Multiple Methane Activation Pathways on Ga-modified ZSM-5 Zeolites Revealed by Solid-State NMR Spectroscopy

Graphical Methane activation : Different types of Ga-CH 3 species were observed in methane activation on Ga-modified ZSM-5 zeolite, evidencing different pathways for heterolytic cleavage of C−H bond of methane. Two-dimensional solid-state NMR experiments provided detailed information on the location and local environment of the Ga-CH 3 species. Methane activation on Ga-modified ZSM-5 zeolites (Ga/ZSM-5) was studied by solid-state NMR spectroscopy. Two types of Ga species, namely highly dispersed oxides and cationic Ga species, were determined by 71 Ga QCPMG NMR. The activation of methane on Ga/ZSM-5 was explored by using 13 C and 1 H MAS NMR. Four types of Ga-CH 3 species along with Ga-OH groups were observed on Ga/ZSM-5, evidencing different pathways for heterolytic cleavage of C−H bond of methane. Two-dimensional (2D) 1 H- 1 H correlation NMR experiments provide detailed information on the location and local environment of the Ga-CH 3 species by correlating the protons in Ga-CH 3 with those in Ga-OH and other hydroxyls on zeolite. The structures of different Ga-CH 3 species were further determined by 2D 1 H- 13 C heteronuclear correlation NMR experiments, which were supported by theoretical calculations. The activation routes of C−H bond in methane were proposed on Ga/ZSM-5 zeolite.