Propane Transformation on Zn-Modified Zeolite. Effect of the Nature of Zn Species on Alkane Aromatization and Hydrogenolysis

With regard to establishing the effect of the nature of Zn species loaded in a zeolite on the aromatization of propane, the transformation of C-13-labeled propane (propane-1-C-13 and propane-2-C-13) has been monitored by H-1 and C-13 (CP) MAS NMR at 296623 K for two zeolite samples, containing exclusively either isolated Zn2+ cations (Zn2+/H-BEA zeolite sample) or small (ZnO)(n) clusters of zinc oxide (ZnO/H-BEA zeolite sample). It has been established that similar intermediates, pi-complex of propene and sigma-allylzinc species, are formed at propane transformation to aromatics on both zeolite samples. However, the formation of the identified intermediates and their evolution to final aromatic products have been detected to occur on Zn2+/H-BEA at lower temperature (by 100 K) as compared to the same transformation on ZnO/H-BEA zeolite. Analysis of the kinetics of propane transformation by H-1 MAS NMR in situ has shown similar regularities for propane aromatization and hydrogenolysis on the different zeolite samples, but the reactions on Zn2+/H-BEA occur 10 times faster than on ZnO/H-BEA. This allows us to conclude on a higher efficiency of Zn2+ cations compared to ZnO species for propane aromatization on Zn-modified zeolites.