Old Chemistry for New Advanced Materials
Many materials and/or their properties were discovered long ago but the lack of possibilities to characterize them together with a posterior massive data income from the scientific community put them in oblivion. Some of the most recent examples are carbon nitrides (rediscovered two times in history) or the chemistry of citric acid and its rediscovery for quantum dots. We try to find our inspiration in those hidden pearls of knowledge and apply such ‘old’ concepts to new materials.
For instance, in 1855 Stenhouse already found that bare carbon was able to oxidize organic gases to a large extent. However, still the field of catalysis is dominated by metals and the role of carbons as ‘not only’ naive supports is mostly unexplored. The main goal of the group is the preparation of new carbonaceous materials and tuning their functionalities and electron density in order to prepare highly selective and active carbon based catalysts.
To achieve such a goal, we approach the problem through different research lines.
Carbocatalysis: dreaming with controlling carbonization
The astounding physicochemical properties of carbon materials earned them a well-deserved ubiquitous presence in industry and society. However, though they have been used for a very long time, carbonization is still known as a very random process. In order to prepare advanced carbon catalysts, a deeper control over carbonization is mandatory. To do so, the group focus on two different approaches:
- Carbonization of stable carbon precursors with encode to produce noble carbons with predictable properties (e.g., electron rich, electron deficient, heteroatom doped).
- The optimization of dehydration step during carbonization to produce carbons at low temperature (LTCs) by thermal treatment in the presence of smart dehydration agents.
By using these approaches during the carbonization step we aim to prepare a library of basic, acid or FLP like heterogeneous carbocatalysts.
Studying binding properties of carbon materials
It is also known that, for a good catalytic performance to take place, there has to be a strong previous interaction of the substrate on top (or nearby) the catalytic active site. Rubisco is the natural CO2 fixation protein in plants. It shows an IAST CO2/O2 selectivity of ~1500. CO2/N2 selectivity larger than 2000 was already obtained using metal–organic materials. Though far from such values, nucleobase/derived carbons show very high selectivity towards CO2 sorption over N2 (IAST selectivity of 100). Since sorption precedes catalysis, understanding the origin of this selectivity can help developing new enzyme like catalysts.
Metal single atom decorated carbons, a step forward towards nanozymes
Doping materials with different metal atoms was done also for many years in materials sciences. Even though the metals were not forming detectable particles, their performance was remarkably different when compared to not doped samples. However, it was not until microscopy techniques were developed enough when single metal atoms were really detectable on the surface of the loaded supports. In catalysis, these materials were named thereafter as metal single atom catalysts (SACs).
In fact, now the topic is hot and more and more research efforts are invested in downsizing metal particles sizes on top of different supports trying to achieve the maximum atomic efficiency. SACs are only possible if the interaction between the loaded single metal atoms and the support is stronger than that of the metal atoms. If not, they would collapse forming small clusters or nanoparticles. The highly heteroatom doped and oxidative resistant carbons that can be produced using the concept of noble carbons allow us to produce different metal SACs using a simple impregnation/calcination step.
The materials prepared combine the advantages of noble carbons (i.e., good performance as basic catalysts and good selectivity towards CO2 sorption) with those of metal SACs, which makes of them excellent candidates to work as enzyme like carbocatalysts (for example towards CO2 reutilization).
 A. Wang, J. Li, T. Zhang, Nature Reviews Chemistry 2018, 2, 65-81.