In situ electrochemical dehydrogenation of ultrathin Co(OH)2 nanosheets for enhanced hydrogen evolution

Transition metal hydroxides/oxyhydroxides have recently emerged as highly active electrocatalysts for oxygen evolution reaction in alkaline water electrolysis, while have not yet been widely investigated for hydrogen evolution electrocatalysts owing to their unfavorable H*-adsorption, making it difficult to construct an overall-water-splitting cell for hydrogen production. In this work, we proposed a straightforward and effective approach to develop an efficient in-plane heterostructured CoOOH/Co(OH)₂ catalyst via in-situ electrochemical dehydrogenation method, in which the dehydrogenated –CoOOH and Co(OH)₂ at the surface synergistically boost the hydrogen evolution reaction (HER) kinetics in base as confirmed by high-resolution transmission electron microscope, synchrotron X-ray absorption spectroscopy, and electron energy loss spectroscopy. Due to the in-situ dehydrogenation of ultrathin Co(OH)₂ nanosheets, the catalytic activity of the CoOOH/Co(OH)₂ heterostructures is progressively improved, which exhibit outstanding hydrogen-evolving activity in base requiring a low overpotential of 132 mV to afford 10 mA/cm² with very fast reaction kinetics after 60 h dehydrogenation. The gradually improved catalytic performance for the CoOOH/Co(OH)₂ is probably due to the enhanced H*-adsorption induced by the synergistic effect of heterostructures and better conductivity of CoOOH relative to electrically insulating Co(OH)₂. This work will open the opportunity for a new family of transition metal hydroxides/oxyhydroxides as active HER catalysts, and also highlight the importance of using in situ techniques to construct precious metal-free efficient catalysts for alkaline hydrogen evolution.     

Intense electrochemical sers signal following hydrogen evolution

Stepping the potential of the electrode to the region of rapid hydrogen evolution prior to performing an oxidation—reduction cycle (ORC) can result in the development of surface-enhanced Raman scattering that is more intense by almost an order of magnitude than an electrode subjected to ORC alone. It is found for the case of chloride adsorbed on silver that the spectral characteristics of the metal-surface—chloride stretching mode at ≈240 cm^?1 are essentially the same as that produced without prior hydrogen evolution. The additional enhancement appears to be due to morphological changes caused by the presence of hydrogen bubbles during the reduction of the silver-chloride phase film.     

电化学方法构筑直结型卟啉高分子

利用电化学方法成功地合成了不含其它连接基团的卟啉高分子,循环伏安图谱中发现该高分子在电极上的沉积为紧密型沉积,所得产物的紫外-可见吸收光谱表明相邻的卟啉环在该高分子链中均成平面直角结构,FT-IR图谱表明卟啉环之间是通过C-C键在meso位上相连,质谱图证明该高分子的链长可以达到13个卟啉环以上。     

Highly sustainable catalytic dehydrogenation of alcohols with evolution of hydrogen gas

The catalytic dehydrogenation of alcohols into aldehydes and ketones in the absence of H-acceptors was studied with several transition metal catalysts in order to develop a large-scale procedure. Applying Ru(OCOCF₃)₂(CO)(PPh₃)₂, the so called Robinson catalyst, several secondary alcohols could be dehydrogenated with high selectivity into the corresponding ketones in relatively short reaction times. Highly effective atom utilization could be realized avoiding solvents and giving hydrogen gas as the sole by-product. However, in contrast to Robinson's work the catalytic dehydrogenation of primary alcohols appeared to be problematic due to decarbonylation with concomitant catalyst deactivation and aldol condensation under the strong acid or basic conditions applied.     

Synthesis of isoxazoles en route to semi-aromatized polyketides: dehydrogenation of benzonitrile oxide-para-quinone acetal cycloadducts

A variety of highly functionalized polycyclic isoxazoles are prepared by a two-step protocol: (1) 1,3-dipolar cycloaddition of o,o'-disubstituted benzonitrile oxides to para-quinone mono-acetals, then (2) dehydrogenation. The cycloaddition proceeds in a regioselective manner, favouring the formation of the 4-acyl cycloadducts, which are suitable intermediates for the synthesis of semi-aromatized polycyclic targets derived from polyketide type-II biosynthesis.     

A kinetic model explaining the enhanced rates of hydrogen evolution on anodically polarized magnesium in aqueous environments

A model to explain the increasing rates associated with hydrogen evolution (HE) originating at the dissolving regions of Mg under anodic polarization is presented. The actively dissolving anodes have been shown experimentally to be the primary source of anomalous evolution of hydrogen. In this model, standard electrochemical laws are used to account for this phenomenon. The fractional coverage of active Mg sites is introduced to localize the cathodic contribution of HE during anodic polarization. A kinetic equation is derived showing that the rate of HE will increase with increasing potential if the charge transfer coefficient associated with the Mg oxidation reaction is greater than the charge transfer coefficient for the HE reaction. Experimental data obtained on high purity Mg galvanodynamically polarized at potentials above and below its E_corr in 0.1 M NaCl solution are presented to validate the model.     

Catalytic properties of Sn-Ce-Rh-O in dehydrogenation and oxidative dehydrogenation reactions

A new, single-phase Sn_0.925Ce_0.07Rh_0.005O₂ gas sensitive material has up to now been used as a catalyst for the bimolecular condensation of aldehydes and C-alkylation of hydroxyarenes with alcohols. It was subjected to the isopropanol test, the oxidative dehydrogenation of cyclohexane test, and the cyclohexene + H₂ test. A general physico-chemical analysis was done, and it included XRD, SEM, mercury porosimetry, TPD NH₃, and IR (pyridine) spectroscopy. The tests results are compliant with the basic character of the catalyst; however, it reveals significant total acidity (0.274 mmol NH₃/g) and the presence of Lewis strong acid centers (0.126 mmol Py/g). The presence of these centers in the dehydrogenating catalysts cause the ability to catalyze both the bimolecular condensation of aldehydes and C-alkylation of hydroxyarenes with alcohols. Published in Russian in Kinetika i Kataliz, 2007, Vol. 48, No. 1, pp. 74–80. The article was submitted by the authors in English.     

Fabrication of an electrode-viologen-hydrogenase heterogeneous system and the electrochemical hydrogen evolution

An indium tinoxide (ITO) electrode was chemically modified by one layer of viologen (VIO) deri vative, which possessed a persistent and reproducible electrochemical response. A monolayer of a thermal stable hydrogenase from Thiocapsa roseopersic ina was stabilized on a synthesized poly-l-lysine subphase surface and transferred on to the electrode for fabrication of an ITO-VIO-hydrogenase heterogeneous system. Electrochemical properties of both the ITO-VIO monolayer and the heterogeneous ITO-VIO-hydrogenase system have been investigated. Hydrogen evolution could be measured by potentiostating the VIO-hydrogenase-covered ITO electrode to “electroplate” [(VIO⁺)_n]_surf and a large increase in hydrogen evolution was observed when using an electrolytesolution containing sodium dithionite. We discuss the possible electron transfer process.     

Accelerating photocatalytic hydrogen evolution and pollutant degradation by coupling organic co-catalysts with TiO2

Accelerating the separation efficiency of photoexcited electron-hole pairs with the help of highly active co-catalysts has proven to be a promising approach for improving photocatalytic activity. Thus far, the most developed co-catalysts for semiconductor-based photocatalysis are inorganic materials; the employment of a specific organic molecule as a co-catalyst for photocatalytic hydrogen evolution and pollutant photodegradation is rare and still remains a challenging task. Herein, we report on the use of an organic molecule, oxamide (OA), as a novel co-catalyst to enhance electron-hole separation, photocatalytic H₂ evolution, and dye degradation over TiO₂ nanosheets. OA-modified TiO₂ samples were prepared by a wet chemical route and demonstrated improved light absorption in the visible-light region and more efficient charge transport. The photocatalytic performance of H₂ evolution from water splitting and rhodamine B (RhB) degradation for an optimal OA-modified TiO₂ photocatalyst reached 2.37 mmol g^-1 h^-1 and 1.43 × 10^?2 min^?1, respectively, which were 2.4 and 3.8 times higher than those of pristine TiO₂, respectively. A possible mechanism is proposed, in which the specific π-conjugated structure of OA is suggested to play a key role in the enhancement of the charge transfer and catalytic capability of TiO₂. This work may provide advanced insight into the development of a variety of metal-free organic molecules as functional co-catalysts for improved solar-to-fuel conversion and environmental remediation.     

Aerobic oxidative dehydrogenation of benzyl alcohols to benzaldehydes by using a cyclometalated ruthenium catalyst

The ruthenium(III) complex bearing phenylpyridine as a cyclometalated ligand serves as an efficient catalyst for the aerobic oxidative dehydrogenation of benzyl alcohols to the corresponding benzaldehydes under mild conditions and for the one-pot synthesis of benzonitriles from benzyl alcohols with ammonia.     

Single-atom Pt promoted Mo2C for electrochemical hydrogen evolution reaction

Hydrogen generation from electrochemical water splitting powered by renewable energy is important to the sustainable society,but the prohibitive cost of current...     

Aerobic oxidative dehydrogenation of N-heterocycles catalyzed by cobalt porphyrin

An efficient catalytic procedure has been developed for the aerobic oxidative dehydrogenation of N-heterocycles by cobalt porphyrin in the absence of any additives. The catalytic system could tolerate various 1,2,3,4-tetrahydroquinoline derivatives and some other N-heterocycles. The corresponding N-heteroaromatics could be obtained in 59–86% yields. The mechanism investigation suggested that the aerobic oxidative dehydrogenation might proceed with imine intermediate through radical paths.     

Aerobic oxidative dehydrogenation of benzylamines catalyzed by a cyclometalated ruthenium complex

The ruthenium(III) complex bearing phenylpyridine as a cyclometalated ligand serves as an efficient catalyst for the aerobic oxidative dehydrogenation of benzylamines to the corresponding benzonitriles under mild conditions.     

Tungsten-containing catalysts for oxidative dehydrogenation of hydrocarbons

Methods for introducing tungsten into the precursors of oxide catalysts for oxidative dehydrogenation (OD) were developed. Tungsten-containing samples of oxide catalysts of various compositions were synthesized and their catalytic properties in OD of ethane were studied. The introduction of tungsten into the catalysts increased the yield of ethylene in all cases. In the series of tungsten-containing catalysts, the ethylene yield increased in the following order of the catalysis: Mg-Al-V-Mo-W-O < Mg-Al-Ni-V-Mo-W-O < Mg-Al-Fe-V-Mo-W < Mg-Al-Cr-V-Mo-W-O.     

Spectral studies of catalysts of oxidative dehydrogenation of dimethyl ether to dimethoxyethane

Spectral methods (diffuse reflectance infrared Fourier transform spectroscopy, EPR) are used to study the adsorption of dimethyl ether and oxygen on a catalyst of oxidative dehydrogenation of dimethyl ether to dimethoxyethane. The formation of O ₂ ^? superoxide paramagnetic species is revealed. A mechanism of the formation of dimethoxyethane is proposed.     

Click reaction in the synthesis of novel thiophosphorylated ligands for electrochemical hydrogen evolution

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Boron nitride for enhanced oxidative dehydrogenation of ethylbenzene

It is demonstrated experimentally and confirmed theoretically that highly defective boron nitride showed outstanding performance for oxidative dehydrogenation o...     

Studies on the oxidative dehydrogenation of propane to propene over Co-V-O catalysts

A series of Co-V-O catalysts were prepared and their catalytic performances for the oxidative dehydrogenation of propane to propene were investigated. It was found that the p-type catalysts showed higher catalytic behavior than the n-type catalyst.     

Formation of hydrogen in oxidative coupling of methane over BaCO3 and MgO catalysts

Hydrogen formed in oxidative coupling of methane （OCM） over BaCO3 and MgO catalysts was measured since the data of H2 selectivity were missing almost in all articles published heretofore. It was found that H2 selectivity achieved about 18%, when C2 hydrocarbon＇s selectivity was maintained at 48%-45% over BaCO3 catalyst at the feed molar ratio of CH4/O2 = 4 in temperature range of 780 °C-820 °C. Under similar conditions, H2 selectivity was about 14%-16% over MgO catalyst, with C2 selectivity maintained at 41%-42%. Possible routes for hydrogen formation in OCM reaction were discussed. Effect of addition of alkali metallic ions was also investigated.