Catalysts 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. 

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. 

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-... 

Dehydrogenation over Molybdena—Alumina. Detailed results have been reported previously (12) for molybdena-alumina catalysts. It appears that freshly prepared molybdena-alumina catalysts are strongly acidic and exhibit very high activity but poor selectivity towards monoolefin formation initially. After about 24 hours, these catalysts become... 

Rather than survey all of the possible modifications that can be made to an alumina surface, we will focus on a subset involved in two different types of surface-catalyzed chemical reactions, namely, the partial oxidation of ethylene to ethylene oxide (EO) and hydrodesulfurization (HDS) processes. Both of these catalytic systems have functional points in common, in that alumina serves as a support (a-alumina for the EO process and 7-alumina for the HDS process) and alkali-metal salts serve as promoters for both reactions. To illustrate this commonality, this section will be divided into three parts (1) the adsorption of alkali-metal salts to 7-alumina, as reflected in the Rb and Cs solid-state NMR spectroscopy of these systems (2) the absorption of ethylene to silver supported on aluminas in the presence and absence of cesium salts, as followed by C NMR spectroscopy, and (3) the solid-state Mo NMR of fresh and reduced/ sulfided molybdena-alumina catalysts. 

Effects of additives on the hydrodesulfurization of dibenzothiophene on nitrided molybdena-alumina catalyst... 

K. Segawa and W.K. Hall, Site selective chemisorptions on molybdena-alumina catalysts, J. Catal, 77(1), 221-231, 1982. 

T. Fransen, O. Vandermeer and P. Mars, Investigation of surface-structure and activity of molybdennm oxide-containing catalysts. 1. Infrared study of surface-structure of molybdena-alumina catalysts, J. CataL, 42(1), 79-86, 1976. 

K. Segawa, N. Koizumi, M. Yamada, A. Nishijima, T. Kabe, A. Ishihara, T. Isoda, I. Moshida, H. Matsumoto, M. Niwa, T. Uchijima, A study on the preparation of supported metal oxide catalysts using JRC-reference catalysts. I. Preparation of a molybdena-alumina catalyst. Part 3. Drying process. Applied Catalysis A General, 170 pp. 343-357, 1998. 

Handzlik, J. and Ogonowski, J. (2000) Theoretical study on active sites of molybdena-alumina catalyst for olefin metathesis, in Corma, A., Melo, F.V., Mendioroz, S. and Fierro, J.L.G. (eds.). Studies in Surface Science and Catalysis 130, pp. 1181-1186. 

Engelhard , J., Goldwasser, J., and Hall, W.K. The isomerization and metathesis of n-butenes IV. Reactions of cw-2-butene over a molybdena-alumina catalyst of varying extents of reduction. J. Mol. Catal. 1982,15,173-185. 

Handzlik, J. and Ogonowski, J. Theoretical study on ethene metathesis proceeding on Mo and Mo methyhdene centers of heterogeneous molybdena-alumina catalysts. J. Mol. Catal. A Chem. 2001,175, 215-225. 

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