Nickel phosphide catalysts (Ni₁₂P₅ and Ni₂P) preferentially cleave sterically hindered ³C–O bonds over unhindered ²C–O bonds, and Ni₂P is up to 50 times more selective toward ³C–O bond cleavage than Ni. Here, we combine kinetic measurements, in situ infrared spectroscopy, and density functional theory (DFT) calculations to describe the mechanism for C–O bond rupture over Ni, Ni₁₂P₅, and Ni₂P catalysts. Steady-state rate measurements and DFT calculations of C–O bond rupture within 2-methyltetrahydrofuran (MTHF) show that quasi-equilibrated MTHF adsorption and dehydrogenation steps precede kinetically relevant C–O bond rupture at these conditions (1–50 kPa MTHF; 0.1–6 MPa H₂; 543 K). Rates for ³C–O and ²C–O bond rupture are inhibited by H₂, and the ratio of these rates increases with [H₂]^1/2, suggesting that the composition of the reactive intermediates for ³C–O and ²C–O rupture differs by one H atom. Site-blocking CO*, NH₃*, and H* inhibit rates without altering the ratio of ³C–O to ²C–O bond rupture, indicating that these C–O bond rupture precursors and transition states bind to identical active sites. DFT-based predictions suggest that these sites are exposed ensembles of 3 Ni atoms on Ni(111) and Ni₂P(001) and 4 Ni atoms on Ni₁₂P₅(001) and that the incorporation of P disrupts extended Ni ensembles and alters the reactivity of the Ni. Increasing the phosphorus to nickel ratio (P:Ni) decreases measured and DFT-predicted activation enthalpies (ΔH^‡, 473–583 K) for ³C–O bond rupture relative to that of ²C–O bond rupture. Selectivity differences between specific C–O bonds within MTHF reflect differences in the H content of reactive intermediates, activation enthalpy barriers, and P:Ni of Ni, Ni₁₂P₅, and Ni₂P nanoparticles.

中文翻译：

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Ni，Ni ₁₂ P ₅和Ni ₂ P催化剂上2-甲基四氢呋喃中C–O键断裂的机理和活性中心

磷化镍催化剂（Ni ₁₂ P ₅和Ni ₂ P）优先裂解空间受阻的³ C-O键，而不是不受阻碍的² C-O键，并且Ni ₂ P对³ C-O键断裂的选择性是Ni的50倍以上。在这里，我们结合动力学测量，原位红外光谱和密度泛函理论（DFT）计算来描述Ni，Ni ₁₂ P ₅和Ni _2上C–O键断裂的机理。磷催化剂。稳态速率测量和2-甲基四氢呋喃（MTHF）中C-O键断裂的DFT计算表明，在这些条件下，准平衡的MTHF吸附和脱氢步骤先于动力学相关的C-O键断裂（1-50 kPa MTHF; 0.1 –6 MPa H ₂； 543 K）。对于价格³ C-O和² C-O键断裂是由H抑制₂，以及它们的速率随[H的比率增加₂ ] ^1/2，表明活性中间体的组合物³ C-O和² C–O断裂相差一个H原子。阻止位点的CO *，NH ₃ *和H *抑制速率而不改变³的比例C–O至^2个C–O键断裂，表明这些C–O键断裂的前体和过渡态与相同的活性位结合。基于DFT的预测表明这些位点是Ni（111）和Ni ₂ P（001）上的3个Ni原子和Ni ₁₂ P ₅（001）上的4个Ni原子的暴露集合，并且P的掺入破坏了扩展的Ni集合。改变镍的反应性 增加的磷镍比（P：Ni）降低了，对于³ C-O键断裂，DFT预测的活化焓（ΔH ^‡，473-583 K）相对于²C–O键断裂。MTHF中特定C–O键之间的选择性差异反映了反应性中间体H含量，活化焓屏障以及Ni，Ni ₁₂ P ₅和Ni ₂ P纳米粒子的P：Ni的差异。