金属-氮-氢体系储氢材料

氢能作为未来理想的清洁能源之一,已经成为全球研究的重要领域,而在氢能的应用中最关键的问题是氢气的存储。近年来,人们的研究集中在固态储氢材料上,许多新型储氢材料不断出现,其中由轻元素组成的金属-氮-氢体系拥有储氢容量高、可逆性好等优点,被认为是最有前景的储氢材料之一。目前金属-氮-氢体系已经发展出许多体系,而研究最多的是Li-N-H和Li-Mg-N-H两种体系。本文重点综述了两者作为可逆储氢材料的研究现状,主要从制备方法、储氢性能、反应机理、理论计算和存在的问题等方面进行了讨论,同时指出了金属-氮-氢储氢体系的发展趋势。

Promoting role of Ru species on Ir-Fe/BN catalyst in 1,2-diols hydrogenolysis to secondary alcohols

Noble metal-based-bimetallic catalysts have been highly investigated and applied in wide applications including biomass transformation via regioselective C−O hydrogenolysis while further modification especially with noble metal is highly promising yet still under investigation.Herein,Ru was found as an effective modifier among the screened noble metals(Ru,Pt,Rh,Pd,Au,and Ag)for Ir-Fe/BN(Ir=5 wt%,Fe/Ir=0.25)catalyst in terminal C−O hydrogenolysis of 1,2-butanediol(1,2-BuD)to 2-butanol(2-BuOH).Only trace amount of Ru(up to 0.5 wt%)was effective in terms of high 2-BuOH selectivity(>60%)and activity(about twice).Larger amount of Ru species(3 wt%)highly enhanced the activity but gave low selectivity to 2-BuOH with by-products of terminal C−C bond scission.Optimized catalyst(Ru(0.5)-Ir-Fe/BN)was reusable at least 4 times and gave moderate 2-BuOH yield(47%)in hydrogenolysis of 1,2-BuD.The promoting effect of Ru addition(0.5 wt%)to Ir-Fe/BN on hydrogenolysis of various alcohols was also confirmed.Combining catalytic tests with various characterizations,the promotion mechanism of Ru species in trimetallic catalysts was clarified.The Ru species in Ru(0.5)-Ir-Fe/BN form alloy with Ir and are enriched at the interface with BN surface,and direct interaction between Ru and Fe was not necessary in Ru-Ir-Fe alloy.The interface of Ir and Fe on the surface of Ir-Fe alloy may work as active sites for 1,2-diols to secondary alcohols via direct C−O hydrogenolysis,in which Ru-modified Ir activates H_(2) to form hydride-like species.The activity of Ru species in C−C bond cleavage was highly suppressed due to the direct interaction with Ir species and less exposed to substrate.Larger loading amount of Ru species(3 wt%)led to the formation Ru-rich trimetallic alloy,which further works as active sites for C−C bond scission.

Doping-induced metal–N active sites and bandgap engineering in graphitic carbon nitride for enhancing photocatalytic H_(2 )evolution performance

Durable and inexpensive graphitic carbon nitride(g-C_(3)N_(4))demonstrates great potential for achieving efficient photocatalytic hydrogen evolution reduction(HER).To further improve its activity,g-C_(3)N_(4)was subjected to atomic-level structural engineering by doping with transition metals(M=Fe,Co,or Ni),which simultaneously induced the formation of metal-N active sites in the g-C_(3)N_(4)framework and modulated the bandgap of g-C_(3)N_(4).Experiments and density functional theory calculations further verified that the as-formed metal-N bonds in M-doped g-C_(3)N_(4)acted as an"electron transfer bridge",where the migration of photo-generated electrons along the bridge enhanced the efficiency of separation of the photogenerated charges,and the optimized bandgap of g-C_(3)N_(4)afforded stronger reduction ability and wider light absorption.As a result,doping with either Fe,Co,or Ni had a positive effect on the HER activity,where Co-doped g-C_(3)N_(4)exhibited the highest performance.The findings illustrate that this atomic-level structural engineering could efficiently improve the HER activity and inspire the design of powerful photocatalysts.

Oxygen and nitrogen-doped metal-free carbon catalysts for hydrochlorination of acetylene

Activated carbon was tested as metal-free catalyst for hydrochlorination of acetylene in order to circumvent the problem of environment pollution caused by mercury and high cost by noble metals. Oxygen-doped and nitrogen-doped activated carbons were prepared and characterized by XPS, TPD and N2 physisorption methods. The influences of the surface functional groups on the catalytic performance were discussed base on these results. Among all the samples tested, a nitrogen-doped sample, AC-n-US00, exhibited the best performance, the acety- lene conversion being 92% and vinyl chloride selectivity above 99% at 240 ~C and C2H2 hourly space velocity 30 h- 1. Moreover, the AC-n-US00 catalyst exhibited a stable performance during a 200 h test with a conversion of acetylene higher than 76% at 210 ~C at a C2H2 hourly space velocity 50 h 1. In contrary, oxygen-doped catalyst had lower catalytic activities. A linear relationship between the amount of pyrrolic-N and quaternary-N species and the catalytic activity was observed, indicating that these nitrogen-doped species might be the active sites and the key in tuning the catalytic performance. It is also found that the introduction of nitrogen species into the sample could significantly increase the adsorption amount of acetylene. The deactivation of nitrogen- doped activated carbon might be caused by the decrease of the accessibility to or the total amount of active sites.

设计新型高容量储氢材料

作者总结了近年来金属胺基化合物-氢化物体系、氨硼烷及其衍生物储氢材料的研究进展。分别重点介绍了这些材料体系的储氢性能、反应机理及反应热力学和动力学性质,并在此基础上强调了储氢材料的设计理念,即改变材料化学组成调变其热力学性能,催化修饰以提升材料脱氢动力学性能。

MXenes for electrocatalysis applications:Modification and hybridization

Two-dimensional carbides,nitrides,and carbonitrides(MXenes)play important roles in promoting the development of sustainable energy because they have abundant reactive sites on their surfaces.An increasing number of MXenes with diverse elements and composites have been predicted and synthesized for electrocatalysis applications since the first report of a Ti-Mo-based MXene for the hydrogen evolution reaction(HER).Herein,we summarize the progress of MXene-based electrocatalysts for the HER,the oxygen evolution reaction,and the oxygen reduction reaction,including regulated pristine MXenes and modified hybrid MXenes,from both theoretical and experimental perspectives.A brief overview on MXene synthesis is presented first,accompanied by a discussion on the relationship between electrocatalytic properties and M,X,T,vacancies,and morphologies.After reviewing strategies in terms of atom substitution,functional modification,defect engineering,and morphology control,we emphasize the construction of heterojunctions between MXenes and other nanostructures,such as metal nanoparticles,oxides,hydroxides,sulfides,and phosphides.We finally discuss prospects for the future development of MXene-based electrocatalysts.

Synergistic trifunctional electrocatalysis of pyridinic nitrogen and single transition-metal atoms anchored on pyrazine-modified graphdiyne

Multifunctional catalysts that integrate high efficiency hydrogen evolution reaction(HER), oxygen evolution reaction(OER) and oxygen reduction reaction(ORR) catalytic activity in a single material are attractive for unitized regenerative fuel cells and overall water splitting technologies. As the best-known HER and ORR electrocatalysts, Pt and its alloys have only moderate OER activity. Ruthenium and iridium oxides exhibit the highest OER activities but not as active as Pt for HER and ORR. Here, we proposed a general principle for achieving trifunctional electrocatalysis for three reactions in a single material. Using the newly-synthesized pyrazine-modified graphdiyne(PR-GDY) as an example, we demonstrated that the synergistic effect of the pyridinic nitrogen and anchored transition-metal(TM) single atoms renders highly-efficient HER/OER/ORR trifunctional electrocatalytic activity. For the Ni-doped PR-GDY, the overpotentials for HER, OER and ORR can be respectively as low as -0.05, 0.29 and 0.38 V, which are comparable or even superior to the best-known single-functional and bi-functional precious electrocatalysts.These computational results offer not only a promising trifunctional electrocatalyst but also a strategy for the design of multifunctional electrocatalysts.

Search for New Opportunities Modification Raschig, Schiff, Andrusov, Hofmann, Colbe and Delepine Reactions

We explored new approaches to replace the nitrogen atoms of arsenic, antimony, bismuth, and discovered a new paths to modify Raschig, Schiff, Andrusov, Hofmann, Colbe, Delepine reactions with arsine, stibine and bismuthine in organometallic chemistry. We have proposed a new mechanism for possible reactions.