Recent reports have shown that plasmonic nanostructures can be used to drive direct photocatalysis with visible photons, where nanostructures act as the light absorber and the catalytic active site. These reports have showcased direct plasmon driven photocatalysis as a route to concentrate and channel the energy of low intensity visible light into adsorbed molecules, enhancing the rates of chemical transformations, and offering pathways to control reaction selectivity. In this perspective, we will discuss the fundamental photophysics of localized surface plasmon resonance (LSPR) excitation in the context of driving chemical transformations. The various demonstrated chemical conversions executed using direct plasmonic photocatalysis will be reviewed. Experimental observations, such as the dependence of photocatalytic rate on illumination intensity and photon energy, will be related to microscopic mechanisms of photocatalysis. In addition, theoretical treatments of various mechanisms within the process of direct plasmonic photocatalysis will be discussed and related to experimental studies. Throughout the Perspective, the possibility of activating targeted adsorbate bonds to allow rational manipulation of reaction selectivity in direct plasmonic photocatalysis will be discussed.

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.

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.

10The mechanism of CO2 reduction by H2 at atmospheric pressure was investigated on 11 Ru(0001) by coupling density functional theory (DFT) calculations with mean-field 12 microkinetic modeling. The initial CO2 hydrogenation step leading to CH4 production was 13 shown to occur through CO2 dissociation and subsequent hydrogenation of CO* to CHO*. 14 The dissociation of CHO* to form CH* and O* was identified as the rate limiting step for CH4 15 formation, while the rate limiting step for CO production through the reverse water gas 16 shift reaction was identified as CO* desorption. Based on a scaling relations analysis of 17 competing CHO* dissociation and CO* desorption, O* adsorption energy was found to be an 18 effective descriptor of differences in selectivity between CO and CH4 production previously 19 observed on late-transition metal catalysts. These mechanistic insights provide critical 20 information to guide the design of catalysts with tunable selectivity for CO2 reduction by H2 21 at atmospheric pressure. 22 1. Introduction 1 More than 85% of the current global energy need is provided by combustion of 2 fossil fuels, which is accountable for continuously increasing atmospheric concentrations of 3 CO2 and accompanying climate change effects.[1] The search for approaches to reduce 4 atmospheric CO2 concentration has become a high priority research area. Recent efforts 5show the potential promise of directly sequestering CO2 from the atmosphere using amine 6 based sorbent materials, among other methods. [2][3][4][5][6] If approaches to directly sequester 7 CO2 from the atmosphere prove successful, it will be important to develop efficient, low 8 temperature and pressure processes for converting CO2 to higher value hydrocarbon 9 feedstocks for chemical and fuel production. The coupling of CO2 sorption technologies 10 with solar-based H2 production through catalytic reduction processes would provide an 11 energy efficient, environmentally friendly and carbon neutral approach for chemical and 12 fuel production. This approach relies, in part, on the development of materials that 13 facilitate catalytic conversion of CO2 and H2 into desired products with high selectivity.14 Because of high energy requirements, C-C coupling reactions are rare at low 15 temperature and pressure and it is expected that C1 molecules (CO, CH3OH and CH4) will be 16 the dominant products of environmentally friendly CO2 reduction processes. CH3OH 17 synthesis from CO2 and H2 on Cu and "Cu-like" catalysts has received significant attention, 18 due the extensive use of CH3OH as a precursor for production of chemicals and liquid fuels. 19However, CH3OH is a minimal side product under low pressure CO2 hydrogenation 20 conditions.[7-9] On the other hand, highly selective catalytic CH4 and CO production has 21 been demonstrated at low temperature (as low as 150 • C) and atmospheric pressure over a 22 range of supported transition metal catalysts (eg. Ni, Ru, Rh, Pd, Pt).[10-15] Supported Ru and Rh catalysts are consistently observed to...