Showing papers on "Cobalt sulfide published in 2005"

NO reduction by CH4 over Pd/Co-sulfated zirconia catalysts

Abstract: A series of sulfated zirconia supported Pd/Co catalysts was synthesized by the sol–gel method and examined for NOx reduction by methane. The NO conversion increased up to a Co/S ratio of 0.43, and then decreased at a higher Co loading (Co/S = 0.95). Sulfate content was also essential for obtaining high selectivity to molecular nitrogen. A catalyst loaded with 0.06 wt.% Pd, 2.1 wt.% Co and 2.1 wt.% S (Pd/Co-SZ-2) exhibited remarkable performance under lean conditions and displayed stability in a long-term durability test using a synthetic reaction mixture containing 10% water vapor. This catalyst exhibited the highest sulfur retention most probably as cobalt sulfide. Besides, the catalytic oxidation of NO to NOy groups was confirmed by FT-IR, in agreement with the general mechanism for the SCR of NO by hydrocarbons. In the absence of oxygen in the feed stream, the catalyst was highly active for NO reduction with methane. IR stretching bands assigned to N2O and adsorbed nitro groups were identified upon adsorbing NO on Pd/Co-SZ-2. This indicates that under rich conditions disproportionation of NO to N2O and NO2 occurs and confirms that the formation of NO2 species is an essential step for NO reduction by CH4.

Comparison of bulk CoMo bimetallic carbide, oxide, nitride and sulfide catalysts for pyridine hydrodenitrogenation

Abstract: Bimetallic cobalt–molybdenum oxide (CoMoO x ) has been prepared and converted into CoMoN x , CoMoC x and CoMoS x materials by temperature-programmed reactions with ammonia, ethane or hydrogen sulfide, respectively. These new bimetallic materials have been characterised using X-ray diffraction (XRD) and solid state NMR and tested for pyridine hydrodenitrogenation (HDN) at various temperatures. The initial HDN activity of the catalysts decreases in order CoMoC x ∼ CoMoN x ∼ CoMoO x > CoMoS x . The stability order of the first three of catalysts is CoMoC x > CoMoN x > CoMoO x , and their activities decrease with the time on stream. In contrast the pyridine conversion over CoMoS x is more stable and activity increases with the time on stream, from 30 to over 50%, this is accompanied by the formation of CoMoSC x material. The high catalytic activity of the CoMoC x catalyst may reflect the ability to hydrocrack pyridine to yield methane. The CoMoS x catalyst system has the highest selectivity to the products cyclopentane (35%) and pentane (27%).

High-resolution spectroscopy of CoS (XΔi4): Examining 3d transition-metal sulfide bonds

Abstract: The pure rotational spectrum of CoS, the cobalt sulfide radical, has been measured using direct absorption techniques in the frequency range of 180-540 GHz This study is the first spectroscopic investigation of any kind of this molecule CoS was created by reacting cobalt vapor with H2S Four spin components were identified in the spectra of this species, one of which exhibited lambda doubling, identifying the ground state as 4Deltai Transitions arising from the lowest spin component of the less abundant Co 35S isotopomer have also been detected, as well as from v=1 and v=2 of the main species The spectra were readily identified because each spin component exhibited an octet pattern arising from the 59Co spin of I=72 The data were fit using Hund's case (a) Hamiltonian, and rotational, fine-structure, hyperfine, and lambda-doubling constants were determined The hyperfine parameters support a delta3pi2 electron configuration and are consistent with some orbital overlap between the metal and sulfur atoms From the rotational constant, the bond length of CoS was calculated to be r0=1977 985 06(10) A This bond length is significantly shorter than that of MnS or FeS, in contrast to the bond distances found in the oxide analogs which are all similar in value These results indicate that the 3d metal sulfides differ somewhat from their oxide counterparts, probably due to the availability of sulfur p orbitals for bonding

Hydrogenolysis of dimethyl disulfide to methanethiol in the presence of cobalt sulfide catalysts

Abstract: The hydrogenolysis of dimethyl disulfide to methanethiol at T = 180–260°C and atmospheric pressure in the presence of supported cobalt sulfide catalysts has been studied. Cobalt sulfide on aluminum oxide exhibits a higher activity than that on a carbon support or silicon dioxide. The maximum reaction rate per gram of a catalyst is observed on an 8% Co/Al2O3 catalyst. At temperatures of up to 200°C and conversions up to 90%, methanethiol is formed with nearly 100% selectivity regardless of the cobalt content, whereas the selectivity for methanethiol under more severe conditions decreases because of its condensation to dimethyl sulfide.

Catalyst, method of preparation thereof, and methylmercaptan production process

Abstract: FIELD: industrial organic synthesis. ^ SUBSTANCE: catalyst is prepared by impregnating alumina with cobalt chloride solution followed by drying and activation, the latter being effected by treating catalyst first with hydrogen sulfide/hydrogen mixture at 380-420 and then with hydrogen at 200-260. Invention also provides catalyst for production methylmercaptan through hydrogenolysis of dimethyl sulfide containing 8.0-15.0% cobalt sulfide applied onto alumina treated by above-indicated method. Process is carried out at dimethyl sulfide supply velocity 13.4 to 128.7 mole/h per 1 g catalyst. ^ EFFECT: increased methylmercaptan production productivity. ^ 3 cl, 1 tbl, 15 ex

Cobalt nanocrystals as starting materials for shape modification and assembly formation

Abstract: Author(s): Erdonmez, Can Kerem | Abstract: Surfactant-coated cobalt nanocrystals can be prepared with a reasonable degree of control over particle size and shape using a thermolytic route. The small crystallite size, enhanced reactivity and tunable interparticle interactions enable use of this material as starting material for demonstration of achievement of novel structures using extremely simple solution-based approaches. In particular, formation of hollow cobalt sulfide nanocrystals upon chemical modification and emergence of long-range orientational order upon drying-mediated assembly of cobalt nanocrystals is reported here.Colloidal preparation of Co nanocrystals has been well-studied. Here, we emphasize general principles and crystallographic/morphological characterization of disk-shaped hcp-Co nanocrystals. Use of surfactant molecules enables achievement of multiple morphologies in one synthetic system.Formation of hollow structures upon in-solution sulfidation of Co nanocrystals is presented and discussed. A Kirkendall-type effect, involving dominant outward mass transport during formation of the ionic shell material explains the results naturally. It is expected that this phenomenon will generalize extensively to formation of hollow structures of an enormous variety of compositions. Detailed study of particle morphology as a function of reaction conditions suggest phenomena likely to be generally relevant to use of this approach. A short report of crystallographic co-alignment into vortex-like structures is also provided. Our current best picture of this process involves an interplay of packing and magnetic interactions between faceted particles.