Influence of Catalyst Preparation

5 Influence of Catalyst Preparation. Pebrine reported on the influence of the synthesis conditions of HZSM-5 on the selectivity toward light olefins. Synthesizing ZSM-5 in the presence of a tetra-urea-cobalt(II) complex resulted in an ethylene yield of 24.3 wt% of the hydrocarbon fraction at 43.7% methanol conversion, whereas the conventionally prepared ZSM-5 yielded only 18 wt% ethylene at the same conditions and conversion. Heering et al. mentioned that the conversion of dimethylether on ZSM-5 catalysts crystallized from a sodium-free gel with 1,6-dicunino-hexane as organic base was more selective toward both ethylene and propylene than on a conventionally prepared zeolite in the sodium form from a gel containing tetrapropylammonium. 

Suzuki et al. studied the effect of crystallization time on the catalytic properties of ZSM-5. The highest selectivity toward light olefins was obtained with the catalyst synthesized in the shortest time but long enough to obtain 100% crystallinity. The decrease in selectivity at longer crystallization times can be attributed to an increase of the Al content at the external surface of the crystallites. This also explained the higher rate of coke formation with these catalysts. Juan found that, after complete crystallization, the olefin selectivity on ZSM-5 decreased as a result of the increase of strong acid sites responsible for the 

The crystal size of the zeolites has been found to be an important factor influencing the conversion of methanol to light olefins. With the use of crystals of 1-2 p a higher selectivity for the production of C2 C olefins and particularly ethylene has been 

3 Methanol Conversion to Olefins on Modified ZSM-5. - To increase the selectivity toward light olefins in the conversion of methanol, several modifications of the Mobil ZSM-5 catalyst were proposed. A distinction can be made between the attempts to increase the shape-selective properties and/or to reduce the acid strength by ion-exchange or impregnation of cations or chemical compounds and the attempts dealing with the isomorphous substitution of lattice aluminum atoms to reduce the acidity. 

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In this paper, we investigate the influence of catalyst preparation on the reactivity of hydrotaleite-derived Pt/Mg(Al)0 for n-hexane reaction. In specific, the effects of Pt metal incorporation, metal alloying, and adding alkali promoter are examined. 

The influence of catalyst preparation on the surface properties of fine carbon black-supported platinum particles of similar size (4nm) was investigated. Different adsorption behavior was indicated by varying shapes and fine structures of the vibrational modes of the dissociatively adsorbed atomic hydrogen on these nanoparticles (58b). 

Whatever the case really is, it is important to investigate the influence of catalyst preparation and operation variables on the hydride formation since by influencing it we are indirectly influencing catalyst hydrogenation activity. 

Influence of catalyst preparation, composition, and structure on activity and selectivity. There is an extensive literature some of which has been covered incidentally already. An excellent review has been published by Ripperger and Saum. Much of the work relates to the catalysts as oxides and so will not be covered in detail in this Report. Variables that influence catalytic properties include preparation e.g., method and order of addition of active components), pretreatment (drying and calcination,pre-reduction sulphiding,composition (e.g., concentration and ratio of active components and the type of support), distribution of active components in catalyst particles,particle size, " and surface area and pore size distribution. 

The influences of catalyst preparation, modifler and substrate structure, of various additives, and of reaction parameters have been reported for both the tartrate modifled Ni catalysts [2,4,11 ] as well as for Cinchona modifled Pt catalysts [2, 3, 7]. In addition, kinetic [2, 4,12,13] and molecular modeling studies [8] have been carried out. This experimental basis allows the discussion of their mode of action with some confidence and a mechanistic picture has been developed in the last few years that can explain the major observations, even though it is not accepted universally. 

The work of Greenfield and Malz (25) on the preparation of arylamines illustrates the sensitivity of yield to hindrance and an influence of catalyst. 

In the enantioselective hydrogenation of isophorone in the presence of (-)-DHVIN modifier the best optical purity was afforded by small dispersion (<0,05) Pd black catalyst (up to 55%) (7). The influence of the preparation method of Pd black on the optical yield was reported (8). A correlation was found between the oxidation state of the metal surface and the enantioselectivity, the catalyst having more oxidised species on its surface giving higher enantiomeric excess, while the Pd black with lower surface area was more enantioselective. 

Sarellas A., Niakolas D., Bourikas K., Vakros J., and Kordulis C. 2006. The influence of the preparation method and the Co loading on the structure and activity of cobalt oxide/y-alumina catalysts for NO reduction by propene. J. Colloid. Interf. Sci. 295 165-72. 

Ataloglou T., Vakros J., Bourikas K., Fountzoula C., Kordulis C., and Lycourghiotis A. 2005. Influence of the preparation method on the structure-activity of cobalt oxide catalysts supported on alumina for complete benzene oxidation. Appl. Catal. B Environ. 57 299-312. 

Less clear is the sequence which leads to the formation of the active species in the case of catalysts prepared from zero-valent nickel complexes and aluminum halides or alkylaluminum halides (method C2). The catalytic properties of these systems, however—in particular, the influence of phosphines (76)—leaves no doubt that the active species is also of the HNiY type discussed above. In this connection, a recent electron spin resonance report that nickel(I) species are formed in the reaction of COD2Ni with AlBr3 (83 ), and the disproportionation of Ni(I) to Ni(II) and Ni(0) in the presence of Lewis acids (69) should be mentioned. 

The influence of different preparation methods upon the structure and reactivity of supported vanadia catalysts has recently been investigated by several laboratories.55 58 These studies concluded that the same surface vanadia species forms on a specific oxide support independent of the preparation method, even when starting with V205 crystals. The reason for this phenomenon is that vanadium oxide spontaneously disperses on oxide supports to form surface vanadia species, which is schematically depicted in Figure 7. 

For the preparation of BR with a narrow MMD the influence of catalyst addition order and catalyst preformation/aging was first recognized by Jenkins et al. [391,392], Catalyst preformation at - 15 °C to - 60 °C and catalyst aging at - 20 °C to - 40 °C were essential to obtain BR with a relatively narrow MMD (Mw/Mn < 3.1) and low intrinsic viscosities. These results were obtained with the catalyst systems NdV or NdN/TEA/ BuCl. The sequence of addition occurred in the following order TEA + Nd component + (BuCl. 

Most kinetic studies on copolymerizations using coordination catalysts have been restricted to the determination of monomer reactivity ratios. There are problems both experimentally and in interpretation since the major simplification assumed to hold for most free radical initiated systems, namely that monomer incorporation is determined only by the monomer concentrations and the four rate coefficients, cannot be taken for granted. Further, catalyst activity and selectivity are influenced by the conditions of catalyst preparation including the manner and order of... 

The influence of the preparation method of methanol catalysts composed of copper associated with rare earth oxides (eg Cu-La2Zr207 and ZnO promoted Cu-La2Zr20y systems) on the catalytic behaviour is discussed. Good activities and improved aging properties are always associated with a high copper surface area and a reasonnable crystallinity of the La2Zr207 pyrochlore. 

Figure 1. Influence of the preparation technique on the activity of Cu-ZnO catalysts...

The physical and chemical properties discussed above are influenced by every step of the preparation process as well as the choice of raw materials. In addition, several preparation routes may be available to obtain a catalyst with specific properties. On developing a catalyst for industrial applications, the influence of the preparation procedure on these properties must be taken into consideration as well as economical production of a material. Examples of industrial catalytic processes and the method of manufacture of the catalysts are shown in Table 1. This table illustrates the many different types of catalysts as well as preparation methods used in industry. 

Guevara-Lara, A., Bacaud, R., and Vrinal, M., Highly active NiMo/TiOj-AIjO, catalysts Influence of the preparation and the activation conditions on the catalytic activity, Appl. Catal. A, 328, 99, 2007. 

Influence of the preparation method on the surface properties and activity of alumina - supported gallium oxide catalysts... 

Preparation and properties of bimetallic Ru-Sn sol-gel catalysts influence of catalyst reduction... 

Our work is a tentative to rationalize the influence of the preparation parameters over the composition, active phase and catalytic activity. Modifying the pH of precipitation between 6.0 and 8.5, the surface area, the bulk, the surface composition and the active phases of the catalysts were modified significantly. Raman spectroscopy has revealed the presence of M0O3 phase only in the catalyst prepared at pH 6.0. From the literature data, we know that the precipitation of the Ni(OH)2 and Co(OH)2 occurs at pH 7 and 7.5, respectively. At pH higher than 7.5 our calculations suggest the presence of nickel or/and cobalt oxides but these phases were not detected with any of the characterization techniques used. 

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