Periodic Reporting for period 5 - OPERANDOCAT (In situ and Operando Nanocatalysis: Size, Shape and Chemical State Effects)
Periodo di rendicontazione: 2022-04-01 al 2023-04-30
Climate change concerns have spurred a growing interest in developing environmentally friendly technologies for energy generation. Conventional energy sources based on fossil fuels (oil, coal, natural gas) must be urgently transitioned due not only to their scarcity, but more importantly, to their dramatic contribution to the green-house effect.
The aim of this project was to provide fundamental understanding on the parameters that affect the performance of catalytic materials used in energy applications involving the electrocatalytic production of green hydrogen from water or the revalorization of the waste product carbon dioxide to produce industrially sought-after chemicals such as methanol or ethanol. Moreover, our work offered the possibility to store renewable energy into chemical bonds.
Systematic research was carried out into how the yield and selectivity of the target products could be increased with low energy consumption through a rational materials design, for instance, by tuning the initial size, shape, composition and support of the catalyst. Our work demonstrated the dynamic nature of catalytic materials in response to changes in their environment, which is key for their utilization in chemical processes driven by intermittent energy sources.
Our research is important for society because it contributes to the development of a new generation of energy materials that are not only more active and energy-efficient, but also more selective and durable.
The aim of this project was to provide fundamental understanding on the parameters that affect the performance of catalytic materials used in energy applications involving the electrocatalytic production of green hydrogen from water or the revalorization of the waste product carbon dioxide to produce industrially sought-after chemicals such as methanol or ethanol. Moreover, our work offered the possibility to store renewable energy into chemical bonds.
Systematic research was carried out into how the yield and selectivity of the target products could be increased with low energy consumption through a rational materials design, for instance, by tuning the initial size, shape, composition and support of the catalyst. Our work demonstrated the dynamic nature of catalytic materials in response to changes in their environment, which is key for their utilization in chemical processes driven by intermittent energy sources.
Our research is important for society because it contributes to the development of a new generation of energy materials that are not only more active and energy-efficient, but also more selective and durable.
This project focused on model heterogeneous catalysts for the gas-phase hydrogenation and electrocatalytic reduction of carbon dioxide as well as the generation of green hydrogen from renewable-electricity driven water splitting. We have addressed the systematic design of catalytically active model nanoparticle pre-catalysts with narrow size and shape distributions and tunable oxidation state, and in situ and operando structural, chemical, and reactivity characterization of such model catalysts as a function of the reaction environment.
Key components of the present project involved:
1. The chemical synthesis of well-defined pre-catalyst materials with control on the initial size, shape, chemical composition and dispersion on the support could be achieved.
2. The detailed monitoring of the evolution of the structure, surface and bulk composition of the above nanoparticle catalysts under reaction conditions using spectroscopic and microscopic methods. These challenging measurements were done operando, i.e. while the nanoscale catalysts were “at work”. A multi-technique approach was employed in order to unveil the complex nature of nanocatalysts.
3. Correlations could be established between the structure, chemical state and reactivity of the nanoparticles under different applied external stimulus (e.g. electrical potential and/or chemical environment) and as a function of the reaction time.
Our comprehensive research lead to a total of 72 publications in high impact scientific journals. A few results are highlighted below.
In the field of thermal catalysis, we investigated the synthesis of methanol from carbon dioxide and hydrogen. Here, we developed synthetic routes to produce size-selected mono- and bimetallic nanoparticles of various compositions (e.g. copper-zinc, copper-nickel). These nanoparticles served as excellent model systems to study the thermal hydrogenation of carbon dioxide. The combination of surface science methods, operando spectroscopy and reactivity measurements allowed us to look in detail at the structural and chemical state of the active catalysts and their evolution under reaction conditions.
In particular, we looked at particle-support interactions for copper-zinc particles on different support materials. We found that zinc oxide is not needed as part of the support, but that minute amounts of zinc within the core of copper-rich copper-zinc particles can still activate the catalyst for methanol synthesis. Moreover, zinc can migrate into a support material (e.g. aluminium oxide), leading to dimethylether selectivity instead of methanol, with the ratio of both products being tunable as a function of the zinc content inside the copper-zinc nanoparticles. We learnt that the choice of the support material can directly affect the catalytic performance of the system [1].
In the field of electrocatalysis, we comprehensively investigated the electrochemical reduction of carbon dioxide under working conditions. By studying model copper single crystal surfaces, we revealed the inactivity of defect-free copper surfaces that were prepared under ultrahigh vacuum conditions. Defect-free copper surfaces favor the production of hydrogen instead of organic multicarbon products [2]. Only the appearance of mesostructural inhomogeneities like step bunches as well as nanoscale roughness allowed the formation of multicarbon products. Moreover, even for identically oriented single crystal surfaces, we could demonstrate that minute changes in the initial structure of Cu surfaces have a drastic effect in their selectivity [3]. This insight broke the paradigm of early studies that distinct surface terminations of copper would lead to a preferred formation of hydrocarbons and fuels with two or more carbon atoms (C2+ products).
The catalytic role of cationic copper species had not yet been unambiguously identified. However, we showed that the continuous regeneration of distorted amorphous Cu1+/2+ domains boost the ethanol formation in an electrically pulsed reaction [4].
Furthermore, we accomplished to perform electron microscopy under electrocatalytic conditions in the liquid phase, strongly contributing to the development of this method [5].
References
[1.] Kordus et al. J. Am. Chem. Soc. 2023, 145, 3016.
[2.] Scholten et al. Angew. Chem. Int. Ed. 2021, 60, 19169.
[3.] Nguyen et al. ACS Energy Lett. 2024, 644.
[4.] Timoshenko et al. Nat. Catal. 2022, 5, 259.
[5.] Arán-Ais et al. Nat. Commun. 2020, 11, 3489.
Key components of the present project involved:
1. The chemical synthesis of well-defined pre-catalyst materials with control on the initial size, shape, chemical composition and dispersion on the support could be achieved.
2. The detailed monitoring of the evolution of the structure, surface and bulk composition of the above nanoparticle catalysts under reaction conditions using spectroscopic and microscopic methods. These challenging measurements were done operando, i.e. while the nanoscale catalysts were “at work”. A multi-technique approach was employed in order to unveil the complex nature of nanocatalysts.
3. Correlations could be established between the structure, chemical state and reactivity of the nanoparticles under different applied external stimulus (e.g. electrical potential and/or chemical environment) and as a function of the reaction time.
Our comprehensive research lead to a total of 72 publications in high impact scientific journals. A few results are highlighted below.
In the field of thermal catalysis, we investigated the synthesis of methanol from carbon dioxide and hydrogen. Here, we developed synthetic routes to produce size-selected mono- and bimetallic nanoparticles of various compositions (e.g. copper-zinc, copper-nickel). These nanoparticles served as excellent model systems to study the thermal hydrogenation of carbon dioxide. The combination of surface science methods, operando spectroscopy and reactivity measurements allowed us to look in detail at the structural and chemical state of the active catalysts and their evolution under reaction conditions.
In particular, we looked at particle-support interactions for copper-zinc particles on different support materials. We found that zinc oxide is not needed as part of the support, but that minute amounts of zinc within the core of copper-rich copper-zinc particles can still activate the catalyst for methanol synthesis. Moreover, zinc can migrate into a support material (e.g. aluminium oxide), leading to dimethylether selectivity instead of methanol, with the ratio of both products being tunable as a function of the zinc content inside the copper-zinc nanoparticles. We learnt that the choice of the support material can directly affect the catalytic performance of the system [1].
In the field of electrocatalysis, we comprehensively investigated the electrochemical reduction of carbon dioxide under working conditions. By studying model copper single crystal surfaces, we revealed the inactivity of defect-free copper surfaces that were prepared under ultrahigh vacuum conditions. Defect-free copper surfaces favor the production of hydrogen instead of organic multicarbon products [2]. Only the appearance of mesostructural inhomogeneities like step bunches as well as nanoscale roughness allowed the formation of multicarbon products. Moreover, even for identically oriented single crystal surfaces, we could demonstrate that minute changes in the initial structure of Cu surfaces have a drastic effect in their selectivity [3]. This insight broke the paradigm of early studies that distinct surface terminations of copper would lead to a preferred formation of hydrocarbons and fuels with two or more carbon atoms (C2+ products).
The catalytic role of cationic copper species had not yet been unambiguously identified. However, we showed that the continuous regeneration of distorted amorphous Cu1+/2+ domains boost the ethanol formation in an electrically pulsed reaction [4].
Furthermore, we accomplished to perform electron microscopy under electrocatalytic conditions in the liquid phase, strongly contributing to the development of this method [5].
References
[1.] Kordus et al. J. Am. Chem. Soc. 2023, 145, 3016.
[2.] Scholten et al. Angew. Chem. Int. Ed. 2021, 60, 19169.
[3.] Nguyen et al. ACS Energy Lett. 2024, 644.
[4.] Timoshenko et al. Nat. Catal. 2022, 5, 259.
[5.] Arán-Ais et al. Nat. Commun. 2020, 11, 3489.
With this project we obtained in depth understanding of the structural and chemical properties of complex catalytic nanoparticle systems that can be now used for the rational design of the new generation of catalysts. We unveiled the role played by the nanoparticle’s chemical state, size and shape, and its evolution under industrially relevant reaction conditions. We achieved paradigm-changing insights for the catalytic conversion of carbon dioxide in thermo- and electrocatalysis in the gas phase and in the liquid phase. The results obtained are expected to open up new routes for the reutilization of carbon dioxide through its direct conversion into valuable chemicals and fuels such as methanol, ethylene and ethanol.
We also contributed to the development of advanced experimental methods for the characterization of electrode materials in a liquid environment under potential control. For instance, thanks to this work we could establish pioneering research efforts in the area of operando electron and atomic force microscopy that involved significant modification of existing equipment and experimental methods. The same applies to the adaptations that we had to undertake to make compatible traditional surface science methods suitable for vacuum operation with thermal and electrocatalytic applications required high pressure gaseous or liquid environments.
We also contributed to the development of advanced experimental methods for the characterization of electrode materials in a liquid environment under potential control. For instance, thanks to this work we could establish pioneering research efforts in the area of operando electron and atomic force microscopy that involved significant modification of existing equipment and experimental methods. The same applies to the adaptations that we had to undertake to make compatible traditional surface science methods suitable for vacuum operation with thermal and electrocatalytic applications required high pressure gaseous or liquid environments.