Figure 1. (a) Illustration of preparation of Pd2‑mpg‑C3N4.
Atom colors: C (dark gray), N (blue), Cl (orange), Pd (dark red). (b) Representative
AC‑HAADF‑STEM image of Pd2‑mpg‑C3N4 with
machine learning-detected atoms (lilac circles) and clusters (yellow circles)
overlaid. (c) The percentage of Pd atoms present in dimers as a function
of atom density derived from automated atom detection across the full set of
acquired images. The purple line shows the numbers expected for a random
distribution of non-interacting atoms. 研究者通过预选前驱体的湿沉积法合成双原子钯基催化剂（Pd2-mpg-C3N4），通过球差电镜与标准化的机器学习原子检测方法相结合，证明了催化剂中存在大量的双原子结构。 Figure 2. (a) N K-edge, (b) C K-edge, and (c) PdK-edge XANES spectra, and (d) Fourier transform of k2-weighted
Pd K-edge EXAFS spectra of the prepared catalysts. Pd foil and PdO were
applied for comparison. 同步辐射显示Pd2-mpg-C3N4催化剂中存在Pd-N/C和Pd-Pd配位结构；而Pd1-mpg-C3N4催化剂中只能观测到Pd-N/C的散射峰，Pd-Pd处的散射峰非常微弱。 Figure 3.(a) Catalytic performance for the
photocatalytic water‑donating transfer hydrogenation using 4-vinylphenol as a
model substrate. Reaction conditions: 4-vinylphenol, 0.15 mmol; deionized
water, 2 ml; 1,4‑dioxane, 3 ml; triethanolamine, 0.5 ml; blue
light, 40 W (l = 427 nm); 318 K; 1 bar; 5
h; N2 atmosphere. (b) The transfer hydrogenation of Pd2‑mpg‑C3N4photocatalyst in the continuous flow fixed-bed reactor system. Reaction
conditions: 4-vinylphenol, 0.3 g; deionized water, 20 ml; 1,4‑dioxane,
30 ml; triethanolamine, 10 ml; LED lattice light source (l = 420 nm);
flow rate, 0.108 mL min-1; 1 bar; N2atmosphere. (c) Reaction scope of the visible‑light‑driven photocatalytic
water‑donating transfer hydrogenation reactions. The reaction scope was performed
under the same photocatalytic reaction conditions as in (a) except for
different reaction times: 5 h (entries 1-4, and 7), 8 h (entries 5-6 and 10),
and 12 h (entries 8-9). The selectivity was calculated from the content of the
desired product and detected side products. 在温和条件下，以生物质化学品4-乙基苯酚为模型底物对比了不同催化剂的性能。相同钯负载量的情况下，Pd2-mpg-C3N4催化剂的产物收率达到了92%，而Pd1-mpg-C3N4和PdNP-mpg-C3N4分别只有47%和1%的收率，这表明调控金属原子结构能够显著提高反应性。随后，使用光催化流动反应设备对Pd2-mpg-C3N4的稳定性进行了评估，结果表明其在8小时的运行过程中性能稳定，没有明显的失活现象。此外，底物拓展实验显示出Pd2-mpg-C3N4具有优秀的底物适应性。 Figure 4.(a) Reaction
energy profiles for 4-vinylphenol hydrogenation on mpg-C3N4,
Pd1-mpg-C3N4, and Pd2-mpg-C3N4systems. VP represents 4-vinylphenol, VPH is hydrogenated VP, and EP stands for
4-ethylphenol. (b) Snapshots of representative intermediates. Most of the atoms
of the surfaces are omitted for clarity. Color code: N (blue), C (dark gray),
Pd (dark red), O (red), H (white). 为了澄清反应机制，研究者进行了DFT计算，结果显示，相比于Pd1-mpg-C3N4和PdNP-mpg-C3N4催化剂，Pd2-mpg-C3N4能明显加速底物的活化和氢化，并且抑制析氢副反应，从而提高以水为氢源光催化转移加氢的反应效率。
