Abstract
Over the last 20 years, the use of metallic nanoparticles (MNPs) in catalysis has awakened a great interest in the scientific community, mainly due to the many advantages of this kind of nanostructures in catalytic applications. MNPs exhibit the characteristic stability of heterogeneous catalysts, but with a higher active surface area than conventional metallic materials. However, despite their higher activity, MNPs present a wide variety of active sites, which makes it difficult to control their selectivity in catalytic processes. An efficient way to modulate the activity/selectivity of MNPs is the use of coordinating ligands, which transforms the MNP surface, subsequently modifying the nanoparticle catalytic properties. In relation to this, the use of N-heterocyclic carbenes (NHC) as stabilizing ligands has demonstrated to be an effective tool to modify the size, stability, solubility and catalytic reactivity of MNPs. Although NHC-stabilized MNPs can be prepared by different synthetic methods, this review is centered on those prepared by an organometallic approach. Here, an organometallic precursor is decomposed under H2 in the presence of non-stoichiometric amounts of the corresponding NHC-ligand. The resulting organometallic nanoparticles present a clean surface, which makes them perfect candidates for catalytic applications and surface studies. In short, this revision study emphasizes the great versatility of NHC ligands as MNP stabilizers, as well as their influence on catalysis.
Highlights
Since the beginning of this century, metallic nanoparticles (MNPs) have emerged in the field of chemistry as new nano-objects with a great potential in catalysis
The aim of this review is to provide a general overview of organometallic NPs ligated by N-heterocyclic carbenes (NHC) ligands, focusing the study on the advantages of the use of molecular tools for their synthesis through an organometallic approach
We have explored the ability of NHC ligands to stabilize and modulate the catalytic properties of MNPs, focusing the survey on organometallic nanoparticles prepared by an organometallic approach, which produces clean surface MNPs ideal for surface studies and catalytic applications
Summary
Since the beginning of this century, metallic nanoparticles (MNPs) have emerged in the field of chemistry as new nano-objects with a great potential in catalysis. X-ray photoelectron spectroscopy (XPS) has been recently presented as a promising tool to study the coordination modes of ancillary ligands on the MNP surface, apart from providing chemical information about the metallic surface atoms [32]. FT-IR, XPS and solid-state MAS-NMR spectroscopy are established techniques for surface studies, which allow the identification of the surface active sites as well as the investigation of the coordination, location and dynamics of surface ligands on NHC-stabilized MNPs. The aim of this review is to provide a general overview of organometallic NPs ligated by NHC ligands, focusing the study on the advantages of the use of molecular tools for their synthesis through an organometallic approach. The last part of this review will focus on the effect of stabilizing NHC ligands related to the stability, solubility and catalytic activity of MNPs
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