Catalysts preparation methods

Today the most efficient catalysts are complex mixed metal oxides that consist of Bi, Mo, Fe, Ni, and/or Co, K, and either P, B, W, or Sb. Many additional combinations of metals have been patented, along with specific catalyst preparation methods. Most catalysts used commercially today are extmded neat metal oxides as opposed to supported impregnated metal oxides. Propylene conversions are generally better than 93%. Acrolein selectivities of 80 to 90% are typical. 

Yeong, K. K., Gavriilidis, A., Zapf, R., Hessel, V., Ejfect of catalyst preparation methods on the performance of a microstructured falling film reactor in nitrobenzene hydrogenation, in Proceedings of the 7th International Conference on Microreaction Technology, IMRET 7, 7-10 September 2003, Lausanne, submitted for publication. 

An excellent review of various catalyst preparation methods has been published,1 and an earlier book devoted to patent literature preparations of hydrogenation catalysts is available.2 Special studies of the formation of metal nanoclusters appeared in 1997 and 1998.3-5 What follows is a general summary of methods of preparation. 

Chromium zeolites are recognised to possess, at least at the laboratory scale, notable catalytic properties like in ethylene polymerization, oxidation of hydrocarbons, cracking of cumene, disproportionation of n-heptane, and thermolysis of H20 [ 1 ]. Several factors may have an effect on the catalytic activity of the chromium catalysts, such as the oxidation state, the structure (amorphous or crystalline, mono/di-chromate or polychromates, oxides, etc.) and the interaction of the chromium species with the support which depends essentially on the catalysts preparation method. They are ruled principally by several parameters such as the metal loading, the support characteristics, and the nature of the post-treatment (calcination, reduction, etc.). The nature of metal precursor is a parameter which can affect the predominance of chromium species in zeolite. In the case of solid-state exchange, the exchange process initially takes place at the solid- solid interface between the precursor salt and zeolite grains, and the success of the exchange depends on the type of interactions developed [2]. The aim of this work is to study the effect of the chromium precursor on the physicochemical properties of chromium loaded ZSM-5 catalysts and their catalytic performance in ethylene ammoxidation to acetonitrile. 

In addition, the catalyst preparation method plays an important role sol immobilization appears superior to incipient wetness or impregnation methods. Gold sol immobilization occurs via citrate reduction of HAuCU, yielding a narrow par-... 

Apopinenene, hydrogenation over amorphous palladium alloys catalyst preparation methods and, 36 358-... 

In the results presented in Table 13.5, the addition of tin affects the kinetic selectivity r differently, depending on the catalyst preparation method. When compared to the monometallic PdO catalyst, r slightly decreases for the coimpregnated PdSn catalyst, but it sharply increases for the PdOSn catalyst prepared via the colloidal oxide synthesis. As the intrinsic kinetic constant rates k do not show significant discrepancies between the different catalysts, the main contribution of the variation of the kinetic selectivity is ascribed to the adsorption constant ratio fBo/ Butenes- In the case of the PdOSn catalyst, formation of but-l-ene is favored compared to its consumption because the X Bo/ Butenes ratio increases, indicating that olefin adsorption is much more destabilized than diene adsorption. Thus, the olefin easily desorbs before being hydrogenated into butane. 

In heterogeneous catalysis by metal, the activity and product-selectivity depend on the nature of metal particles (e.g., their size and morphology). Besides monometallic catalysts, the nanoscale preparation of bimetallic materials with controlled composition is attractive and crucial in industrial applications, since such materials show advanced performance in catalytic processes. Many reports suggest that the variation in the catalyst preparation method can yield highly dispersed metal/ alloy clusters and particles by the surface-mediated reactions [7-11]. The problem associated with conventional catalyst preparation is of reproducibility in the preparative process and activity of the catalyst materials. Moreover, the catalytic performances also depend on the chemical and spatial nature of the support due to the metal-support interaction and geometrical constraint at the interface of support and metal particles [7-9]. 

Various a,a,a, a -tetraaryl-l,3-dioxolane-4,5-dimethanols have been prepared from (R,R)-tartrate, which are called TADDOLs by Seebach et al. They studied the influence of the Ti catalyst preparation methods, the presence of molecular sieves, and the TADDOL structure in the enantioselective Diels-Alder reaction of acryloyl oxazolidinones [41] (Eq. 8A.22). Seebach also prepared polymer- and dendrimer-bound Ti-TADDOLates and used in catalytic asymmetric cycloadditions [42],... 

Vendors consider this information proprietary and are hesitant to reveal catalyst preparation methods and properties that may jeopardize their marketing position. No attempt has been made in Table XXIII to identify advantages or redundancies in different manufacturers catalyst products. 

The reactor system of Zech et al. [35] is a good example of an integrated approach as it combines devices from different suppliers into a complex screening system. The reactor was manufactured at IMM (Fig. 4.4) and the sampling device delivered by AMTEC in Chemnitz. The catalyst preparation method was developed at the TU Chemnitz. The latter consists of an x/y-positioning robot supervised by a CCD camera. The sampling capillary was connected to a quadmpole mass spectrometer. This set-up has been used to screen up to 35 catalysts a day. 

Perego, C. and Villa, P. (1997) Catalyst preparation methods. Catal. Today, 34, 281. 

Figure 1 illustrates these four catalyst preparation methods and the anticipated Pt-Sn cluster structures. Note that the conventional preparation methods are expected to yield Pt° and Sn4+/Sn2+ oxides on A1203, while the SMAD methods are expected to yield Pt° and Sn° combinations of differing morphologies. 

As is known structure and properties of CNT and CNF obtained by CVD method in great extent depends on catalyst used in this process. Even for catalysts of the same composition, for instance, well-known Fe203-Mo03/Al203 system, properties and yield of nanocarbon materials strongly depends on the catalyst preparation method. 

Catalysts Preparation method dAu(nm) Rate (molco gXis 1) TOF at 353K(s-1)a... 

Perego C, Villa P. Catalyst preparation methods. Catalysis Today. I997 34(3 4) 28l 305. 

Understanding the role of cafalysf promofers is not a simple matter. Confusion in the interpretation of promofer effects has resulted because different groups have reported contrasting results for the same promoters. The effects of promofers on vanadium phosphate performance was summarized by Ballarini ef al. (8) (Table 1). As illustrated by the work by Sananes-Schulz et al. (196), the catalyst preparation method can alter the effect of the promoter, as can the method of doping. Hutchings and... 

Other catalyst preparation methods include cementation of iron oxide powders with compounds such as Al3(N03)j potasaum waterglass or sodium borate. The imprecation of high surface-area supports such as silica or alumina gels with metal salts have also been investigated. These methods usually lead to catalysts of low activity. 

In the case of catalytic dense membranes such as palladium alloy sheets or tubes, a smooth membrane surface suffers from a small active surface area per unit volume of catalyst. This drawback can be remedied to some extent by adopting some conventional catalyst preparation methods to roughen the membrane suiface(s) to ensure that only the region near the surface is affected unlike the Raney metal catalysts where the entire matrix is leached. For example, Gryaznov [1992] suggested the use of thermal diffusion of a chemically active metal into a Pd alloy sheet followed by acid treatment to remove this metal. 

The effect of phosphorus on PD depends on the catalyst preparation method. The PD of catalysts prepared by impregnation decreases with phosphorus loading, whereas that of catalysis derived from the hydrogel or sol-gel methods tends to increase in some cases. Introduction of phosphorus compounds in the sol-gel procedure may affect the hydrolysis and condensa-... 

Figure 2. Activity to methanol as a frmction of the catalysts preparation method and the reaction mixture (1=523 K, P= 3 MPa, SV= 10 h ). a) Turnover rates b) Specific rates.

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