On packing and covering polyhedra in infinite dimensions

We consider the natural generalizations of packing and covering polyhedra in infinite dimensions, and study issues related to duality and integrality of extreme points for these sets. Using appropriate finite truncations we give conditions under which complementary slackness holds for primal/dual pairs of the infinite linear programming problems associated with infinite packing and covering polyhedra. We also give conditions under which the extreme points are integral. We illustrate an application of our results on an infinite-horizon lot-sizing problem. Keywords: Covering polyhedron; Packing polyhedron; Infinite linear program; Complementary slackness; Integral extreme poin

Deep Hydrodesulfurization of Dibenzothiophenes Over NiW Sulfide Catalysts Supported on Sol–Gel Titania–Alumina

This work showed that the use of Al2O3–TiO2 as carriers has a positive effect on the activity of supported NiW catalysts in the hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene carried out in a batch reactor at 320 _C and total H2 pressure of 5.5 MPa. Two Al2O3–TiO2 mixed oxides with Al/Ti atomic ratios of 10 and 2 were synthesized by sol–gel method together with the pure Al2O3 synthesized as reference support. For NiW/ Al2O3–TiO2 and NiW/Al2O3 catalysts, a metal load of 17 and 5.5 wt% of W and Ni were considered respectively. It was found that both Al2O3–TiO2-supported catalysts exhibited higher activity than alumina-supported one. The catalyst with a largest TiO2 content (NiW/AT2) demonstrated to be 23 % more active with respect to NiW/Al2O3. Solids were characterized by temperature-programmed reduction (TPR), high resolution transmission electronic microscopy and X-ray photoelectronic spectroscopy (XPS) techniques. A decrease in support–metal interaction (from TPR) was observed when Ti content increased, which could lead to a higher amount of NiWS phase (from XPS). Besides, a slight increase in the slabs length in WS2 was observed for titania-containing catalyst with respect to NiW/Al2O3, indicating that the dispersion can still be optimized. The atomic ratio Al/Ti = 2 of the NiW/Al2O3– TiO2 catalyst proved to be a potential substitute for current catalysts for sulfur reduction in ultra-clean diesel

State of Art of Alkaline Earth Metal Oxides Catalysts Used in the Transesterification of Oils for Biodiesel Production

Biodiesel produced through catalytic transesterification of triglycerides from edible and non-edible oils and alcohol is considered an alternative to traditional petro-diesel. The interest in the use of alkaline earth metal oxides as heterogeneous basic catalysts has increased due to their availability, non-toxicity, the capacity to be reused, low cost, and high concentration of surface basic sites that provide the activity. This work is a compilation of the strategies to understand the effect of the source, synthesis, and thermal treatment of MgO, CaO, SrO, and BaO on the improvement of the surface basic sites density and strength, the morphology of the solid structure, stability during reaction and reusability. These parameters are commonly modified or enhanced by mixing these oxides or with alkaline metals. Also, the improvement of the acid-base properties and to avoid the lixiviation of catalysts can be achieved by supporting the alkaline earth metal oxides on another oxide. Additionally, the effect of the most relevant operation conditions in oil transesterification reactions such as methanol to oil ratio, temperature, agitation method, pressure, and catalysts concentration are reviewed. This review attempts to elucidate the optimum parameters of reaction and their application in different oil

Effect of the Structural and Electronic Properties of Rh/CeXZr1-XO2 Catalysts on the Low-temperature Ethanol Steam-reforming

Rh catalysts supported on CexZr1–xO2 (with x= 0-1) materials were synthesized by precipitation method. The influence of the two different cerium salt precursors, ammonium cerium(IV) nitrate and cerium(III) nitrate hexahydrate, over the structure and catalytic activity in steam reforming reaction was investigated. The synthesized catalysts were characterized by various techniques, such as N2 adsorption-desorption, temperature-programmed desorption, X-ray diffraction, Raman spectroscopy, diffuse reflectance UV-Vis, and X-ray photoelectron spectroscopy. The use of ammonium cerium (IV) nitrate as a cerium precursor resulted in solid CexZr1-xO2 solutions with improved oxygen mobility and specific surface area. The catalytic evaluation exhibited the support composition and structure impact on its activity and product yield. The Rh supported on Ce0.5Zr0.5O2 solid solution rendered the higher activity and H2 and CO2 yields among both series, related to improved oxygen mobility and greater Rh0 dispersion. The formation of surface defects adjacent to Rh clusters by strong metal-support interaction effect was suggested by Raman analysis. The close contact between the Rh0 site and oxygen vacancy could be favoring cyclic-like ethanol adsorption and favored the breaking of the C–C bond and further oxidation of adsorbed CO and CHX species

Custom-Made Ion Exchange Membranes at Laboratory Scale for Reverse Electrodialysis

Salinity gradient power is a renewable, non-intermittent, and neutral carbon energy source. Reverse electrodialysis is one of the most efficient and mature techniques that can harvest this energy from natural estuaries produced by the mixture of seawater and river water. For this, the development of cheap and suitable ion-exchange membranes is crucial for a harvest profitability energy from salinity gradients. In this work, both anion-exchange membrane and cation-exchange membrane based on poly(epichlorohydrin) and polyvinyl chloride, respectively, were synthesized at a laboratory scale (255 cm2) by way of a solvent evaporation technique. Anion-exchange membrane was Surface modified with poly(ethylenimine) and glutaraldehyde, while cellulose acetate was used for the cation exchange membrane structural modification. Modified cation-exchange membrane showed an increase in surface hydrophilicity, ion transportation and permselectivity. Structural modification on the cation-exchange membrane was evidenced by scanning electron microscopy. For the modified anion exchange membrane, a decrease in swelling degree and an increase in both the ion Exchange capacity and the fixed charge density suggests an improved performance over the unmodified membrane. Finally, the results obtained in both modified membranes suggest that an enhanced performance in blue energy generation can be expected from these membranes using the reverse electrodialysis technique

Characterization of structural and optical properties of the mesoporous Ce-MCM-41 hybrid materials

Ce-modified mesostructured MCM-41-type hybrid materials with different Si/Ce molar ratios (Si/Ce = 10, 30 and 50) were synthesized by the surfactant-assisted hydrothermal method and their structural and optical properties were characterized by small angle X-ray scattering (SAXS), field emission scanning electron microscopy (FE-SEM) equipped with embedded EDS system, ultraviolet and visible diffuse reflectance (UV–vis DR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Ce-MCM-41 samples show highly ordered 2D porous hexagonal mesostructures and oval and spherical morphologies with particle size between 300 and 600 nm, depending on the incorporated Ce amount. Incorporation of Ce4+ into ordered mesoporous silica generates oxygen defects in ceria-silica composites with the formation of Ce3+ species as confirmed by the XPS analyses. Cerium incorporation modified their structural regularity and resulted in an effective red shifting of the band gap (2.82 eV at 2.64 eV) due to the creation of intermediate energy states. Both asymmetry and broadening of Raman active F2g mode confirmed the presence of the structural defects. These ordered mesoporous Ce-MCM-41 hybrid materials are potentially attractive for their use as novel photocatalysts in the degradation of organic pollutants present in wastewater employing UV and visible light