Characterization of ZnAl2O4 Obtained by Different Methods and Used as Catalytic Support of Pt

In this work the synthesis of a ZnAl₂O₄ spinel to be used as a support of metals and its characterization were studied. The methods used for the ZnAl₂O₄ preparation were: ceramic method (CM), mechanochemical synthesis in humid medium (HMS) and coprecipitation (COPR). ZnAl₂O₄ CM and ZnAl₂O₄ HMS showed negligible acidity, but the ZnAl₂O₄ COPR displayed a low acidity. The spinels obtained by COPR and HMS showed higher specific surface area and pore volumes than that prepared by the ceramic method. In addition the catalytic performance of Pt supported on the prepared spinel was evaluated in the n-butane dehydrogenation reaction. The Pt catalysts prepared with ZnAl₂O₄ COPR presented better activity and selectivity to olefins than the ones prepared with ZnAl₂O₄ HMS and ZnAl₂O₄ CM, which could be correlated with a higher metallic dispersion and lower particle sizes, detected by TEM. The acidity of ZnAl₂O₄ COPR, observed by isopropanol dehydration and TPD of pyridine, and the sequence of specific surface areas of the different spinels (ZnAl₂O₄ COPR > ZnAl₂O₄ HMS > ZnAl₂O₄ CM) are other important factors to define the final dispersion of the catalysts.     

Preparation of recoverable Ru catalysts for liquid-phase oxidation and hydrogenation reactions

We here report the synthesis, characterization and catalytic performance of new supported Ru(III) and Ru(0) catalysts. In contrast to most supported catalysts, these new developed catalysts for oxidation and hydrogenation reactions were prepared using nearly the same synthetic strategy, and are easily recovered by magnetic separation from liquid phase reactions. The catalysts were found to be active in both forms, Ru(III) and Ru(0), for selective oxidation of alcohols and hydrogenation of olefins, respectively. The catalysts operate under mild conditions to activate molecular oxygen or molecular hydrogen to perform clean conversion of selected substrates. Aryl and alkyl alcohols were converted to aldehydes under mild conditions, with negligible metal leaching. If the metal is properly reduced, Ru(0) nanoparticles immobilized on the magnetic support surface are obtained, and the catalyst becomes active for hydrogenation reactions.     

Fluid-Dynamic Study of Deformable Materials in Spouted-Bed Dryer

The present work is concerned with a fluid-dynamic study in spouted beds using deformable dice pieces of red guava. Data are presented on structural variations of the bed due to changes of regime during drying. Variation of physical properties (size and density) results from the volumetric shrinkage of these materials. Alterations in the fluid-dynamic stability of the spouted bed were correlated with Archimedes number. Along the process, the transition from fixed bed to fluidization can be observed, followed by stable spout and slugging. Mapping of the different regimes as a function of the moisture content is also presented.     

Knowledge‐based algorithms in fixed‐grid GA shape optimization

Shape optimization through a genetic algorithm (GA) using discrete boundary steps and the fixed‐grid (FG) finite‐element analysis (FEA) concept was recently introduced by the authors. In this paper, algorithms based on knowledge specific to the FG method with the GA‐based shape optimization (FGGA) method are introduced that greatly increase its computational efficiency. These knowledge‐based algorithms exploit the information inherent in the system at any given instance in the evolution such as string structure and fitness gradient to self‐adapt the string length, population size and step magnitude. Other non‐adaptive algorithms such as string grouping and deterministic local searches are also introduced to reduce the number of FEA calls. These algorithms were applied to two examples and their effects quantified. The examples show that these algorithms are highly effective in reducing the number of FEA calls required hence significantly improving the computational efficiency of the FGGA shape optimization method. Copyright © 2003 John Wiley & Sons, Ltd.     

Deep levels in the band gap of CdTe films electrodeposited from an acidic bath—PICTS analysis

The deep traps detected in a CdTe thin film electrodeposited from an acidic bath are discussed. CdTe thin films were developed on flexible metallic substrates by electro deposition. The films were nearly stiochiometric, highly uniform and exhibit good crystallinity. The films were characterized using XRD, SEM, AUGER and AFM. The crystallites exhibited a strong preference for the (1 1 1) plane. The grain size of the film was in the range 0.2–0.4 μm. The photoinduced current transient spectroscopic technique was effectively used to identify the electron and hole traps. Two hole traps and one electron trap was detected. The activation energies of those deep traps were 0.37 and 0.42 eV for the hole traps and 0.41 eV for the electron trap.     

Packed bed structure: Evaluation of radial particle distribution

A model describing the radial distribution of monosized spheres in randomly packed beds up to distances of about two particle diameters from the vessel wall is presented here. The model is based on the existence of a highly ordered layer of particles adjacent to the wall followed by a more diffuse, but still identifiable, second layer. Expressions generated from simple geometrical concepts (intersection between a cylindrical surface and a sphere) straightforwardly allow calculating the radial voidage profile given the radial distribution of particle centers and vice versa. These expressions are employed to fit the model to measures of voidage profiles within a wide range of aspect ratios, a = (R_T/R_P). The model can be used to accurately predict radial voidage profiles, but it is stressed that the identification of particle distribution constitutes more valuable information than an empirical expression for describing voidage variations.     

Robust output regulation under uncertainties of physical parameters

In this paper the robust output regulation problem is solved for linear time-invariant systems whose matrices are assumed to depend on some parameters, each of which possibly affects all the elements of the matrices describing the system, thus playing the role of a ‘physical’ parameter. The robustness here obtained is the preservation of the output regulation property under perturbations of such parameters. Both the conditions for the existence of a solution and a design procedure of the compensator are given.     

Ratio of in vivo incorporation of3H arachidonic acid and14C linoleic acid into liver lipids from normal and diabetic rats

Normal and streptozotocin diabetic rats were injected via the portal vein with a labeled solution containing³H arachidonic acid and¹⁴C linoleic acid (³H/¹⁴C ratio, 0.5) during a 1 min period. Livers were quickly frozen, pulverized, and the lipids extracted and fractioned by thin layer chromatography. The incorporation of³H and¹⁴C into liver lipids was measured and the percentage distribution of radioactivity into the different lipid fractions was determined. The incorporation of¹⁴C linoleic acid and³H arachidonic acid into liver lipids is apparently reduced in rats with severe diabetes. The higher³H/^14C ratio found in the 1,2 diglycerides from diabetic rats may be explained by the apparently smaller incorporation of¹⁴C linoleic acid or by an isotopic dilution attributable to the great availability of this acid in diabetic rats. On the other hand, the higher³H/¹⁴C ratio observed in triglycerides and phospholipids from diabetic rats, due to a relatively large incorporation of³H arachidonic acid into this fraction, may be explained by the affinity of the enzymes involved in their synthesis for some 1,2-diglyceride units. Insulin was unable to correct the changes observed in the diabetic rats.     

The influence of the synthesis routes of MgAl2O4 on its properties and behavior as support of dehydrogenation catalysts

In order to synthesize MgAl₂O₄, three methods were used: (a) a solid phase reaction of MgO and γ-Al₂O₃ oxides at 900 °C for 24 h (ceramic method), (b) wet milling during 24 h of the mixture of oxides followed by the reaction at 900 °C for 12 h (mechanochemical synthesis), and (c) coprecipitation of Mg(NO₃)₂·6H₂O and Al(NO₃)₃·9H₂O with ammonia solution followed by a calcination in a flow of air at 800 °C during 4 h (coprecipitation method). The synthesized materials were characterized by XRD, BET isotherm, isopropanol dehydration reaction, TGA/DTA and SEM. The results indicate that in all the cases the MgAl₂O₄ spinel was formed. Besides, a residue of MgO in the samples obtained by the ceramic method and mechanochemical synthesis was found, which was eliminated by purification. The surface area of MgAl₂O₄ obtained by mechanochemical synthesis and coprecipitation method are much higher than that of the spinel synthesized by the ceramic method. Pt (0.3%) catalysts were prepared by impregnating the three supports with H₂PtCl₆. The metallic dispersion of Pt/MgAl₂O₄ obtained by mechanochemical synthesis was higher than that of Pt catalysts supported on the other spinels, in agreement with the catalytic behavior observed in n-butane dehydrogenation reaction and test reactions of the metallic phase.     

Using capacitance measurements as the detection method in antigen-containing layer-by-layer films for biosensing

The layer-by-layer technique is employed here to immobilize antigen-containing liposomes, so-called proteoliposomes, onto Au-interdigitated substrates, which are capable of molecular recognition of anti-pasteurellosis antibodies. Detection was carried out using a novel strategy entirely based upon capacitance measurements, and to enhance sensitivity, we combine the response of three different sensing units in a similar procedure used for taste sensors. With the three-electrode array immunoglobulin G (IgG) against pasteurellosis is detected at concentrations as low as nanograms per milliliter. Furthermore, because of the molecular recognition capability, a distinction can be made between specific and nonspecific IgG. The concepts behind the biosensors reported here may have a large impact for clinical tests, as the procedures to detect the antibody take only a few minutes and the biosensors are relatively low cost.