Showing papers in "Cattech in 2001"

Silicon Carbide: A Novel Catalyst Support for Heterogeneous Catalysis

Abstract: Progress in developing a new class of support materials based on silicon carbide (SiC)is reviewed. Silicon carbide has superior mechanical and thermal properties which, coupled to chemical inertness,avoids several of the problems inherent in the use of commercial oxide and carbon based supports and catalysts. High surface area SiC can now be prepared easily in a commercially viable shape,with good mechanical properties,and at reasonable cost.I t can be shaped directly into monolith or honeycomb forms including some catalytically active material, rendering fabrication simple and cost effective. Furthermore, it can be modified for specific catalytic applications through the addition of metals. In many respects, it combines the best properties of oxide and carbon based supports without suffering many of their disadvantages.

Eurokin - Chemical reaction kinetics in practice.

Abstract: The chemical reactions taking place in the chemical reactor form the heart of any chemical process. Reaction kinetics are the translation of our understanding of the chemical processes into a mathematical rate expression that can be used in reactor design and rating. Because of the importance of correct and safe design of chemical reactors, chemical reaction kinetics is a key aspect of research and development in chemical industries, in research institutes, and academic centers, as well as in industrial laboratories. There is, and there will always be, a strong need for knowledge and a skill base concerning the determination of reaction kinetics and their application in the form of a kinetic model. This paper is a result of cooperation within Eurokin, a consortium of over 10 European companies and 4 universities. An industrial questionnaire in 1995 highlighted that industry is not only a little conservative in the methods it uses to determine kinetics, but also that there was a wide awareness of the scope for improvement. Eurokin was thus founded in 1998 to try and establish the best practices and to facilitate development work in kinetics and associated areas. The paper briefly explains some underlying theory of heterogeneously catalyzed chemical reactions and their kinetics. It deals specifically with the acquisition of kinetic data, and gives recommendations for the selection of the experimental reactor and conditions. A primary aim of this paper is discuss kinetic experimentation and modeling through a series of case studies, attempting to illustrate good practice, methods in kinetic modeling, pitfalls, and recommendations. The paper closes with some recommendations and a perspective on the future needs of industrial reaction kinetics.

Fuels and Chemicals Manufacturing; Guidelines for Understanding and Minimizing the Production Costs

Abstract: With increasing frequency,scientists and engineers are expected to understand and estimate the economic impact of their research and development effortsHere,we provide simple concepts and tools used to understand the major cost contributions (eg,feed,investment or catalyst,and chemicals) for existing and emerging manufacturing technologies of chemicals and fuelsParticular attention will be paid to (i)selectivity and productivity for existing plants,(ii)energy management and its impact on investment costs,and (iii)cheaper feedstocks and their potential impact on investment costs

Assembling molecular guidance systems for heterogeneous enantioselective catalysis

Abstract: Creating successful heterogeneous enantioselective catalysts remains an important goal for the chemicals and pharmaceuticals industries, with considerable attention being focused on chirally modified metals as promising candidates. Here, recent surface science results are reviewed, which throw a new and intriguing light on these modified metal surfaces, highlighting new phenomena such as complex adsorption phases, two-dimensional organization, and the surprising creation of extended chiral surfaces. This molecular level information provides an important and fresh input into future design strategies.

Photocatalysis and Photosorption in the Earth's Atmosphere

Abstract: The troposphere of Earth is abundant in particles of solid and liquid aerosols which have a large specific surface area and can be activated by visible light and mild ultraviolet (UV) solar radiation with wavelengths λ > 300 nm for promoting different photocatalytic and photoadsorption processes. This paper discusses possible heterogeneous photocatalytic and photosorption phenomena on the surface of solid tropospheric aerosols. These phenomena can proceed in nature at ambient conditions and can make an important contribution to the global chemistry of the Earth's atmosphere. For example, the particles of semiconductor metal oxides like TiO2, ZnO, and Fe2O3 are able to photocatalyze oxidation of organic compounds from the atmosphere by air oxygen and even mineralize them. For insulator metal oxides like SiO2, Al2O3, MgO, and CaO, which are the main components of tropospheric solid aerosols, a substantial depletion of many halogen-containing organic compounds (freons) is possible via their destructive photoadsorption. All mentioned processes appear to be driven by mild solar UV radiation and can proceed in the troposphere, in contrast to direct photochemistry which can take place only in the upper layers of the atmosphere.

Catalysis in the 21st Century, Lessons from the Past, Challenges for the Future

Abstract: Catalysis is a science relying on many disciplines. The advent of industrial catalytic technologies in the last century has, most often, resulted from a sequential interaction between chemists and chemical engineers, both communities developing their own fundamental and applied sciences, i.e., a multidisciplinary process. Some of the major lessons learned in the past century, and related achievements, are illustrated and discussed. Challenges for catalysis research in the 21st century are identified, based on the current knowledge of catalysis researchers, recent fundamental and applied developments, and current or long-term objectives of the global chemical industry.

The Effect of Silanization on the Catalytic and Sorption Properties of Zeolites

Abstract: Silanizing a zeolite can result in significant beneficial changes to their catalytic and sorptive properties. It has been shown, however, that it is necessary to carefully control the reaction conditions when silanizing a zeolite. Apart from considerations such as the different effects of using vapor or liquid deposition procedures and static or flow systems, deposition temperature and the number of silanization/calcination cycles are of great importance. By careful control of the number of cycles it is possible to systematically modify the diffusional properties of the zeolite while at the same time inertizing the external surface acidity. On the basis of the changes in adsorption properties of the silanized zeolite it is suggested that diffusional changes are more likely due to blockage of pore entrances,resulting in a greater diffusion pathway, than due to a controlled narrowing of the pore openings. By careful control of the number of cycles (i.e., silanization followed by calcination)it is possible to systematically change the diffusional properties to whatever extent is desired. It is shown that the amount of Si deposited/nm2 is a good indicator of the process of silanization. The conversion of TEOS and the products of the silanization reaction at different temperatures have been used to propose a reaction pathway. Results shown for a variety of reactions indicate that silanized zeolites are able to significantly increase the yield of particular isomers as a result of the diffusional constraints resulting from the silanization process.

Theory in Heterogeneous Catalysis; an Experimentalist's View

Abstract: This is a report of an inorganic chemist on the status of theoretical efforts in heterogeneous catalysis. It is intended to highlight trends and opportunities in the area. Only theories aiming at an atomistic description of reactions are considered. The examples are taken from the areas of interest of the author and are used to illustrate some of the general statements. No effort is made to enter into technical details of theoretical concepts or to give an account on current literature.