Periodic Reporting for period 4 - MOF-reactors (Metal-Organic Frameworks as Chemical Reactors for the Synthesis of Well-Defined Sub-Nanometer Metal Clusters)
Berichtszeitraum: 2023-09-01 bis 2024-12-31
The use and development of traditional metals has guided the technological evolution and humankind progress during thousands of years. A paradigmatic shift occurred the last century with the appearance of metal nanoparticles (NPs), that are now heavily utilized in engineering, catalysis and biomedical science, and are still a focus of interest because of their huge potential in nanotechnology. The metal technological roadmap has by–passed a third form of matter with completely different properties, i.e. aggregations of less than 10 atoms that fall in the sub–nanometric regime, here called SNMCs. The present project envisions that SNMCs are irremediably called to trigger unforeseen technological solutions in the next years provided that their design, manufacture and use is properly understood and developed.
The crucial step of any flourishing cluster–based technology is the synthesis and stabilization of well–defined structures at multi–gram scale. This project aims to achieve this ambitious objective with an innovative synthetic methodology based on the use of metal-organic frameworks (MOFs) as chemical nanoreactors to synthesise, in-situ, large amounts of stable and well-characterised highly reactive SNMCs. The main objective is the preparation of new powerful catalysts capable to generously surpass the state–of–the–art catalysts in some organic reactions of industrial interest such as hydrogenation or organic compounds, with high economic impact.
As a conclusion, during the 70 months of the project, the most relevant objectives set at the beginning have been successfully achieved. Optimal synthetic procedures have been developed for the preparation of robust, functional, and crystalline metal-organic frameworks, which have, in turn, enabled the rational and controlled synthesis of both homo- and heterometallic subnanometric metal clusters. Additionally, the remarkable catalytic activity of these metallic species has been conclusively demonstrated in a large number of industrially relevant reactions, with a conceptual understanding of the mechanisms responsible for this activity. Finally, the groundwork has been laid for the large-scale production of these materials, facilitating their industrial application.
The crucial step of any flourishing cluster–based technology is the synthesis and stabilization of well–defined structures at multi–gram scale. This project aims to achieve this ambitious objective with an innovative synthetic methodology based on the use of metal-organic frameworks (MOFs) as chemical nanoreactors to synthesise, in-situ, large amounts of stable and well-characterised highly reactive SNMCs. The main objective is the preparation of new powerful catalysts capable to generously surpass the state–of–the–art catalysts in some organic reactions of industrial interest such as hydrogenation or organic compounds, with high economic impact.
As a conclusion, during the 70 months of the project, the most relevant objectives set at the beginning have been successfully achieved. Optimal synthetic procedures have been developed for the preparation of robust, functional, and crystalline metal-organic frameworks, which have, in turn, enabled the rational and controlled synthesis of both homo- and heterometallic subnanometric metal clusters. Additionally, the remarkable catalytic activity of these metallic species has been conclusively demonstrated in a large number of industrially relevant reactions, with a conceptual understanding of the mechanisms responsible for this activity. Finally, the groundwork has been laid for the large-scale production of these materials, facilitating their industrial application.
1. Preparation of new robust and crystalline MOFs using oxamidato- and oxamato-based ligands derived from biomolecules and robust aromatic amines derivatives of chiral amino acids as ligands. These MOFs show tuneable pore size and functionality, as a direct consequence of the size and chemical nature of the chosen amino acid residues, which must be capable to anchor to the pores the desired metallic species in subsequent Tasks. These materials have been also explored with excellent results in other fields such as water environmental remediation. In this context, we have reported a new MOF derived from the amino acid L-serine that can be used in the molecular recognition and sorbent extraction of hydrophilic vitamins in juices. Another MOF has been also used for the efficient capture and separation of greenhouse gases and neonicotinoid insecticides, organic dyes, antibiotics and recreational drugs. We have also developed a family of multivariate MOFs (which are being used for the in-situ preparation of heterometallic SNMCs) that shows excellent properties in the capture of organic and inorganic contaminants and also in enzymatic catalysis, mimicking the active centers of enzimes. Finally, some of these MOFs are being processed as mixed matrix membranes (MMM-MOFs) and/or FOAM-MOFs and explored their application in different technological applications.
2. We have carried out the MOF-driven preparation of different SNMCs and single atom catalysts (SACs) using the MOFs described in the previous section. In so doing, we have achieved the formation of different well-defined ligand-free Ag2 and Au3 SNMCs and Pt and Pd SACs. In addition, such small species have been characterised by using SC-XRD, being the first examples of SNMCs and SACs characterised crystallographically within MOFs. As planned, we have explored their catalytic activity which is outstanding in some cases. For example, Pd SACs have shown excellent activity and reusability in the selective oxidation of primary alcohols to carboxylic acids. Other SNMCs are showing also excellent results in industrially relevant reactions like the water gas-shift reaction or the selective hydrogenation of olefins and paraffins.
3. The sequential step-by-step synthesis of homometallic (Task 2) and heterometallic (Task 3) SNMCs has been also carried out. We have synthesised unprecedented examples of SNMCs of growing nuclearity (Task 2) and heterometallic SNMCs (Task 3). These species show and outstanding catalytic behaviours in different reactions of industrial interest. For example, the AgFe species showed a unique catalytic activity for the direct conversion of styrene to phenylacetylene in one-pot. Moreover, AuPd nanoclusters exhibited outstanding activity in the semihydrogenation reaction of acetylene in ethylene, surpassing the state of the art catalysts.
4. The last point related to the objectives of the project has consisted of the multigram–scale manufacture of SNMCs and industry scalability. For that, we have taken advantage of the results obtained in previous Tasks. A large plethora of interesting materials have been prepared and tested in catalysis. The next step consisted on scaling-up their preparation. For that synthetic pathways were optimised (also aiming at making them economically viable). In so doing, direct large syntheses (more than 100 g) have been carried out in only one step, which indeed constituted a challenge for MOFs syntheses.
In general, all the results obtained here have been disseminated through the most common means in Science, such as publications, participation in scientific conferences through invited lectures, and the development of patents (www.mupomat.com). In addition, a significant portion of the results obtained in this project form one of the fundamental pillars for the near future of the MUPOMAT group. In this regard, the group has taken initial steps toward establishing a spin-off focused on the industrial application of MOFs.
2. We have carried out the MOF-driven preparation of different SNMCs and single atom catalysts (SACs) using the MOFs described in the previous section. In so doing, we have achieved the formation of different well-defined ligand-free Ag2 and Au3 SNMCs and Pt and Pd SACs. In addition, such small species have been characterised by using SC-XRD, being the first examples of SNMCs and SACs characterised crystallographically within MOFs. As planned, we have explored their catalytic activity which is outstanding in some cases. For example, Pd SACs have shown excellent activity and reusability in the selective oxidation of primary alcohols to carboxylic acids. Other SNMCs are showing also excellent results in industrially relevant reactions like the water gas-shift reaction or the selective hydrogenation of olefins and paraffins.
3. The sequential step-by-step synthesis of homometallic (Task 2) and heterometallic (Task 3) SNMCs has been also carried out. We have synthesised unprecedented examples of SNMCs of growing nuclearity (Task 2) and heterometallic SNMCs (Task 3). These species show and outstanding catalytic behaviours in different reactions of industrial interest. For example, the AgFe species showed a unique catalytic activity for the direct conversion of styrene to phenylacetylene in one-pot. Moreover, AuPd nanoclusters exhibited outstanding activity in the semihydrogenation reaction of acetylene in ethylene, surpassing the state of the art catalysts.
4. The last point related to the objectives of the project has consisted of the multigram–scale manufacture of SNMCs and industry scalability. For that, we have taken advantage of the results obtained in previous Tasks. A large plethora of interesting materials have been prepared and tested in catalysis. The next step consisted on scaling-up their preparation. For that synthetic pathways were optimised (also aiming at making them economically viable). In so doing, direct large syntheses (more than 100 g) have been carried out in only one step, which indeed constituted a challenge for MOFs syntheses.
In general, all the results obtained here have been disseminated through the most common means in Science, such as publications, participation in scientific conferences through invited lectures, and the development of patents (www.mupomat.com). In addition, a significant portion of the results obtained in this project form one of the fundamental pillars for the near future of the MUPOMAT group. In this regard, the group has taken initial steps toward establishing a spin-off focused on the industrial application of MOFs.
Preparation of well-defined ligand-free SNMCs and SACs attracts attention of many chemists in the world due to the large potential technological applications of these species (i.e. catalysis). However, the gram-scale preparation of stable SNMCs and SACs and their proper characterization constitutes a great challenge. This project approach relied on the use of MOFs to allow their gram-scale formation and to stabilise such naked tiny species. As stated in previous points, we have achieved excellent results that can be considered to be beyond the state of the art and they are listed below:
- A high degree of functionalization of the formed MOFs that can be achieved pre- or postsynthetically.
- Use of single-crystal X-ray diffraction (SC XRD) as a powerful characterization tool for MOFs and the MOF-driven species formed within their channels.
- Preparation of homo- and heterometallic ligand-free SNMCs.
- Multigram-scale preparation of these hybrid materials.
- The catalytic activities of some of these species has been explored confirming their high activity and in some cases surpassing the state of the art catalysts.
- A high degree of functionalization of the formed MOFs that can be achieved pre- or postsynthetically.
- Use of single-crystal X-ray diffraction (SC XRD) as a powerful characterization tool for MOFs and the MOF-driven species formed within their channels.
- Preparation of homo- and heterometallic ligand-free SNMCs.
- Multigram-scale preparation of these hybrid materials.
- The catalytic activities of some of these species has been explored confirming their high activity and in some cases surpassing the state of the art catalysts.