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首页> 外文期刊>Physical chemistry chemical physics: PCCP >On the relationship between the basicity of a surface and its ability to catalyze transesterification in liquid and gas phases: the case of MgO
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On the relationship between the basicity of a surface and its ability to catalyze transesterification in liquid and gas phases: the case of MgO

机译：关于表面的碱度与其在液相和气相中催化酯交换反应能力之间的关系：MgO的情况

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Gas or liquid phase transesterification reactions are used in the field of biomass valorization to transform some platform molecules into valuable products. Basic heterogeneous catalysts are often claimed for these applications but the role of basicity in the reaction mechanism depending on the operating conditions is still under debate. In order to compare the catalyst properties necessary to perform a transesterification reaction both in liquid and gas phases, ethyl acetate and methanol, which can be easily processed both in these two phases, were chosen as reactants. The catalyst studied is MgO, known for its basic properties and its ability to perform the reaction. By means of appropriate thermal treatments, different kinds of MgO surfaces, with different coverages of natural adsorbates (carbonates and hydroxyls groups), can be prepared and characterized by means of CO2 adsorption followed by IR spectroscopy and hept-1-ene isomerization model reaction. New results on the basicity of the natural MgO surface (covered by carbonate and hydroxyl groups) are first given and discussed. The catalytic behavior in the transesterification reaction is then determined as a function of the adsorbate coverage. It is shown that the transesterification activity in the liquid phase is directly correlated with the kinetic basicity of the surface in agreement with the mechanism already proposed in the literature. On the reverse, no direct correlation with the basicity of the surface was established with the transesterification activity in the gas phase. A very high activity, in the gas phase, was observed and discussed for the natural surface pre-treated at 623 K. Preliminary DFT modeling of ester adsorption and methanol adsorption capacity determination were performed to investigate plausible reaction routes.
机译：气相或液相酯交换反应用于生物质增值领域，以将某些平台分子转化为有价值的产物。碱性多相催化剂通常被要求用于这些应用，但是碱性在反应机理中的作用取决于操作条件仍在争论中。为了比较在液相和气相中均进行酯交换反应所必需的催化剂性能，选择了在这两个相中均易于加工的乙酸乙酯和甲醇作为反应物。所研究的催化剂是MgO，以其基本性质和进行反应的能力而闻名。通过适当的热处理，可以制备并覆盖自然吸附物（碳酸盐和羟基）的不同种类的MgO表面，并通过CO2吸附，红外光谱和庚-1-烯异构化模型反应进行表征。首先给出并讨论了天然MgO表面碱性的新结果（被碳酸盐和羟基覆盖）。然后确定酯交换反应中的催化行为，作为被吸附物覆盖率的函数。结果表明，液相中的酯交换活性与表面的动力学碱性直接相关，这与文献中已经提出的机理一致。相反，气相中的酯交换活性与表面的碱度没有直接关系。对于在623 K预处理的天然表面，在气相中观察到并讨论了非常高的活性。进行了酯吸附的初步DFT建模和甲醇吸附能力的测定，以研究可能的反应路线。

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