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首页> 外文会议>ACS National Meeting Exposition >ON THE WAY TO BIOFUELS FROM FURAN: DISCRIMINATING DIELS-ALDER AND RINGOPENING MECHANISMS
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ON THE WAY TO BIOFUELS FROM FURAN: DISCRIMINATING DIELS-ALDER AND RINGOPENING MECHANISMS

机译：在呋喃的生物燃料的途中：区分Diels-Alder和旋转机制

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We performed kinetics experiments and quantum calculations to investigate the reaction of furan to benzofuran catalyzed by the acidic zeolite HZSM-5, which is a key step in the conversion of biomass to biofuels through catalytic fast pyrolysis. The reaction was studied experimentally by placing the zeolite in contact with solution-phase furan and detecting the benzofuran product over the temperature range 270-300°C, yielding an apparent activation energy of 72 ± 3 kJ/mol. The reaction was modeled in gas and zeolite phases to determine the energetics of the following two competing pathways: a Diels-Alder mechanism often assumed in interpretations of experimental data, and a ring-opening pathway predicted by the chemoinformatic software RING. Quantum calculations on the zeolite/guest system were performed using the ONIOM embedded cluster approach. We computed the energetics of reactants, products, and all intermediate steps. Locating relevant transition states fell beyond our computational resources because of system size and the ruggedness of the energy land- scape. The Diels-Alder mechanism in the gas phase was found to pass through a high-energy intermediate roughly 380 kJ/mol above the reactant energy, which reduces to approximately 200 kJ/mol in HZSM-5. In contrast, the ring-opening mechanism passes through a gas-phase intermediate roughly 500 kJ/mol above the reactant energy, which falls to approximately 50 kJ/mol in HZSM-5. The energy of the ring-opening mechanism over HZSM-5 fits into the experimentally- determined energy “budget” of 72±3 kJ/mol. These experimental and computational results highlight the importance of the ring-opening mechanism for this key step in making biofuels. Our results strongly indicate that, in the cavities of HZSM-5, the condensation of two fu- ran molecules to form benzofuran and water does not proceed by a Diels-Alder reaction between the reactants.
机译：我们进行了动力学实验和量子计算，以研究呋喃对酸性沸石HZSM-5催化的苯并呋喃的反应，这是通过催化快速热解转换生物质至生物燃料的关键步骤。通过将沸石与溶液-Apace Furan接触并在270-300℃的温度范围内检测到苯并呋喃产物来实验研究反应，从而产生72±3kJ / mol的表观活化能。该反应在气体和沸石相中进行建模，以确定以下两个竞争途径的能量学：通常在实验数据的解释中假设的DIELS - 桤木机制，以及由化学信息软件环预测的开环通路。使用Oniom嵌入式群集方法执行沸石/客人系统上的量子计算。我们计算了反应物，产品和所有中间步骤的能量学。由于系统尺寸和能量土地的坚固性，定位相关的转型状态超出了我们的计算资源。发现气相中的导蛋白酰胺机制通过高能中间体大约380kJ / mol以上反应能量，其在HZSM-5中降低至约200kJ / mol。相反，开环机构通过大约500kJ / mol以上的气相中间体，其在反应物能量之上，其在Hzsm-5中落到约50kJ / mol。 HZSM-5上的开环机构的能量适合72±3kJ / mol的实验确定的能量“预算”。这些实验和计算结果突出了开环机构在制作生物燃料的关键步骤的重要性。我们的结果强烈表示，在HZSM-5的腔体中，两个FU-RAN分子的凝结形成苯并呋喃和水的凝结不会通过反应物之间的DIEL- ald反应进行。

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