As an important non-metallic catalyst, carbon nanotubes, nanodiamonds, graphene and other nano-carbon material catalysts show catalytic performance comparable to or better than that of traditional metal catalysts in many catalytic reactions.Oxygen, nitrogen, boron, sulfur, They are also important factors to control the catalytic performance.It is important to understand and summarize the chemical properties and catalytic activity of surface functional groups to further optimize and develop the nano-carbon material catalyst.
Recently, Li Bo, a researcher at the Department of Catalytic Materials Research, Institute of Metal Research, Chinese Academy of Sciences, researcher Su Dangsheng et al. Used first-principles calculations and quantum chemical methods. Starting from the chemical properties of various surface functional groups, oxygen, nitrogen, boron , Sulfur and other functional groups in the alkane dehydrogenation reaction, carbon monoxide oxidation, oxygen reduction, selective hydrogenation and other catalysis catalytic reactions, and summarizes the regulation of the general role of surface functional groups and the mechanism of action, as follows:
1. The gain and loss of oxygen and nitrogen functional groups and electronic properties and acid.Based on the oxidation of nitric acid can be successfully introduced into the carbon nanotubes carbonyl, carboxyl, hydroxyl and other oxygen functional groups.How to quantitatively accurately describe the different oxygen functional groups And the change of activity of the same oxygen functional groups in different chemical environments is a difficult problem.Due to the coexistence of a variety of oxygen functional groups on the catalyst, it is difficult to give an accurate description by experimental means.Using the Fukui function, For the first time, functional theory calculations are used to characterize the electronic capabilities of quantified oxygen functional groups. The calculated results can help the experimental work to distinguish the chemical activities of different oxygen functional groups and determine the active sites in the reaction (Chemistry - A European Journal 2014, 20, 7890-7894). The introduction of nitrogen functional groups on the nano-carbon material can effectively enhance the basicity of the catalyst.Parridine, pyrrole, quaternary nitrogen and graphite nitrogen are common nitrogen functional groups on the carbon nanomaterials.How to distinguish the basicity of different nitrogen functional groups is to optimize the catalytic performance The researchers succeeded by using proton adsorption and acid dissociation constants calculations The basic sizes of the four different nitrogen functional groups were accurately quantified. The results show that pyridine nitrogen is the most basic functional group, which lays the foundation for the determination of the active sites in the base catalysis (Phys. Chem. Chem. Phys 2015, 17, 6691-6694.).
Oxidative dehydrogenation of low alkanes The active sites, reaction pathways and mechanism of oxidative dehydrogenation are studied.The oxidative dehydrogenation is one of the most successful chemical reactions using nanocarbon catalysts.Firstly, the first principle reveals the catalytic activity of ethane The oxidative dehydrogenation pathway (J. Mater. Chem. A 2014, 2, 5287-5294) revealed a reaction that was not the same as the previously reported mechanism of active site regrowth. The researchers calculated that oxygen removal energy is a Characterization of the activity parameters of the catalyst for the oxidative dehydrogenation of carbon nanomaterials.Further calculation results indicate the catalytic activity of carbon atoms which are not previously noticed and linked to the oxygen functional group and verify that the carbonyl group alone can also be used as the oxidative dehydrogenation (Chem. Commun. 2014, 50, 11016-11019). By analyzing the aromaticity of carbon nanomaterials, it is shown that the catalytic activity of carbon atoms is caused by the decrease of aromaticity (Chemistry - An Asian Journal 2016 , 11, 1668-1671).
3. The mechanism of direct dehydrogenation of low-paraffins Nanodiamonds exhibit excellent catalytic performance in the direct dehydrogenation of alkanes, which not only surpass traditional metal catalysts but also have advantages over other nanocarbon catalysts such as carbon nanotubes The stability and selectivity of the nanostructured diamond nanocrystals have been revealed by first-principles calculations, revealing the unique sp2 @ sp3 core-shell structure and catalytic properties of nanocrystalline diamonds from the aspects of catalyst structure, energy barrier, charge transfer and size effect The structure-activity relationship provides theoretical support for the further design and optimization of catalysts for non-metallic carbon nanomaterials (ACS Catalysis 2017, 7, 3779-3785.).
Hydrogen molecules are important reactants in chemical reactions and have traditionally used precious metals as catalysts to activate hydrogen molecules. Researchers used the catalytic concept of Frustrated Lewis Pair to design a theoretical model for boron-nitrogen Co-doped double-layer graphene catalyst system. Calculations show that the carbon material catalysts exhibit similar catalysis as noble metal catalysts (Phys. Chem. Phys. 2016, 18, 11120-11124) .Further researchers try The catalytic reaction of cinnamic aldehyde molecular selective hydrogenation was tested to demonstrate a method of increasing cinnamyl alcohol selectivity with good cinnamyl alcohol selectivity (ChemCatChem 2014, 6, 3246-3253).
5. The functional group of the supporter regulates the metal catalyst. The researchers constructed several different configurations of boron and nitrogen heteroatoms on the nanocarbon material. Due to the difference in electronegativity, the boron and nitrogen heteroatoms behave better for the supported monatomic gold catalyst The opposite of the regulation role of charge analysis showed that in the nitrogen-doped carrier electron transfer from the gold atom to the carrier; in the boron-doped carrier on the opposite direction of electron transfer, the gold atom presents a different valence, which directly Resulting in different forces and mechanisms between the carbon monoxide and the oxygen species of the reactants, and the stronger the interaction between the gold and carbon monoxide molecules on the nitrogen-doped carrier; the stronger the gold and oxygen molecules on the boron-doped carrier . The different reaction forces with reactant molecules lead to different reaction mechanisms for the oxidation of carbon monoxide on different supports.In addition to the traditional LH and ER reaction mechanisms, a tri-molecular reaction mechanism has also been found , Deepen understanding of the role of vector regulation (J. Mater. Chem. A 2017, 5, 16653-16662) .In addition, researchers also studied graphene Single-hole, double-hole, and Stone-Wales defect sites on the carbon nanotube support are responsible for the regulation of the nitrogen-atom loaded gold catalyst, and the curvature effects of the carbon nanotubes are illustrated by comparison (Phys. Chem. , 19, 22344-22354).
The general regulation and mechanism of the regulation of functional groups The calculations show that the introduction of nitrogen atoms into the carbon nanomaterials in the dehydrogenation reaction can increase the electron-donating ability of the oxygen functional groups, thereby enhancing the olefin desorption and increasing the catalyst selectivity J. 2013, 8, 2605-2608.) Compared with the nitrogen atom doping, the boron atom is one valence electron less than the carbon atom, so a hole is generated. The calculation results show that the hole generated by the boron atom can activate the oxygen molecule to generate Reactive species that catalyze the partial oxidation of methane to formaldehyde (Journal of Physical Chemistry C 2013, 117, 17485-17492). By large-scale computational screening, the researchers found that functional groups on carbon material catalysts follow the BEP rules in dehydrogenation reactions and that carbon The hydrogen bond breaking distance is also linear with the energy barrier (Nanoscale 2015, 7, 16597-16600).
Relevant research results have been published in ACS Catalysis, Nanoscale, J. Mater. Chem. A, Chem. Comm., Etc. The latest achievements as Feature Article published in Chemical Communications. The study has been the National Natural Science Foundation of metal outstanding scholars Project, Sinopec, the State Super Guangzhou center funding.
Figure 1. (a) Common Oxygen Functional Groups on Nanocarbon Materials (b) Order of Affinity of Oxygen Functional Groups
Figure 2. Oxidative dehydrogenation of propane over mono-carbonyl groups
Figure 3. Ethane oxidation dehydrogenation kinetic parameters calculated by microscopic reaction kinetics (a) Pre-exponential factor (b) Reaction equilibrium constant (c) Reaction conversion frequency
Figure 4. Hydrogen molecule activation mechanism
Figure 5. Schematic diagram of the structure-activity relationship between the nanosized diamond sp2 @ sp3 core-shell structure and the catalytic performance
Figure 6. Oxidative dehydrogenation of carbon nanomaterials
