【Background Introduction】

With the rapid development of the global economy, human demand for energy has increased dramatically. However, the excessive use of fossil fuels has caused a serious energy crisis, and the carbon dioxide (CO 2 ) released also caused a serious greenhouse effect. Therefore, how to effectively solve the energy crisis and environmental pollution has become a worldwide challenge. Among them, converting CO 2 into chemical fuel is one of the most effective solutions. However, the CO 2 molecular structure is very stable, the conversion process is complex, and the product potential is similar, resulting in low CO 2 catalytic efficiency and poor product selectivity. Over the past few decades, researchers have done a lot of research to improve the reduction performance of CO 2 . Recent studies have shown that under actual working conditions, the catalysts involved may undergo continuous reconstruction, leading to controversy about the active site and reaction mechanism of CO 2 reduction. Therefore, it is very necessary to monitor the dynamic evolution of catalysts and reaction intermediates in real time under experimental conditions.

【Achievement Introduction】

Based on this, the team of Academician Xie Yi and Professor Sun Yongfu (co-corresponding author) of Hefei National Research Center for Microscale Physical Sciences at the University of Science and Technology of China jointly reported on the progress and development prospects of in-situ CO 2 reduction. First, the working principles and detection modes of various in-situ characterization techniques are introduced. Next, we systematically summarized the latest progress of in-situ research on catalyst evolution during CO 2 reduction. In addition, the in-situ monitoring of reaction intermediates and in-situ research on the progress of catalytic products are also highlighted, with particular emphasis on how to combine theoretical calculations to reveal the reaction mechanism in detail. Finally, based on existing representative research results, some prospects and suggestions for future in-situ CO 2 reduction are provided. The research results were published in the internationally renowned journal J. Am. Chem. Soc. Entitled "Progress and Perspective for In Situ Studies of CO 2 Reduction" .

【Graphic analysis】

Figure 1. A series of characterization techniques used to study CO 2 reduction in situ

Figure 2. Schematic diagram of in-situ UV-vis, Raman and FTIR characterization techniques

(A) Schematic diagram of in-situ ultraviolet-visible spectroscopy (UV-vis);

(B) Schematic diagram of Raman spectrum in situ;

(C) Schematic diagram of in-situ Fourier transform infrared spectroscopy (FTIR).

Figure 3. Schematic representation of in-situ XRD, XPS, and XAS characterization techniques

(A) Schematic diagram of in-situ X-ray diffraction (XRD);

(B) Schematic diagram of in-situ X-ray photoelectron spectroscopy (XPS);

(C) Schematic diagram of in-situ X-ray absorption spectroscopy (XAS).

Figure 4. Schematic diagram of in-situ ESR, TEM, MS characterization technology

(A) Schematic diagram of in-situ electron spin resonance spectrum (ESR);

(B) Schematic diagram of in-situ transmission electron microscope (TEM);

(C) Schematic diagram of in-situ mass spectrometry (MS).

Figure 5. Monitoring the phase change of the catalyst during CO 2 reduction

(A) In-situ XRD pattern of Pd / C catalyst during CO 2 reduction;

(Bc) In-situ XAFS spectrum of Pd particles during CO 2 reduction;

(D) The relationship between product selectivity and phase change of Pd particles;

(E) In- situ Raman signal of SnO 2 nanoparticles during CO 2 reduction .

Figure 6. Monitoring the valence state of the catalyst during CO 2 reduction

(A) In situ environmental pressure X-ray photoelectron spectroscopy of O 1s in Cu foil;

(B) In situ environmental pressure X-ray photoelectron spectroscopy of C 1s in Cu (111);

(C) In situ environmental pressure X-ray photoelectron spectroscopy of O 1s in Cu (111).

Figure 7. Monitoring the local coordination environment, electron transfer behavior and active center changes of the catalyst during the CO 2 reduction process

(Ad) In-situ XAS measurement of Zn nanoparticles;

(Ef) In- situ ESR signal of MOF (NNU-28) sample during CO 2 reduction reaction.

Figure 8. Monitoring the evolution of reaction intermediates during CO 2 reduction

(A) In-situ Raman spectroscopy during CO 2 reduction;

(B) ¹³ C isotope-labeled Raman measurement of Cu 2 O / CuO @ Ni during CO 2 reduction ;

(Cd) In- situ FTIR spectroscopy of S-vacancy CuIn 5 S 8 nanosheets during CO 2 reduction;

(D) In-situ FTIR spectra of original CuIn 5 S 8 nanosheets during CO 2 reduction.

Figure 9. Monitoring the formation of catalytic products during CO 2 reduction

(A) Compare the date of GC and SIFT-MS;

(B) Semi-logarithmic graphs of SIFT date of methane (C1), ethylene (C2) and propylene (C3) of Cu nanoneedles;

(C) In-situ setting of electrochemical mass spectrometry;

(D) Possible mechanism for the formation of multi-carbon products on Cu catalysts from acetaldehyde intermediates.

Figure 10. Combining in-situ research and theoretical calculations to infer the reaction mechanism

(A) In-situ FTIR spectrum of metallic CuS nanosheets during the reduction of CO 2 ;

(B) Gibbs free energy of metallic CuS nanosheets in the process of CO 2 reduction;

(C) Calculate the Gibbs free energy of S-vacancy CuIn 5 S 8 nanosheets to reduce CO 2 to CH 4 and CO;

(D) Calculate the Gibbs free energy of the original CuIn 5 S 8 nanosheets to reduce CO 2 to CH 4 and CO.

【Summary and Outlook】

In summary, in-situ research is playing an increasingly important role in the field of CO 2 reduction. Through the real-time detection of catalysts, reaction intermediates and catalytic products, the dynamic process of CO 2 reduction reaction can be clearly revealed , which is helpful to accurately understand the catalytic mechanism and design an efficient CO 2 catalytic system. In this article, the author first briefly introduces various in-situ characterization techniques, and then details the in-situ research progress in exploring the evolution of catalysts during the CO 2 reduction process. In addition, recent studies on the in-situ monitoring of the progress of the intermediates and catalytic products of the CO 2 reduction reaction are also summarized , where the reaction path can be inferred from the real-time characterization results. At the same time, it also investigated how to combine theoretical calculations with in-situ studies to further explore the possible reaction mechanism of CO 2 reduction. However, there are still many challenges and opportunities for future research in this field. From this point of view, the author provides some suggestions for exploring the in-situ study of CO 2 reduction reaction, as follows: (1) directly observe the evolution of active sites in situ with atomic resolution; (2) visualize the active sites in real time The formed reaction intermediates; (3) Simultaneously image the morphology and reaction of the active site under working conditions; (4) Theoretical analysis combining in-situ research and mechanical learning. In short, with the development of in-situ research technology and the deepening of research, it can be expected that more results will appear in the field of CO 2 reduction.

Literature link: Progress and Perspective for In Situ Studies of CO 2 Reduction ( J. Am. Chem. Soc. , 2020 , DOI: 10.1021 / jacs.0c02973)

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