1,721,113 research outputs found
Enhancement of the low temperature activity in NO reduction in lean conditions by SMSI effect in Pt/CeO2-ZrO2 on alumina catalyst
No full textA treatment with H-2 at 800 degreesC followed by mild reoxidation (C) increases the low temperature (C) steady-state activity in the reduction of NO by propene in the presence Of O-2 of a Pt(1.5%)/(ZrO2-CeO2 on Al2O3) catalyst. The effect is not present for a lower temperature treatment with H-2 or for reoxidation above 300 degreesC. Transient reactivity tests together with characterization data (H-2-TPR, O-2 uptake, H-2 chemisorption) indicate that the high temperature reduction modifies the characteristics of ceria-zirconia and induced metal-support interaction effects, both responsible of the enhanced catalytic activity at low temperature
Methane oxy-reforming coupled with a water gas shift membrane reactor for pure hydrogen production
No full textPure H2 production by methane oxy-reforming over Rh-Mg-Al hydrotalcite-derived catalysts coupled with a Pd membrane
No full textRh-Mg-Al hydrotalcites were synthesized by coprecipitation, then calcined and reduced to obtain catalysts active in the oxy-reforming of methane. In particular, it was shown that an increased activity can be obtained by reducing the Mg/Al ratio or increasing the Rh amount. In addition, the influence of pellet dimension and catalyst amount at same contact time was demonstrated to be negligible thanks to the characteristics of oxy-reforming which allows to work at low contact times without a sharp temperature rise. Moreover, a newly developed thermal treatment of the synthesized hydrotalcite was able to provide an active catalyst with an increased amount of reduced Rh over its surface, which provided very good performances. Finally, a hydrogen-selective Pd-membrane was integrated after the oxy-reforming and was able to separate H2 from the outlet mixture providing pure hydrogen in different conditions with high recoveries
Proccedings of the 1st World Congress on “Environmental Catalysis – For a Better World and Life”
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Surface structure and reactivity of VTiO catalysts prepared by solid-state reaction 1. Formation of a VIV interacting layer
No full textThe solid-state interaction between V2O5 and TiO2 in the 700-800 K range of temperatures gives rise to the formation of VIV sites even in the absence of reducing agents. A VIV interacting layer covering the entire surface of TiO2 anatase may be created in the absence of any indication of partial transformation to the rutile phase. The nature, amount, and distribution of these VIV sites are characterized by means of titration combined with selective extraction, reactivity measurements in o-xylene oxidation, evaluation of redox properties, and by XRD, XPS, and ESR analyses. The amount of VIV depends on the crystallographic nature (anatase or rutile) and surface area of the TiO2 and on the conditions (temperature, time, and type of atmosphere) of the heat treatment. In the anatase sample the VIV sites can be reduced to VIII, but not oxidized to VV due to the strong interaction with the titania surface. In rutile samples part of the VIV may be reduced to VIII, but also oxidized to VV. The remaining VIV sites are present in solid solution in the rutile matrix and are not accessible to redox reagents. The model of a VIV-modified TiO2 (anatase) surface is discussed with reference to the problem of surface diffusion of vanadium species on the anatase surface. In TiO2 (rutile)-based samples, due to the competition of the migration of vanadium ions toward the bulk of the rutile with respect to surface diffusion, V2O4-like islands form that are coherently intergrown into the main rutile TiO2 matrix. © 1991
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