A molecular MoS₂ edge site mimic for catalytic hydrogen generation

Inorganic solids are an important class of catalysts that often derive their activity from sparse active sites that are structurally distinct from the inactive bulk. Rationally optimizing activity is therefore beholden to the challenges in studying these active sites in molecular detail. Here, we report a molecule that mimics the structure of the proposed triangular active edge site fragments of molybdenum disulfide (MoS(2)), a widely used industrial catalyst that has shown promise as a low-cost alternative to platinum for electrocatalytic hydrogen production. By leveraging the robust coordination environment of a pentapyridyl ligand, we synthesized and structurally characterized a well-defined Mo(IV)-disulfide complex that, upon electrochemical reduction, can catalytically generate hydrogen from acidic organic media as well as from acidic water.     

Study by synchrotron radiation of the structure of a working catalyst at high temperatures and pressures

A relation among activity, composition, and structure was determined for a working catalyst by means of a stainless-steel reactor cell of novel design that permitted operation at temperatures and pressures similar to those in industrial reactors. Molybdenum K-edge x-ray absorption spectra were used to probe the structural environment of molybdenum in CoMoS/[unknown]-alumina catalysts while hydro-desulfurization of benzothiophene was proceeding at high temperature and pressure. For catalyst samples with different contents of cobalt, radial structure functions obtained from extended x-ray absorption fine structure data presented the same features as those obtained from the spectra of MoS(2)/[unknown]-alumina reference samples. Moreover, Mo-S and Mo-Mo coordination numbers were maximum for the sample with an atomic ratio of Co to (Co + Mo) of 0.33; this sample was also the most active catalyst tested.     

The active site of methanol synthesis over Cu/ZnO/Al2O3 industrial catalysts

One of the main stumbling blocks in developing rational design strategies for heterogeneous catalysis is that the complexity of the catalysts impairs efforts to characterize their active sites. We show how to identify the crucial atomic structure motif for the industrial Cu/ZnO/Al(2)O(3) methanol synthesis catalyst by using a combination of experimental evidence from bulk, surface-sensitive, and imaging methods collected on real high-performance catalytic systems in combination with density functional theory calculations. The active site consists of Cu steps decorated with Zn atoms, all stabilized by a series of well-defined bulk defects and surface species that need to be present jointly for the system to work.     

六氟丙酮水合物加氢制备六氟异丙醇

[目的]研究六氟异丙醇（HFIP）的最佳制备条件。[方法]采用液相催化剂加氢法还原六氟丙酮（HFA）,制备六氟异丙醇。[结果]在1.0%催化剂用量,反应体系pH值5.0,反应温度110℃,反应压力2.5 MPa的条件下,反应时间提高为5 h,HFA转化率提高为97%以上,选择性提高为98%以上。[结论]通过试验,找到了适合六氟异丙醇制备的一种钯碳催化剂。     

In situ formation of an oxygen-evolving catalyst in neutral water containing phosphate and Co2+

The utilization of solar energy on a large scale requires its storage. In natural photosynthesis, energy from sunlight is used to rearrange the bonds of water to oxygen and hydrogen equivalents. The realization of artificial systems that perform "water splitting" requires catalysts that produce oxygen from water without the need for excessive driving potentials. Here we report such a catalyst that forms upon the oxidative polarization of an inert indium tin oxide electrode in phosphate-buffered water containing cobalt (II) ions. A variety of analytical techniques indicates the presence of phosphate in an approximate 1:2 ratio with cobalt in this material. The pH dependence of the catalytic activity also implicates the hydrogen phosphate ion as the proton acceptor in the oxygen-producing reaction. This catalyst not only forms in situ from earth-abundant materials but also operates in neutral water under ambient conditions.     

Platinized chloroplasts: a novel photocatalytic material

Colloidal platinum was prepared and precipitated directly onto photosynthetic thylakoid membranes from aqueous solution and entrapped on fiberglass filter paper. This composition of matter was capable of sustained simultaneous photoevolution of hydrogen and oxygen when irradiated at any wavelength in the chlorophyll absorption spectrum. Experimental data support the interpretation that part of the platinum metal catalyst is precipitated adjacent to the photosystem I reduction site of photosynthesis and that electron transfer occurs across the interface between photosystem I and the catalyst. Photoactivity of the material was dependent on the nature of the ionic species from which the platinum was precipitated. All photoactive samples were prepared from the hexachloroplatinate(IV) ion, whereas samples prepared by precipitation of the tetraammineplatinum(II) ion showed no hydrogen evolution activity and only transient oxygen activity. This system is among the simplest known for photosynthetically splitting water into molecular hydrogen and oxygen.     

A perovskite oxide optimized for oxygen evolution catalysis from molecular orbital principles

The efficiency of many energy storage technologies, such as rechargeable metal-air batteries and hydrogen production from water splitting, is limited by the slow kinetics of the oxygen evolution reaction (OER). We found that Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ) (BSCF) catalyzes the OER with intrinsic activity that is at least an order of magnitude higher than that of the state-of-the-art iridium oxide catalyst in alkaline media. The high activity of BSCF was predicted from a design principle established by systematic examination of more than 10 transition metal oxides, which showed that the intrinsic OER activity exhibits a volcano-shaped dependence on the occupancy of the 3d electron with an e(g) symmetry of surface transition metal cations in an oxide. The peak OER activity was predicted to be at an e(g) occupancy close to unity, with high covalency of transition metal-oxygen bonds.     

Machining oxide thin films with an atomic force microscope: pattern and object formation on the nanometer scale

An atomic force microscope (AFM) has been used to machine complex patterns and to form free structural objects in thin layers of MoO(3) grown on the surface of MoS(2). The AFM tip can pattern lines with 相似文献   

Nanotribology and Nanofabrication of MoO3 Structures by Atomic Force Microscopy

Atomic force microscopy was used to characterize the sliding of molybdenum oxide (MoO3) nanocrystals on single-crystal molybdenum disulfide (MoS2) surfaces. Highly anisotropic friction was observed whereby MoO3 nanocrystals moved only along specific directions of the MoS2 surface lattice. The energy per unit area to move the MoO3 nanocrystals along their preferred sliding direction was an order of magnitude less than required to slide macroscopic MoS2-bearing contacts. This extreme friction anisotropy was exploited to fabricate multicomponent MoO3 nanostructures. These reversibly interlocking structures could serve as the basis for devices such as mechanical logic gates.     

ZnCl2催化纤维素液化的初步研究

以微晶纤维素为研究对象,Lewis酸ZnCl2为催化剂,系统考察反应温度、反应时间、氢气压力、ZnCl2用量等对催化液化效果的影响。结果表明：随着反应温度的升高、反应时间的延长、氢气压力的升高、氯化锌用量的增加,纤维素的转化率均有提高;反应温度为320℃、反应时间30min、氢气压力2MPa,催化剂（氯化锌）10％时,纤维素催化液化效果最佳,其转化率可达92．0％。     

Morphology of nascent ziegler-natta polymers

In the polymerization of alpha-olefins with heterogeneous Ziegler-Natta catalysts, the polymer is formed directly as long fibrillar units with folder chains. It is proposed that the fibrils are formed by the crystallization of polymer chains growing from the active sites on the catalyst surface, a process which is likened to root growth in whiskers.     

Raney Ni-Sn catalyst for H2 production from biomass-derived hydrocarbons

Hydrogen (H2) was produced by aqueous-phase reforming of biomass-derived oxygenated hydrocarbons at temperatures near 500 kelvin over a tin-promoted Raney-nickel catalyst. The performance of this non-precious metal catalyst compares favorably with that of platinum-based catalysts for production of hydrogen from ethylene glycol, glycerol, and sorbitol. The addition of tin to nickel decreases the rate of methane formation from C-O bond cleavage while maintaining the high rates of C-C bond cleavage required for hydrogen formation.     

Hydrogen release: new indicator of fault activity

The hydrogen concentration in soil gas has been measured in the area around the Yamasaki Fault, one of the active faults in southwestern Japan. Degassing of a significant amount of hydrogen (up to more than 3 percent by volume) has been observed for sites along the fault zone. The hydrogen concentration in soil gas at sites away from the fault zone was about 0.5 part per million, almost the same as that found in the atmosphere. The spatial distribution of sites with high hydrogen concentrations is quite systematic. A hypothesis on the production of hydrogen by fault movements is postulated.     

Dimer preparation that mimics the transition state for the adsorption of H2 on the Si(100)-2 x 1 surface

A chemically induced dimer configuration was prepared on the silicon (Si) (100) surface and was characterized by scanning tunneling microscopy (STM) and spectroscopy (STS). These prepared dimers, which are essentially untilted and differ both electronically and structurally from the dynamically tilting dimers normally found on this surface, are more reactive than normal dimers. For molecular hydrogen (H2) adsorption, the enhancement is about 10(9) at room temperature. There is no appreciable barrier for the H2 reaction at prepared sites, indicating the prepared configuration closely approximates the actual dimer structure in the transition state. This previously unknown ability to prepare specific surface configurations has important implications for understanding and controlling reaction dynamics on semiconductor surfaces.     

Intermetallic Compounds of the Type MNi5 as Methanation Catalysts

Catalytic reactions of carbon monoxide with hydrogen have been studied in which intermetallic compounds of the formula MNi(5) (where M is thorium, uranium, or zirconium) have been used as the catalysts. The materials perform effectively as methanation catalysts; ThNi(5) has a specific activity exceeding that of a typical commercial oxide-supported methanation catalyst by a factor of about 5. This material also shows superior resistance to hydrogen sulfide poisoning. Nickel, formed as a decomposition product of the MNi(5) intermetallic compound, is probably the active species, but its properties are influenced by the nature of M in the precursor MNi(5) system.     

TiO2表面特性的改变对其光催化降解高聚物活性的影响

以250W高压汞灯为光源，采用固定相TiO2,Pt/TiO2和Fe^3 /TiO2光化氧化降解聚乙烯醇（PVA），研究了不同表面处理方式对TiO2光催经活性的影响。结果表明，通过光化学沉积法在TiO2表面上担载1．0Pt制备的催化剂对PVA具有很好的光催化活性，此时光照60min后，PVA的光解率可达78．4％，但过量的Pt却降低了TiO2的光催化活性。研究还表明，高温灼烧法在TiO2表面上担载Fe^3 无助于提高TiO2降解PVA的光催化活性，随着Fe^3＋含量的升高，TiO2对PVA的光催化活性明显下降。结合SEM手段，认为TiO2活性的降低可能与其比表面积的降解有关。     

Combinatorial electrochemistry: A highly parallel, optical screening method for discovery of better electrocatalysts

Combinatorial screening of electrochemical catalysts by current-voltage methods can be unwieldy for large sample sizes. By converting the ions generated in an electrochemical half-cell reaction to a fluorescence signal, the most active compositions in a large electrode array have been identified. A fluorescent acid-base indicator was used to image high concentrations of hydrogen ions, which were generated in the electrooxidation of methanol. A 645-member electrode array containing five elements (platinum, ruthenium, osmium, iridium, and rhodium), 80 binary, 280 ternary, and 280 quaternary combinations was screened to identify the most active regions of phase space. Subsequent "zoom" screens pinpointed several very active compositions, some in ternary and quaternary regions that were bounded by rather inactive binaries. The best catalyst, platinum(44)/ruthenium(41)/osmium(10)/iridium(5) (numbers in parentheses are atomic percent), was significantly more active than platinum(50)/ruthenium(50) in a direct methanol fuel cell operating at 60 degreesC, even though the latter catalyst had about twice the surface area of the former.     

Inclusion systems of organic molecules in restacked single-layer molybdenum disulfide

Novel materials have been obtained by restacking single-layer molybdenum disulfide (MoS(2)) with organic molecules included between the layers. A large variety of organic molecules can be included between layers of MoS(2) and other transition-metal dichalcogenides. The films with the included organics are formed at the interface between an aqueous suspension of the MoS(2) and a water-immiscible organic liquid. The organic molecules are not necessarily electron donors. A highly oriented, conducting film of restacked MoS(2) containing ferrocene is presented as an example.     

Hydrogen produced from hydrohalic acid solutions by a two-electron mixed-valence photocatalyst

Energy conversion cycles are aimed at driving unfavorable, small-molecule activation reactions with a photon harnessed by a transition metal complex. A challenge that has occupied researchers for several decades is to create molecular photocatalysts to promote the production of hydrogen from homogeneous solution. We now report the use of a two-electron mixed-valence dirhodium compound to photocatalyze the reduction of hydrohalic acid to hydrogen. In this cycle, photons break two RhII-X bonds of a LRh0-RhIIX2 core in the presence of a halogen trap to regenerate the active LRh0-Rh0 catalyst, which reacts with hydrohalic acid to produce hydrogen.