Used Catalysts (used + catalyst)

Distribution by Scientific Domains

Selected Abstracts

Kinetics and mechanism of myristic acid and isopropyl alcohol esterification reaction with homogeneous and heterogeneous catalysts

Tuncer Yalçinyuva
The reaction of myristic acid (MA) and isopropyl alcohol (IPA) was carried out by using both homogeneous and heterogeneous catalysts. For a homogeneously catalyzed system, the experimental data have been interpreted with a second order, using the power-law kinetic model, and a good agreement between the experimental data and the model has been obtained. In this approach, it was assumed that a protonated carboxylic acid is a possible reaction intermediate. After a mathematical model was proposed, reaction rate constants were computed by the Polymath* program. For a heterogeneously catalyzed system, interestingly, no pore diffusion limitation was detected. The influences of initial molar ratios, catalyst loading and type, temperature, and water amount in the feed have been examined, as well as the effects of catalyst size for heterogeneous catalyst systems. Among used catalysts, p -toluene sulfonic acid (p -TSA) gave highest reaction rates. Kinetic parameters such as activation energy and frequency factor were determined from model fitting. Experimental K values were found to be 0.54 and 1.49 at 60°C and 80°C, respectively. Furthermore, activation energy and frequency factor at forward were calculated as 54.2 kJ mol,1 and 1828 L mol,1 s,1, respectively. © 2008 Wiley Periodicals, Inc. 40: 136,144, 2008 [source]

Fluorescence EXAFS for the in situ study on the state of promotors in catalysis

Jan-Dierk Grunwaldt
The fluorescence EXAFS (FLEXAFS) technique has been combined with an in situ cell and on-line gas analysis. For this purpose a seven-element silicon drift detector has been used, which has high count rate capabilities and can be operated at room temperature. The potential of this technique is shown by the study of the state of copper promoter atoms in Fe-Cr based high temperature shift (HTS) catalysts. The FLEXAFS measurements revealed that Cu (0.17,1.5 wt%) is present in the metallic state under working conditions of the catalysts but easily re-oxidizes upon air exposure. The reduction behaviour of copper depends strongly on the copper concentration and the pre-treatment, i.e. if the catalysts have been calcined or used in the HTS reaction. For used catalysts, a Cu(I) phase was detected as intermediate during reduction. Its stability was especially high at low copper concentration. [source]

Commercial carbon nanotubes as heterogeneous catalysts in energy related applications

J. Zhang
Abstract We report the application of commercial carbon nanotubes (CNTs) in two important heterogeneously catalyzed reactions, i.e., NH3 decomposition and oxidative dehydrogenation of ethylbenzene (EB). For NH3 decomposition, CNTs were used as supports for Co,Mo nanoparticles. The structure of fresh and used catalysts was characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and line-scan energy dispersive X-ray (EDX). Most of the nanoparticles are individually separated and the synergism mainly increases the long-term stability rather than the activity. For the oxidative dehydrogenation, the metal-free CNTs display a superior performance as compared to the Fe-doped CNTs. The outstanding results in both reactions predict an extremely promising future of commercial nanocarbons in modern catalysis. [source]

The water-gas shift reaction: from conventional catalytic systems to Pd-based membrane reactors,a review

D. Mendes
Abstract The water-gas shift (WGS) reaction is a well-known step for upgrading carbon monoxide to hydrogen in the production of synthesis gas. For more than 90 years after its first industrial application, many issues in respect of the catalyst, process configuration, reactor design, reaction mechanisms and kinetics have been investigated. More recently, a renewed interest in the WGS reaction carried out in hydrogen perm-selective membrane reactors (MRs) has been observed because of the growing use of polymeric electrolyte membrane (PEM) fuel cells that operate using high-purity hydrogen. Moreover, MRs are viewed as an interesting technology in order to overcome the equilibrium conversion limitations in traditional reactors. This article reviews the most relevant topics of WGS MR technology,catalysis and membrane science. The most used catalysts and relevant progress achieved so far are described and critically reviewed. The effects of the most important parameters affecting the WGS in MRs are detailed. In addition, an overview on the most used membranes in MRs is also presented and discussed. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]