Deoxygenation of methyl laurate as a model compound on Ni-Zn alloy and intermetallic compound catalysts: Geometric and electronic effects of oxophilic Zn
Deoxygenation of methyl laurate as a model compound on Ni-Zn alloy and intermetallic compound catalysts: Geometric and electronic effects of oxophilic Zn
复制标题
月桂酸甲酯作为模型化合物在 Ni-Zn 合金和金属间化合物催化剂上的脱氧：亲氧性 Zn 的几何和电子效应
DOI：
10.1016/j.apcatb.2017.10.040
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发表时间：
2018-05-01
影响因子：
22.1
通讯作者：
Chen, Jixiang
中科院分区：
文献类型：
--
作者：
Pan, Zhengyi;Wang, Rijie;Chen, Jixiang
以二价（Ni²⁺和Zn²⁺）与三价离子（Al³⁺）原子比为3的层状双氢氧化物（LDHs）制备了一系列具有不同Ni/Zn原子比的Ni - Zn双金属催化剂。在650℃下用H₂还原由煅烧后的LDHs得到的混合氧化物时，在Ni/Zn比≥2时合成了具有面心立方（fcc）结构的富镍合金，而在Ni/Zn原子比为1和1/2时生成了具有四方L1₀结构的Ni - Zn金属间化合物（IMC），在Ni/Zn比为1/8时生成了具有立方结构的Ni - Zn IMC。高角度环形暗场扫描透射电子显微镜 - 能谱（HAADF - STEM - EDS）、H₂化学吸附和磁性测量表明，Ni和Zn原子在催化剂中均匀分布，并且Ni原子的集团随着Ni/Zn比的降低而减少。X射线光电子能谱（XPS）和一氧化碳程序升温脱附（CO - TPD）表征揭示了从Ni到Zn的电荷转移。在以月桂酸甲酯作为模型化合物脱氧生成类柴油烃的反应中，尽管Zn的加入降低了月桂酸甲酯的转化率，这主要是由于Ni含量的降低，但推测Ni和Zn之间存在协同效应以提高周转频率（TOF），并且在Ni/Zn比为1/1和1/2的催化剂上获得了更高的TOF。由于Zn的高亲氧性，这种协同效应也促进了加氢脱氧途径。随着Ni/Zn比的降低，C₁₁烃与C₁₂烃及含氧化合物之间的摩尔比降低。特别是在反应温度为330℃时，在Ni - Zn IMC上该比值小于0.2，远低于金属Ni催化剂上的60.5。与金属Ni相比，富镍合金和金属间化合物（尤其是金属间化合物）对C - C键氢解和CO/CO₂甲烷化表现出较低的反应活性，并且随着Ni/Zn原子比的降低和反应温度的升高，这种现象更加显著。特别是在400℃时当月桂酸甲酯的转化率接近100%时，金属Ni催化剂主要生成甲烷，这是由C - C键氢解以及CO/CO₂的完全甲烷化产生的，并且对C₁₁和C₁₂的总选择性（即S_{C₁₁ + C₁₂}）仅为1.1%。然而，当Ni/Zn原子比为……
A series of Ni-Zn bimetallic catalysts with different Ni/Zn atomic ratios were prepared from layered double hydroxides (LDHs) with an atomic ratio of 3 between divalent (Ni2+ and Zn2+) and trivalent ions (Al3+). After the mixed oxides derived from calcined LDHs were reduced with H-2 at 650 degrees C, Ni-rich alloy with a fcc structure was synthesized at Ni/Zn ratios >= 2, while an Ni-Zn intermetallic compound (IMC) with a tetragonal L1(0) structure was generated at Ni/Zn atomic ratios of 1 and 1/2, and an Ni-Zn IMC was generated with a cubic structure at Ni/Zn ratio of 1/8. HAADF-STEM-EDS, H-2 chemisorption and magnetic measurements showed that Ni and Zn atoms were uniformly distributed in catalysts, and the ensembles of Ni atoms decreased with decreasing Ni/Zn ratios. XPS and CO-TPD characterizations revealed a charge transfer from Ni to Zn. In the deoxygenation of methyl laurate as a model compound to diesel-like hydrocarbons, although the addition of Zn reduced the conversion of methyl laurate, mostly due to the decrease in Ni content, a synergetic effect between Ni and Zn was suggested to enhance turnover frequency (TOP), and higher TOFs were obtained on the catalysts with Ni/Zn ratios of 1/1 and 1/2. Because of the high oxophilicity of Zn, this synergetic effect also promoted the hydrodeoxygenation pathway. With decreasing Ni/Zn ratios, the molar ratio between C-11 hydrocarbons and both C-12 hydrocarbons and oxygenates decreased. Particularly, it was smaller than 0.2 on Ni-Zn IMC when the reaction temperature was 330 degrees C, and much lower than that of 60.5 on the metallic Ni catalyst. Compared with metallic Ni, Ni-rich alloys and IMCs (especially IMCs) showed lower reactivity for C-C bond hydrogenolysis and CO/CO2 methanation, which was more remarkable with decreasing Ni/Zn atomic ratios and increasing reaction temperatures. Particularly, when the conversion of methyl laurate was close to 100% at 400 degrees C, the metallic Ni catalyst dominatingly gave methane, which was derived from C-C bond hydrogenolysis as well as complete methanation of CO/CO2, and the total selectivity to C-11 and C-12 (i.e., SC11+C-12) was only 1.1%. However, when the Ni/Zn atomic ratio was