Study of Zn and Ga Exchange in H-[Fe]ZSM-5 and H-[B]ZSM-5 Zeolites

Abstract

The catalytic properties of H-[Fe]ZSM-5 and H-[B]ZSM-5 were explored after addition of Zn or Ga. TPD−TGA of 2-propanamine adsorbed on Znand Ga-exchanged H-[Fe]ZSM-5 showed a decrease in Brønsted-acid site densities and the formation of new dehydrogenation sites, similar to what is observed following exchange in H-[Al]ZSM-5 and in amorphous silica−alumina. Exchanged Zn cations in [Fe]ZSM-5 also exhibited Lewis-acid character, as demonstrated by the appearance of a υ(CN) stretch at 2310 cm −1 upon adsorption of CD 3 CN. By contrast, the sites in H-[B]ZSM-5 were not capable of protonating 2-propanamine, did not form dehydrogenation sites when Zn or Ga were added, and showed no evidence for sites with Lewis-acid character from the FTIR spectroscopy of CD 3 CN. Neither H(Zn)-[Fe]ZSM-5 nor H(Zn)-[B]ZSM-5 catalyzed reactions of n-hexane at 773 K, but the TPD−TGA of adsorbed propene on H(Zn)-[Fe]ZSM-5 showed strong interactions between the Zn and olefins that might be responsible for the dehydrocyclization of light alkanes in Zn-exchanged, Al-containing zeolites.

Infrared Spectroscopy of Zn(Acetylene)n+ Complexes: Ligand Activation and Nascent Polymerization

“…Kallo has reported efficient hydrogenation of acetylene using zinc zeolites . Recently, zinc atom zeolites have been used in catalytic reactions for endothermic fuel combustion. − Singly charged zinc has a valence electron configuration of 3d 10 4s 1 , and the unpaired s electron is likely to cause very different reactivity than the unpaired d electrons of other transition metals.…”

Tuning Morphology of Zn/HZSM‐5 for Catalytic Performance in Methanol Aromatization

“…As Table shows, the concentration of acid sites decreases after the post‐treatments on pure HZSM‐5. The density of acid sites for 5 % Zn/HZSM‐5 is decreased due to the interaction of Zn metal species in protonic sites . The acidity of the 5 % Zn/HZSM‐5 sample is reduced by silanization, which may be attributed to reduced effective content in HZSM‐5 catalysts.…”

Heat-Flow Measurements for n-Hexane Reactions on H-ZSM-5 and H(Zn)-ZSM-5: Implications for Endothermic Reforming in Hypersonic Aircraft

“…An alternative to acid-catalyzed cracking and metal-catalyzed dehydrogenation is the aromatization of alkanes over Ga- and Zn-exchanged zeolites. − The formation of small aromatics and H 2 from alkanes is highly endothermic, and the rates for n -hexane conversion are comparable to those reported for the acidic zeolites. The metal-exchanged zeolites are very stable against coking.…”