Shanghai University AEM: MOFs-based heterogeneous catalysts: new opportunities for energy-related CO2 conversion

【Preface】

Environmental and energy related issues have become the main issues of public concern. Throughout the ages, the overexploitation and overuse of carbonized fuels such as coal, oil and natural gas have provided energy for nearly 200 years. However, excessive use of these fossil fuels and the ensuing greenhouse effect / energy crisis has become one of the most important issues that humanity must face. Global observations indicate that large amounts of greenhouse gas emissions mainly come from the consumption of fossil fuels, leading to global warming and melting glaciers. In order to reduce the greenhouse effect, scientists call on the world to reduce the use of conventional fossil fuels to reduce carbon dioxide emissions, and vigorously seek environmentally friendly alternatives; on the other hand, the establishment of carbon trading and carbon storage technology also needs to be steadily promoted. It is worth noting that researchers have tried various efforts to capture and fix carbon dioxide, including biomass, physical and chemical methods. However, most current methods of reducing CO 2 concentration are time-consuming and even easier to reach capacity limits. Not only that, the use of some isolation methods, such as ocean dumping, may trigger another environmental disaster.

MOFs have great application prospects in the field of CO 2 reduction. It can be used directly as a catalyst or component to promote CO 2 reduction in a mixed catalytic system . The interior of MOFs can be designed with open metal sites, specific heteroatoms, functionalized organic ligands, interaction with other building blocks, hydrophobicity, defects, porosity, and embedded nanoscale metal catalysts, which has Better CO 2 reduction performance MOFs are essential. Because of the poor electronic conductivity of MOFs and the inaccessibility of all catalytically active sites to the reactants, the stability of MOFs in water and ultraviolet light irradiation needs to be further improved. In order to achieve better results, it is necessary to use MOF to construct more complex materials to solve the problem of CO 2 capacity and reducing capacity in one material . In the future, the materials used by MOFs to reduce carbon dioxide emissions should be economical and environmentally friendly. The key to promoting catalysis include structural defects in MOFs, open metal sites of metal clusters, Lewis acid sites of metal clusters and organometallic joints, and MOFs functionalized with promoters.

【Achievement Introduction】

Metal organic frameworks (MOFs) with high surface area and adjustable chemical structure have attracted great attention from researchers. Recently, the use of solar energy for carbon dioxide conversion to produce valuable chemicals or fuels has become extremely attractive. The interior of MOFs can be designed as nanoscale metal catalysts with defects, heteroatoms and embedded, for the development of CO 2 conversion. Recently, Dr. Chen Wenqian and Associate Professor Tang Liang from Shanghai University (Communications) published a review article in Advanced Energy Materials entitled "MOFs-Based Heterogeneous Catalysts: New Opportunities for Energy-Related CO2 Conversion" This article reviews the recent research progress of MOFs-based CO 2 conversion catalysts, including photocatalysis and electrocatalysis. In particular , the preparation and mechanism of MOFs based on CO 2 conversion were discussed. These examples are expected to provide a deeper understanding in the preparation of highly active and stable CO 2 conversion materials based on MOFs .

【Graphic introduction】

Figure 1. MOFs synthesis method

MIL-53 (Fe) synthesis (a) electronic heating at 424K for 18 hours, (b) z microwave at 424K for 30min, (c) ultrasonication with 60% power for 15min.

Figure 2. CO 2 reduction mechanism

latimer-Frost diagram, used for multi-electron, multi-proton CO 2 reduction in a homogeneous aqueous solution at pH 7 ;

Figure 3. MOFs-based metal heterogeneous catalyst materials

(a) ESR spectra of Pt / NH 2 -MIL-125 (Ti) and (b) Au / NH 2 -MIL-125 (Ti);

Figure 4. Synthesis and performance of UiO-66 / CNNS

(a) Schematic diagram of UiO-66 / CNNS preparation;

(b) TEM and HRTEM images of UiO-66 / CNNS;

(c, d) PL diagrams of UiO-66 / CNNS and UiO-66 / bulk CN;

(e) Three catalysts produce CO;

(f) UiO-66 / CNNS photocatalytic CO2 reduction mechanism;

Figure 5. UiO-66-NH 2 optical response

(a) Schematic diagram of Cd 0.2 Zn 0.8 S @ UiO-66-NH 2 photogenerated electron and hole transport;

(b) PL diagram of Cd 0.2 Zn 0.8 S @ UiO-66-NH 2 ;

(c) Cd 0.2 Zn 0.8 S @ UiO-66-NH 2 photocurrent diagram;

Figure 6. Preparation and performance of Au & Pt @ ZIF

(a) Schematic diagram of Au & Pt @ ZIF light formation and temperature change;

(b) TEM picture of Au & Pt @ ZIF;

(c) Product yield comparison of platinum nanocube, Pt @ ZIF, Au & Pt @ ZIF and Pt @ ZIF + Au at 100 ° C and 150 ° C with and without light for 3h

Figure 7. The rate of photocatalytic conversion of CO2 to CO using different catalysts

(a) MAF-X27-CI, (b) MAF-X27-OH, (c) MOF-74-Co, (d) Co-ZIF-9, (e) MAF-X27l-Cl, (f) MAF X27l-OH.

Figure 8. Morphology design of MOFs

(a) CO 2 adsorption curve (273 K), (b) SEM image, (c) TEM image, (d) synthesis scheme;

Figure 9. Changes in internal chemical structure

(a) Ti (solid icons) and Zr (hollow icons) in solids and the colors of corresponding solutions and solids;

(b) Ti 2p of XPS diagram;

(c) UV spectra of NH 2 -UiO-66 (Zr) and Ti-doped NH 2 -UiO-66 (Zr);

(d, e) Band structures of NH 2 -UiO-66 (Zr) and Ti-doped NH 2 -UiO-66 (Zr);

(f, g) ESR diagrams of different samples;

(h) NH 2 -Uio-66 (Zr / Ti) photocatalytic mechanism;

Figure 10. MOFs derived catalyst

(a, b) Bright field TEM images of GNP / NH 2 -MIL-125 (Ti) and GNP / TiO 2 ;

(c) Output of CH 4 in different samples ;

1. d) XRD pattern of pyrolysis products;

Figure 11. Preparation of ZnO @ Co 3 O 4

(a) Schematic diagram of preparation of ZIF-8-derived ZnO and ZIF-8 @ ZIF-67-derived ZnO @ Co 3 O 4 ;

(b, c) SEM images of ZIF-8 and ZIF-8 @ ZIF-67;

(d) TEM image of ZnO @ Co 3 O 4 ;

(e, f) XRD chart;

(g, h) C1s of XPS diagrams of ZnO and ZnO @ Co 3 O 4 ;

Figure 12. CO 2 electrocatalytic reduction

(a) Electrocatalytic reduction of carbon dioxide by metallic copper;

(b) Cu-MOF electrocatalytic reduction of carbon dioxide;

Figure 13. Reaction path

(a) Electrochemical catalytic conversion of CO 2 to CH4 in ionic liquid by Zn-MOF / CP and (b) Possible charge transport path of Re-SURMOF;

【to sum up】

Materials with the function of reducing CO 2 while combining conductivity, magnetism, and fluorescence remain a major challenge. The generation of multifunctional MOF-based materials in the future can provide new ways for functional MOF-based materials, and at the same time provide opportunities for MOF to open up a new field, as well as opportunities for industrial applications.

Literature link: MOFs-Based Heterogeneous Catalysts: New Opportunities for Energy-Related CO 2  Conversion , (Advanced Energy Materials, 2018, DOI: 10.1002 / aenm.201801587)

Information source: material cattle