In order to enhance catalytic activity in the dehydrogenation and aromatization of light paraffins, a set of potential catalysts: (i) V(f)-ZSM-5 (originating from direct synthesis), (ii) V(ex)-ZSM-5 (“ex””: partial exchange of H+in H-ZSM-5 by VO2+ions), and (iii) solid exchange of H in H-ZSM-5 for Ga, In, and V by baking the mixtures of ZSM-5 with the respective oxides were investigated by physical (XRD, IR, ESR, MAS-NMR spectroscopy, and adsorption) and chemical methods. In the “as synthesized””V(f)-ZSM-5 sample V4+ions reside in framework positions according ESR and 51V-MAS-NMR spectra. Coincidence between experimental and theoretical spectra could be attained only by supposing the existence of two different framework surroundings. The structure of V(f)-ZSM-5 is strained: heating (especially in the presence of water vapour) causes release of V from the framework. Severe conditions cause clustering of V4+in the voids with the annihilation of hyperfine splitting in the ESR spectra. Catalytic results demonstrate that in the presence of modifyers propane and n-butane conversion turns from cracking to dehydrogenation and aromatization pathways.
ASJC Scopus subject areas
- Condensed Matter Physics
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry