Reactivity of oxygen species formed upon N2O dissociation over Fe–ZSM-5 zeolite: CO oxidation as a model
Reactivity of oxygen species formed upon N2O dissociation over Fe–ZSM-5 zeolite: CO oxidation as a model
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DOI：
10.1016/j.catcom.2010.05.001
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发表时间：
2010-07
影响因子：
3.7
通讯作者：
H. Guesmi;D. Berthomieu;L. Kiwi-Minsker
中科院分区：
文献类型：
--
作者：
H. Guesmi;D. Berthomieu;L. Kiwi-Minsker
本文用密度泛函理论（DFT）研究了N_2O在Fe/ZSM-5沸石上解离生成的α-氧对CO的氧化能力。考虑了在ZSM-5中交换的两个α位[Fe-O]+和[Fe-（μO）-（μOH）-Fe]+，因为它们最近被证明在N_2O分解中具有活性。[O-Fe-O]+和[OFe-（μO）-（μOH）-FeO]+中α-氧和铁的计算电子性质、电荷转移和频率分析表明，孤立的FeII特征和双核Fe-ZSM-5位的FeIV特征。CO在氧原子上的加成揭示了沿着氧化反应，孤立铁的价态为II，并保持相对恒定，而计算出双核铁从IV到II的明显变化。根据密度泛函理论计算，CO从铁活性中心向α-氧的加成导致Fe-α-氧键长的显著增加。无论α-位是什么，CO的加入都是强烈放热的，并导致稳定的极小值，类似于吸附在铁活性位上的CO2。这种反应性与众所周知的α-氧的高反应性和低温下快速形成CO2的反应性一致。由计算的焓值可知，CO在双核[OFe-（μO）-（μOH）-FeO]+上的吸附比在孤立的[O-Fe-O]+上的吸附稍有利.熵参数的比较表明，相反的α-氧的氧化能力，从孤立的比那些从双核铁网站。
The oxidative power toward CO of α-oxygen formed upon N2O dissociation over isolated and binuclear Fe/ZSM-5 zeolite is investigated by means of DFT calculations. The two α-sites [Fe–O]+and [Fe–(μO)–(μOH)–Fe]+exchanged in ZSM-5 were considered since their activity in the N2O decomposition was recently shown. Computed electronic properties, charge transfers and frequency analysis of α-oxygen and iron in [O–Fe–O]+and [OFe–(μO)–(μOH)–FeO]+suggest a FeIIcharacter for the isolated and FeIVfor the binuclear Fe–ZSM-5 sites. Addition of CO on oxygen atoms reveals that along the oxidation reaction the valence state for the isolated iron is II and remains relatively constant while a clear change from IV to II is calculated for the binuclear iron. According to DFT calculations CO addition on the α-oxygen from the iron active sites induces a significant length increase of the Fe–α-oxygen bond. Whatever the α-sites, the addition of CO is strongly exothermic and leads to stable minima resembling an adsorbed CO2on iron active site. This reactivity is in line with the well known high reactivity of α-oxygen and the rapid CO2formation at low temperatures. Based on the calculated enthalpy values, the adsorption of CO is slightly more favourable on binuclear [OFe–(μO)–(μOH)–FeO]+than over isolated [O–Fe–O]+iron site. A comparison of the entropic parameters suggests the opposite with a stronger oxidative power of α-oxygen from isolated over those from binuclear iron site.