n-Butane transformation on Zn/H-BEA. The effect of different Zn species (Zn²⁺ and ZnO) on the reaction performance

Using solid-state ¹H and ¹³C MAS NMR spectroscopy, the performance of H-BEA zeolite, modified with either Zn²⁺ cations (Zn²⁺/H-BEA) or ZnO clusters (ZnO/H-BEA), has been investigated with respect to n-butane transformation by aromatization and hydrogenolysis pathways. ¹³C-labeled n-butane has been used to follow the main stages of n-butane transformation on both Zn²⁺/H-BEA and ZnO/H-BEA with ¹³C MAS NMR at 298–623 K. Similar surface species, including n-butylzinc, n-butene, allyl-like oligomers, are formed as the intermediates on both zeolites. The kinetics of n-butane transformation has been monitored with ¹H MAS NMR in situ at 543–573 K. Kinetics modeling reveals that Zn²⁺/H-BEA is more active for n-butane transformation than ZnO/H-BEA. A remarkable difference in the rates and the pathways of hydrogenolysis for Zn²⁺/H-BEA and ZnO/H-BEA has also been established. Propane and methane are hydrogenolysis products on ZnO/H-BEA whereas ethane is produced by the reaction on Zn²⁺/H-BEA. ¹³C NMR data and the kinetics analysis provide an insight on the occurrence of joint methane and n-butane conversion on Zn-modified zeolites under non-oxidative conditions.