Time-Dependent Density Functional Theory Study of Copper(II) Oxo Active Sites for Methane-to-Methanol Conversion in Zeolites
Time-Dependent Density Functional Theory Study of Copper(II) Oxo Active Sites for Methane-to-Methanol Conversion in Zeolites
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DOI：
10.1021/acs.inorgchem.0c03279
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发表时间：
2021-01-05
影响因子：
4.6
通讯作者：
Odoh, Samuel O.
中科院分区：
文献类型：
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作者：
Curtis, Kevin;Panthi, Dipak;Odoh, Samuel O.
铜交换沸石是用于甲烷-甲醇分步转化（MMC）的有用材料。然而，在铜交换沸石上的甲醇产率通常是适度的，从而激发了对开发在中等温度下活化、提供更高产率并提供优异的甲醇选择性的活性位点物质的兴趣。紫外-可见（UV-vis）光谱是表征活性位点及其在分步MMC过程中演变的主要工具。然而，使用Tamm-Dancoff含时密度泛函理论（TDA-DFT）计算铜氧活性位点的紫外-可见光谱可能是相当有问题的。这导致了利用基于多参考方法、绿色函数和Bethe-Salpeter方程的昂贵方法。在这项工作中，我们研究了[CuO]（+），[Cu_2 O]（2+），[Cu_2 O_2]（2+），[Cu_3 O_3]（2+）物种的光学光谱在沸石中的MMC牵连。对于较大的物种，我们研究了如何与实验数据的协议，提高了越来越大的集群模型。对于[CuO]（+），我们比较了TDA-DFT与受限活性空间二阶微扰理论RASPT 2。我们发现[CuO]（+）的特征峰具有多参考行为。激发态具有多种组态态函数，具有双激发特征。这些影响可能是传统TDA-DFT方法效用不佳的原因。事实上，我们获得了良好的协议与实验数据和RASPT 2后，占2 h/2 p激发TDA-DFT与先前描述的配置相互作用的单打和双打，CIS（D）风格的计划。[CuO]（+）、[Cu 2 O]（2+）以及[Cu 2 O2]（2+）物种的情况也是如此。使用远程校正的双杂交，欧米茄B2 PLYP，我们提供了第一次计算证据的实验紫外-可见光谱的[Cu 3 O3]（2+）活性位点模体。
Copper-exchanged zeolites are useful materials for step-wise methane-to-methanol conversion (MMC). However, methanol yields on copper-exchanged zeolites are often modest, spurring interest in the development of active-site species that are activated at moderate temperatures, afford greater yields, and provide excellent methanol selectivities. Ultraviolet-visible (UV-vis) spectroscopy is a major tool for characterizing the active-sites and their evolution during the step-wise MMC process. However, computation of the UV-vis spectra of the copper-oxo active sites using Tamm-Dancoff time-dependent density functional theory (TDA-DFT) can be quite problematic. This has led to utilization of expensive methods based on multireference approaches, Green functions, and the Bethe-Salpeter equation. In this work, we examined the optical spectra of [CuO](+), [Cu2O](2+), [Cu2O2](2+), and [Cu3O3](2+) species implicated in MMC in zeolites. For the larger species, we examined how agreement with experimental data is improved with increasingly larger cluster models. For [CuO](+), we compared TDA-DFT against restricted active space 2nd-order perturbation theory, RASPT2. We found that signature peaks for [CuO](+) have multireference behavior. The excited states have many configuration state functions with a double excitation character. These effects are likely responsible for the poor utility of conventional TDA-DFT methods. Indeed, we obtain good agreement with experimental data and RASPT2 after accounting for 2h/2p excitations within TDA-DFT with a previously described configuration interaction singles and doubles, CIS(D)-style scheme. This was the case for [CuO](+), [Cu2O](2+), as well as a [Cu2O2](2+) species. Using a long-range corrected double-hybrid, omega B2PLYP, we provide for the first time computational evidence for the experimental UV-vis spectrum of the [Cu3O3](2+) active site motif.