Structure catalyst life

This pore size distribution was shown to provide an optimum pore structure for platinum reforming catalyst activity, selectivity and catalyst life. This catalyst eventually was commercialized and became the famous RD-150 still in use in only slightly modified form. 

The catalyst system originated from the Knapsak catalyst (76) for the am-moxidation and catalysts found in Nippon Kayaku (78-80) for simple oxidation. A number of catalyst systems have been indicated in the patents in the past 25 years, and some of them are used practically in the industrial production. Strictly speaking, almost all catalyst systems may be designed and prepared on the same principle irrespective of their different compositions. The catalyst system is generally expressed as shown in Fig. 5. The first four elements are essential and consist of a fundamental structure of the catalyst system, and the other elements are added for the enhancement of the catalyst life and mechanical strength and minor improvement of the catalytic activity and selectivity. 

Newson (1975) was among the first to develop a pore plugging model of demetallation to predict catalyst life. By using the pore structure model of Wheeler (1951), the pellet was assumed to have N pores of identical length but with a specified distribution of pore radii. Metal deposition was assumed to be a first-order reaction over an outer fraction of the pore length and to have a uniform thickness. This model showed that the broadness of the size distribution had little effect on the catalyst life for the same average radii, but that increasing the radii from 45 to 65 A more than doubled the catalyst life. The restricted form of the diffusivity (see Section IV,B,5) was not employed in this model. 

Catalyst life might be extended by the development of low-ash lubricating oils and by modifying carrier properties such as surface chemistry, pore structure, and surface area, to create contamination-resistant catalysts. 

For catalyst design purposes it is first necessary to translate the catalyst performance parameters into a physical picture of catalyst structure. As we shall see, different performance parameters can give rise to different structural features and so a compromise is generally required. For example it is commonly found in industrial applications that initial catalyst activity may be sacrificed in favour of improved catalyst stability, since a lower activity and a prolonged operating catalyst life is in general preferable to a higher initial activity that decays rapidly. First, we should therefore discuss some of the relationships between the catalyst performance parameters and physical structure. 

Because of their salt-like structure, the quaternary ammonium salts enable a selective continuous separation of phosphine oxides and degradation products during the hydroformylation reaction and thus a prolongation of catalyst life-time [38]. The amine backbone can be re-used. The finally recovery of valuable metal, anions, or cations is possible by simple neutralization reactions. 

Catalyst coking in the liquid phase is one of the least understood aspects of hydrotreating. Little is known about the structure and morphology of the coke. This is also the case for the exact location of coke on the surface in relation to the active phase. The present paper presents data concerning coke in the very first period of the catalyst life. 

C for 30 min. and having a surface area of 20 m g was preferred. The preparation and structure of this support is described elsewhere (ref. 9). This HT-alumina is relatively unreactive to W0 and satisfactory catalysts have been prepared with loadings of 1 % by weight. Better catalyst life is achieved with 6% WOj/HT-alumina and the tests described here were made on such catalysts. 

Mordenite is a large pore zeolite with elliptical pores defined by 12 oxygen atoms and major and minor axes of 7.1 A and 5.9 A, respectively.35 Figure 9.17 provides a schematic for mordenite s structure.34 These dimensions mean that n-and isoparaffins can enter the pores where they react under the acidic conditions. However, these pore dimensions have also been interpreted to mean that larger molecules can also enter the pores36 and react to form coke,37 limiting catalyst life. 

Co(II) or Cu(II) histidine or imidazole complexes were immobilized in porous matrices (montmorillonite and MCM-41) via two methods (introduction of preformed complex or complex formation within the ion-exchanged host substances). It was found that immobilization in general and the latter method in particular increased catalytic activity and catalyst life time in the decomposition reactions of hydrogen peroxide relative to the matrix-free complexes. The immobilized materials were characterized by experimental and computational methods and the structures of the guest molecules inside the hosts were also investigated. 

From 1940, when synthesis gas first was prodnced from natural gas rather than coal, single-stream ammonia plants were developed and the process was subject to an ongoing series of improvements. Improved catalysts based on the same natural magnetite were made as the internal structure of magnetite and the function of the promoters could be investigated with modem analytical procedures. Catalyst life with purer synthesis gas can now exceed 15 years. 

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