Molybdena, deposition

Initially tests were conducted in glass equipment at atmospheric pressure. It was discovered that a more durable catalyst could be made if the Group VI metal oxide were deposited on an alumina support. The best support found for this reaction was alumina, and the first commercial catalyst was made by impregnating a material very similar to activated alumina 1 with a molybdenum salt solution, followed by drying and calcining at a temperature above 1000° F. Interestingly enough, the supported chromia catalyst which showed a marked superiority over the supported molybdena catalyst at atmospheric... 

By temperature compensations, such results can be sustained for periods of a few hundred hours. However, a slow continuing deactivation occurs, and eventually the catalyst must be regenerated by combustion of the deposited coke. After regeneration, reasonable dehydrogenation results are again obtained after a rapid initial deactivation of the catalyst. Steam was found to be a particularly useful diluent with this type of catalyst. In contrast to this, the best results with molybdena-alumina for catalytic reforming are obtained over fresh catalyst and when steps such as dilution with hydrogen are employed to repress the initial rapid deactivation. 

The amount of coke deposited on molybdena/alumina at the time it affords reasonable dehydrogenation selectivity is somewhat variable and depends on the surface area of the alumina support. Carbon contents of selective catalysts have been generally to be in the range of 5 to 20 wt %. 

After a preliminary study of the properties of a number of platinum and nickel catalysts deposited on various carriers (activated carbon, chromia, alumina, molybdena, etc.) a platinum-alumina catalyst was selected for the present investigation with a 0.5 % Pt content. Cyclopentane (238.2 g) was passed over the catalyst at 0.43 hr. i space velocity, 20 atmospheres hydrogen pressure, and a temperature of 460 . As a result 184.3 grams of liquid product were obtained containing 9 % by volume of aromatics including benzene (81.9%), toluene, and p-xylene, and also w-pentane,... 

The benefical effects of phosphorus has stimulated research on its influence on molybdena based catalysts. However, most of the above mentioned literature essentially focused on the influence of phosphorus on the catalytic properties of the modified system and its effect on the dispersion on the active phase deposited on the alumina surface has not yet been investigated. Also, very few works deal with the influence of the sequence of phosphorus incorporation during the preparation step of the MoP/Al,0j catalysts on the surface acidity, dispersion and distribution of the supported phases. As the phosphate ions strongly interact with alumina, competing with molybdate ions, a factor of possible importance is the preparation procedure. 

The authors are collaborating in an extensive joint study in which the preparation, characterisation and function of a range of supported platinum catalysts is being evaluated. In part, this study will compare platinum catalysts prepared using conventional supports (e.g. silica, alumina) with those using less conventional supports (e.g. molybdena) or those prepared by less conventional methods (e.g. metal vapour deposition). The restricted object of the present paper is to compare the conventional Pt/silica prepared within this programme with the standard reference silica-supported Pt codenamed EUROPT-1 for which full preparation and characterisation details have been published (refs. 1-5). 

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