Periodic Reporting for period 1 - NANOCO2RE (Nanocrystals for CO2 Reduction)
Reporting period: 2020-09-15 to 2022-09-14
Numerous challenges in Europe are intimately related to the exploitation of foreign, currently non-renewable, and polluting energy resources. A well-known example lies in the use of petrol and methane as fuels in engines and heating systems. Europe is largely dependent on foreign countries in the import of these goods, yet its industrial and societal fabric is highly reliant on their immediate and reasonably-priced availability for consumption. Further, their combustion releases CO2 in the atmosphere, which plays a determining and detrimental role in the context of global warming and climate change. These criticalities have a negative impact at the environmental and socio-economic level, and underlie a number of geo-political dependences. In turn, enabling the cost-efficient upgrade of CO2 into fuels and other value-added chemicals would drive a positive change for the environment and for our society.
Notwithstanding several breakthroughs, the process to convert CO2 into fuels does not yet meet the techno-economic figures of merit that determine the viable commercialisation of CO2 recycling devices. The overarching goal of NANOCO2RE consisted in providing novel theoretical elements to identify better catalysts for CO2 upgrade. More in particular, the focus of the Action was centered towards the optimization of the performance of a class of system, which is a prominent candidate in enabling cost-efficient CO2 upgrade: Cu-based heterogeneous catalysts.
The figures of merit that describe the performance of heterogeneous catalysts are their activity, selectivity, and stability. The activity of a catalyst refers to the amount of reagent it transforms within a fixed unit of time. The selectivity of a catalyst describes its ability in converting the reagent into a single product, rather than a multiplicity. The stability of a catalyst labels its propensity in not diminishing its activity and/or selectivity when in operation, over a fixed period of time.
The catalytic activity, selectivity, and stability of a heterogeneous catalyst can be engineered by modifying a number of intrinsic and extrinsic variables. The catalyst size, composition, and shape belong to the former family. The chemistry of the support, solvent, and ligands interacting with the catalyst belong to the latter. The rational design of heterogeneous catalysts, in turn, hinges on the understanding of how to optimize the effects determined by this high-dimensional number of variables.
Notwithstanding several breakthroughs, the process to convert CO2 into fuels does not yet meet the techno-economic figures of merit that determine the viable commercialisation of CO2 recycling devices. The overarching goal of NANOCO2RE consisted in providing novel theoretical elements to identify better catalysts for CO2 upgrade. More in particular, the focus of the Action was centered towards the optimization of the performance of a class of system, which is a prominent candidate in enabling cost-efficient CO2 upgrade: Cu-based heterogeneous catalysts.
The figures of merit that describe the performance of heterogeneous catalysts are their activity, selectivity, and stability. The activity of a catalyst refers to the amount of reagent it transforms within a fixed unit of time. The selectivity of a catalyst describes its ability in converting the reagent into a single product, rather than a multiplicity. The stability of a catalyst labels its propensity in not diminishing its activity and/or selectivity when in operation, over a fixed period of time.
The catalytic activity, selectivity, and stability of a heterogeneous catalyst can be engineered by modifying a number of intrinsic and extrinsic variables. The catalyst size, composition, and shape belong to the former family. The chemistry of the support, solvent, and ligands interacting with the catalyst belong to the latter. The rational design of heterogeneous catalysts, in turn, hinges on the understanding of how to optimize the effects determined by this high-dimensional number of variables.
A first practical objective of the NANOCO2RE project was to rationalize the interplay between the catalyst composition and its selectivity. To this end, the project targeted systems where experimental data were available: Cu-Zn and Cu-Ga nanocrystals where the amount of Cu was at least 70%. A second, more general, objective was then to screen via computational methods the predicted properties of other Cu-rich bimetallic systems, so as to identify novel candidates.
While a small amount (up to 10%) of Zn favors selectivity towards methane, a larger amount is found to be beneficial in the making of ethylene. With the help of the project, it was observed that a low amount of Zn atoms in the neighborhood of the Cu catalytic site lowers the barrier in accessing a key intermediate in the conversion of CO2 to methane. An increased amount of Zn instead favors other conversion pathways by strengthening the adsorption of alternative competitive intermediates on Cu, as well as by acting as a catalytic site in competitions with the Cu ones.
In the case of Cu-Ga, small Ga quantities also impart the catalyst an improved methane selectivity via the above mentioned mechanism. Larger amounts of Ga instead drive a change in the most energetically favorable phase of the catalyst, rendering it less selective towards desirable products. Finally, the screening of Cu-rich bimetallic enabled to pinpoint promising compositions among first-row and late groups metals, which hold the promise of an improved selectivity .
A second set of objectives was focused on rationalizing shape effects on the catalyst activity and selectivity, and on drivers of structural (in)stability. To this end, the project advanced the state of the art by: i) gathering a cohesive vision on past reports linking shape and performance of Cu catalysts, ii) speculating on the design of well-defined nanocrystals rich in steps and terraces as promising candidates for increased performance, iii) developing a proof of concept, based on advanced machine learning methods, to probe in a fast and accurate manner the thermal (in)stability of nanocatalysts.
The results of the project have been disseminated in peer-reviewed papers in high-impact journals, and at national and international conferences. Social media and events for the general public also enabled the advertisement of the project and its achievements to the general public.
While a small amount (up to 10%) of Zn favors selectivity towards methane, a larger amount is found to be beneficial in the making of ethylene. With the help of the project, it was observed that a low amount of Zn atoms in the neighborhood of the Cu catalytic site lowers the barrier in accessing a key intermediate in the conversion of CO2 to methane. An increased amount of Zn instead favors other conversion pathways by strengthening the adsorption of alternative competitive intermediates on Cu, as well as by acting as a catalytic site in competitions with the Cu ones.
In the case of Cu-Ga, small Ga quantities also impart the catalyst an improved methane selectivity via the above mentioned mechanism. Larger amounts of Ga instead drive a change in the most energetically favorable phase of the catalyst, rendering it less selective towards desirable products. Finally, the screening of Cu-rich bimetallic enabled to pinpoint promising compositions among first-row and late groups metals, which hold the promise of an improved selectivity .
A second set of objectives was focused on rationalizing shape effects on the catalyst activity and selectivity, and on drivers of structural (in)stability. To this end, the project advanced the state of the art by: i) gathering a cohesive vision on past reports linking shape and performance of Cu catalysts, ii) speculating on the design of well-defined nanocrystals rich in steps and terraces as promising candidates for increased performance, iii) developing a proof of concept, based on advanced machine learning methods, to probe in a fast and accurate manner the thermal (in)stability of nanocatalysts.
The results of the project have been disseminated in peer-reviewed papers in high-impact journals, and at national and international conferences. Social media and events for the general public also enabled the advertisement of the project and its achievements to the general public.
The project promoted robust and transferable methods to rationalize composition-dependent trends in the selectivity of Cu-rich bimetallic catalysts. Their application and validation took place for the case of Cu-Zn and Cu-Ga systems. Their exploitation is currently ongoing in the screening of Cu-rich dilute alloys of other 26 possible compositions. By the same token, the project delivered a retrospective on shape-effects on Cu catalysts performance, advocated on novel design strategies to improve their performance, and provided a general and cost-effective route to predict thermal (in)stability of catalysts via numerical simulations.
These results have a potential impact at the scientific, technological, and societal level. Identifying novel and more performant catalysts for CO2 upgrade indeed represent a unique opportunity in the development and commercialization of devices which close the carbon loop in the making and using of fuels and value-added chemicals. As described in the first section of this report, the latter is an urgent milestone necessary to overcome challenges at the socio-economic, geo-political, and environmental level.
These results have a potential impact at the scientific, technological, and societal level. Identifying novel and more performant catalysts for CO2 upgrade indeed represent a unique opportunity in the development and commercialization of devices which close the carbon loop in the making and using of fuels and value-added chemicals. As described in the first section of this report, the latter is an urgent milestone necessary to overcome challenges at the socio-economic, geo-political, and environmental level.