Chemically accurate predictions for water adsorption on Brønsted sites of zeolite H-MFI,Physical Chemistry Chemical Physics

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Chemically accurate predictions for water adsorption on Brønsted sites of zeolite H-MFI
Physical Chemistry Chemical Physics ( IF 2.9 ) Pub Date : 2024-09-04 , DOI: 10.1039/d4cp02851a
Henning Windeck ₁ , Fabian Berger ₁ , Joachim Sauer _{1,

2}

Affiliation

We investigate the adsorption of water molecules in the zeolite H-MFI at isolated Brønsted acid sites (BAS) for loadings of 1, 2, and 3 H₂O/BAS. We consider two approaches to the O₃Al–O(H)–Si sites: the Brønsted-type approach of H₂O to the acidic proton and the Lewis-type approach to the aluminium atom of the AlO₄ tetrahedron. From the twelve crystallographically inequivalent framework sites for Al, a representative set of six active site positions is chosen. For them, we calculate CCSD(T)-quality adsorption energies at MP2-quality adsorption structures for different approaches, 48 in total. The Brønsted-type approach is favoured for most cases but the Lewis-type approach has similar stability for some framework positions. We predict heats of adsorption per molecule ranging from 60 to 76, 56 to 65, and 56 to 64 kJ mol⁻¹ for loadings of 1, 2, and 3 H₂O/BAS, respectively. For 1 H₂O/BAS, the experimental result (70 kJ mol⁻¹) falls into the range of our predictions, whereas for 2 and 3 H₂O/BAS, the measured adsorption heats per molecule (74 and 70 kJ mol⁻¹, respectively) are larger than our predictions. For 2 H₂O/BAS, the ion-pair structure generated by proton transfer to the water dimer competes with the neutral adsorption complex. The DFT adsorption energies (PBE+D2) deviate significantly from the CCSD(T)-quality reference energies, by up to 25 kJ mol⁻¹ for 1 H₂O/BAS, 25 kJ mol⁻¹ per H₂O for 2 H₂O/BAS, and 18 kJ mol⁻¹ per H₂O for 3 H₂O/BAS. Specifically, PBE+D2 overstabilises the ion-pair structure, i.e. in many cases the PBE+D2 error is much larger for ionic than for neutral adsorption structures.

中文翻译：

对 H-MFI 沸石布朗斯台德位点上的水吸附进行化学准确预测

我们研究了在 1、2 和 3 H ₂ O/BAS 负载量下，H-MFI 沸石中孤立的布朗斯台德酸位点 (BAS) 上水分子的吸附情况。我们考虑O ₃ Al-O(H)-Si 位点的两种方法：H ₂ O 酸性质子的布朗斯台德型方法和AlO ₄四面体铝原子的路易斯型方法。从 Al 的 12 个晶体学不等价的骨架位点中，选择了一组具有代表性的六个活性位点位置。对于它们，我们计算了不同方法在 MP2 质量吸附结构上的 CCSD(T) 质量吸附能，总共 48 种方法。布朗斯台德型方法在大多数情况下受到青睐，但刘易斯型方法对于某些框架位置具有类似的稳定性。我们预测对于 1、2 和 3 H ₂ O/BAS 的负载量，每个分子的吸附热分别为 60 至 76、56 至 65 和 56 至 64 kJ mol ^-1 。对于 1 H ₂ O/BAS，实验结果 (70 kJ mol ⁻¹ ) 落入我们的预测范围内，而对于 2 和 3 H ₂ O/BAS，测量的每个分子的吸附热 (74 和 70 kJ mol ^{− 1} ）比我们的预测要大。对于2 H ₂ O/BAS，质子转移到水二聚体产生的离子对结构与中性吸附络合物竞争。 DFT 吸附能 (PBE+D2) 与 CCSD(T) 质量参考能的偏差显着，1 H ₂ O/BAS 的偏差高达 25 kJ mol ^-1，2 H 的每 H ₂ O 偏差高达 25 kJ mol ^-1 ₂ O/BAS，以及对于3 H ₂ O/BAS，每H ₂ O 18 kJ mol ^-1 。具体而言，PBE+D2 使离子对结构过度稳定，即，在许多情况下，离子吸附结构的PBE+D2 误差比中性吸附结构的误差大得多。

更新日期：2024-09-05

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