Bulk catalyst

Bulk catalysts have the highest concentration of active metals. However, the active metals may have low dispersion and a high probability exists that inactive crystalline compounds, for example, C0M0O4 (NiMo04 , will be formed during their thermal treatment [41-43]. 

Drying and Calcination of Catalysts Prepared by Comixing/Coextrusion and Coprecipitation Routes 

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One of the key factors controlling the reaction rate in multiphasic processes (for reactions talcing place in the bulk catalyst phase) is the reactant solubility in the catalyst phase. Thanks to their tunable solubility characteristics, the use of ionic liquids as catalyst solvents can be a solution to the extension of aqueous two-phase catalysis to organic substrates presenting a lack of solubility in water, and also to moisture-sensitive reactants and catalysts. With the different examples presented below, we show how ionic liquids can have advantageous effects on reaction rate and on the selectivity of homogeneous catalyzed reactions. 

The alumina content of the E-cat is the total weight percent of alumina (active and inactive) in the bulk catalyst. The alumina content... 

Depending on the process requirements catalysts are produced in a variety of ways. Fig. 3.12 shows some typical processes used in catalyst manufacture. In all cases the process starts from a solution. The various process steps used arc explained in subsequent sections. Solid catalysts can be subdivided in bulk catalysts and supports and catalysts prepared by impregnation of shaped supports. 

The results presented in this paper therefore show that V and Mo species supported on alumina can give rise to a catalyst which has a high selectivity for the oxidation of propane to propene and a reasonable selectivity to acrolein and that both species are essential to give the optimal behaviour. Contrary to our previous observations and what observed for bulk catalysts [5], the presence of Nb and W seem to have little effect, perhaps because the methods used here restrict the active phase to a monolayer whereas previously prepared materials may have contained multilayer oxidic species. 

Similarly, Bond et al. [4] confirmed that the microwave stimulation of methane transformation reactions in the presence of a number of rare earth basic oxides to form C2 hydrocarbons (ethene, ethane) was achieved at a lower temperature and with the increased selectivity. Microwave irradiation resulted in an increase of the ethene/ethane ratio, which was desirable. The results obtained were explained by the formation of hot spots (Sect. 10.3.3) of higher temperature than the bulk catalyst. This means that methane is activated at these hot spots. 

These highly porous glasses retain a rigid and exposed interfacial surface area (typically 300-1000 m g ), whereas conventional organic polymer beads swell and shrink in different solvents, often with unpredictable effects on catalysis Functionalization of a monolithic (largest dimension 1 mm) gel affords a bulk catalyst sample. This obviates the need for filtration to recover the catalyst tweezers can be used instead ... 

Ni-Pd. Moss et al. (252) reported that 60% Pd (in bulk) catalysts (i.e., those which have almost 100% Pd in the surface) had almost the same activity in ethane hydrogenolysis as pure Ni, although pure Pd itself is not very active. This might be an indication that for this reaction mixed ensembles of Pd-Ni can operate. In this respect it is interesting that Driessen recently found that in contrast to this, a 75% Pd (bulk) catalyst [the exchange reaction detected (255) the presence of some Ni in the surface of a catalyst of this composition] showed no activity in methanation, compared to Ni. 

Anderson and Kemball (41) investigated the exchange of both these compounds on metal films at low temperatures, and Burwell and his colleagues S9, 37, Ji2) have used bulk catalysts and also films over a wider range of temperature. There is now a good measure of agreement between the views of the two schools. 

The character of the exchange reaction of most hydrocarbons is similar on films and on bulk catalysts of the same metal. 

The surface concentration of 2-methylpropene and oxygen ions is not a function of PC4h8 and P021/2 only but also depends on the positive hole concentration in the valence band of the bulk catalyst, An in-... 

Ni-Ta-Nb oxide catalysts also show high activity for the conversion of ethane to ethylene in primary screening tests. For further optimization bulk catalysts were prepared to perform secondary screening in an 48-channel fixed-bed reactor at 300 °C (see Table 3.4).The highest selectivity (86%) for ethylene was achieved with an Nio.62Tao.ioNbo.28°x catalyst [7]. 

Heterogeneous catalysis deals with reactions between species that are adsorbed onto the surface of a catalyst. The role of the catalytic surface is to provide an energetically favorable pathway for the reaction. In order to find an explanation for the catalytic activity of substances, it is essential that we examine the properties of the surface, rather than at a collective property of the bulk catalyst. 

Chemical applications Sealants, adhesives, insulation films, bulk catalyst carriers... 

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