Periodic Reporting for period 3 - SCALMS (Engineering of Supported Catalytically Active Liquid Metal Solutions)
Período documentado: 2021-09-01 hasta 2023-02-28
Supported Catalytically Active Liquid Metal Solution (SCALMS) systems represent a new concept for promoting chemical reactions in a clean and sustainable manner through catalysis. Traditionally, two types of catalysts are common, namely homogeneous and heterogeneous ones. In homogeneous catalysis, single metal complexes dissolved in an appropriate solvent and stabilised by dedicated ligands, act as active sites. Homogeneous catalysis is usually highly selective and efficient due to the uniform nature of the catalytic sites, but product/catalyst separation is often tedious. In heterogeneous catalysis, the catalytic reaction occurs at metal surfaces. The use of precious metals, like Pt, Rh or Pd, as catalytic active metal is most promising. As only the surface atoms take part in the reaction, supported metal nanoparticles are often used to maximise the share of surface atoms. Still as the nanoparticles contain hundreds to several thousands of metal atoms, only a small fraction of the precious metals is contributing to the catalytic activity. Consequently, heterogeneous catalysis is less efficient with respect to the precious metal inventory. Note, that heterogeneous catalysts constitute the major part of industrially applied catalyst materials (approx. 90 %). For several high-temperature applications, the heterogeneous catalysts suffer from deactivation, mainly induced by sintering of catalyst particles or blocking of the active surface by coke deposition (coking). Improving the efficiency and stability of such catalysts is a major challenge. Here, our SCALMS systems offer unique benefits. In SCALMS materials, a matrix metal is doped with small amounts of (precious or non-precious) active metal. The resulting is deposited in the form of very small droplets onto a porous support material. Given the right composition, these alloys become liquid at reaction temperature. We found that under these conditions single atoms of the active metal, stabilised at the liquid alloy interface, act as highly active catalytic sites with often unique reactivity and performance. Due to the single atom nature, the SCALMS concepts allows for a very effective use of the dissolved precious metal component. In addition, the highly dynamic nature of the liquid alloy interface prevents classical deactivation pathways, such as coking and agglomeration (sintering). With these unique benefits, we anticipate that SCALMS systems will gain a major role in future production processes in the chemical industry, ranging from chemicals synthesis to storage of renewable energy in the form of hydrogen, methanol or ammonia. Our progress in SCALMS materials development will directly lead to energy and emission reductions, and thus to greener and more benign processes.
Since the beginning of the ERC SCALMS project in 09/2019 the SCALMS concept has been successfully tested and developed for a variety of important chemical transformations. Dehydrogenation of alkanes is a very important pathway to produce alkenes and aromatic compounds in the chemical industry. Highly active and stable SCALMS materials have been identified and compared with the state-of-the-art industrial heterogeneous catalysts. For propane, butane and cyclic alkane dehydrogenations, the results have been published in high-ranked, peer-reviewed journals already. Our results show that SCALMS systems allow for technically very interesting, in some cases unique reactivities. As a very important feature of these catalysts, coke formation in high-temperature processes under reductive conditions is suppressed to a great extent.
We demonstrated that rhodium, an element that has barely been reported as active metal for selective dehydrogenation reactions, becomes a very active, selective, and robust dehydrogenation catalyst when exposed to propane in the form of a RhGa-SCALMS system (Raman et al. ACS Catal. 2019, 9(10), 9499). We expect that the incorporation of other elements into SCALMS material systems will lead to more examples of unexpected and/or unique reactivity in our future work.
We found that Ga ultrasonication in alcohol solvents followed by adsorption on the porous support is a surprisingly simple alternative to the so far applied, tedious chemical SCALMS preparation route. The developed sonication method is characterised by simplicity, generality, scalability, process safety and practically perfect atom efficiency. The method will pave the way for an industrial production of SCALMS materials for large-scale catalytic applications.
We found that Ga ultrasonication in alcohol solvents followed by adsorption on the porous support is a surprisingly simple alternative to the so far applied, tedious chemical SCALMS preparation route. The developed sonication method is characterised by simplicity, generality, scalability, process safety and practically perfect atom efficiency. The method will pave the way for an industrial production of SCALMS materials for large-scale catalytic applications.