Metal nanoparticles have received intense scientific attention in the field of catalysis. Precise engineering of nanomaterials' size, shape and surface composition, including adsorbed capping ligands, is of utmost importance to control activity and selectivity, and distinguish colloidally prepared metal nanoparticle catalysts from traditional heterogeneous catalysts. The interface between the material and the reaction medium is where the key interactions occur; therefore, catalysis occurs under the influence of capping ligands. In this Perspective review, we focus on the choice of capping ligands (or stabilizing agents), and their role and fate in different steps from preparation to catalysis. Evaluating the influence of the ligands on the catalytic response is not trivial, but the literature provides examples where the ligands adsorbed on the nanoparticle surface dramatically change the activity and selectivity for a particular reaction, while acting either as a dynamic shell or a passivation coating. Steric and electronic effects resulting from the presence of adsorbed ligands have been proposed to influence the catalytic properties. Attempts to remove the capping ligands are discussed, even though they are not always successful or even necessary. Finally, we outline our personal understanding and perspectives on the use of ligands or functionalized supports to tune the activity and selectivity of supported metal nanoparticles.

The localized surface plasmon resonance (LSPR) excitation in plasmonic nanoparticles has been used to accelerate several catalytic transformations under visible-light irradiation. In order to fully harness the potential of plasmonic catalysis, multimetallic nanoparticles containing a plasmonic and a catalytic component, where LSPR-excited energetic charge carriers and the intrinsic catalytic active sites work synergistically, have raised increased attention. Despite several exciting studies observing rate enhancements, controlling reaction selectivity remains very challenging. Here, by employing multimetallic nanoparticles combining Au, Ag, and Pt in an Au@Ag@Pt core–shell and an Au@AgPt nanorattle architectures, we demonstrate that reaction selectivity of a sequential reaction can be controlled under visible light illumination. The control of the reaction selectivity in plasmonic catalysis was demonstrated for the hydrogenation of phenylacetylene as a model transformation. We have found that the localized interaction between the triple bond in phenylacetylene and the Pt nanoparticle surface enables selective hydrogenation of the triple bond (relative to the double bond in styrene) under visible light illumination. Atomistic calculations show that the enhanced selectivity toward the partial hydrogenation product is driven by distinct adsorption configurations and charge delocalization of the reactant and the reaction intermediate at the catalyst surface. We believe these results will contribute to the use of plasmonic catalysis to drive and control a wealth of selective molecular transformations under ecofriendly conditions and visible light illumination.

The selective hydrogenation of alkynes to alkenes is an important synthetic process in the chemical industry. It is commonly accomplished using palladium catalysts that contain surface modifiers, such as lead and silver. Here we report that the adsorption of nitrogen-containing bases on gold nanoparticles results in a frustrated Lewis pair interface that activates H 2 heterolytically, allowing an unexpectedly high hydrogenation activity. The so-formed tight-ion pair can be selectively transferred to an alkyne, leading to a cis isomer; this behavior is controlled by electrostatic interactions. Activity correlates with H 2 dissociation energy, which depends on the basicity of the ligand and its reorganization on activation of hydrogen. High surface occupation and strong Au atom−ligand interactions might affect the accessibility and stability of the active site, making the activity prediction a multiparameter function. The promotional effect found for nitrogen-containing bases with two heteroatoms was mechanistically described as a strategy to boost gold activity.

Pyrolysis of Au(OAc) 3 in the presence of 1,10phenanthroline over TiO 2 furnishes a highly active and selective Au nanoparticle (NP) catalyst embedded in a nitrogen-doped carbon support, Au@N-doped carbon/TiO 2 catalyst. Parameters such as pyrolysis temperature, type of support, and nitrogen ligands as well as Au/ligand molar ratios were systematically investigated. Highly selective hydrogenation of numerous structurally diverse alkynes proceeded in moderate to excellent yield under mild conditions. The high selectivity toward the industrially important alkene substrates, functional group tolerance, and the high recyclability makes the catalytic system unique. Both high activity and selectivity are correlated with a frustrated Lewis pairs interface formed by the combination of gold and nitrogen atoms of N-doped carbon that, according to density functional theory calculations, can serve as a basic site to promote the heterolytic activation of H 2 under very mild conditions. This "fully heterogeneous" and recyclable gold catalyst makes the selective hydrogenation process environmentally and economically attractive.

The localized surface plasmon resonance (LSPR) excitation in plasmonic nanoparticles can enhance or mediate chemical transformations. Increased reaction rates for several reactions have been reported due to this phenomenon; however, the fundamental understanding of mechanisms and factors that affect activities remains limited. Here, by investigating hydrogenation reactions as a model transformation and employing different reducing agents, H and NaBH , which led to different hydrogenation reaction pathways, we observed that plasmonic excitation of Au nanoparticle catalysts can lead to negative effects over the activities. The underlying physical reason was explored using density functional theory calculations. We observed that positive versus negative effects on the plasmonic catalytic activity is reaction-pathway dependent. These results shed important insights on our current understanding of plasmonic catalysis, demonstrating reaction pathways must be taken into account for the design of plasmonic nanocatalysts.