Coordination of Two N2 Molecules to One Ni+ Site in Ni–ZSM-5: An FTIR Spectroscopy Study

Abstract

Ni+ cations were produced in a Ni–ZSM-5 zeolite by partial reduction with CO, and the ability of the Ni+ and Ni2+ sites to coordinate 14N2, 15N2, and/or CO molecules was studied by FTIR spectroscopy. With Ni+ cations, CO produces mono-, di-, and tricarbonyl species while only mono- and dicarbonyls are formed with Ni2+. Adsorption of 14N2 at 100 K results in formation of Ni2+–14N2 adducts (band at 2343 cm–1) and geminal Ni+(14N2)2 complexes (νs at 2287 and νas at 2270 cm–1). The Ni+(14N2)2 complexes lose their ligands stepwise during evacuation at 100 K, and two kinds of monoligand Ni+–14N2 species are formed (2252 and 2238 cm–1). After 15N2 adsorption, the Ni+(15N2)2 complexes were observed at 2211 and 2194 cm–1: the two Ni+–15N2 species at 2178 and 2163 cm–1, and the Ni2+–15N2 adducts at 2264 cm–1. To prove the geminal structure, coadsorption of 14N2 and 15N2 was studied. It resulted in formation of Ni+(14N2)(15N2) species that were characterized by 14N–14N and 15N–15N stretchings at 2277 and 2201 cm–1, ...