Surface Functionalized Metal Catalysts

The development and understanding of catalytic systems composed of metal nanoparticles (MNPs) on molecularly modified surfaces (MMSs) have attracted tremendous attention in the field of materials chemistry in recent years, especially for applications in catalysis where it opened a conceptually new strategy for the design of multifunctional catalysts (MNPs@MMSs) with tailor-made reactivity. MNPs@MMSs are hybrid materials assembled through judicious associations of supports, molecular modifiers, and MNPs, using a combination of molecular (“homogeneous”) and material (“heterogeneous”) approaches. These complex yet fascinating materials have shown great potential in catalysis, where the synergistic interactions between MNPs@MMSs components provide important benefits including for example enhanced catalytic performance (e.g., activity, selectivity) and improved life-time. Thus, MNPs@MMSs stimulate interdisciplinary research activities involving organometallic chemistry, material science, synthetic organic chemistry, and catalysis. This chapter presents a non-exhaustive overview of the various methods available to prepare and characterize MNPs@MMSs materials, and provides selected examples of the application of MNPs@MMSs to a wide range of catalytic transformations including reduction, oxidation, and coupling reactions.

Polymeric catalytic membranes, adapted for the immobilization of metal nanoparticles (MNPs) with the objective of being applied in hydrogenation reactions, are reviewed in this chapter, highlighting the works including a rational design and full characterization of the catalytic membrane reactors. The most relevant contributions concern zero-valent MNPs (mono- and bimetallic systems) of late transition metals (groups 8–10), involving a significant variety of (un)functionalized polymers. Both batch and continuous-flow processes are discussed, with the latter being of particular interest for large-scale applications. The literature analysis carried out evidences that there is still room for developing innovative polymeric catalytic membranes, regarding both design and applications. Thus, for instance, well-defined stereo-controlled polymeric membranes for enantioselective hydrogenations or multi-step processes involving a series of polymeric catalytic reactors would be of interest, particularly for the production of fine chemicals under smooth conditions.

This chapter looks into the influence of the functionalization of the surface of metal nanoparticles (MNPs) with ligands on their catalytic performance in two crucial reactions, the hydrogen evolution reaction (HER) and the CO₂ reduction reaction (CO₂RR). The birth of the surface functionalization of MNPs with ligands was greatly inspired by the advanced knowledge accumulated on molecular metal catalysts, whose physical and chemical properties can be tuned by coordinating appropriate ligands to the metal active center. This field of research has profited from the progress in the synthetic methods for the generation of MNPs and the evolution of the spectroscopic and analytical techniques for their exhaustive characterization, as well as the improvement of the computational techniques. Relevant examples will illustrate how the functionalization of the surface of MNPs allow to modulate the energy profile of catalytic intermediate species through electronic effects and regulate the product selectivity through hydrophobic/hydrophilic effects. Another key parameter is the tuning of the number of surface-active sites as a function of the metal to ligand ratio and the chemical nature of the coordinating ligand. Furthermore, in some peculiar cases, second coordination sphere effects have even been described in analogy to biological enzymes.

The scientific community has widely studied the synthesis of metal nanoparticles (MNPs) and their applications in a plethora of catalytic transformations for the last 25 years. In these nanometric structures, the catalytic activity and selectivity can be modulated by the controlled tuning of the surface properties of the particles through the use of coordinating donor ligands bound to the metal surface. Among the ligands employed for MNP stabilization, N-heterocyclic carbene (NHC) derivatives have emerged in the last 15 years as a prominent class of compounds due to their strong electron-donor properties and structural diversity. Herein, we discuss the unique ability of NHC ligands to control the reactivity of nanosized metal catalytic systems by describing the synthetic procedures employed for the preparation of NHC-stabilized nanoparticles, their characterization, and the applications of these nanosystems in different catalytic reactions, such as hydrogenation, C-C and C-X bond forming reactions, H/D exchange, oxidation, and electrocatalytic processes.

Metal nanoparticles (MNPs) functionalized with hydrosoluble ligands have emerged as versatile tools in various fields, including catalysis and biomedical applications, among others. This chapter explores recent advances in the synthesis, characterization, and applications of water-soluble MNPs stabilized by diverse ligands. The significance of working with water is emphasized, driven by the imperative for environmentally friendly and sustainable chemistry. To address the challenge of achieving solubility and stability in aqueous environments for MNPs, a range of hydrosoluble ligands have been explored. These ligands, including carboxylic acids, polymers, surfactants, thiols, phosphines, N-heterocyclic carbene (NHC) ligands, proteins, peptides, and bio-extracts, play crucial roles in conferring water solubility, mitigating aggregation and enhancing the catalytic properties of MNPs. The chapter provides a comprehensive overview of the synthesis methods, structural characterization techniques, and applications of water-soluble MNPs across various metal species, including Au, Ru, Pd, Pt, Ag, Rh, Fe, and Cu. Applications of water-soluble MNPs discussed in this chapter encompass mainly catalytic processes and biomedical applications including imaging. The unique properties of MNPs functionalized with hydrosoluble ligands offer opportunities for tailored applications with enhanced selectivity, activity, and biocompatibility.

In the starting exploration of magnetically induced catalysis, organometallic nanoparticles (NPs) have proven themselves to serve as efficient and versatile heating agents, demonstrating remarkable potential for diverse liquid-phase reactions. The present chapter delves into the synthesis and application of various organometallic magnetic NPs (MagNPs), i.e., Fe_2.2C, FeCo, FeNi₃, and NiCo NPs. These magnetic cores, decorated with metals like Ru, Cu, or Ni, exhibit remarkable performance in hydrogenation and hydrodeoxygenation reactions, with promising results in the valorization of biomass derivatives under low hydrogen pressures. The superior catalytic activity compared to those achieved under similar apparent conditions through conventional heating, as well as some recent advances in stability, add to the well-proven advantages of this technology, such as rapid heating, improved energy efficiency, and adaptability to renewable energy sources. The present chapter also establishes the need for precise temperature control, optimized ligand strategies, and strategic stability enhancement in aqueous media, signaling avenues for future progress in magnetically induced catalysis.

This chapter focuses on the functionalization of heterogeneous catalysts of group 8–10 by capping ligands. The synthetic approaches used for the introduction of ligands were particularly looked at, and according to the type of ligands, three main approaches were used: the colloidal formation of metal nanoparticles (MNPs) stabilized by ligands and their subsequent deposition over a solid support, the direct synthesis by colloidal formation of the ligand-capped active phase in the presence of the support, and the ligand functionalization of a previously synthesized heterogeneous catalyst. Depending on the aim of the study and the catalytic application, one of the synthetic strategies was selected. The ligands were shown to have a range of effect on the catalytic performance of the catalyst by tuning the electronic properties of the metal(s), the steric hindrance at the metal surface, or blocking some of the catalyst active sites. These modifications can therefore influence the activity, the selectivity, and/or the stability of the materials, and as such, ligand functionalization appears as a powerful method to fine-tune the properties of heterogeneous catalysts.