Facile Synthesis of Highly Efficient Amorphous Mn‐MIL‐100 Catalysts: Formation Mechanism and Structure Changes during Application in CO Oxidation. Issue 35 (30th May 2018)

• Record Type: Journal Article
• Authors: Zhang, Xiaodong; Li, Hongxin; Lv, Xutian; Xu, Jingcheng; Wang, Yuxin; He, Chi; Liu, Ning; Yang, Yiqiong; Wang, Yin
• Is Part Of: Chemistry. Volume 24:Issue 35(2018)
• Page Start: 8822
• Page End: 8832
• Publication Date: 2018-05-30
• Subjects: amorphous materials -- heterogeneous catalysis -- manganese -- metal–organic frameworks -- oxidation; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201800773
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: A comprehensive study was carried out on amorphous metal‐organic frameworks Mn‐MIL‐100 as efficient catalysts for CO oxidation. This study focused on explaining the crystalline–amorphous–crystalline transformations during thermolysis of Mn‐MIL‐100 and studying the structure changes during the CO oxidation reaction. A possible formation mechanism of amorphous Mn‐MIL‐100 was proposed. Amorphous Mn‐MIL‐100 obtained by calcination at 250 °C (a‐Mn‐250) showed a smaller specific surface area (4 m 2 g −1 ) but high catalytic activity. Furthermore, the structure of amorphous Mn‐MIL‐100 was labile during the reaction. When a‐Mn‐250 was treated with reaction atmosphere at high temperature (giving used‐a‐Mn‐250‐S), the amorphous catalysts transformed into Mn2 O3 . Meanwhile, the BET surface area (164 m 2 g −1 ) and catalytic performance both sharply increased. In addition, used‐a‐Mn‐250‐S catalyst transformed from Mn2 O3 into Mn3 O4, and this resulted in a slight decrease of catalytic activity in the presence of 1 vol % water vapor in the feed stream. A schematic mechanism of the structure changes during the reaction process was proposed. The success of the synthesis relies on the increase in BET surface area by using CO as retreatment atmosphere, and the enhanced catalytic activity was attributed to the unique structure, a large quantity of surface active oxygen species, oxygen vacancies, and good low‐temperature reduction behavior. Abstract : Amorphous catalysts : A cost‐effective and simple method involving calcination of Mn‐MIL‐100 was developed to prepare amorphous manganese metal–organic framework (MOF; a‐Mn‐MOF) catalysts. The calcination temperature has a remarkable impact on the crystallization and catalytic activity of a‐Mn‐MOF catalysts in CO oxidation. The high catalytic activity for CO oxidation of the catalysts was attributed to good low‐temperature reduction behavior and a high quantity of surface active oxygen species and oxygen vacancies.