2-丙醇脱水反应热化学的密度泛函理论计算
Density Functional Theory Calculations of the thermochemistry of the dehydration of 2-propanol
AI总结：
本研究依托NWChemEx项目，利用NWChem开展密度泛函理论计算研究2-丙醇水相脱水的热化学性质，验证了模型有效性，明确了基组对计算精度的影响，得出低温反应热力学不利、高温可促进反应的结论。
摘要：
电子结构理论为理解复杂化学环境中的化学转化和过程提供了基础。我们的工作聚焦于NWChemEx项目，该项目选定了两项相互关联的科学挑战，以应对先进生物质衍生燃料及其他高附加值化合物的生产问题，其中一项便是沸石催化剂上的2-丙醇脱水反应。本研究采用密度泛函理论（DFT）计算，探究了2-丙醇的水相脱水反应。在NWChemEx代码仍处于开发阶段的背景下，我们利用NWChem计算对2-丙醇脱水的热化学性质进行了考量与分析。要对本研究中的反应开展符合实际的建模，需要使用扩展原子模型进行模拟。我们通过将2-丙醇脱水的预测结果与1-丙醇脱水研究的计算结果进行对比，验证了所建计算模型的有效性。我们采用第一性原理DFT计算研究2-丙醇的水相脱水反应，考察了2-丙醇反应的焓变，并针对精度逐步提升的基组——cc-pVDZ、cc-pVTZ、cc-pVQZ、cc-pV5Z和cc-pV6Z——计算了几何优化的能量。反应路径上的各类过渡态和极小值点，可为NWChemEx科学挑战的计算工作提供关键参考。在本工作中，我们明确了计算精度如何依赖于基组的选择，并确定了要获得足够精确的结果所需的基组类型。我们还计算了作为热力学参数的反应自由能随温度的变化关系，发现低温下该反应在热力学上是不利的。不过，2-丙醇脱水会使熵增加，这凸显了需要高温条件来促进该反应的进行。
英文摘要：
Electronic structure theory provides a foundation for understanding chemical transformations and processes in complex chemical environments. Our work is focused on the NWChemEx project that has selected two interrelated science challenges that address the production of advanced biomass-derived fuels and other value-added chemical compounds. One of which is the dehydration of 2-propanol over a zeolite catalyst. Aqueous phase dehydration of 2-propanol was investigated using density functional theory (DFT) calculations. We considered and analyzed the thermochemistry of the dehydration of 2-propanol using NWChem calculations while the NWChemEx code is still under development. Realistically modeling the reaction in this study properly requires simulations using extended atomistic models. We validated our computational models by comparing the predicted outcomes for 2-propanol dehydration with the calculated results from 1-propanol dehydration studies. We used the first-principles DFT calculations to investigate aqueous phase dehydration of 2-propanol, examine the enthalpy of the 2-propanol reaction and computed the energy for geometry optimization for increasingly better basis sets: cc-pVDZ, cc-pVTZ, cc-pVQZ, cc-pV5Z, and cc-pV6Z. The various transition states and minima along the reaction pathway are critical to inform the NWChemEx science challenge calculations. In this work, we established how the accuracy of the calculations depends on the basis sets, and we determined what basis sets are needed to achieve sufficient accurate results. We also calculated the reaction free energy as a function of temperature as thermodynamic parameter. We found that at low temperature the reaction is thermodynamically unfavorable. Nevertheless, dehydrating 2-propanol increases entropy, underscoring the need for high temperatures to facilitate the reaction.
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