metal. We propose that this effect is a result of the introduction of adsorbate-induced allowable electronic transitions at the interface, which facilitate surface plasmon dephasing via photon absorption. The results suggest that designed chemical interfaces with well-defined electronic structures may enable engineering of hot electron distributions, which could be important for understanding and controlling plasmon-mediated photocatalysis and, more generally, hot carrier transfer processes.

Nitrate Removal via a Formate Radical-Induced Photochemical Process.

Removal of excess nitrate is critical to balance the nitrogen cycle in aquatic systems. This study investigated a novel denitrification process by tailoring photochemistry of nitrate with formate. Under UV light irradiation, short-lived radicals (i.e., HO•, NO2•, and CO3•-) generated from nitrate photolysis partially oxidized formate to highly reductive formate radical (CO2•-). CO2•- further reduced nitrogen intermediates generated during photochemical denitrification (mainly NO•, HNO, and N2O) to gas-phase nitrogen (i.e., N2O and N2). The degradation kinetics of total dissolved nitrogen was mainly controlled by the photolysis rates of nitrate and nitrite. The distribution of final products was controlled by the reaction between CO2•- and N2O. To achieve a simultaneous and complete removal of dissolved nitrogen (i.e., nitrate, nitrite, and ammonia) and organic carbon, the formate-to-nitrate stoichiometry was determined as 3.1 ± 0.2 at neutral pH in deionized water. Solution pH impacted the removal rates of nitrate and nitrite but not that of total dissolved nitrogen or formate. The presence of dissolved organic matter at levels similar to those in groundwater had a negligible impact on the photochemical denitrification process. A high denitrification efficiency was also achieved in a synthetic groundwater matrix. Outcome from this study provides a potential denitrification technology for decentralized water treatment and reuse facilities to abate nitrate in local water resources.

Kaposi's Sarcoma-Associated Herpesvirus Hijacks RNA Polymerase II To Create a Viral Transcriptional Factory.

Locally concentrated nuclear factors ensure efficient binding to DNA templates, facilitating RNA polymerase II recruitment and frequent reutilization of stable preinitiation complexes. We have uncovered a mechanism for effective viral transcription by focal assembly of RNA polymerase II around Kaposi's sarcoma-associated herpesvirus (KSHV) genomes in the host cell nucleus. Using immunofluorescence labeling of latent nuclear antigen (LANA) protein, together with fluorescence in situ RNA hybridization (RNA-FISH) of the intron region of immediate early transcripts, we visualized active transcription of viral genomes in naturally infected cells. At the single-cell level, we found that not all episomes were uniformly transcribed following reactivation stimuli. However, those episomes that were being transcribed would spontaneously aggregate to form transcriptional "factories," which recruited a significant fraction of cellular RNA polymerase II. Focal assembly of "viral transcriptional factories" decreased the pool of cellular RNA polymerase II available for cellular gene transcription, which consequently impaired cellular gene expression globally, with the exception of selected ones. The viral transcriptional factories localized with replicating viral genomic DNAs. The observed colocalization of viral transcriptional factories with replicating viral genomic DNA suggests that KSHV assembles an "all-in-one" factory for both gene transcription and DNA replication. We propose that the assembly of RNA polymerase II around viral episomes in the nucleus may be a previously unexplored aspect of KSHV gene regulation by confiscation of a limited supply of RNA polymerase II in infected cells.IMPORTANCE B cells infected with Kaposi's sarcoma-associated herpesvirus (KSHV) harbor multiple copies of the KSHV genome in the form of episomes. Three-dimensional imaging of viral gene expression in the nucleus allows us to study interactions and changes in the physical distribution of these episomes following stimulation. The results showed heterogeneity in the responses of individual KSHV episomes to stimuli within a single reactivating cell; those episomes that did respond to stimulation, aggregated within large domains that appear to function as viral transcription factories. A significant portion of cellular RNA polymerase II was trapped in these factories and served to transcribe viral genomes, which coincided with an overall decrease in cellular gene expression. Our findings uncover a strategy of KSHV gene regulation through focal assembly of KSHV episomes and a molecular mechanism of late gene expression.

Hot Charge Carrier Transmission from Plasmonic Nanostructures.

Surface plasmons have recently been harnessed to carry out processes such as photovoltaic current generation, redox photochemistry, photocatalysis, and photodetection, all of which are enabled by separating energetic (hot) electrons and holes-processes that, previously, were the domain of semiconductor junctions. Currently, the power conversion efficiencies of systems using plasmon excitation are low. However, the very large electron/hole per photon quantum efficiencies observed for plasmonic devices fan the hope of future improvements through a deeper understanding of the processes involved and through better device engineering, especially of critical interfaces such as those between metallic and semiconducting nanophases (or adsorbed molecules). In this review, we focus on the physics and dynamics governing plasmon-derived hot charge carrier transfer across, and the electronic structure at, metal-semiconductor (molecule) interfaces, where we feel the barriers contributing to low efficiencies reside. We suggest some areas of opportunity that deserve early attention in the still-evolving field of hot carrier transmission from plasmonic nanostructures to neighboring phases.

Balancing Near-Field Enhancement, Absorption, and Scattering for Effective Antenna-Reactor Plasmonic Photocatalysis.

Efficient photocatalysis requires multifunctional materials that absorb photons and generate energetic charge carriers at catalytic active sites to facilitate a desired chemical reaction. Antenna-reactor complexes are an emerging multifunctional photocatalytic structure where the strong, localized near field of the plasmonic metal nanoparticle (e.g., Ag) is coupled to the catalytic properties of the nonplasmonic metal nanoparticle (e.g., Pt) to enable chemical transformations. With an eye toward sustainable solar driven photocatalysis, we investigate how the structure of antenna-reactor complexes governs their photocatalytic activity in the light-limited regime, where all photons need to be effectively utilized. By synthesizing core@shell/satellite (Ag@SiO2/Pt) antenna-reactor complexes with varying Ag nanoparticle diameters and performing photocatalytic CO oxidation, we observed plasmon-enhanced photocatalysis only for antenna-reactor complexes with antenna components of intermediate sizes (25 and 50 nm). Optimal photocatalytic performance was shown to be determined by a balance between maximized local field enhancements at the catalytically active Pt surface, minimized collective scattering of photons out of the catalyst bed by the complexes, and minimal light absorption in the Ag nanoparticle antenna. These results elucidate the critical aspects of local field enhancement, light scattering, and absorption in plasmonic photocatalyst design, especially under light-limited illumination conditions.

Quantitative and Atomic-Scale View of CO-Induced Pt Nanoparticle Surface Reconstruction at Saturation Coverage via DFT Calculations Coupled with in Situ TEM and IR.

Atomic-scale insights into how supported metal nanoparticles catalyze chemical reactions are critical for the optimization of chemical conversion processes. It is well-known that different geometric configurations of surface atoms on supported metal nanoparticles have different catalytic reactivity and that the adsorption of reactive species can cause reconstruction of metal surfaces. Thus, characterizing metallic surface structures under reaction conditions at atomic scale is critical for understanding reactivity. Elucidation of such insights on high surface area oxide supported metal nanoparticles has been limited by less than atomic resolution typically achieved by environmental transmission electron microscopy (TEM) when operated under realistic conditions and a lack of correlated experimental measurements providing quantitative information about the distribution of exposed surface atoms under relevant reaction conditions. We overcome these limitations by correlating density functional theory predictions of adsorbate-induced surface reconstruction visually with atom-resolved imaging by in situ TEM and quantitatively with sample-averaged measurements of surface atom configurations by in situ infrared spectroscopy all at identical saturation adsorbate coverage. This is demonstrated for platinum (Pt) nanoparticle surface reconstruction induced by CO adsorption at saturation coverage and elevated (>400 K) temperature, which is relevant for the CO oxidation reaction under cold-start conditions in the catalytic convertor. Through our correlated approach, it is observed that the truncated octahedron shape adopted by bare Pt nanoparticles undergoes a reversible, facet selective reconstruction due to saturation CO coverage, where {100} facets roughen into vicinal stepped high Miller index facets, while {111} facets remain intact.

Catalyst Architecture for Stable Single Atom Dispersion Enables Site-Specific Spectroscopic and Reactivity Measurements of CO Adsorbed to Pt Atoms, Oxidized Pt Clusters, and Metallic Pt Clusters on TiO2.

Oxide-supported precious metal nanoparticles are widely used industrial catalysts. Due to expense and rarity, developing synthetic protocols that reduce precious metal nanoparticle size and stabilize dispersed species is essential. Supported atomically dispersed, single precious metal atoms represent the most efficient metal utilization geometry, although debate regarding the catalytic activity of supported single precious atom species has arisen from difficulty in synthesizing homogeneous and stable single atom dispersions, and a lack of site-specific characterization approaches. We propose a catalyst architecture and characterization approach to overcome these limitations, by depositing ∼1 precious metal atom per support particle and characterizing structures by correlating scanning transmission electron microscopy imaging and CO probe molecule infrared spectroscopy. This is demonstrated for Pt supported on anatase TiO2. In these structures, isolated Pt atoms, Ptiso, remain stable through various conditions, and spectroscopic evidence suggests Ptiso species exist in homogeneous local environments. Comparing Ptiso to ∼1 nm preoxidized (Ptox) and prereduced (Ptmetal) Pt clusters on TiO2, we identify unique spectroscopic signatures of CO bound to each site and find CO adsorption energy is ordered: Ptiso ≪ Ptmetal < Ptox. Ptiso species exhibited a 2-fold greater turnover frequency for CO oxidation than 1 nm Ptmetal clusters but share an identical reaction mechanism. We propose the active catalytic sites are cationic interfacial Pt atoms bonded to TiO2 and that Ptiso exhibits optimal reactivity because every atom is exposed for catalysis and forms an interfacial site with TiO2. This approach should be generally useful for studying the behavior of supported precious metal atoms.

Isolated metal active site concentration and stability control catalytic CO2 reduction selectivity.

CO2 reduction by H2 on heterogeneous catalysts is an important class of reactions that has been studied for decades. However, atomic scale details of structure-function relationships are still poorly understood. Particularly, it has been suggested that metal particle size plays a unique role in controlling the stability of CO2 hydrogenation catalysts and the distribution of active sites, which dictates reactivity and selectivity. These studies often have not considered the possible role of isolated metal active sites in the observed dependences. Here, we utilize probe molecule diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) with known site-specific extinction coefficients to quantify the fraction of Rh sites residing as atomically dispersed isolated sites (Rhiso), as well as Rh sites on the surface of Rh nanoparticles (RhNP) for a series of TiO2 supported Rh catalysts. Strong correlations were observed between the catalytic reverse water gas shift turn over frequency (TOF) and the fraction of Rhiso sites and between catalytic methanation TOF and the fraction of RhNP sites. Furthermore, it was observed that reaction condition-induced disintegration of Rh nanoparticles, forming Rhiso active sites, controls the changing reactivity with time on stream. This work demonstrates that isolated atoms and nanoparticles of the same metal on the same support can exhibit uniquely different catalytic selectivity in competing parallel reaction pathways and that disintegration of nanoparticles under reaction conditions can play a significant role in controlling stability.

Controlling catalytic selectivity on metal nanoparticles by direct photoexcitation of adsorbate-metal bonds.

Engineering heterogeneous metal catalysts for high selectivity in thermal driven reactions typically involves the synthesis of nanostructures with well-controlled geometries and compositions. However, inherent relationships between the energetics of elementary steps limit the control of catalytic selectivity through these approaches. Photon excitation of metal catalysts can induce chemical reactivity channels that cannot be accessed using thermal energy, although the potential for targeted activation of adsorbate-metal bonds is limited because the processes of photon absorption and adsorbate-metal bond photoexcitation are typically separated spatially. Here, we show that the use of sub-5-nanometer metal particles as photocatalysts enables direct photoexcitation of hybridized adsorbate-metal states as the dominant mechanism driving photochemistry. Activation of targeted adsorbate-metal bonds through direct photoexcitation of hybridized electronic states enabled selectivity control in preferential CO oxidation in H2 rich streams. This mechanism opens new avenues to drive selective catalytic reactions that cannot be achieved using thermal energy.

Catalytic and photocatalytic transformations on metal nanoparticles with targeted geometric and plasmonic properties.

Heterogeneous catalysis by metals was among the first enabling technologies that extensively relied on nanoscience. The early intersections of catalysis and nanoscience focused on the synthesis of catalytic materials with high surface to volume ratio. These synthesis strategies mainly involved the impregnation of metal salts on high surface area supports. This would usually yield quasi-spherical nanoparticles capped by low-energy surface facets, typically with closely packed metal atoms. These high density areas often function as the catalytically active surface sites. Unfortunately, strategies to control the functioning surface facet (i.e., the geometry of active sites that performs catalytic turnover) are rare and represent a significant challenge in our ability to fine-tune and optimize the reactive surfaces. Through recent developments in colloidal chemistry, chemists have been able to synthesize metallic nanoparticles of both targeted size and desired shape. This has opened new possibilities for the design of heterogeneous catalytic materials, since metal nanoparticles of different shapes are terminated with different surface facets. By controlling the surface facet exposed to reactants, we can start affecting the chemical transformations taking place on the metal particles and changing the outcome of catalytic processes. Controlling the size and shape of metal nanoparticles also allows us to control the optical properties of these materials. For example, noble metals nanoparticles (Au, Ag, Cu) interact with UV-vis light through an excitation of localized surface plasmon resonance (LSPR), which is highly sensitive to the size and shape of the nanostructures. This excitation is accompanied by the creation of short-lived energetic electrons on the surface of the nanostructure. We showed recently that these energetic electrons could drive photocatalytic transformations on these nanostructures. The photocatalytic, electron-driven processes on metal nanoparticles represent a new family of chemical transformations exhibiting fundamentally different behavior compared with phonon-driven thermal processes, potentially allowing selective bond activation. In this Account, we discuss both the impact of the shape of metal nanoparticles on the outcome of heterogeneous catalytic reactions and the direct, electron-driven photocatalysis on plasmonic metal nanostructures of noble metals. These two phenomena are important examples of taking advantage of physical properties of metal materials that are controlled at nanoscales to affect chemical transformations.