Journal ArticleDOI
Structure and nuclearity of active sites in Fe-zeolites: comparison with iron sites in enzymes and homogeneous catalysts
Adriano Zecchina,Mickaël Rivallan,Mickaël Rivallan,Gloria Berlier,Carlo Lamberti,Gabriele Ricchiardi +5 more
TLDR
It is concluded that Fe-ZSM-5 and Fe-silicalite are not the ideal samples conceived before and that many types of species are present, some active and some other silent from adsorptive and catalytic point of view.Abstract:
Fe-ZSM-5 and Fe-silicalite zeolites efficiently catalyse several oxidation reactions which find close analogues in the oxidation reactions catalyzed by homogeneous and enzymatic compounds. The iron centres are highly dispersed in the crystalline matrix and on highly diluted samples, mononuclear and dinuclear structures are expected to become predominant. The crystalline and robust character of the MFI framework has allowed to hypothesize that the catalytic sites are located in well defined crystallographic positions. For this reason these catalysts have been considered as the closest and best defined heterogeneous counterparts of heme and non heme iron complexes and of Fenton type Fe2+ homogeneous counterparts. On this basis, an analogy with the methane monooxygenase has been advanced several times. In this review we have examined the abundant literature on the subject and summarized the most widely accepted views on the structure, nuclearity and catalytic activity of the iron species. By comparing the results obtained with the various characterization techniques, we conclude that Fe-ZSM-5 and Fe-silicalite are not the ideal samples conceived before and that many types of species are present, some active and some other silent from adsorptive and catalytic point of view. The relative concentration of these species changes with thermal treatments, preparation procedures and loading. Only at lowest loadings the catalytically active species become the dominant fraction of the iron species. On the basis of the spectroscopic titration of the active sites by using NO as a probe, we conclude that the active species on very diluted samples are isolated and highly coordinatively unsaturated Fe2+ grafted to the crystalline matrix. Indication of the constant presence of a smaller fraction of Fe2+ presumably located on small clusters is also obtained. The nitrosyl species formed upon dosing NO from the gas phase on activated Fe-ZSM-5 and Fe-silicalite, have been analyzed in detail and the similarities and differences with the cationic, heme and non heme homogeneous counterparts have been evidenced. The same has been done for the oxygen species formed by N2O decomposition on isolated sites, whose properties are more similar to those of the (FeO)2+ in cationic complexes (included the [(H2O)5FeO]2+
“brown ring” complex active in Fenton reaction) than to those of ferryl groups in heme and non heme counterparts.read more
Citations
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Journal ArticleDOI
Review of Pt-based bimetallic catalysis: from model surfaces to supported catalysts.
TL;DR: The chiral stationary phase for high-performance liquid chromatography showed good chiral recognition ability and the chiral phase showed good Raman recognition ability, which is important for future generations of racemates.
Journal ArticleDOI
Direct Conversion of Methane to Value-Added Chemicals over Heterogeneous Catalysts: Challenges and Prospects
TL;DR: This work focuses mainly on the fundamentals of C-H activation and analyzes the reaction pathways toward selective routes of OCM, MDA, and MTOAH to provide some insights into their reaction mechanisms and implications for future development of highly selective catalysts for direct conversion of methane to high value-added chemicals.
Journal ArticleDOI
Interface-Confined Ferrous Centers for Catalytic Oxidation
Qiang Fu,Wei-Xue Li,Yunxi Yao,Hongyang Liu,Hai-Yan Su,Ding Ma,Xiang-Kui Gu,Limin Chen,Zhen Wang,Hui Zhang,Bing Wang,Xinhe Bao +11 more
TL;DR: The interface confinement effect can be used to stabilize the coordinately unsaturated ferrous sites by taking advantage of strong adhesion between ferrous oxides and metal substrates, and it is shown that the structural ensemble was highly efficient for carbon monoxide oxidation at low temperature under typical operating conditions of a proton-exchange membrane fuel cell.
Journal ArticleDOI
A single iron site confined in a graphene matrix for the catalytic oxidation of benzene at room temperature.
Dehui Deng,Xiaoqi Chen,Liang Yu,Xing Wu,Qingfei Liu,Yun Liu,Huaixin Yang,Huanfang Tian,Yongfeng Hu,Peipei Du,Rui Si,Junhu Wang,Xiaoju Cui,Haobo Li,Jianping Xiao,Tao Xu,Jiao Deng,Fan Yang,Paul N. Duchesne,Peng Zhang,Jigang Zhou,Litao Sun,Jianqi Li,Xiulian Pan,Xinhe Bao +24 more
TL;DR: Experimental measurements and density functional theory calculations indicate that the formation of the Fe═O intermediate structure is a key step to promoting the conversion of benzene to phenol, paving the way toward highly efficient nonprecious catalysts for low-temperature oxidation reactions in heterogeneous catalysis and electrocatalysis.
Journal ArticleDOI
Reactivity of Surface Species in Heterogeneous Catalysts Probed by In Situ X-ray Absorption Techniques
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References
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TL;DR: Corma et al. as mentioned in this paper used the Dupont Award on new materials (1995), and the Spanish National Award “Leonardo Torres Quevedo” on Technology Research (1996) on technology research (1996), to recognize the performance of zeolites as catalysts for oil refining and petrochemistry.
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Journal ArticleDOI
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