Zeolites molybdenum loaded

Temperature-programmed desorption of ammonia from molybdenum-loaded Y-zeolites... 

Table I shows the results of catalytic activity in the WG5 reaction, expressed as the reaction rate constants, for the series of nickel-free and nickel enriched molybdenum loaded Y-zeolites. The data concerning alumina based Co-Mo industrial catalysts are presented only for comparison reasons.

Studies performed in previous years (ref.3-5) over molybdenum loaded zeolites in HDS reaction showed that reactivity of these catalysts depends on the type of zeolite used, concentration of transition metal and the way of preparation. However, preparation of molybdenum based catalysts applying ammonium heptamolybdate usually results in low dispersion of molybdenum sulfides and relatively low activity. Recent studies showed that saturation of Y-zeolites with molybdenum carbonyl can produce catalysts with high molybdenum dispersion (ref.6, 7). Subsequent sulfidation of these catalysts leads toward highly dispersed, supported sulfided molybdenum species (ref. 8,9) exhibiting high reactivity in HDS and water-gas shift reaction (ref. 9,10). 

Most of molybdenum loaded Y-zeolites contain 2 Mo atoms per supercage, what gives approximately concentration of 10 wt.%. 

The effect of SO2 adsorption at different temperatures has been studied by ESR on three molybdenum-loaded zeolites with and without cobalt or H ions. In comparison with the outgassing-only treatments, the presence of SO2 lowers the temperature needed to reduce the molybdenum and leads to the generation of different radicals (SO2, SOj", S2 and O2 ). The formation of these radicals depends on the outgassing pretreatment and the temperature of interaction with SO2. The generation of sulfur radicals, observed when the sample is outgassed at room temperature and heated in the presence of SO2 at T > 523 K, is related to the molybdenum ions and the acidity of the sample, suggesting an increased stabilization of these species on protonated molybdenyl groups. 

In order to obtain more information on the interaction of SO2 and molybdenum ions we have studied, by ESR, the effect of SO2 treatments on molybdenum loaded zeolites. On this support the molybdenum can be in a more dispersed condition than on AI2O3 and occupy different positions in the zeolite... 

Molybdenum/zeolite catalysts prepared by impregnating zeolites with ammonium hepiamolybdate solution generally give rise to poor dispersion of molybdenum [2]. In contrast, ion exchange would be an ideal method for loading active metal species onto supports. Few cationic forms are available as simple salts of molybdenum of high oxidation... 

This paper describes the successful incorporation of molybdenum and molybdenum-nickel clusters into zeolites with 12-membered ring by aqueous ion exchange and application of the resulting materials to HDS reaction of benzothiophene. Stoichiometry of the ion exchange was examined by elemental analysis. UV-visible spectroscopy and EXAFS measurements were carried out to investigate the structure of molybdenum species loaded on zeolites. 

The incorporation of metal oxides on mesoporous andmicroporous substrates often results in inhomogeneities in the distribution of the oxide phase across the pore network. This is particularly critical in the case of zeolites, in which the dimensions of the channels are too small to facilitate the diffusion of the oxide phases during the preparation steps. As a result of this, molybdenum oxide-loaded zeolites are... 

It can be used to load metals which cannot be introduced by cationic exchange because they are in the form of anions in the pH range where zeolites are stable. Thus, molybdenum and rhenium were loaded in Y zeohtes by adsorption and thermal decomposition of Mo(CO)g [37-42] andRe2(CO)io [37,58], respectively. 

The decomposition under partial pressure of ammonia of Mo(CO)g loaded in EMT zeolite by chemical vapor deposition and subsequent nitridation under flowing ammonia were used to prepare encaged molybdenum nitride clusters [263]. XPS measurement showed that molybdenum nitride was formed at a nitridation temperature as low as 723 K TEM measurements indicated that the nitride phase was homogeneously dispersed in the zeolite micropores as clusters smaller than 1 nm. 

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