Effect of the NiO particle size on the activity of Mo/HZSM-5 catalyst physically mixed with NiO in methane dehydroaromatization

Abstract

Methane dehydroaromatization is an effective reaction that directly converts methane to benzene, toluene, xylene (BTX), and hydrogen in a non-oxidative atmosphere. Our previous study reported that when commercial NiO was added to Mo/HZSM-5 via a simple physical mixing method, the methane conversion and BTX selectivity were significantly improved. In this study, the efficiency of NiO particles with various sizes (4, 22, 36, 45, and 101 nm) as promoters was evaluated, and it was found that NiO(36 nm) has the optimum size for enhancing the activity of Mo/HZSM-5. The results of temperature-programmed reduction of methane, X-ray diffraction, transmission electron microscopy, and CO chemisorption revealed that among the samples analyzed, NiO(36 nm)-Mo/HZSM-5 had the highest dispersion of MoCx active sites because it had the lowest reduction temperature for NiO and MoOx. When the NiO particle size was smaller than 22 nm, the formation of inactive NiMoO4 was preferred, which caused the severe agglomeration and low dispersion of MoCx.