Activation of Heterogeneous Catalysts
Nontraditional Approaches to the Activation of Heterogeneous Catalysts for Environmentally Important Processes
Tech Area / Field
- CHE-IND/Industrial Chemistry and Chemical Process Engineering/Chemistry
- CHE-SYN/Basic and Synthetic Chemistry/Chemistry
8 Project completed
Senior Project Manager
Institute of Organic Chemistry, Russia, Moscow
- VNIIEF, Russia, N. Novgorod reg., Sarov
- DuPont Corporate Technology Transfer\nRuhr Universität Bochum, Germany, Bochum\nThe Nottingham Trent University, UK, Nottingham\nNorthwestern University, UK, Evanston\nDupont de Nemours, USA, DE, Newark
Project summaryThe project is devoted to the development of nontraditional methods for activation and preparation of heterogeneous catalysts. The aim of the project is to improve the available methods and to develop new methods for physical action (like treatment with plasma, gamma radiation, electron and neutron beams) on the structure of heterogeneous catalysts, to examine the effects of physical activation on the structure of heterogeneous catalysts in detail using physicochemical techniques and, finally, employ the methods of physical activation for tuning the fundamental properties of the catalysts such as catalytic activity, selectivity and stability. These studies are required for the development of efficient methods for improving activity, selectivity and stability of catalysts by physical action. The mechanisms of activation will be develop to make positive structural changes produced by physical activation stable and to eliminate annealing effects resulting in the disappearance of these positive changes.
Heterogeneous catalysis forms the basis of high technology; it is widely used in industry and has a strong environmental impact in the world. Catalysis finds application in such branches of industry as chemical and petrochemical waste treatment, purification of flue gases and exhausts, wasteless processes for synthesis of valuable basic and fine chemicals, oil and gas processing, production of high-octane gasoline. Activation of heterogeneous catalysts used in these processes is the most important step in the preparation because active centers of the catalyst are formed at this stage. Not only the activity, but also the selectivity of catalytic processes can be affected by varying the conditions and methods of catalyst activation.
The commonly used methods for the activation of heterogeneous catalysts are based on thermal treatment. Thus, calcination in oxidative atmospheres (most frequently, in an air flow) to convert intermediates into stable species (as a rule, oxides) is one of the most important stages in the preparation of heterogeneous catalysts. For the activation of catalysts containing metals as active phases, they are reduced in a hydrogen flow before the reaction. High-temperature treatment is also used for the regeneration of deactivated catalysts (for example, for burning coke formed at the catalyst surface).
However, conventional thermal treatment cannot often provide the required activity, selectivity, or stability of the catalyst. The reason is that the treatments at high temperatures may induce a number of undesirable processes leading to the decay of the catalyst structure. As a result, the catalytic activity decreases. Moreover, a wide variety of active sites of different nature and strength are generated by such a treatment; among them are active sites that catalyze undesirable side reactions. Presently, polyfunctional catalysts of more complex structure and composition with highly organized active centers are used in industry and laboratory practice. These catalysts are more sensitive to thermal treatment and require gentle methods of activation and regeneration. Thus, the development of new nontraditional methods for catalyst activation and regeneration becomes more urgent.
These methods require alternative techniques for supplying energy to the catalyst surface other than thermal heating. The use of physical effects on catalysts under high-energy irradiation (gamma radiation, electron and neutron beams) or plasma treatment (cold glow-discharge plasma, afterglow UHF plasma, etc.) has attracted the major attention. In particular cases, with the use of these methods, energy can be delivered to the active centers of the catalyst for activation and regeneration. Thus, undesirable effects typical of commonly used thermal heating can be eliminated.
Moreover, physical methods can generate specific active centers at the catalyst surface, which cannot be obtained by conventional heating. The synthesis of metal and semiconductor nanoparticles is a promising application of physical methods in catalysis. Gamma-radiolysis was successfully used for this purpose. For example, cobalt and nickel nanoparticles on the surface of alumina and platinum nanoparticles in zeolite A were prepared using this approach, and the catalytic properties of these nanoparticles were examined.
Note that studies performed at the IOC RAS concerning the nontraditional activation of heterogeneous catalysts also demonstrated that this area of research is promising. Microwave irradiation was found to considerably increase the activity of supported metal catalysts. Zeolite-based catalysts were also successfully regenerated by plasma treatment.
The aim of this project is to combine the experience of IOC RAS in the preparation and characterization of heterogeneous catalysts with the facilities and expertise of specialists at the RFNC-VNIIEF in the generation and use of various kinds of radiation.
The following studies will be performed within this project:
(1) Study of the effect of physical activation techniques on the structure of metal particles in supported catalysts.
(2) Complex study of the effect of physical activation on the acid-base properties of heterogeneous catalysts.
(3) Study of the effect of physical factors on metal complex catalysts.
(4) Development of the new methods of physical action on the catalyst structure for improving the activity, selectivity, and stability of heterogeneous catalysts.
Catalysts prepared using nontraditional activation methods and traditional systems will be tested in a wide range of catalytic reactions including the following:
· paraffin hydroisomerization;
· hydrogenation of acetylene, dienes, and aromatic hydrocarbons;
· selective oxidation of benzene and its derivatives to phenols;
· ethylene epoxidation;
· methane aromatization;
· other redox reactions.
The systems listed below will be examined in relation to the effect of physical activation on the catalytic and physicochemical properties:
· transition and noble metals (Pt, Pd, Ni) supported on various carriers;
· zeolites of various structural types, compositions, and with different acid-base properties (particular attention will be paid to high-silica zeolites: ZSM-5, BETA, mordenite);
· binary and mixed oxides including those modified with supported cations and anions;
· metal and semiconductor nanoclusters encapsulated in various matrices;
· heterogenized metal complexes on various supports.
For studying physical effects, the following equipment available at the RFNC-VNIIEF will be used: an LU-10-20 electron accelerator, a high-frequency plasma generator, and a low-temperature glow-discharge plasma generator. The catalyst characterization and study of physical effects will be performed using physical and physicochemical techniques available at the RFNC-VNIIEF and IOC RAS: IR spectroscopy, EPR spectroscopy, X-ray photoelectron spectroscopy (XPS), electron microscopy, atomic emission (AES) and atomic absorption spectroscopy (AAS), X-ray diffraction analysis, etc.
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