A kind of new pyrochlore compounds with catalytic activity for the oxidation reaction of carbon monoxide and propylene

A series of new compounds with a formula RE₂M_2/3Nb_4/3O₇ (RE=Nd, Sm, Eu; M=Cu, Co, Zn) have been synthesized by a wet chemical method and the lattice parameters of the compounds have also been determined. The new compounds possess a pyrochlore structure and belong to hexagonal system. Most of the compounds have a certain catalytic activity for the oxidation reaction of carbon monoxide and propylene. The conversion efficiency of carbon monoxide and propylene on the surface of some compounds can be close to 100% at near 450°C. The compounds are insulator and the resistibility also is larger than 10⁵ ohm·cm even if at 500°C. The compounds are a new kind of oxidation catalysts. The catalytic oxidation process of carbon monoxide and propylene on the surface of the compounds involves the oxidation-reduction of the cations in the compound and the catalytic process is a co-catalytic one. The effects of various metal cations in the compounds on the catalytic activity for the oxidation of carbon monoxide and propylene have been discussed.     

Catalytic activity of HY-type zeolite for the disproportionation of nitrogen monoxide

The disproportionation of NO on HY-type zeolite was carried out at 15°C by a pulsed microreactor. The catalytic activity began to appear at the pretreatment temperature 500°C and showed its maximum in the region of 600 to 700°C. The Lewis acid sites of HY-type zeolite seem to act as the active sites. TPD profiles after the reaction were composed of three peaks. The amount of peak β also showed its maximum at the pretreatment temperature ca. 600°C.     

Preparation and characterization of VO-ZSM5 catalyst for the selective reduction of NO with ammonia

The structural characteristics and catalytic behavior of VO-ZSM5 catalysts, obtained by oxidative degradation of vanadyl acetyl acetonate, were characterized by FTIR spectroscopy and XRD analysis. The organometallic precursor was analysed during the preparation and activation steps. The thermal decomposition of the organometallic compound led to the formation of V-oxides anchored to the aluminosilicate surface in a stressed ligand field instead of an ordered oxide structure. The catalysts which were prepared by impregnation of a planar complex of V on ZSM5 were active for the selective reduction of NO with ammonia.     

Vanadium carbide with periodic anionic vacancies for effective electrocatalytic nitrogen reduction

Although electrocatalytic nitrogen reduction reaction (NRR) has been considered as an emerging pathway to produce ammonia (NH₃) under ambient conditions owing to its low energy consumption, it still lacks efficient the electrocatalysts to dissociate inert NN bonds. Here, we develop an efficient approach to produce vanadium carbide with abundant periodic carbon vacancies (12.5 at. %) and mesoporous structure as electrocatalysts for NRR via a carbothermic reaction. The typical synthesis protocol involves the use of zinc vanadate decorated vanadium pentoxide nanosheets to homogeneously guide the nucleation and growth of metal organic frameworks (MOFs) on their surface, thus facilitating the in-situ formation of unique vanadium carbide during the subsequent carbothermic reaction. Owing to the optimized substrate-adsorbate binding strength, the intrinsic periodic carbon vacancies of the resultant vanadium carbide could act as coordinatively unsaturated sites to adsorb and activate nitrogen through π-back-donation process, thus promoting the reduction of N₂ to NH₃. As a consequence, a high yield rate and high Faradaic efficiency with good stabilities are achieved for producing NH₃ under ambient conditions.     

Bimetallic PdCo catalyst for selective direct formylation of amines by carbon monoxide

A highly efficient and selective bimetallic Pd0.88Co0.12 nanoparticle catalyst was developed for the direct N-formylation of amines by carbon monoxide.This catalyst is compatible with a wide range of substrates,affording various synthetically useful formamides under practical and mild reaction conditions.     

Modeling for plasma-enhanced catalytic reduction of nitrogen oxides

In this work, we simulated the whole processes of plasma-enhanced selective catalytic reduction for nitrogen oxides removal with hydrocarbon additive. The simulation model consists of plasma simulation and catalysis simulation. First, single filamentary microdischarge in dielectric barrier discharge was calculated to evaluate the radical production yield as a function of specific input energy. Second, the chemical reaction process in the discharge reactor was simulated to find the gas reforming property by the plasma. This plasma simulation was applied to NO oxidation process in atmospheric pressure N₂/O₂/NO/C₃H₆ mixtures under various discharge conditions. Finally, the catalytic reaction process was modeled using simple mass balance equations in gas-phase and on catalyst surface. The catalytic reaction simulation was tested for the reduction of nitrogen oxides on γ-Al₂O₃ catalyst in N₂/O₂/NO/C₃H₆ and in N₂/O₂/NO₂/C₃H₆.     

Virial coefficients for carbon monoxide,ethylene, and propylene,at temperatures up to 1500K

For the paired model potential (12-7, ) we have calculated the second and the third virial coefficients; for the fourth coefficient we have used a semiempirical expression. We present the boundary of applicability for the derived equation of state.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 57, No. 4, pp. 590–593, October, 1989.     

Sialons and related nitrogen ceramics

Although silicon nitride is at present a leading contender for gas turbines and other hightemperature engineering applications, it is only the first of a wide field of nitrogen ceramics, other members of which offer better prospects for technological exploitation. “Sialons” are phases in the Si-Al-O-N and related systems and are comparable in variety and diversity with the mineral silicates. They are built up of one-, two-, and threedimensional arrangements of (Si, Al) (O, N)₄ tetrahedra in the same way that the fundamental structural unit in the silicates is the SiO₄ tetrahedron. These new oxynitrides include structure types based uponα andΒ silicon nitrides, silicon oxynitride, aluminium nitride and silicon carbide, eucryptite, spinel, melilite and apatite. They are being explored for their thermal, mechanical, chemical and electrical properties.     

黑磷负载的单原子催化剂用于电催化N2还原

设计和开发高选择性、高活性的单原子电催化剂是实现在常规环境条件下合成氨的关键.本论文利用密度泛函理论对P配体在N₂还原反应(NRR)中的应用前景进行了预测,并且提出了一种高性能NRR单原子催化剂的设计准则.理论计算结果显示, W@BP(0.40 eV)、Ta@BP(0.47 eV)和Nb@BP(0.53 eV)由于具有低反应自由能、高稳定性和导电性,在高效电催化NRR中潜力巨大.特别是,几乎所有金属中心对*N₂中间体的吸附能力都比*H更强,这表明以P为配体的单原子催化剂具有较强的NRR选择性,且*N₂H中间体的吸附自由能可作为描述符,反映这一系列催化剂的催化活性.此外,计算结果显示,金属中心向P配体转移的电子数目与NRR活性存在着火山关系,带有适度正电荷的金属中心具有优异的电催化NRR活性.该发现为高性能单原子催化剂的设计提供了理论指导.     

NH3选择性催化还原NOx催化剂及其中毒研究进展

选择性催化还原(SCR)技术广泛应用于燃煤电厂锅炉的烟气脱硝过程中,SCR工艺中的核心是高效稳定的催化剂.如何提高SCR催化剂的脱硝效率、稳定性和抗中毒能力,一直是国内外科研人员的研究重点之一.目前钒基催化剂广泛应用于工业生产中,但钒基催化剂具有生物毒性,操作温度高且N2选择性低,因此对环境友好且稳定高效的新型催化剂成...     

Cobalt doped Fe-Mn@CNTs catalysts with highly stability for low-temperature selective catalytic reduction of NOx

In this paper,we report the fabrication of cobalt-doped de-NOx catalyst by pyrolyzing an analogous metal-organic framework-74(MOF-74)containing Fe&Mn.The result...     

Low-temperature selective catalytic reduction of NO with CO over Nix-MOF-5

Journal of Materials Science - The catalyst with a high NO conversion rate and good sulfur resistance is the key to CO-selective catalytic reduction (CO-SCR). Ni doping MOF-5 was synthesized...