Synergistic Contribution of the Acidic Metal Oxide–Metal Couple and Solvent Environment in the Selective Hydrogenolysis of Glycerol: A Combined Experimental and Computational Study Using ReOx–Ir as the Catalyst,ACS Catalysis

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Synergistic Contribution of the Acidic Metal Oxide–Metal Couple and Solvent Environment in the Selective Hydrogenolysis of Glycerol: A Combined Experimental and Computational Study Using ReOx–Ir as the Catalyst
ACS Catalysis ( IF 11.3 ) Pub Date : 2018-12-04 00:00:00 , DOI: 10.1021/acscatal.8b03079
Jithin John Varghese ₁ , Liwei Cao _{1,

2} , Christopher Robertson _{1,

2} , Yanhui Yang _{1,

3,

4} , Lynn F. Gladden _{1,

2} , Alexei A. Lapkin _{1,

2} , Samir H. Mushrif _{1,

3,

5}

Affiliation

Comprehensive mechanistic insights into the aqueous-phase hydrogenolysis of glycerol by the ReO_x–Ir catalyst were obtained by combining density functional theory (DFT) calculations with batch reaction experiments and detailed characterization of the catalysts using X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared techniques. The role and contribution of the aqueous acidic reaction medium were investigated using NMR relaxometry studies complemented with molecular dynamics and DFT calculations. At higher glycerol concentration, the enhanced competitive interaction of glycerol with the catalyst improved the conversion of glycerol. Sulfuric acid increased the concentration of glycerol within the pores of the catalyst and enhanced the propensity for dissociative adsorption of glycerol on the catalyst, explaining the promotional effect of acid during hydrogenolysis. Partially reduced and dispersed Brønsted acidic ReO_x clusters on metallic Ir nanoparticles facilitated dissociative attachment of glycerol and preferential formation of the primary propoxide. The formation of the dominant product, 1,3-propanediol (1,3-PDO), results from the selective removal of the secondary hydroxyl of glycerol, with a comparatively low activation barrier of 123.3 kJ mol^–1 in the solid Brønsted acid-catalyzed protonation–dehydration mechanism or 165.2 kJ mol^–1 in the direct dehydroxylation mechanism. The formation of 1-propanol (1-PO) is likely to follow a successive dehydroxylation pathway in the early stages of the reaction. Although 1,3-PDO is less reactive than 1,2-propanediol (1,2-PDO), it preferentially adsorbs on the catalyst in a mixture containing glycerol to form 1-PO. The thermodynamically favorable pathway involving dehydrogenation, dehydroxylation, and hydrogenation elementary steps led to the dominant production of 1,2-PDO on pure Ir catalyst with a high C–O bond cleavage barrier of 207.4 kJ mol^–1. The optimum ReO_x–Ir catalyst with an Ir/Re ratio of 1 exploits the synergy of the sites of both the components. The detailed insights presented here would guide the rational selection of catalysts for the hydrogenolysis of polyols and the optimization of reaction parameters.

中文翻译：

甘油选择性加氢水解过程中酸性金属氧化物-金属对和溶剂环境的协同贡献：以ReO _x -Ir为催化剂的实验与计算研究相结合

ReO _x对甘油水相氢解的全面机理的见解通过将密度泛函理论（DFT）计算与间歇反应实验相结合，并使用X射线衍射，X射线光电子能谱和傅里叶变换红外技术对催化剂进行了详细表征，从而获得了–Ir催化剂。使用NMR弛豫分析研究以及分子动力学和DFT计算，研究了酸性水溶液反应介质的作用和贡献。在较高的甘油浓度下，甘油与催化剂的增强的竞争相互作用提高了甘油的转化率。硫酸增加了催化剂孔中甘油的浓度，并增强了甘油在催化剂上的解离吸附倾向，这说明了酸在氢解过程中的促进作用。金属Ir纳米颗粒上的_x簇促进了甘油的解离附着和伯丙醇的优先形成。选择性产物1,3-丙二醇（1,3-PDO）的形成是由于选择性除去甘油的仲羟基而产生的，在固体布朗斯台德酸中，活化势垒较低，为123.3 kJ mol^–1。催化质子化-脱水机理或165.2 kJ mol^–1在直接脱羟基的机制。1-丙醇（1-PO）的形成可能会在反应的早期阶段遵循连续的脱羟基途径。尽管1,3-PDO的反应性不如1,2-丙二醇（1,2-PDO），但它优先吸附在含有甘油的混合物中的催化剂上以形成1-PO。涉及脱氢，脱羟基和氢化基本步骤的热力学有利途径导致在纯Ir催化剂上以207.4 kJ mol ^–1的高C-O键裂解势垒主导生产1,2-PDO 。最佳ReO _xIr / Re比率为1的–Ir催化剂利用了两个组分位点的协同作用。本文提供的详细见解将指导多元醇氢解催化剂的合理选择和反应参数的优化。

更新日期：2018-12-04

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