Periodic Reporting for period 4 - SCALMS (Engineering of Supported Catalytically Active Liquid Metal Solutions)
Reporting period: 2023-03-01 to 2024-08-31
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 developed for a variety of technically important chemical transformations and many new and highly relevant fundamental insights on catalysis at liquid metal interfaces have been collected.
Short alkane dehydrogenation: Highly active and long-term stable Ga-Pt SCALMS materials were prepared via two different synthesis routes. The top-down ultrasonication method yields Ga droplets that were then deposited on the outer surface of the support material, in an atom efficient manner. A new bottom-up reductive method starts from wet impregnation of gallium nitrate. Catalysts prepared by the latter route outperform the top-down catalysts as well as commercial ones in terms of stability and integral productivity. No detectable deactivation under the harsh reaction conditions of 550 °C and 70 vol.% propane flow was detected over 100 h time on stream. These findings pave the way towards a disruptive PDH process design with catalyst regeneration/replacement after months instead of days.
Dehydrogenation of longer and cyclic alkanes: Detailed kinetic investigations of heptane dehydrogenation revealed a low activation barrier for heptene formation, while all undesired side reactions exhibit higher barriers. These differences can explain the high selectivity towards olefin formation, which could be maintained over 14 h time on stream. For dehydrogenation of methycyclolhexane stable operation was observed for more than 80 h time on stream. Given the importance of cyclic compounds for chemical hydrogen storage and release, these findings can contribute to the development of more efficient energy storage processes in the future.
Selective oligomerization of short olefins: The first non-noble metal Ga-Ni SCALMS material was developed for the continuous gas-phase oligomerization of ethene. A particular striking discovery with very high potential for technical implementation is the excellent catalytic performance and remarkable thermal stability of Ga-Ni SCALMS system. Furthermore, at temperatures above 200 °C the catalyst is very selective for the formation of butenes, while longer olefins are formed to a minor amount only. Such very selective oligomerization is highly promising for industrial implementation, since catalyst recycling and product separation, typically energy and chemical intense in traditional processes, can be circumvented. With high pressure steam generation at elevated temperatures the SCALMS oligomerization process has the potential to improve the overall economics for new, greenfield processes.
All results have been published in 22 high-ranked, peer-reviewed journals and show that SCALMS systems allow for technically very interesting, in some cases unique catalyst performances and thus more efficient process design options.
Short alkane dehydrogenation: Highly active and long-term stable Ga-Pt SCALMS materials were prepared via two different synthesis routes. The top-down ultrasonication method yields Ga droplets that were then deposited on the outer surface of the support material, in an atom efficient manner. A new bottom-up reductive method starts from wet impregnation of gallium nitrate. Catalysts prepared by the latter route outperform the top-down catalysts as well as commercial ones in terms of stability and integral productivity. No detectable deactivation under the harsh reaction conditions of 550 °C and 70 vol.% propane flow was detected over 100 h time on stream. These findings pave the way towards a disruptive PDH process design with catalyst regeneration/replacement after months instead of days.
Dehydrogenation of longer and cyclic alkanes: Detailed kinetic investigations of heptane dehydrogenation revealed a low activation barrier for heptene formation, while all undesired side reactions exhibit higher barriers. These differences can explain the high selectivity towards olefin formation, which could be maintained over 14 h time on stream. For dehydrogenation of methycyclolhexane stable operation was observed for more than 80 h time on stream. Given the importance of cyclic compounds for chemical hydrogen storage and release, these findings can contribute to the development of more efficient energy storage processes in the future.
Selective oligomerization of short olefins: The first non-noble metal Ga-Ni SCALMS material was developed for the continuous gas-phase oligomerization of ethene. A particular striking discovery with very high potential for technical implementation is the excellent catalytic performance and remarkable thermal stability of Ga-Ni SCALMS system. Furthermore, at temperatures above 200 °C the catalyst is very selective for the formation of butenes, while longer olefins are formed to a minor amount only. Such very selective oligomerization is highly promising for industrial implementation, since catalyst recycling and product separation, typically energy and chemical intense in traditional processes, can be circumvented. With high pressure steam generation at elevated temperatures the SCALMS oligomerization process has the potential to improve the overall economics for new, greenfield processes.
All results have been published in 22 high-ranked, peer-reviewed journals and show that SCALMS systems allow for technically very interesting, in some cases unique catalyst performances and thus more efficient process design options.
Short alkane dehydrogenation: 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.
We developed a new and scalable SCALMS preparation and activation method that results in catalysts which are stable over 100 h time on stream under the harsh conditions of propane dehydrogenation, namely 550 °C, atmospheric pressure, 70 vol.% propane flow.
Selective oligomerization of short olefins: We developed Ga-Ni SCALMS materials that dimerize ethene with > 90% selectivity into butenes, while C6 and C8 compounds are formed in small amounts and higher olefins are below the detection limit. Our process innovation using the Ga-Ni SCALMS system enables operation at significantly higher temperature compared to state-of-the-art homogeneous liquid-phase processes (e.g. SHOP). This improves the exergy of the produced heat in the exothermal oligomerization reaction and facilitates better heat integration.
We have gained fundamental insights into catalytic processes on supported liquid metal alloys. In particular, we were able to demonstrate conditions under which well-dispersed liquid alloy droplets can be formed and stabilized on oxidic supports. In addition, we discovered the first examples of ternary SCALMS systems active in alkane dehydrogenation. Based on the knowledge gained, we expect that the inclusion of other (non-noble metal) elements in SCALMS material systems will lead to further examples of unexpected and/or unique reactivity in our future work.
We developed a new and scalable SCALMS preparation and activation method that results in catalysts which are stable over 100 h time on stream under the harsh conditions of propane dehydrogenation, namely 550 °C, atmospheric pressure, 70 vol.% propane flow.
Selective oligomerization of short olefins: We developed Ga-Ni SCALMS materials that dimerize ethene with > 90% selectivity into butenes, while C6 and C8 compounds are formed in small amounts and higher olefins are below the detection limit. Our process innovation using the Ga-Ni SCALMS system enables operation at significantly higher temperature compared to state-of-the-art homogeneous liquid-phase processes (e.g. SHOP). This improves the exergy of the produced heat in the exothermal oligomerization reaction and facilitates better heat integration.
We have gained fundamental insights into catalytic processes on supported liquid metal alloys. In particular, we were able to demonstrate conditions under which well-dispersed liquid alloy droplets can be formed and stabilized on oxidic supports. In addition, we discovered the first examples of ternary SCALMS systems active in alkane dehydrogenation. Based on the knowledge gained, we expect that the inclusion of other (non-noble metal) elements in SCALMS material systems will lead to further examples of unexpected and/or unique reactivity in our future work.