Formation and thermal stability of Ni+ cationic sites in Ni-ZSM-5

Ni-ZSM-5 zeolite reduced in CO was characterized by DRIFTS measurements of adsorbed CO, N-2, and H-2 molecules and EPR spectroscopy. The results indicate that N-2 and H-2 molecules adsorbed on Nil ions are strongly perturbed, resulting in large bathochromic shifts of their vibration frequencies. Ni+ sites in Ni-ZSM-5 are stable up to moderately high temperatures (550-600 K). At higher temperatures, the Ni+ sites are converted to Ni-0 and Ni2+ according to the following disproportionation reaction: 2Ni(+) -> Ni-2 + Ni-0.