Kinetics of the selective reduction of NO with CH4 over an In-Fe2O3/HZSM-5 catalyst

A kinetic model presented for the selective reduction of NO with CH4 over an InFe2O3/HZSM-5 catalyst by considering the process as a combination of two simultaneous reactions: NO+O2CH4 (reaction 1) and O-2+CH4 (reaction 2). Linear regression calculation was employed to find the kinetic parameters. It was found that although the activation energies of the two reactions were almost identical, the reaction rate constants were dramatically different, namely, k(1)much greater than k(2), indicating that the NO+O-2+CH4 reaction was more preferable to take place on the In-Fe2O3/HZSM-5 catalyst as compared with the O-2+CH4 reaction.

An in-situ modified sol-gel process for monolith catalyst preparation used in the partial oxidation of methane

An in-situ modified sol-gel method for the preparation of a Ni-based monolith-supported catalyst is reported. With the presence of a proper amount of plasticizer and binder, and at an optimized pH value, the stable boehmite sol was modified with metal ions (Ni, Li, La) successfully without distinct growth of the particle size. Monolith-supported Ni-based/gamma-Al2O3 catalysts were obtained using the modified sol as the coating medium with several cycles of dip-coating and calcination. Combined BET, SEM-EDS, XRD and H-2-TPR investigations demonstrated that the derived monolith catalysts had a high specific surface area, a relatively homogeneous surface composition, and a high extent of interaction between the active component and the support. These catalysts showed relatively stable catalytic activities for partial oxidation of methane (POM) to syngas under atmospheric pressure. The monolith catalysts prepared by this sol-gel method also demonstrated an improved resistance to sintering and loss of the active component during the reaction process.

Continuous oxygen ion transfer medium as a catalyst for high selective oxidative dehydrogenation of ethane

An oxygen permeable mixed ion and electron conducting membrane (OPMIECM) was used as an oxygen transfer medium as well as a catalyst for the oxidative dehydrogenation of ethane to produce ethylene. O2- species transported through the membrane reacted with ethane to produce ethylene before it recombined to gaseous O-2, so that the deep oxidation of the products was greatly suppressed. As a result, 80% selectivity of ethylene at 84% ethane conversion was achieved, whereas 53.7% ethylene selectivity was obtained using a conventional fixed-bed reactor under the same reaction conditions with the same catalyst at 800 degreesC. A 100 h continuous operation of this process was carried out and the result indicates the feasibility for practical applications.

The effect of additives on Cu/HZSM-5 catalyst for DME synthesis

The addition of ZnO or ZrO2 into CuO/HZSM-5 was investigated for DME synthesis from syngas by using the reactive frontal chromatography method, TPR and in situ TPR. These promoters enhanced the catalytic activity of Cu/HZSM-5 and promotion with ZnO and ZrO2 produced a maximum activity, which could be explained by the improvement of the dispersion of Cu and the promotion of CuO reduction. The Cu+ species existing during the reaction have been detected, based on which a Cu-0 <-> Cu+1 redox cycle model was put forward.

Polymer-supported palladium-manganese bimetallic catalyst for the oxidative carbonylation of amines to carbamate esters

The polymer-supported bimetallic catalyst PVP-PdCl2-MnCl2 (PVP=poly(N-vinyl-2-pyrrolidone)) exhibits high activity and selectivity for the oxidative carbonylation of amines with carbon monoxide and oxygen to carbamate esters under atmospheric pressure in the presence of a base (NaOAc). This catalyst is prepared by the addition of MnCl2 to the alcoholic solution of PVP-PdCl2 in situ. A remarkable bimetallic synergic effect and the role of PVP in PVP-PdCl2-MXn (MXn=the second transition metal component such as NiCl2, CoCl2, MnCl2 and FeCl3) gives rise to an obvious increase in the conversion and selectivity for the reaction. Among the second metal components tested, Mn-Pd exerts the strongest synergic effect. (C) 1999 Elsevier Science B.V. All rights reserved.

A remarkable synergic effect of water-soluble bimetallic catalyst in the hydrogenation of aromatic nitrocompounds

Hydrogenation of nitrobenzene can be catalyzed by the water-soluble catalyst PdCl2(TPPTS)(2) (TPPTS = tris(m-sulfonatophenyl)phosphine trisodium salt) under normal pressure at 65 degrees C in H2O/toluene biphasic solvent system. The exhibits higher catalytic activity and selectivity for the hydrogenation of aromatic nitrocompounds, compared with PdCl2(TPPTS)(2) or H2PtCl6 alone. The transmission electron micrographs demonstrate that the monometallic catalyst is composed of ultrafine palladium particles of almost uniform size while the particles of bimetallic catalyst are more widely distributed in size than those of the monometallic ones. (C) 1999 Elsevier Science B.V. All rights reserved.

Investigation of platinum utilization and morphology in catalyst layer of polymer electrolyte fuel cells

Platinum utilization in the gas-diffusion catalyst layer and thin-film catalyst layer is investigated. The morphology of PTFE and Nafion in a simulated catalyst layer is examined by scanning electronmicroscopy (SEM) and transmission electron microscopy (TEM). The results show that the platinum utilization of the thin-film catalyst layer containing only Pt/C and Nafion is 45.4%. The low utilization is attributed to the fact that the electron conduction of many catalyst particles is impaired by some thick Nafion layers or clumps. For the gas-diffusion (E-TEK) electrode, the platinum utilization is mainly affected by the proton conduction provided by Nafion. The blocking effect of PTFE on the active sites is not serious. When the electrode is sufficiently impregnated with Nafion by an immersion method, the platinum utilization can reach 77.8%. Transmission electron micrographs reveal that although some thick Nafion layers and clumps are observed in the Pt/C + Nafion layer, the distribution of Nafion in the catalyst layer is basically uniform. The melted PTFE disperses in the catalyst layer very uniformly. No large PTFE clumps or wide net-like structure is observed. The reactant gas may have to diffuse evenly in the catalyst layer. (C) 1999 Elsevier Science S.A. All rights reserved.

Ag-ZSM-5 catalyst for the catalytic decomposition of NO

The catalytic decomposition of NO over Ag-ZSM-5 catalyst prepared by ion-exchange was investigated. The exchanged silver in the zeolite was reduced and it collected in the course of the reaction to form silver particles of about 20 nm. The catalytic reaction induced a pronounced restructuring of the Ag particles through preferential formation of the (111) facets. These facets were shown to hind a tightly bound oxygen species (O-gamma). The O-gamma species occupies the active sites for NO adsorption resulting in catalyst deactivation. It could be removed by appropriate reducing agents, such as CO, to recover the active sites at elevated temperatures.