Periodic Reporting for period 3 - MOF-reactors (Metal-Organic Frameworks as Chemical Reactors for the Synthesis of Well-Defined Sub-Nanometer Metal Clusters)
Reporting period: 2022-03-01 to 2023-08-31
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.
2. We have carried out the MOF-driven preparation and atomic-level SCXRD characterisation of different SNMCs and single atom catalysts (SACs) using the MOFs described in the previous section. For that, we have followed the programmed strategy, based on the controlled insertion of the desired metal salts that are anchored to the network by interacting with specific functional groups or retained by electrostatic interactions in case of anionic frameworks. 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. These results have been already published (see publications list).
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 (Au, Au3 and Au5 and Pt, Pt2 and Pt4) (Task 2) and heterometallic SNMCs (Task 3) like Ag2Au2, Au2Pd2, CuPd, AuPt, AgPt, AgFe and PdPt. All these species show and outstanding catalytic behaviours in different reactions of industrial interest such as the activation of formic acid, hydrogenation reactions, Water Gas Shift Reaction (WGSR), etc. In particular, the AgFe species show a unique catalytic activity for an unmet reaction. In particular the direct conversion of styrene to phenylacetylene in one-pot, that is not shown by the Fe and Ag analogues, separately, which confirm the uniqueness of heterometallic NCs. This work has already been submitted to a high impact scientific journal (JACS). Other results will be submitted to highly reputed journals during next months.
4. The last point related to the objectives of the project consists of the multigram–scale manufacture of SNMCs and industry scalability. For that, we must take advantage of the results obtained in previous Tasks. As mentioned above, a large plethora of interesting materials have been prepared and tested in catalysis. The next step consists of their large scale preparation. Obviously, this is the less developed step but we are already working on that and direct large syntheses (500 g) have been carried out. Right now we are exploring the large-scale preparation of SNMCs and SACs, which will be fully developed during the final period of the projectas well as the large scale catalytic reactions, which will be also optimised during this next period.
- A high degree of functionalization of the formed MOFs that can be achived pre- or postsynthetically.
- Use of single-crystal X-ray diffraction (SC XRD) as a characterization tool.
- multigram-scale preparation of these hybrid materials.
- Preparation of heterometallic ligand free SNMCs.
- The catalytic activities of some of these species surpass the state of the art catalysts.
For the next part of the project we aim to:
1. Prepare even more stable MOFs .
2. Focus on the preparation of more heterometallic SNMCs.
3. Exploration of the catalytic activity of the prepared heterometallic SNMCs.
4. Large scale preparation of both MOFs and MOF-driven SNMCs and SACs.
5. Unveil mechanisms governing the catalytic reactionsusing SC XRD and theoretical calculations.