title: Solid-Solid heterogeneous catalysis: the role of potassium in promoting the dehydrogenation of the Mg(NH(2))(2)/2 LiH composite.
abstract: Considerable efforts have been devoted to the catalytic modification of hydrogen storage materials. The K-modified Mg(NH2 )2 /2 LiH composite is a typical model for such studies. In this work, we analyze the origin of the kinetic barrier in the first step of the dehydrogenation and investigate how K catalyzes this heterogeneous solid-state reaction. Our results indicate that the interface reaction of Mg(NH2 )2 and LiH is the main source of the kinetic barrier at the early stage of the dehydrogenation for the intensively ball-milled Mg(NH2 )2 /2 LiH sample. K can effectively activate Mg(NH2 )2 as well as promote LiH to participate in the dehydrogenation. Three K species of KH, K2 Mg(NH2 )4 , and Li3 K(NH2 )4 likely transform circularly in the dehydrogenation (KH↔K2 Mg(NH2 )4 ↔KLi3 (NH2 )4 ), which creates a more energy-favorable pathway and thus leads to the overall kinetic enhancement. This catalytic role of K in the amide/hydride system is different from the conventional catalysis of transition metals in the alanate system.
authors.affiliation: State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023 (PR China), Fax: (+86) 411-84685940; Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027 (PR China).
authors.forename: Jianhui
authors.initials: J
authors.lastname: Wang
authors.forename: Ping
authors.initials: P
authors.lastname: Chen
authors.forename: Hongge
authors.initials: H
authors.lastname: Pan
authors.forename: Zhitao
authors.initials: Z
authors.lastname: Xiong
authors.forename: Mingxia
authors.initials: M
authors.lastname: Gao
authors.forename: Guotao
authors.initials: G
authors.lastname: Wu
authors.forename: Chu
authors.initials: C
authors.lastname: Liang
authors.forename: Cao
authors.initials: C
authors.lastname: Li
authors.forename: Bo
authors.initials: B
authors.lastname: Li
authors.forename: Jieru
authors.initials: J
authors.lastname: Wang
mesh_terms: D002384:Catalysis; D006859:Hydrogen / Q000737:chemistry*; D007700:Kinetics; D018020:Lithium Compounds / Q000737:chemistry*; D017616:Magnesium Compounds / Q000737:chemistry*; D008956:Models, Chemical; D017672:Nitrogen Compounds / Q000737:chemistry*; D011188:Potassium / Q000737:chemistry*
chemical_list: D018020:Lithium Compounds; D017616:Magnesium Compounds; D017672:Nitrogen Compounds; D006859:Hydrogen; D011188:Potassium
keywords: dehydrogenation; heterogeneous catalysis; hydrides; magnesium; potassium