Dioxygen Activation on Cu-MOR Zeolite: Theoretical Insights into the Formation of Cu2O and Cu3O3 Active Species,Inorganic Chemistry

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Dioxygen Activation on Cu-MOR Zeolite: Theoretical Insights into the Formation of Cu2O and Cu3O3 Active Species
Inorganic Chemistry ( IF 4.3 ) Pub Date : 2018-08-09 00:00:00 , DOI: 10.1021/acs.inorgchem.8b01329
M. Haris Mahyuddin ₁ , Takahiro Tanaka , Aleksandar Staykov , Yoshihito Shiota , Kazunari Yoshizawa

Affiliation

The utilization of low-cost and abundant oxygen (O₂) as an oxidant in the activation of copper-exchanged zeolites is highly important for the direct, selective oxidation of methane to methanol at low temperatures. While two motifs of active sites, i.e., the [Cu₂(μ-O)]²⁺ and [Cu₃(μ-O)₃]²⁺, have been experimentally observed in mordenite (MOR) zeolite, the mechanisms of their formation from the reaction of Cu-MOR with O₂ are still unclear. In this study, we performed density functional theory (DFT) calculations for O₂ activation over 2[Cu₂]²⁺-MOR and [Cu₃O]²⁺-MOR zeolites. For the reaction on the dicopper species, we found two possible reaction routes: O–O bond cleavage leading to (1) formation of a [Cu₂(μ-O)]²⁺ active species and a trans-μ-1,2-peroxo-Si₂ species and (2) simultaneous formation of two [Cu₂(μ-O)]²⁺ active species neighboring to each other. These routes are both exothermic but require completely different O–O bond activation energies. For the reaction on the tricopper species, we suggest a peroxo-Cu₃O species as the intermediate structure with two transition states (TSs) involved in the reaction. The first TS where a significant rearrangement of the tricopper site occurs is found to be rate-determining, while the second TS where the peroxo bond is cleaved results in a smaller activation barrier. This reaction, in contrast to the dicopper case, is slightly endothermic. The present study provides theoretical insights that may help design of better Cu-exchanged zeolite catalysts for methane hydroxylation to methanol.

中文翻译：

Cu-MOR沸石上的双氧活化：Cu ₂ O和Cu ₃ O ₃活性物种形成的理论见解

在铜交换的沸石的活化中利用低成本和丰富的氧气（O ₂）作为氧化剂对于在低温下将甲烷直接，选择性地氧化为甲醇非常重要。尽管在丝光沸石（MOR）中已通过实验观察到了活性位点的两个基序，即[Cu ₂（μ-O）] ²⁺和[Cu ₃（μ-O）₃ ] ²⁺，但它们的机理Cu-MOR与O ₂的反应形成的机理尚不清楚。在这项研究中，我们对2 [Cu ₂ ] ²⁺ -MOR和[Cu ₃ O]上的O ₂活化进行了密度泛函理论（DFT）计算。²⁺ -MOR沸石。对于双铜物种的反应，我们发现了两种可能的反应途径：O-O键断裂导致（1）形成[Cu ₂（μ-O）] ²⁺活性物种和反式-μ-1,2 -过氧-Si ₂物种和（2）同时形成彼此相邻的两个[Cu ₂（μ-O）] ²⁺活性物种。这些途径都是放热的，但需要完全不同的O–O键活化能。对于三铜物种的反应，我们建议使用过氧铜₃O物种是中间结构，具有两个过渡态（TSs）参与反应。发现发生了三铜位点显着重排的第一个TS是速率决定的，而过氧键断裂的第二个TS则导致较小的活化障碍。与双铜的情况相反，该反应是轻微吸热的。本研究提供了理论上的见解，可能有助于设计更好的铜交换沸石催化剂，以甲烷甲烷化为甲醇。

更新日期：2018-08-09

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