Chemically accurate predictions for the effect of water on the structure and reactivity of zeolite catalysts

从化学角度准确预测水对沸石催化剂结构和反应性的影响

• 批准号: 514934444
• 负责人: Professor Dr. Joachim Sauer
• 金额: --
• 依托单位: Arbeitsgruppe Quantenchemie der Festkörper/ Katalyse
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/514934444?language=en
• 关键词: Chemically; accurate; predictions; effect; water

We aim at quantum chemical ab initio predictions for hydration and hydrolysis of acidic zeolite catalysts and on the effect of water on their reactivity in industrially relevant hydrocarbon synthesis and transformations reactions. If predictions can be made for ideal zeolite structures with bridging Si-O(H)-Al groups as active sites with chemical accuracy (±4 kJ/mol for energies) disagreement with experiment points to defects or other imperfections of the samples used. We focus on the presence of extra-framework aluminium oxo-hydroxo (EFAl) species which form under hydrothermal conditions during synthesis, post-synthesis dealumination or catalytic conversion. The currently dominating computational approach, density functional theory with an additional parameterized dispersion term (DFT-D), does not yield reliable results for the reactivity of zeolites and their interaction with water. Adsorption energies and the stability of protonated water clusters are overestimated, and energy barriers are too low. O–H bonds are too long, too weak and too much stretched when engaged in H bonds which results in much too large red-shifts of O–H stretching frequencies. Crucial for the success of this project is therefore the implementation of a hybrid QM:QM method (QM – quantum mechanics) which combines second order Møller-Plesset perturbation theory (MP2) and Coupled Cluster (CC) theory for the reaction/adsorption site with DFT-D for the full periodic structure and is applicable to realistic models (1,000 atoms). Previous implementations for hydrocarbon reactions in zeolites (hybrid MP2:DFT-D+ΔCC method) have been shown to yield chemically accurate results for elementary reaction and adsorption steps. With the implemented and tested methods, we will generate an extensive set of chemically accurate data as reference for the selection of computationally more efficient (DFT-D) methods that are needed for broader application. With reliable QM:QM structures for different types of surface OH groups in zeolite H-MFI, calculated O–H stretching frequencies and 1H-NMR chemical shifts will permit to assign “free” and H-bonded OH groups to different crystallographic positions or to EFAl species. We will be also able to reject or accept suggested EFAl structure models based on disagreement or agreement between predicted spectroscopic signatures and experiment. We will study the interaction of water with ideal zeolite structures as well as with hydrolysed Si-O-Al bridges and other EFAl models. Comparison will be made with observed isotherms and calorimetric data using a new multi-site adsorption model.

我们的目标是量子化学从头算预测酸性沸石催化剂的水合和水解，以及水对其在工业上相关的烃合成和转化反应中的反应活性的影响。如果能够以化学精度(能量为±4kJ/mol)预测以Si-O(H)-Al基团为活性中心的理想沸石结构，则与实验结果不符的是所用样品的缺陷或其他缺陷。我们关注的是在合成、合成后脱铝或催化转化过程中，在水热条件下形成的骨架外铝氧-羟基(Efal)物种的存在。目前占主导地位的计算方法，即附加参数化色散项的密度泛函理论(DFT-D)，对于沸石的反应性及其与水的相互作用并不能产生可靠的结果。质子化水团簇的吸附能和稳定性被高估，能垒太低。当参与H键时，O-H键太长、太弱、太伸缩，导致O-H伸缩频率红移太大。因此，该项目成功的关键是实施了一种混合的QM：QM方法(QM-量子力学)，该方法结合了反应/吸附位置的二阶M&Plesset微扰理论(MP2)和耦合团簇(CC)理论，以及全周期结构的DFT-D，适用于现实模型(1,000个原子)。以前的分子筛中烃类反应的实现(混合MP2：DFT-D+ΔCC方法)已经被证明为基本反应和吸附步骤产生了化学上准确的结果。通过实施和测试的方法，我们将生成一组广泛的化学准确数据，作为选择更有效的计算(DFT-D)方法的参考，这些方法是更广泛应用所需的。利用分子筛H-MFI中不同类型表面羟基的可靠的QM：QM结构，计算的O-H伸缩频率和1H-核磁共振化学位移将允许将“自由”和氢键的OH基团分配给不同的晶位或Efal物种。我们也将能够拒绝或接受基于预测的光谱特征和实验之间的不一致或一致的建议的EFAL结构模型。我们将研究水与理想沸石结构的相互作用，以及与水解的Si-O-Al桥和其他Efal模型的相互作用。用一个新的多点吸附模型与观察到的等温线和量热数据进行比较。