Molybdena alumina

Stepwise Ce dehydrocyclization was observed over potassia-chromia-alumina as well as potassia-molybdena-alumina catalysts (9, 10). Higher operating temperatures (450°-500°C) of these catalysts facilitate the appearance of unsaturated intermediates in the gas phase. Radiotracer studies indicate a predominant Ce ring closure of C-labeled n-heptane over pure chromia (132,132a). 

The top three spectra of Fig. 29 represent an effort to use the spectra to identify the environment of cobalt in a typical cobalt-molybdena-alumina catalyst of approximate composition 5% cobalt, 10% M0O3. The X-ray... 

Fra. 29. Spectra of cobalt-molybdena-alumina catalyst and related compositions, C oMo04, and a coprecipitated cobalt alumina catalyst (all three samples were calcined in air) also spectrum of cobalt-alumina catalyst reduced in hydrogen. 

Hydrodesulfurization uses sulfided cobalt/molybdena/alumina, or alternately with nickel and tungsten substituted for Co and Mo. 

A differential flow microreactor was used for the preparation of the nitrided catalyst and the TPD, TPR, and NH3-TPD measurements. Nitriding of the molybdena-alumina and alumina was carried out by temperature-programed reaction with NH3 (NH3-TPR).1719 The MoCV A1203 precursor was oxidized at 723 K for 24 h, cooled to 573 K, reacted with NH3 at 49.6 (xmols-1 from 573 to 773, 973 or 1173 K at a rate of 0.0167 Ks-1, held at the nitriding temperature for 3 h, and then cooled to room temperature (RT) in flowing NH3. The catalysts were characterized by TPD, TPR, and NH3-TPD under in situ conditions, while BET and diffuse reflectance FTIR measurements were carried out after passivation. For the diffuse reflectance FTIR study, the catalysts after NH3 treatment... 

Surface molybdenum species and acid sites on nitrided molybdena-alumina catalysts... 

It is obvious that there are many differences in results found and interpretations made on the state of molybdena-alumina catalysts, especially the sulfided state. Nevertheless, some common ground exists in these investigations, and we shall try to present a general picture of the state of these catalysts, pointing out areas of major disagreement that still persist. We shall limit our discussion to catalysts below 15% Mo and 4% Co, which encompasses the formulations of most commercial catalysts. 

Shuikin (370) passed methyl and dimethyl cyclohexanes over nickel at 330-350°. In addition to the usual demethylation and dehydrogenation reactions, he found evidence of methyl transfer methylcyclohexane gave some p-xylene, while dimethylcyclohexane gave some trimethylbenzene. Platinum at these temperatures did not cause this methyl transfer. Plate and O. A. Golovina (306) reported that appreciable demethylation of 2,2,4-trimethylpentane took place over molybdena-alumina at 150-250°C. and was accompanied by the formation of small amounts of aromatics. 

The properties of silica- and/or alumina-supported molybdena catalysts for propene metathesis were studied by Handzlik and coworkers. These materials could be prepared by thermal spreading of Mo02(acac)2 with well-dispersed molybdenum in a wide range of its loading. The selective metathesis activity depends on the substrate and on the surface molybdenum concentration. For example, a higher activity is found for the molybdena-alumina system at high Mo loadings. 

The composition of a reforming catalyst is dictated by the composition of the feedstock and the desired reformate. The catalysts used are principally molybdena-alumina, chromia-alumina, or platinum on a silica-alumina or alumina base. The nonplatinum catalysts are widely used in regenerative process for feeds containing, for example, sulfur, which poisons platinum catalysts, although pretreatment processes (e.g., hydrodesulfurization) may permit platinum catalysts to be employed. 

Granular xerogels such as alumina, molybdena-alumina, silica, and aluminosilicate were impregnated with a solution of niekel nitrate and then dried and heated for 2 hours at 500° in an air oven. 

During the Second World War methylcyclohexane was transformed into toluene over molybdena/alumina catalysts. An attempt was made to use the same process for the catalytic reforming of naphtha in order to increase the octane number by carrying out isomerisation, cyclisation and dehydrogenation of... 

Hydrodesulfurization of Dibenzothiophene on a Nitrided Supported Molybdena-Alumina Catalyst... 

Problem 9.11 Metal-oxide catalyzed polymerization of ethylene was carried out in benzene solution in a stirred autoclave with a suspension of hydrogen-reduced molybdena-alumina catalyst (Friedlander and Oita, 1957). The pressure was maintained nearly constant by repressuring the autoclave with ethylene as it was consumed in the polymerization process. Temperatures of 200-275°C were studied. The ethylene concentration in solution was controlled by adjusting the pressure (in the range 625 to 1000 psi) at any particular temperature. The ethylene uptake rate (rate of pressure drop, dPIdt) was mea-... 

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