Periodic Reporting for period 4 - CATACOAT (Nanostructured catalyst overcoats for renewable chemical production from biomass)
Berichtszeitraum: 2022-06-01 bis 2023-09-30
The chemical industry is facing a cataclysmic shift in the coming century, as it will be forced to move away from fossil-based resources towards renewable carbon sources such as carbon dioxide and plants. However, these molecular streams, due notable to their heterogeneity, reactivity and moisture content, are highly incompatible with widely used catalytic materials in industry, which tend to be water-sensitive and unselective when many oxygen functionalities are present. Therefore, there is an urgent need to develop the next generation of catalytic materials and processes.
The premise of this ERC project was that surface engineering of heterogeneous catalysts could provide some of these much-needed materials. As shown by recent breakthroughs using atomic layer deposition (ALD), the deposition of thin layers of metal oxides can be used to improve the stability and selectivity of traditional catalytic materials during renewable catalysis. Specifically, our goal was to expand the use of these overcoating processes by using solution-phase deposition methods as well as surface functionalization to make catalysts more active, selective, and especially stable. These developments were combined with the tailoring of several biomacromolecules, including lignin to develop unique renewable processing solutions.
The premise of this ERC project was that surface engineering of heterogeneous catalysts could provide some of these much-needed materials. As shown by recent breakthroughs using atomic layer deposition (ALD), the deposition of thin layers of metal oxides can be used to improve the stability and selectivity of traditional catalytic materials during renewable catalysis. Specifically, our goal was to expand the use of these overcoating processes by using solution-phase deposition methods as well as surface functionalization to make catalysts more active, selective, and especially stable. These developments were combined with the tailoring of several biomacromolecules, including lignin to develop unique renewable processing solutions.
We had demonstrated that we can deposit overcoats using novel solution-phase synthetic techniques based on stoichiometric precursor injections, and use them to stabilize base metal hydrogenation catalysts during liquid-phase processing of biomass-derived molecules (Héroguel et al. App. Cat. B, 2017). We have now demonstrated that by carefully measuring ligand release, we can precisely inject the necessary precursor quantities to achieve exact monolayer by monolayer growth of multiple materials leading to coating qualities in solution that are indistinguishable from gas-phase ALD (Le Monnier et al. Advanced Materials, 2019). This work demonstrated that it was possible to grow atomically thin films onto high surface area dispersed materials. Various types of layers (oxide, phosphate, and sulfide) were deposited onto a wide range of substrates with varied shapes and surface properties. The ability to deposit such layers on dispersed materials is not only desirable in the field of heterogeneous catalysis but also in the fields of microelectronics, optics, sensing and energy conversion.
In doing this work, we clearly identified and were able to take advantage of the growth of clusters as opposed to films, which is a feature that is uniquely accessible in this liquid phase technique. This has opened up a new area of research where we build catalytic clusters atom-by-atom, which fits into our general goal of controlling catalytic active sites but does so in an unexpected way. We have notably used this technique to show that we can systematically explore catalytic promotional effects using different combinations of metal atoms (Le Monnier et al. ACS Sus. Chem. Eng. 2022). More recently, we have used this tehcnique to make CO2 hydrogenation catalysts with unprecedented activities both on a per metal basis and based on turnover frequencies that are normalized by active site.
In parallel, we have also developed slightly less precise, but extremely simple, coating methods that use non-hydrolytic sol-gel or chelation chemistry. This has resulted in controlled increases in activity, selectivity, and reduced deactivation for several reactions (Héroguel et al. J. Cat., 2018, Du et al. J. Mat. Chem. A, 2019 and Du et al. Small, 2018). We have used this method for controlling the particle size of nanoparticles and accessing particularly small Pd nanoparticles (Du et al. ACS Catalysis, 2020). This approach relied on the synthesis of an atomically dispersed material using coordinated Pd complexes. Unlike with nanoparticles, using atomically dispersed Pd before reductive treatment enabled us to limit the particle growth during thermal activation steps, yielding highly accessible, sinter-resistant Pd clusters less than 2 nm in diameter. Notably, engineering the Pd-ZrO2 interface of Pd/ZrO2 into inverted ZrO2-Pd interface using ZrO2 overcoat leads to an unprecedented 100% CO selectivity during CO2 hydrogenation, which is an important result in the context of CO2 utilization.
Because we were interested in building renewable processes notably from lignin, which is the largest natural source of renewable aromatic molecules, we have to control not only our catalytic material but also our substrate. The issue with lignin is that it rapidly condenses upon extraction, which makes it very difficult to actually upgrade it catalytically once isolated. Catalyst engineering can thus be completely ineffectual if it is employed on condensed/destroyed lignin. We recently reported a strategy that prevents condensation by functionalization with aldehydes during lignin extraction procedure (Shuai et al. Science 2016). However, we had not developed a method to successfully isolate this lignin to explore catalyst engineering independent of other biomass fractions. To address this, we recently developed a protocol, to protect lignin with aldehydes and isolate it in the first scalable procedure for producing 100 gram-scale quantities of bench-stable aldehyde-stabilized lignin, , which can be catalytically upgraded at near theoretical yields (Talebi et al. Nature Protocols, 2019). We have been successful in using the overcoating chemistry described above to stabilize these lignin conversion catalysts, which could help address a major challenge in biorefining (Talebkeikhah et al. Adv. Energy Materials, 2023).
This work has been disseminated in many of the most prestigious catalysis conference (Gordon conference on catalysis, North American Catalysis Meeting, Europacat, etc.) but also featured in mainstream venues like Swiss Public Radio programs or highlighted in start-up presentations. In particular, these technologies are now exploited (and often presented) by our EPFL spin-off Bloom Biorenewables that has been ranked in the top 10 of the best start-ups in Switzerland for two straight years.
In doing this work, we clearly identified and were able to take advantage of the growth of clusters as opposed to films, which is a feature that is uniquely accessible in this liquid phase technique. This has opened up a new area of research where we build catalytic clusters atom-by-atom, which fits into our general goal of controlling catalytic active sites but does so in an unexpected way. We have notably used this technique to show that we can systematically explore catalytic promotional effects using different combinations of metal atoms (Le Monnier et al. ACS Sus. Chem. Eng. 2022). More recently, we have used this tehcnique to make CO2 hydrogenation catalysts with unprecedented activities both on a per metal basis and based on turnover frequencies that are normalized by active site.
In parallel, we have also developed slightly less precise, but extremely simple, coating methods that use non-hydrolytic sol-gel or chelation chemistry. This has resulted in controlled increases in activity, selectivity, and reduced deactivation for several reactions (Héroguel et al. J. Cat., 2018, Du et al. J. Mat. Chem. A, 2019 and Du et al. Small, 2018). We have used this method for controlling the particle size of nanoparticles and accessing particularly small Pd nanoparticles (Du et al. ACS Catalysis, 2020). This approach relied on the synthesis of an atomically dispersed material using coordinated Pd complexes. Unlike with nanoparticles, using atomically dispersed Pd before reductive treatment enabled us to limit the particle growth during thermal activation steps, yielding highly accessible, sinter-resistant Pd clusters less than 2 nm in diameter. Notably, engineering the Pd-ZrO2 interface of Pd/ZrO2 into inverted ZrO2-Pd interface using ZrO2 overcoat leads to an unprecedented 100% CO selectivity during CO2 hydrogenation, which is an important result in the context of CO2 utilization.
Because we were interested in building renewable processes notably from lignin, which is the largest natural source of renewable aromatic molecules, we have to control not only our catalytic material but also our substrate. The issue with lignin is that it rapidly condenses upon extraction, which makes it very difficult to actually upgrade it catalytically once isolated. Catalyst engineering can thus be completely ineffectual if it is employed on condensed/destroyed lignin. We recently reported a strategy that prevents condensation by functionalization with aldehydes during lignin extraction procedure (Shuai et al. Science 2016). However, we had not developed a method to successfully isolate this lignin to explore catalyst engineering independent of other biomass fractions. To address this, we recently developed a protocol, to protect lignin with aldehydes and isolate it in the first scalable procedure for producing 100 gram-scale quantities of bench-stable aldehyde-stabilized lignin, , which can be catalytically upgraded at near theoretical yields (Talebi et al. Nature Protocols, 2019). We have been successful in using the overcoating chemistry described above to stabilize these lignin conversion catalysts, which could help address a major challenge in biorefining (Talebkeikhah et al. Adv. Energy Materials, 2023).
This work has been disseminated in many of the most prestigious catalysis conference (Gordon conference on catalysis, North American Catalysis Meeting, Europacat, etc.) but also featured in mainstream venues like Swiss Public Radio programs or highlighted in start-up presentations. In particular, these technologies are now exploited (and often presented) by our EPFL spin-off Bloom Biorenewables that has been ranked in the top 10 of the best start-ups in Switzerland for two straight years.
The stoichiometrically limited deposition method goes beyond traditional ALD by offering unprecedented control over the deposited structures, especially in the context of cluster formation. This notably enabled a synthesis method for heterogeneous catalysts that goes beyond single-atom catalyst synthesis by providing additional control over the composition and the structure of the surrounding catalytic site. Our approach based on liquid-phase atomic layer deposition, provides an atomic control over the atomic cluster surrounding the active atom by building coordination spheres shell by shell. As a proof of concept, we have explored a series of simple multi-nuclear catalytic clusters to create model catalysts that, to our knowledge are not accessible in other ways. We have also used this to make catalysts that show unprecedented activities in iimportant reactions like CO2 hydrogenation, which could have important sustainability implications. Beyond the project, we plan to use this technique as a major platform to build new catalytic structures, which will hopefully allow us to further reach activities and selectivities that are beyond the reach of current catalyst preparation techniques.
In the context of chelation chemistry, a highlight in this project is that we incorporated an atomically dispersed Pd “pre-catalyst” in our synthesis procedure. The resulting final catalyst possessed ultra-small metal nanoparticles and unique interfacial sites. We will similarly expand the use of this technique beyond just a single metal (currently palladium) to explore more interesting reaction possibilities.
We have now shown that this technique can be used to create remarkably stable catalysts for lignin conversion. We want to ultimately use these catalysts to scale up lignin conversion notably in collaboration with commercial partners, including our own spin-off.
In the context of chelation chemistry, a highlight in this project is that we incorporated an atomically dispersed Pd “pre-catalyst” in our synthesis procedure. The resulting final catalyst possessed ultra-small metal nanoparticles and unique interfacial sites. We will similarly expand the use of this technique beyond just a single metal (currently palladium) to explore more interesting reaction possibilities.
We have now shown that this technique can be used to create remarkably stable catalysts for lignin conversion. We want to ultimately use these catalysts to scale up lignin conversion notably in collaboration with commercial partners, including our own spin-off.