Mo/H-ZSM

In connection with the aromatization of methane induced by Mo-H-ZSM-5 catalysts (see Section 3.5.2), Mo2C on H-ZSM-5 prepared by carburation of M0O3 was studied in the aromatization of ethane,427 ethylene,428 and propane 429 The high dehydrogenation activity of Mo2C and the ability of H-ZSM-5 to induce aromatization of alkenes makes this an active and selective catalyst for aromatics production. 

Thus, Mo,H-ZSM-5 samples prepared via SSIE proved to be catalyst precursors which, after activation (reduction, carburization), activated CH4 molecules and produced hydrocarbons such as C2H4, C2H6, CgHg, CgHg, benzene, toluene, and naphthalene. At higher Mo contents, however, (inactive) aluminum molybdates, Al2(Mo04)3, formed by extracting framework Al that led to a loss of crystallinity. 

A Mo exchanged ZSM-5 Reduced in H, at 450 C for 1 hr (the fresh sample had almost same product yield and distribution)... 

The distribution among aromatic products was also altered by the presence of molybdenum (Fig. 1). The relative yields of para and meta isomers of xylenes and ethyltoluenes were increased over Mo exchanged ZSM-5 and over the physical mixture of MoO and H-ZSM-5 (no aromatics were detected over the impregnated catalyst), but this effect was not found for the partially poisoned catalyst. 

The disproportionation of toluene was the dominant reaction on Mo exchanged ZSM-5 and mordenite (0.4 wt % Mo). Compared with H-ZSM-5 and H-mordenite, the Mo exchanged samples had a much better resistance to deactivation, and this efftect was more pronounced on Mo mordenite, especially when was used as carrier gas. The variation in the distribution of xylene isomers with the conversion is plotted in Fig. 2. The Mo zeolites enhanced the relative yield of para + meta xylenes. 

It is assumed, however, that complex cation species such as FeCL, VO(OH), MoCl4 or CrOo + with extra-framework ligands are located on caiion positions rather Uian Fe +, V , Mo or Cr . This is suggested [33] because of the large distance between the framework A1 centres in the highly dliceous zeolites, e.g. in the H-ZSM-5 zeolite used (Si/Al=35). 

Lazar, K. Micheaud, N. Mihalyi, M. R., Pal-Borbely, G. and Beyer, H. K., Attempts to exchange iron into H-Y and H-ZSM-5 zeolites by in situ formed chloride-containing mobile species, Reaction Kinetics and Catalysis Letters 74(2), 289-298 (2001). Kucherov, A. V. and Slinkin, A. A., Zeolite modification by in situ formed reactive gas-phase species. Preparation and properties of Mo-containing zeolites, Studies in Surface Science and Catalysis 118(Preparation of Catalysts VII), 567-576 (1998). 

This section presents a summary and comparison of four different projects carried out at Leverhulme Centre for Innovative Catalysis, University of Liverpool, UK on propane (amm)oxidation over Mo-V-Sb-Nb mixed oxides, V- and W-modified Keggin structure HPCs and Ga exchanged H-ZSM-5. These three examples represent the main groups of catalytic materials for propane oxidation to acrylic acid (see Section 13.3). The results, which will be discussed here, on the effect of the different redox and acid-base properties on the reaction, aim at bringing further insight into the catalytic transformation of propane. Introduction of steam or ammonia to the propane oxygen mixture over some of the catalysts is demonstrated to be a crucial parameter for more selective reaction. 

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