重磅！馬丁/石川教授團隊最新Science：Au/α-MoC實現超低溫水氣轉化

—前言—

北京時間6月23日，Science在線發表了來自北京大學馬丁教授團隊利用α-MoC負載的原子層Au納米團簇作為催化劑，實現了低溫高效水氣轉化反應(DOI:10.1126/science.aah4321),論文的共同通訊作者還包括大連理工大學石川教授以及布魯克海文國家重點實驗室的José A. Rodriguez教授。這是馬丁教授，石川教授等繼Pt/MoC重整制氫Nature文章後的又一力作，祝賀！

水氣轉化（WGS，CO+H2O--CO2+H2）是一個非常重要的產氫以及CO去除的反應，在很多能源相關的化學過程中都有重要應用。由於這個反應是個放熱反應，受熱力學平衡限制，低溫更有利於反應的進行。而在H2燃料電池的應用中，一般H2來自於C-H化合物的重整反應，裡面或多或少會存在一定量的CO，這些CO對燃料電池中的催化劑具有毒化作用，因此也同樣需要催化劑來低溫，高效而且穩定地催化WGS反應。

本文，作者以α-MoC作為載體，負載了原子層Au納米團簇（Au layered clusters），實現了超低溫水氣轉化。Au與α-MoC的界面對於催化反應而言至關重要。其中，α-MoC可以在303K下活化H2O分子，而CO則吸附在鄰近的Au位點上，並易於跟α-MoC上水分解產生的表面OH基團發生反應，進而表現出非常高的WGS活性。

—圖文快解—

圖一. 2% Au/α-MoC催化劑的結構表徵和催化性能。

(A) In-situ XRD (λ=0.3196 ?) of 2% Au/α-MoC catalyst under WGS reaction conditions at various temperatures. (B) CO conversion on different catalysts at various temperatures. (Reaction condition: 10.5% CO, 21% H2O, 20% N2 in Ar; GHSV: 180,000 hours?1). (C) The activity of different catalysts (unit molCO/(molmetal.s), (measured at CO conversion below 15% in 11% CO-26% H2O-26% H2-7% CO2-30% N2). (D) Kinetic orders of the reactants and products. (E) Apparent activation energy Eapp of various catalysts in 10.5% CO-21% H2O-20% N2-Ar balance.

圖二. 催化反應機理研究以及電鏡表徵

Water adsorption (at 303 K) followed by CO-TPSR on 2% Au/α-MoC (A), α-MoC (B) and 2% Au/SiO2 (C). Signals of H2 (m/z=2), H2O (m/z=18), CO (m/z=28) and CO2 (m/z=44) were detected. (D and E) High-resolution HAADF-STEM images of 2% Au/α-MoC fresh catalyst, with single atoms of Au marked in blue circles and Au layered-structures highlighted in yellow. The Au clusters were further identified by elemental analysis (figs. S18 and S19). (F) HAADF-STEM image of 2% Au/α-MoC catalyst after reaction in which sample still contains both single-atom Au and Au layered-clusters. (G) HAADF-STEM image of the NaCN leached 2% Au/α-MoC catalyst, showing predominantly single atom Au, most of which overlap with Mo sites in the support lattice. Note that the very bright features in this image are caused by overlapping MoC particles, as confirmed by elemental mapping (figs. S18 and S19).

圖三. DFT理論計算揭示催化反應路徑

(A) H2O dissociation and CO reforming at lower coverage, (B) O-assisted H2O dissociation on the boundary oxidized by 3 O atoms and (C) CO reforming at high coverage. The energies of gaseous molecules have included the zero-point energy (ZPE) and entropy correction at 423 K. Au, Mo, C, O and H atoms are shown in gold, cyan, gray, red and white, respectively; while in order to make a distinction for the C atom from CO, it is represented by dark gray.

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