可見(jiàn)光催化CO₂還原制高附加值化學(xué)品是一種極具吸引力且環(huán)保的方法，不僅解決能源短缺問(wèn)題，同時(shí)減少二氧化碳排放。然而，目前這種人工光還原CO₂的效率，遠(yuǎn)遠(yuǎn)達(dá)不到工業(yè)上大規(guī)模生產(chǎn)的要求。在多相催化中，一般一個(gè) CO₂ 分子只能被一個(gè)催化位點(diǎn)活化。

因此，制備C₂等多碳化學(xué)品，需要相鄰多位點(diǎn)間協(xié)同作用。因此，由于有限的還原能力和活性位的高度分散性，單位點(diǎn)催化劑（例如：?jiǎn)卧哟呋瘎┯|發(fā)C-C偶聯(lián)顯得非常具有挑戰(zhàn)性。該研究基于從頭算–非絕熱分子動(dòng)力學(xué)模擬發(fā)現(xiàn)了：光照下單一催化位點(diǎn)發(fā)生有趣的雙重活化（熱致活化和光致活化）CO₂分子，并誘導(dǎo)C-C偶聯(lián)生成高附加值C₂H₆。

Fig. 2 Optical properties.

來(lái)自浙江工業(yè)大學(xué)化工學(xué)院工業(yè)催化研究所莊桂林教授團(tuán)隊(duì)針對(duì)光催化CO₂還原反應(yīng)（如本文壓題圖）成功地設(shè)計(jì)了一種穩(wěn)定且高效的單原子催化劑Ti@C₄N₃，并提出了單位點(diǎn)雙重活化的概念。即該研究發(fā)現(xiàn)負(fù)載高價(jià)態(tài)Ti⁴⁺到C₄N₃載體，打開(kāi)能帶發(fā)生導(dǎo)體到半導(dǎo)體轉(zhuǎn)變，形成具有平帶特征且由Ti-3d態(tài)組成導(dǎo)帶底（CBM），這種高度局域的CBM有效提高光生電子從活性位到反應(yīng)底物的傳輸效率和壽命( 38.21 ps )。

進(jìn)一步原位光照下含時(shí)密度泛函理論(rt-TDDFT)模擬研究（如圖3）揭示：高空速的CO₂流過(guò)Ti@C₄N₃催化劑表面經(jīng)歷了2個(gè)活化過(guò)程：(1) 無(wú)光照時(shí)，高Lewis 酸位的Ti通過(guò)給反饋π鍵以熱誘導(dǎo)方式活化一個(gè)CO₂, 部分CO₂ 分子以范德華力作用弱吸附在位點(diǎn)附近。( 2 )可見(jiàn)光照時(shí)，催化劑的價(jià)帶附近電子被激發(fā)到導(dǎo)帶上；而CBM上電子態(tài)主要布居在Ti-3d態(tài)上。

Fig. 4 Reaction pathways. Schematic illustration of the possible reaction pathways for CO2RR on Ti@C4N3.

因此某個(gè)弱吸附CO₂容易通過(guò)Ti@C₄N₃的CBM從Ti位點(diǎn)獲得光電子，從而發(fā)生光誘導(dǎo)活化。催化機(jī)理研究表明如圖4，在E_a?= 0.19 eV能壘下，兩個(gè)活性的CO₂非常容易偶聯(lián)為草酸鹽，進(jìn)一步經(jīng)過(guò)多步還原高選擇性產(chǎn)生C₂H₆(?E_a?= 1.09 eV )。該研究在CO₂雙重活化的發(fā)現(xiàn)將對(duì)可見(jiàn)光催化劑的設(shè)計(jì)提供一種新的思路。相關(guān)論文近期發(fā)布于npj?Computational Materials?9:?220?(2023)。

Editorial Summary

Can a Single Catalytic Site Activate Multiple CO₂Molecules in Photocatalysis: One or More?

Visible light catalysis for CO₂ reduction to high-Value chemicals is an attractive and environmentally friendly approach, not only addressing energy shortages but also mitigating carbon dioxide emissions. However, the current efficiency of artificial light-driven CO₂ reduction falls far short of the requirements for large-scale industrial production. In heterogeneous catalysts, typically, only one CO₂ molecule can be activated by one catalytic site. Therefore, the preparation of multi-carbon chemicals, such as C₂, requires cooperative interactions between adjacent catalytic sites. Due to limited reduction capacity and the high dispersion of active sites, triggering C-C coupling in single-site catalysts, such as single-atom catalysts, proves to be highly challenging. This study, based on first-principles non-adiabatic molecular dynamics simulations, discovered intriguing dual activation (thermal and photoinduced) and C-C coupling at a single site during the photo-reduction of CO₂.?

Fig. 6 Schematic diagram of two CO2 molecules coupled.

Professor Zhuang Guilin’s team from the Institute of Industrial Catalysis, School of Chemical Engineering, Zhejiang University of Technology, successfully designed a stable and efficient single-atom catalyst, Ti@C₄N₃, for photocatalytic CO₂ reduction, introducing the concept of dual activation at the single site. The study revealed that loading a high-valence Ti⁴⁺ onto the C₄N₃carrier induces a band transition from a conductor to a semiconductor and forms a Ti-3d component with flat-band characteristics, effectively enhancing the efficiency and lifetime of photo-generated electrons (38.21 ps). Real-time time-dependent density functional theory (RT-TDDFT) simulations under in situ light exposure found that, as high-speed CO₂ passed over the catalyst surface, two processes occur: (1) Without light, CO₂ at the high Lewis acid site Ti activates one CO₂ through thermally induced feedback to the π bond, and some CO₂ molecules weakly adsorb near the site through van der Waals forces. (2) Under visible light, electrons in the valence band are excited to the catalyst’s CBs; since the electron states on the CBM are mainly localized on the Ti-3d states, a weakly adsorbed CO₂ easily gains photogenerated electrons from the Ti@C₄N₃‘s CBM at the Ti site, leading to photoinduced activation. Mechanistic studies suggest that under a low energy barrier (E_a = 0.19 eV), coupling two active CO₂ molecules to form oxalate is highly facile, and oxalate is further selectively reduced to C₂H₆ (E_a= 1.09 eV). The discovery of dual activation in CO₂ opens up new avenues for the design of visible-light catalysts. This research was recently published in npj Computational Materials 9: 220 (2023).

原文Abstract及其翻譯

Dual Activation and C-C Coupling on Single Atom Catalyst for CO₂Photoreduction (光照下單原子催化劑雙重活化CO₂和C-C偶聯(lián))

Fu-li Sun, Cun-biao Lin, Wei Zhang, Qing Chen, Wen-xian Chen, Xiao-nian Li & Gui-lin Zhuang*?

Abstract An excellent single-atomic photocatalyst, Ti@C₄N₃, is theoretically found to effectively convert CO₂ to C₂H₆by density functional theory (DFT) calculations and non-adiabatic molecular dynamics (NAMD) simulations. The Ti@C₄N₃ photocatalyst has remarkable stability both thermally, chemically, and mechanically. Electronically, it has strong absorption properties (l= 327.77 and 529.61 nm), suitable band positions, and a long photogenerated electron lifetime (τ_e= 38.21 ps), allowing photogenerated electrons to migrate to the surface. Notably, the high-valence active site effectively activates two CO₂through dual activation: Under light irradiation, the weakly adsorbed CO₂undergoes photo-induced activation by the photoelectron of conduction band minimum (CBM); without light, the high Lewis acidity of the Ti site induces CO₂activation through back-donating π-bond.Contrast simulation results uncovered that dual activation of CO₂is attributed to the thermal and photonic synergy. Furthermore, two activated CO₂ species under light easily couple to form oxalate with the barrier of 0.19 eV, and further reduced to C₂H₆ with a low activation energy of 1.09 eV.

摘要結(jié)合密度泛函理論（DFT）計(jì)算和非絕熱分子動(dòng)力學(xué)（NAMD）模擬結(jié)果發(fā)現(xiàn)了一種優(yōu)異的單原子光催化劑Ti@C₄N₃可以有效地將CO₂轉(zhuǎn)化為C₂H₆。 Ti@C₄N₃光催化劑具有顯著的熱穩(wěn)定性、化學(xué)穩(wěn)定性和機(jī)械穩(wěn)定性。在電子性質(zhì)方面，它具有很強(qiáng)的光吸收特性（l = 327.77和529.61 nm）、合適的帶邊位置和較長(zhǎng)的光生電子壽命（τ_e = 38.21 ps），且允許光生電子有效遷移到表面。值得注意的是，高價(jià)態(tài)活性位點(diǎn)通過(guò)雙重模式有效地活化了兩個(gè)CO₂分子，即：在光照射下，弱吸附的CO₂受到導(dǎo)帶底（CBM）光電子的誘導(dǎo)活化；在無(wú)光照下，Ti位點(diǎn)的高路易斯酸性通過(guò)反饋π鍵誘導(dǎo)CO₂活化。對(duì)比模擬結(jié)果發(fā)現(xiàn)，CO₂的雙重活化歸因于熱能和光子的協(xié)同作用。此外，兩個(gè)被活化的CO₂分子在光照下很容易耦合形成草酸鹽，反應(yīng)能壘低至0.19 eV；并進(jìn)一步經(jīng)過(guò)多步還原生成C₂H₆，且速控步的活化能僅為1.09 eV。