Mo/ZSM-5 Catalysts for Methane Aromatization. Study of the Mo Precursor Species in Impregnation Solution of Ammonium Heptamolybdate
E. V. Matus, L. T. Tsykoza, Z. R. Ismagilov and V. V. Kuznetsov
G. K. Boreskov Institute of Catalysis, Siberian Branch of the Russian Academy of Sciences,
Pr. Academika Lavrentyeva 5, Novosibirsk 630090 (Russia), E-mail:zri@catalysis.nsk.su
Abstract
A change in the ratio between monomeric and polymeric molybdenum species regarding the concentration and pH of the impregnation solutions will probably make a significant effect on the nature and number of active sites of Mo/ZSM-5 catalysts. To provide the control of molybdenum species in solutions, we have studied the dependence of structure of molybdenum species in the initial impregnation solutions of ammonium heptamolybdate on the concentration and pH of these solutions (from electron absorption spectra). When the concentration of solutions is low or pH increases, there are no polymeric molybdenum species. Besides, there is a region where monomeric and polymeric species exist at a time. At higher concentrations or when pH decreases, monomeric species transform almost completely into polymeric species.
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