Characterisation of heterogeneous catalysts (Chemical Industries Series, Vol.15), Edited by Francis Delannay, Marcell Dekker Inc., New York, 1984, x + 424 pp., Price:SFr 185; ISBN 0-8247-7100-1 (original) (raw)
ChemInform Abstract: Reaction Mechanism and Deactivation Modes of Heterogeneous Catalytic Systems
ChemInform, 2011
Solving the problem of catalyst deactivation is essential in process design. To do this, various aspects of the kinetics of processes with catalyst deactivation, and their different mechanisms, are discussed. Catalyst deactivation often cannot be avoided, but more knowledge on its mechanism can help to find kinetic means to reduce its harmful consequences. When deactivation is caused by coke, the generation of coke precursors is the determining step in the deactivation kinetics. Different types of deactivation were distinguished that lead to different evolution of the process. The phenomenon of non-uniform coking can be linked to catalyst surface non-uniformity. For the class of catalysts with more than one type of active sites, an explanation was suggested for the observed trends in the deactivation modes. For catalytic processes using catalyst particles of industrial size, the influence of intraparticle diffusion resistance is important. The analysis showed that for a number of processes, the decrease of the reaction rate due to deactivation is less under diffusion control. For certain reaction mechanisms, there exist operation conditions where the rate of the process under diffusion control exceeds the rate in the kinetic control regime. A significant problem is the change of selectivity in the course of catalyst deactivation. The selectivity may either decrease or increase, and depends on the reaction mechanism during deactivation. The changes are larger when there is no diffusion resistance. The intentional poisoning of catalysts and its influence on catalyst activity and selectivity for the process of ethylene oxide production was discussed.
Concluding remarks: progress toward the design of solid catalysts
Faraday Discussions, 2016
The 2016 Faraday Discussion on the topic "Designing new Heterogeneous Catalysts" brought together a group of scientists and engineers to address forefront topics in catalysis and the challenge of catalyst design-which is daunting because of the intrinsic nonuniformity of the surfaces of catalytic materials. "Catalyst design" has taken on a pragmatic meaning which implies the discovery of new and better catalysts on the basis of fundamental understanding of catalyst structure and performance. The presentations and discussion at the meeting illustrate rapid progress in this understanding linked with improvements in spectroscopy, microscopy, theory, and catalyst performance testing. The following essay includes a statement of recurrent themes in the discussion and examples of forefront science that evidences progress toward catalyst design. Catalysis and catalyst design Catalysis is the key to control of chemical change, in processes ranging from the biological to the technological. It is used to make products including chemicals, fuels, materials, food, beverages, and personal care products, and together these have a value of roughly 5-10 trillion dollars (US) per year worldwide. Catalysis is also essential for the removal of environmental pollutants such as those generated in motor vehicles and fossil fuel-fired power plants. Thus, the science underlying catalytic technology is essential. Catalysis science is also challenging, because almost all large-scale industrial catalysts are solids. These work at their surfaces-and these surfaces are notoriously nonuniform in both composition and structure, often being substantially different from simple terminations of the bulk material-and they undergo changes when exposed reactants.
The use of a localized heating protocol in heterogeneous catalysis
Journal of Molecular Catalysis A: Chemical, 2003
The catalyzed decomposition of ethylene has been used as a probe reaction to ascertain the advantages of exclusive heating of a supported metal catalyst by a current stimulated technique. This approach has been found to result in the elimination of certain side reactions generally encountered in conventional catalytic reactor systems associated with thermal decomposition of gas phase molecules. We have found that by restricting the heated zone to the catalyst surface the ubiquitous formation of pyrolytic carbon arising from thermal decomposition of hydrocarbons can be effectively mitigated. In addition, major differences in the selectivity patterns were observed from the localized heating system compared to that found when the same catalyst was reacted in a conventional flow system. The difference in behavior of the catalyst under these diverse conditions is rationalized according to the notion that the flow of an electric current through the support not only served to resistively heat the sample, but also induced electronic perturbations in the metal surface atoms.
Characterization of acidic and basic properties of heterogeneous catalysts by test reactions
2005
4.3 Hydrotalcite derived from mixed Mg-Al oxides………………………………………...61 4.3.1 Acid-base properties of the hydrotalcite derived from mixed magnesium aluminium oxides…………………………………………………………………………………63 4.3.2 X-ray diffraction (XRD)……………………………………………………………..64 4.3.3 Infrared spectroscopy (FTIR)………………………………………………………..66 4.3.4 Structural and chemical composition of the mixed magnesium aluminium oxides…68 4.3.5 BET measurements…………………………………………………………………..69 4.4. Methyl butynol conversion……………………………………………………………...73 4.4.1 Catalytic activity of methyl butynol over different silica alumina with different ratios at different reaction temperatures 120 °C, 180 °C……………………………73 4.4.2 Influence of reaction temperature and treatment preparations of the sample reaction behavior……………………………………………………………..77 4.4.3 Influence of the deactivation process on the methyl butynol catalytic activity ……..83 4.4.4 The dependency of the selectivity of 3-methyl-3-buten-1-yne as a function of the conversion depending on the silica content over different l ratios…………………...86 4.4.5 The formation of 3-methyl-3-butyn-2-one as a function of the conversion depending on the silica content over different silica alumina ratios……………………………..87 4.4.6 Correlations and formation of 3-methyl-3-butyn-2-one as primary product over silica alumina solids………………………………………………………………….89 4.5 Effect of water on the conversion of methyl butynol……………………………………93 4.6 Determination of activation energy in the methyl butynol conversion………………….96 4.7 Basicity of hydrotalcite derived from mixed magnisium oxides studied by methyl butynol test reaction……………………………………………………………104 4.8 Conversion of isopropanol……………………………………………………………...108 4.9 Knoevennagel condensation…………………………………………………………….112 5. Conclusions………………………………………………………………..118 6. References…………………………………………………………………122 7. Appendix…………………………………………………………………..128
International Journal of Chemical Kinetics, 2016
Non-steady-state kinetic measurements contain a wealth of information about catalytic reactions and other gas-solid chemical interactions, which is extracted from experimental data via kinetic models. The standard mathematical framework of microkinetic models, which are typically used in computational catalysis and for advanced modeling of steady-state data, encounters multiple challenges when applied to non-steady-state data. Robust phenomenological models, such as the steady-state Langmuir-Hinshelwood-Hougen-Watson equations, are presently unavailable for non-steady-state data. Herein, a novel modeling framework is proposed to fulfill this need. The rate-reactivity model (RRM) is formulated in terms of experimentally observable quantities including the gaseous transformation rates, concentrations, and surface uptakes. The model is linear with respect to these quantities and their pairwise products, and it is also linear in terms of its parameters (reactivities). The RRM parameters have a clear physicochemical meaning and fully characterize the kinetic behavior of a specific