Insights into the hydrogen generation and catalytic mechanism on Co-based nanocomposites derived from pyrolysis of organic metal precursor.

Hydrogen generation from boron hydride is important for the development of hydrogen economy. Cobalt (Co) element has been widely used in the hydrolysis of boron hydride. Pyrolysis is a common method for materials synthesis in catalytic fields. Herein, Co-based nanocomposites derived from the pyrolysis of organic metal precursors and used for hydrolysis of boron hydride are summarized and discussed. The different precursors consisting of MOF, supported, metal, and metal phosphide precursors are summarized. The catalytic mechanism consisting of dissociation mechanism based on oxidative addition-reduction elimination, pre-activation mechanism, SN2 mechanism, four-membered ring mechanism, and acid-base mechanism is intensively discussed. Finally, conclusions and outlooks are conveyed from the design of high-efficiency catalysts, the characterization of catalyst structure, the enhancement of catalytic activities, the investigation of the catalytic mechanism, and the catalytic stability of active structure. This review can provide guidance for designing high-efficiency catalysts and boosting development of hydrogen economy.

P-bridged Fe-X-Co coupled sites in hollow carbon spheres for efficient hydrogen generation.

Non-precious metals have shown attractive catalytic prospects in hydrogen production from ammonia borane hydrolysis. However, the sluggish reaction kinetics in the hydrolysis process remains a challenge. Herein, P-bridged Fe-X-Co coupled sites in hollow carbon spheres (Fe-CoP@C) has been synthesized through in situ template solvothermal and subsequent surface-phosphorization. Benefiting from the optimized electronic structure induced by Fe doping to enhance the specific activity of Co sites, bimetallic synergy and hollow structure, the as-prepared Fe-CoP@C exhibits superior performances with a turnover frequency (TOF) of 183.5 min-1, and stability of over 5 cycles for ammonia borane hydrolysis, comparable to noble metal catalysts. Theoretical calculations reveal that the P-bridged Fe-X-Co coupled sites on the Fe-CoP@C catalyst surfaces is beneficial to adsorb reactant molecules and reduce their reaction barrier. This strategy of constructing hollow P-bridged bimetallic coupled sites may open new avenues for non-precious metal catalysis.

CoP/Co heterojunction on porous g-C3N4 nanosheets as a highly efficient catalyst for hydrogen generation.

Designing non-precious catalysts to synergistically achieve a facilitated exposure of abundant active sites is highly desired but remains a significant challenge. Herein, a hetero-structured catalyst CoP-Co supported on porous g-C3N4 nanosheets (CoP-Co/CN-I) was prepared by pyrolysis and P-inducing strategy. The optimal catalyst achieves a turnover frequency (TOF) of 26 min-1 at room temperature and the apparent activation energy (Ea) is 35.5 kJ·mol-1. The catalytic activity is ranked top among the non-precious metal phosphides or the other supports. Meanwhile, the catalytic activity has no significant decrease even after 5 cycles. The CoP/Co interfaces provide richly exposed active sites, optimize hydrogen/water absorption free energy via electronic coupling, and thus improve the catalytic activity. The experimental results reveal that the CoP/Co heterojunction improves the catalytic activity due to the construction of dual-active sites. This research facilitates the innovative construction of non-noble metal catalysts to meet industrial demand for heterogeneous catalysis.

Zirconia-Pillaring in Layered HNb3 O8 and HNbMoO6.

In this work, the pillaring of two layered niobium-based oxides (HNb3 O8 and HNbMoO6 ) with zirconia was investigated in detail. Two novel zirconia-pillared layered metal oxides, zirconia-pillared layered HNb3 O8 and zirconia-pillared layered HNbMoO6 , have been successfully prepared. Both pillared products exhibited a higher thermal stability exceeding 673 K. For the pillaring of layered HNb3 O8 , two different pre-expanding agents, 1-dodecanamine and 1,12-dodecanediamine, were alternatively used, and two kinds of zirconium-pillaring solutions containing zirconium(IV) polyoxocations obtained through two different ways were employed. The 1,12-dodecanediamine-pre-expanded layered intermediate was applicable and 1-dodecanamine-pre-expanded one was not applicable to the intercalation of zirconium(IV) polyoxocations in interlayer regions of the layered niobium-based oxides. More interestingly, the zirconium-pillaring solutions prepared by using an appropriate amount of diethylene glycol as stabilizing agent was advantage for constructing the ordered zirconia-pillared product, whereas the zirconium-pillaring solutions obtained in the case of absence of diethylene glycol seemed not to conduct well an ions-exchange reaction with the alkylamine-pre-expanded layered intermediates. The order degree of zirconia-pillared layered transition metal oxides was closely related to the host sheets. The zirconia-pillared layered HNb3 O8 contained more defects, while the zirconia-pillared layered HNbMoO6 had fewer defects.