Shuang Xue,Tian Lan,Guofeng Zhao,Qiang Nie,Chao Meng,Xinyi Xu,Yong Lu
Water gas shift reaction (WGSR) is urgently calling for an alternative to the Fe-Cr catalyst. Ni-based catalysts are taken into consideration but remain challenging because of their high methanation activity. Here we report a highly active and selective NiC x /Ni-foam catalyst with clearly detectable Ni 3 C phase, facilely obtainable by endogenous growth of NiC 2 O 4 onto a Ni-foam and subsequent H 2 -reduction treatment. The preferred catalyst with high content of NiC x is capable of converting 63.6% or 94.3% CO at 350 °C or 400 °C with trace or < 0.8% CH 4 formation for a feed gas with H 2 O/CO/Ar molar ratio of 4/1/9, and is stable for at least 110 h. It is experimentally and theoretically unveiled that the Ni 3 C facilitates the dissociative activation of H 2 O and favors CO to form carboxylate species (favorable for CO 2 formation) rather than active Ni(CO) n intermediates for CH 4 formation thereby enabling the catalyst with high WGSR activity and selectivity.
Liu Gongquan,Zhao Yi-Lei,He Fangyuan,Zhang Peng,Ouyang Xingyu,Tang Hongzhi,Xu Ping
Biodegradation of aromatic and heterocyclic compounds requires an oxidative ring cleavage enzymatic step. Extensive biochemical research has yielded mechanistic insights about catabolism of aromatic substrates; yet much less is known about the reaction mechanisms underlying the cleavage of heterocyclic compounds such as pyridine-ring-containing ones like 2,5-hydroxy-pyridine (DHP). 2,5-Dihydroxypyridine dioxygenase (NicX) from Pseudomonas putida KT2440 uses a mononuclear nonheme Fe(II) to catalyze the oxidative pyridine ring cleavage reaction by transforming DHP into N -formylmaleamic acid (NFM). Herein, we report a crystal structure for the resting form of NicX, as well as a complex structure wherein DHP and NFM are trapped in different subunits. The resting state structure displays an octahedral coordination for Fe(II) with two histidine residues (His 265 and His 318 ), a serine residue (Ser 302 ), a carboxylate ligand (Asp 320 ), and two water molecules. DHP does not bind as a ligand to Fe(II), yet its interactions with Leu 104 and His 105 function to guide and stabilize the substrate to the appropriate position to initiate the reaction. Additionally, combined structural and computational analyses lend support to an apical dioxygen catalytic mechanism. Our study thus deepens understanding of non-heme Fe(II) dioxygenases.
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