Nanopartículas catalíticas… ¿polvo mágico?

Con el inicio de la investigación en materiales con dimensiones nanométricas, pronto se descubrieron sus bondades enlazadas con su excepcional relación área superficial/ volu­men, siendo uno de los ámbitos de mayor potencial de aplicación el de catalizadores. En particular, en las nanopartículas de metales del grupo del platino (rutenio, osmio, rodio, iridio, paladio, platino) se han invertido muchas horas de investigación para encontrar catalizadores con estas dimensiones que mejoren el desempeño cuando son empleados en una escala dimensional mayor. Entre la comunidad, algunos investigadores denominaban las nanopartículas de dichos metales involucradas en procesos catalíticos polvo mágico (magic dust), por las pro­piedades maravillosas que se les atribuyen, pero, ¿realmente se han encontrado grandes mejoras en cuanto al costo/beneficio de los materiales nanoestructurados? o, ¿cuáles han sido las aportaciones generadas con este tipo de investigaciones? En este trabajo se hace una descripción de los avances y descubrimientos en el área de catálisis homogénea (en una sola fase) con catalizadores nanoparticulados de estos metales, que se aplican principalmente en el área de la energía.

Gold, Palladium and Mesoporous Oxide-based Nanocatalysts for redox processes and sustainable catalysis : synthesis and catalytic evaluation

Abstract: Transition metals' exceptional ability and properties at the nanoscale level transcend their corresponding bulk metals in chemical transformation both in the laboratories and the industries. However, the nanoparticles are prone to particle growth and agglomeration at this nanoscale state, inhibiting their excellent performance and compromising their uniqueness. Hence, the stability of the particles presents a significant factor in governing their innovative attributes. Therefore, organic polymers, such as polyvinylpyrrolidone (PVP) and dendrimer, were considerably employed as soft templates to ensure stability and prevent the agglomeration of these nanoparticles in a homogeneous phase. These synthesized nanoparticles include AuPVP, PdPVP, AuPdPVP nanoparticles, and CuDENs. Although conventional homogeneous catalysts possess a vast tendency to enhance high conversion and product selectivity in chemical reactions, nevertheless, they present limiting phenomenon of recoverability, recyclability, and deactivation at high temperatures. Therefore, to circumvent these limitations, we fabricated metal nanoparticles through the dispersion of metals onto an insoluble and solid mesoporous silica and metal oxide support by adapting a dual templating approach, followed by a galvanic replacement protocol. In addition, inverse micelle, sol-gel, and wet impregnation methods were also employed to design ideal heterogeneous catalysts such as Cun@SiO2, Au@SiO2, Pd@SiO2, CoMMO, and MnMMO, which are capable of high operating procedures, easy recoverability, and reusability for oxidation and reduction reactions. Different analytical techniques were used to characterize and obtain the properties of these catalysts. These techniques include nitrogen sorption with Brunauer-Emmett-Teller (BET) and Barret-Joyner-Halenda (BJH) to examine the surface area, pore size, and pore volume distribution, high-resolution transmission electron microscopy (H-TEM) for internal morphologies, powder X-ray diffraction (p-XRD), for the diffraction patterns of the materials. While thermogravimetric analysis (TG) was performed to determine the sample’s thermal stability, Fourier transform infrared spectroscopy (FT-IR) identified the specific functional groups present. Scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) obtained the surface morphologies and identification of metal composition. In addition, hydrogen-temperature programmed reduction (H2-TPR) was used to examine the reducibility of the catalyst...Ph.D. (Chemistry

Preparation, Functionalization, Modification, and Applications of Nanostructured Gold: A Critical Review

This is the final version. Available on open access from MDPI via the DOI in this recordGold nanoparticles (Au NPs) play a significant role in science and technology because of their unique size, shape, properties and broad range of potential applications. This review focuses on the various approaches employed for the synthesis, modification and functionalization of nanostructured Au. The potential catalytic applications and their enhancement upon modification of Au nanostructures have also been discussed in detail. The present analysis also offers brief summaries of the major Au nanomaterials synthetic procedures, such as hydrothermal, solvothermal, sol-gel, direct oxidation, chemical vapor deposition, sonochemical deposition, electrochemical deposition, microwave and laser pyrolysis. Among the various strategies used for improving the catalytic performance of nanostructured Au, the modification and functionalization of nanostructured Au produced better results. Therefore, various synthesis, modification and functionalization methods employed for better catalytic outcomes of nanostructured Au have been summarized in this review.Engineering and Physical Sciences Research Council (EPSRC)Saudi Aramco Chair Programm

Untangling the role of the capping agent in nanocatalysis : recent advances and perspectives

Capping agents (organic ligands, polymers, surfactants, etc.) are a basic component in the synthesis of metal nanoparticles with controlled size and well-defined shape. However, their influence on the performances of nanoparticle-based catalysts is multifaceted and controversial. Indeed, capping agent can act as a "poison", limiting the accessibility of active sites, as well as a "promoter", producing improved yields and unpredicted selectivity control. These effects can be ascribed to the creation of a metal-ligand interphase, whose unique properties are responsible for the catalytic behavior. Therefore, understanding the structure of this interphase is of prime interest for the optimization of tailored nanocatalyst design. This review provides an overview of the interfacial key features affecting the catalytic performances and details a selection of related literature examples. Furthermore, we highlight critical points necessary for the design of highly selective and active catalysts with surface and interphase control

Formation of the active surface of supported nano gold catalysts for liquid-phase selective oxidation of primary alcohols

Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Química Física Aplicada. Fecha de Lectura: 10-06-2021The works here presented were supported by the Tomsk Polytechnic University Competitiveness Enhancement Program, projects VIU-RSCBMT- 65/2019 and VIU-RSCBMT-197/2020, Russian Foundation of Basic Research, project 18-29-24037, Tomsk Polytechnic University Task Program “Science” project FSWW-2020-0011, Scholarship of the President of the Russian Federation for training abroad in 2016/17 and 2017/2018 (Russia). This work was also partially supported by Fundação para a Ciência e a Tecnologia (FCT), Portugal, through project UIDB/00100/2020 of the Centro de Química Estrutural, Investigador FCT IF/01381/2013/CP1160/CT0007 project and Associate Laboratory LSRE-LCM – UID/EQU/50020/2019, UIDB/50006/2020 – funded by national funds through FCT/MCTES (PIDDAC) (Portugal), MINECO project CTQ2017-86170-R (Spain) and CONACYT project 279889 and PAPIIT-UNAM projects IT200114, IN105114 and IN107715 (Mexico)

Towards the rational design of nanoparticle catalysts

This research is focused on development of routes towards the rational design of nanoparticle catalysts. Primarily, it is focused on two main projects; (1) the use of imidazolium-based ionic liquids (ILs) as greener media for the design of quasi-homogeneous nanoparticle catalysts and (2) the rational design of heterogeneous-supported nanoparticle catalysts from structured nanoparticle precursors. Each project has different studies associated with the main objective of the design of nanoparticle catalysts. In the first project, imidazolium-based ionic liquids have been used for the synthesis of nanoparticle catalysts. In particular, studies on recyclability, reuse, mode-of-stability, and long-term stability of these ionic-liquid supported nanoparticle catalysts have been done; all of which are important factors in determining the overall “greenness” of such synthetic routes. Three papers have been published/submitted for this project. In the first publication, highly stable polymer-stabilized Au, Pd and bimetallic Au-Pd nanoparticle catalysts have been synthesized in imidazolium-based 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6) ionic liquid (Journal of Molecular Catalysis A: Chemical, 2008, 286, 114). The resulting nanoparticles were found to be effective and selective quasi-homogeneous catalysts towards a wide-range of hydrogenation reactions and the catalyst solution was reused for further catalytic reactions with minimal loss in activity. The synthesis of very pure and clean ILs has allowed a platform to study the effects of impurities in the imidazolium ILs on nanoparticle stability. In a later study, a new mode of stabilization was postulated where the presence of low amounts of 1-methylimidazole has substantial effects on the resulting stability of Au and Pd-Au nanoparticles in these ILs (Chemical Communications, 2009, 812). In further continuation of this study, a comparative study involving four stabilization protocols for nanoparticle stabilization in BMIMPF6 IL is described, and have shown that nanoparticle stability and catalytic activity of nanoparticles is dependent on the overall stability of the nanoparticles towards aggregation (manuscript submitted). The second major project is focused on synthesizing structurally well-defined supported catalysts by incorporating the nanoparticle precursors (both alloy and core shell) into oxide frameworks (TiO2 and Al2O3), and examining their structure-property relationships and catalytic activity. a full article has been published on this project (Journal of Physical Chemistry C, 2009, 113, 12719) in which a route to rationally design supported catalysts from structured nanoparticle precursors with precise control over size, composition, and internal structure of the nanoparticles has been shown. In a continuation of this methodology for the synthesis of heterogeneous catalysts, efforts were carried out to apply the same methodology in imidazolium-based ILs as a one-pot media for the synthesis of supported-nanoparticle heterogeneous catalysts via the trapping of pre-synthesized nanoparticles into porous inorganic oxide materials. Nanoparticle catalysts in highly porous titania supports were synthesized using this methodology (manuscript to be submitted)

Carbon-carbon coupling reactions catalysed by palladium nanoparticles supported on the green alga Ulva armoricana

Magister Scientiae - MSc (Chemistry)The synthesis of nanomaterials, especially metallic nanoparticles, has attracted an enormous amount of interest over the past decade. They exhibit unique properties that allow the multiple applications in a variety of fields in science and technology. Their applications are limited by the efficiency and control of their synthesis to produce nanoparticles of certain size and shape. With ever mounting concern for the environment, a great amount of research has recently been extended to synthetic procedures that are carried out with limited or no toxicity to human health and the environment. One method involves the use of biological (or biogenic) materials for nanoparticle synthesis. This method is particularly attractive due to the fact that it is a relatively cheap, simple and environmentally friendly method compared to that of conventional chemical methods of synthesis

Synthesis, characterization, and catalytic applications of metallic nanoparticles in Tetraalkylphosphonium ionic liquids

In recent years, ionic liquids have emerged as one of the most promising alternatives to traditional volatile organic solvents when it comes to catalytic reactions. Stable metal nanoparticles suspended in ionic liquids, are catalytic systems that mimic aspects of nanoparticles on solid supports, as well as traditional metal-ligand complexes used in organometallic catalysis. While alkylimidazolium ionic liquids, with or without appended functionalities, have been earmarked as the media of choice for the dispersal of nanoparticles, the tetraalkylphosphonium family of ionic liquids has largely been overlooked, despite their facile synthesis, commercial availability, chemical resemblance to surfactants traditionally used for nanoparticle stabilization, stability under basic conditions, and wide thermal as well as electrochemical windows. It is only recently that a number of research groups have given this family of novel alternative solvents the recognition it deserves, and used metal NPs dispersed in these ILs as catalysts in reactions such as hydrogenations, oxidations, C-C cross-couplings, hydrodeoxygenations, aminations, etc. This thesis investigates the synthesis, characterization, and catalytic applications of transition metal nanoparticles in tetraalkylphosphonium ionic liquids. The ionic liquids described in this thesis functioned as the reaction media as well as intrinsic nanoparticle stabilizers during the course of the catalytic processes. Metallic nanoparticles synthesized in these ionic liquids proved to be stable, efficient and recyclable catalytic systems for reactions of industrial significance, such as hydrodeoxygenations, hydrogenations, and oxidations. It was demonstrated that stability and catalytic activity of these systems were profoundly dependent on the properties of the ionic liquids, such as the nature of the alkyl chains attached to the phosphonium cation, and the coordination ability of the anion. Since heat-induced nanoparticle sintering was a problem, a procedure was devised to redisperse the aggregated and/or sintered nanoparticles so as to restore their initial sizes and catalytic activities. The presence of halides as counter-ions in tetraalkylphosphonium ionic liquids was seen to facilitate the oxidative degradation of agglomerated metal nanoparticles, which was a key step in our redispersion protocol. It was demonstrated that this redispersion protocol, when applied to heat-sintered nanoparticles, produces nanostructures that resemble the freshly made nanoparticles not only in size but also in catalytic activities. The presence of by-products from the borohydride reduction step used to generate the nanoparticles in the ionic liquids actually facilitated multistep reactions such as hydrodeoxygenation of phenol, where a Lewis Acid was necessary for a dehydration step. Finally, an attempt was made to utilize nanoparticles of an earth-abundant metal (iron) as a hydrogenation catalyst in a variety of alternative solvents (including tetraalkylphosphonium ionic liquids) in order to enhance the “green”ness of the catalyst systems. X-ray absorption spectroscopy (XAS) of the iron- nanoparticles/ionic liquid systems at the Canadian Light Source revealed significant details about the chemical interaction between iron and the ionic liquid matrices, which added to our understanding of this neoteric family of catalysts