Morales F.,University Auto Noma Metropolitana Iztapalapa |
Viniegra M.,University Auto Noma Metropolitana Iztapalapa |
Arroyo R.,University Auto Noma Metropolitana Iztapalapa |
Cordoba G.,University Auto Noma Metropolitana Iztapalapa |
Zepeda T.A.,National Autonomous University of Mexico
Materials Research Innovations | Year: 2010
CuO/ZrO2 catalysts were prepared by in situ sol-gel and impregnation methods, with CuO concentrations of 1 and 3.6 mol.-% calcined at 400°C. The catalysts were characterised by S BET, XRD, diffuse reflectance ultraviolet-visible spectroscopy and temperature programmed reduction (H2). The catalytic activity was performed in the CO oxidation. The XRD, diffuse reflectance ultraviolet-visible spectroscopy and temperature programmed reduction results showed that the dispersion of Cu species depends on the method of preparation and on the copper loading. The CuO/ZrO2 catalysts prepared by impregnation procedure showed higher catalytic activity than those prepared by the in situ sol-gel method. This observation can be explained by the presence of small particles of CuO on the catalyst prepared by impregnation (higher dispersion), which does not occur in the catalysts obtained by the in situ sol-gel method due to an important amount of Cu2+ ions that were incorporated into the support network, which are considered catalytically inactive. © W. S. Maney & Son Ltd. 2010.
Escobar J.,Mexican Institute of Petroleum |
De Los Reyes J.A.,University Auto noma Metropolitana Iztapalapa |
Viveros T.,University Auto noma Metropolitana Iztapalapa |
Valle-Orta M.,PEMEX |
Barrera M.C.,University of Veracruz
Fuel | Year: 2014
Compensation effects were found in isopropanol dehydration over alumina (A), titania (T) and corresponding mixed oxides (Al/Ti=2 and 25mol ratio, AT2 and AT25, respectively) synthesized by low-temperature sol-gel. Prepared materials (calcined in the 573-1173K) range were characterized by several techniques (N2 physisorption, XRD, thermal analysis and SEM). In general, Al2O3 had the highest reaction rate (at 473K) in propylene formation meanwhile both mixed oxides had much lower activity. TiO2 had minimal dehydrating activity that, nevertheless, was the highest intrinsic one (in areal basis). Constable plots were obtained for materials annealed at various temperatures, but for titania series. A clear isokinetic temperature (Tθ ) was observed for alumina series whereas for AT25 materials, a Tθ pole was registered but for the sample calcined at the most severe condition. Meanwhile, two Tθ poles were identified for AT2 solids, the first one corresponding to materials calcined at moderate temperature whereas the other set apart solids annealed under severe conditions. As expected, no isokinetic temperature was observed in Arrhenius plots corresponding to alcohol dehydration over TiO2 materials. © 2014 Elsevier Ltd.
Solis-Daun J.,University Auto Noma Metropolitana Iztapalapa
IFAC Proceedings Volumes (IFAC-PapersOnline) | Year: 2011
The aim of this paper is to design regular feedback controls for the global asymptotic stabilization (GAS) of systems with compact convex control value sets (CVS) U with 0 ∈ intU, in the framework of Artstein-Sontag's control Lyapunov function (CLF) approach. Convex theory allows us to reveal the intrinsic geometry involved in the CLF stabilization problem, and to show that it is solvable if there is an optimal control ω̄ (x). We study the existence, uniqueness and continuity of ω̄(x) depending on properties of U, and how to attain higher regularity in terms of the geometry (curvature) of U. However, in view that ω̄ (x) is singular, we consider a general form of admissible feedbacks for the gas of a system, provided a CLF is known. Then, we propose an explicit formula for suboptimal admissible feedback controls. Finally, based on a method to approximate compact convex sets, we design regular feedback controls for the gas of systems with compact convex CVS U with 0 ∈ intU, at expenses of small overflows in the control values. © 2011 IFAC.