Ruthenium deposited on MCM-41 as efficient catalyst for hydrolytic dehydrogenation of ammonia borane and methylamine borane

Ultrafine Ru nanoparticles are successfully deposited on MCM-41 by using a simple liquid impregnationreduction method, and further investigated for catalytic hydrolysis of ammonia borane and methylamine borane. Among all the catalysts tested, 1.12 wt% Ru/MCM-41 exhibits the highest catalytic activity, with turnover frequency value of 288 min^-1.     

Nanostructured Ni2P as a Robust Catalyst for the Hydrolytic Dehydrogenation of Ammonia–Borane

Ammonia–borane (AB) is a promising chemical hydrogen‐storage material. However, the development of real‐time, efficient, controllable, and safe methods for hydrogen release under mild conditions is a challenge in the large‐scale use of hydrogen as a long‐term solution for future energy security. A new class of low‐cost catalytic system is presented that uses nanostructured Ni₂P as catalyst, which exhibits excellent catalytic activity and high sustainability toward hydrolysis of ammonia–borane with the initial turnover frequency of 40.4 mol_(H2) mol_(Ni2P)^?1 min^?1 under air atmosphere and at ambient temperature. This value is higher than those reported for noble‐metal‐free catalysts, and the obtained Arrhenius activation energy (E_a=44.6 kJ mol^?1) for the hydrolysis reaction is comparable to Ru‐based bimetallic catalysts. A clearly mechanistic analysis of the hydrolytic reaction of AB based on experimental results and a density functional theory calculation is presented.     

Facile Synthesis of Platinum–Cerium(IV) Oxide Hybrids Arched on Reduced Graphene Oxide Catalyst in Reverse Micelles with High Activity and Durability for Hydrolysis of Ammonia Borane

Highly dispersed Pt‐CeO₂ hybrids arched on reduced graphene oxide (Pt‐CeO₂/rGO) were facilely synthesized by a combination of the reverse micelle technique and a redox reaction without any additional reductant or surfactant. Under a N₂ atmosphere, the redox reaction between Ce³⁺ and Pt²⁺ occurs automatically in alkaline solution, which results in the formation of Pt‐CeO₂/rGO nanocomposites (NCs). The as‐synthesized Pt‐CeO₂/rGO NCs exhibit superior catalytic performance relative to that shown by the free Pt nanoparticles, Pt/rGO, Pt‐CeO₂ hybrid, and the physical mixture of Pt‐CeO₂ and rGO; furthermore, the nanocomposites show significantly better activity than the commercial Pt/C catalyst toward the hydrolysis of ammonia borane (NH₃BH₃) at room temperature. Moreover, the Pt‐CeO₂/rGO NCs have remarkable stability, and 92 % of their initial catalytic activity is preserved even after 10 runs. The excellent activity of the Pt‐CeO₂/rGO NCs can be attributed not only to the synergistic structure but also to the electronic effects of the Pt‐CeO₂/rGO NCs among Pt, CeO₂, and rGO.     

Synthesis of a multinanoparticle-embedded core/mesoporous silica shell structure as a durable heterogeneous catalyst

A multi-nanoparticle-embedded amorphous aluminum/magnesium oxides (AAMO) core/mesoporous silica (mSiO(2)) shell structure has been successfully synthesized by calcining the presynthesized catalyst precursor-containing layered double hydroxide (LDH) core/mesoporous silica shell composite. The well-dispersed catalytic nanoparticles were fixed at the interface between AAMO core and mesoporous SiO(2) shell, i.e., at the inner pore mouths of the mesoporous SiO(2) shell, which could effectively prevent nanoparticles from growth and/or aggregation with each other and in the meantime allow efficient access of reactants to the catalytic NPs. The final core/shell composite was found to be an efficient and highly recyclable heterogeneous catalyst.     

MOF热解法制备Ni/C核壳材料及其催化苯乙炔加氢性能研究

通过水热合成法以硝酸镍和2,5-二羟基对苯二甲酸为原料成功合成Ni-MOF-74.以此为前体,在Ar气氛下热解制备了一系列介孔结构丰富、尺寸均匀的纳米Ni/C核壳催化剂.Ar气氛下通过延长热解时间（400℃,6 h）或提高热解温度（≥500℃）可以得到完全热解产物,粒子尺寸随热解温度的升高而增大.H₂-TPR结果表明随着热解温度的提高,镍与表面碳层之间的相互作用增强,材料还原性能降低.TEM和Ar离子溅射XPS给出了Ni/C纳米材料为核壳结构的直接证据.由于表面碳层的化学惰性,隔离作用和电子调控作用,使得部分镍物种能够以单质镍（Ni⁰）形式稳定存在.其次,表面碳壳的存在减弱了颗粒间的相互作用,有利于催化剂在反应体系中均匀分散.以苯乙炔选择加氢反应为探针,在高压釜式反应器中测试Ni/C的催化性能.研究发现Ni/C在苯乙炔加氢反应中表现出了非常优异的催化活性（0.833 mmol•min^-1•g_cat.^-1）和稳定性.其与几种催化剂的加氢活性由弱到强的顺序为：Ni < NiSi_x < 负载型Ni₂Si < Ni/C < Pd < Pt.     

核壳结构Cu@CoW的合成和对硼氨配合物水解的催化性能

分别以硼氨配合物和硼氢化钠为还原剂合成了核壳结构的Cu@CoW三元合金催化剂和非核壳结构的CuCoW三元合金催化剂,25℃下,Cu0.4@Co0.5W0.1三元合金催化剂对于硼氨配合物水解反应的TOF(转换频率)值达到0.369 0 molH2·molcat-1·s-1,明显高于非核壳结构的Cu0.4Co0.5W0.1催化剂,接近Pt、Pd等贵金属的催化活性,反应的活化能为49 kJ·mol-1。与非核壳结构的CuCoW合金相比,核壳结构的Cu@CoW三元合金催化剂的催化性能及稳定性均有明显提高。     

核壳结构Cu@CoW的合成和对硼氨配合物水解的催化性能

分别以硼氨配合物和硼氢化钠为还原剂合成了核壳结构的Cu@CoW三元合金催化剂和非核壳结构的CuCoW三元合金催化剂,25℃下,Cu_0.4@Co_0.5W_0.1三元合金催化剂对于硼氨配合物水解反应的TOF（转换频率）值达到0.3690mol_H2·mol_cat^-1·s^-1,明显高于非核壳结构的Cu_0.4Co_0.5W_0.1催化剂,接近Pt、Pd等贵金属的催化活性,反应的活化能为49kJ·mol^-1。与非核壳结构的CuCoW合金相比,核壳结构的Cu@CoW三元合金催化剂的催化性能及稳定性均有明显提高。     

Synthetic scope of alcohol transfer dehydrogenation catalyzed by Cu/Al2O3: a new metallic catalyst with unusual selectivity

A method for the anaerobic oxidation of a wide series of alcohols including cyclohexanols and steroidal alcohols, has been set up. It relies on a transfer dehydrogenation reaction from the substrate alcohol to styrene catalyzed by a heterogeneous, reusable copper catalyst under very mild liquid-phase experimental conditions (90 degrees C, N(2)) and shows unusual selectivity. Thus, the method is selective for the oxidation of secondary and allylic alcohols even in the presence of unprotected primary and benzylic alcohols. Electronic effects and the choice of the hydrogen acceptor account for the selectivity observed.     

The supramolecular structures and reactivities of some complexes of chiral crown ethers with borane ammonia

Whereas 1 1 crystalline complexes have been isolated between borane ammonia and methyl 4,6-O-benzylidene-2,3-dideoxy--d-galactopyranosido [2,3-b]-1,4,7,10,13,16-hexaoxacyclo-octadecane (1), methyl 4,6-O-benzylidene-2,3-dideoxy--d-mannopyranosido [2,3-b] (methyl 4,6-O-benzylidene-2,3-dideoxy--d-mannopyranosido [2,3-k]-1,4,7,10,13,16-hexaoxacyclo-octadecane (3), and (1R,2R,7R,24R)-3,5,8,11,14,17,20,23,26,28-decaoxatricyclo-[21.4.0.0^2,7]octacosane (4), the hosts, methyl, 4,6-O-benzylidene-2,3-dideoxy--d-mannopyranosido[2,3-b] 1,4,7,10,13,16-hexaoxacyclo-octadecane (2) and 1,4 1,4 3,6 3,6-tetra-anhydro-2,2 5,5-bis-O-oxydiethylenedi-d-mannitol (5) have yielded 2 1 (guest:host) crystalline complexes with borane ammonia as guest. X-ray analyses of the supramolecular structures of BH₃NH₃ ·1, (BH₃NH₃)₂ ·2, BH₃NH₃ ·3, BH₃NH₃ ·4, and (BH₃NH₃)₂ ·5 have been carried out and BH₃NH₃ ·1, BH₃NH₃ ·2, and (BH₃NH₃)₂ ·5 have been shown to reduce acetophenone with enantiomeric excesses of 5, 13, and 10% respectively. Supplementary Data relating to this article (atomic coordinates of the hydrogen atoms and thermal parameters) are deposited with the British Library as Supplementary Publication No. SUP 82017 (74 pages).Dedicated to Professor H. M. Powell.     

Ni2P Nanoalloy as an Air-Stable and Versatile Hydrogenation Catalyst in Water: P-Alloying Strategy for Designing Smart Catalysts

Non-noble metal-based hydrogenation catalysts have limited practical applications because they exhibit low activity, require harsh reaction conditions, and are unstable in air. To overcome these limitations, herein we propose the alloying of non-noble metal nanoparticles with phosphorus as a promising strategy for developing smart catalysts that exhibit both excellent activity and air stability. We synthesized a novel nickel phosphide nanoalloy (nano-Ni₂P) with coordinatively unsaturated Ni active sites. Unlike conventional air-unstable non-noble metal catalysts, nano-Ni₂P retained its metallic nature in air, and exhibited a high activity for the hydrogenation of various substrates with polar functional groups, such as aldehydes, ketones, nitriles, and nitroarenes to the desired products in excellent yields in water. Furthermore, the used nano-Ni₂P catalyst was easy to handle in air and could be reused without pretreatment, providing a simple and clean catalyst system for general hydrogenation reactions.     

Towards the design of novel boron‐ and nitrogen‐substituted ammonia‐borane and bifunctional arene ruthenium catalysts for hydrogen storage

Electronic‐structure density functional theory calculations have been performed to construct the potential energy surface for H₂ release from ammonia‐borane, with a novel bifunctional cationic ruthenium catalyst based on the sterically bulky β‐diketiminato ligand (Schreiber et al., ACS Catal. 2012, 2, 2505). The focus is on identifying both a suitable substitution pattern for ammonia‐borane optimized for chemical hydrogen storage and allowing for low‐energy dehydrogenation. The interaction of ammonia‐borane, and related substituted ammonia‐boranes, with a bifunctional η⁶‐arene ruthenium catalyst and associated variants is investigated for dehydrogenation. Interestingly, in a number of cases, hydride‐proton transfer from the substituted ammonia‐borane to the catalyst undergoes a barrier‐less process in the gas phase, with rapid formation of hydrogenated catalyst in the gas phase. Amongst the catalysts considered, N,N‐difluoro ammonia‐borane and N‐phenyl ammonia‐borane systems resulted in negative activation energy barriers. However, these types of ammonia‐boranes are inherently thermodynamically unstable and undergo barrierless decay in the gas phase. Apart from N,N‐difluoro ammonia‐borane, the interaction between different types of catalyst and ammonia borane was modeled in the solvent phase, revealing free‐energy barriers slightly higher than those in the gas phase. Amongst the various potential candidate Ru‐complexes screened, few are found to differ in terms of efficiency for the dehydrogenation (rate‐limiting) step. To model dehydrogenation more accurately, a selection of explicit protic solvent molecules was considered, with the goal of lowering energy barriers for H‐H recombination. It was found that primary (1°), 2°, and 3° alcohols are the most suitable to enhance reaction rate. © 2014 Wiley Periodicals, Inc.