¹H MAS NMR In Situ Reaction Monitoring Reveals the Particular Effects of Zn²⁺ and ZnO Species on the Kinetics of Isobutane Transformation on Zn-Modified Zeolites

Establishing the role of metal species in the reaction of alkane aromatization on metal-modified zeolites is a challenging task aiming at understanding the mechanism of the alkane transformation and improving the zeolite catalyst performance. Herein, the kinetics of isobutane transformation on BEA zeolites, modified with either Zn²⁺ cations (Zn²⁺/H-BEA) or ZnO clusters (ZnO/H-BEA), has been monitored with ¹H MAS NMR spectroscopy in situ at 543–573 K. It is established that the rates for the alkane dehydrogenation, hydrogenolysis, and aromatization steps are higher for Zn²⁺/H-BEA than for ZnO/H-BEA zeolite, implying higher efficiency of Zn²⁺/H-BEA compared to ZnO/H-BEA zeolite for isobutane transformation. An occurrence of the reaction of isobutane with methane to yield propane on both zeolites has been evidenced by kinetic analysis. The kinetic parameters of the reaction have been compared with earlier derived parameters for n-butane transformation on the same zeolites. It is inferred that Zn²⁺/H-BEA exhibits higher activity than ZnO/H-BEA for both n-butane and isobutane aromatization. At the same time, Zn²⁺/H-BEA is more active for n-butane aromatization than for isobutane transformation to aromatics.