Ni/MMT-promoted TiO2 nanocatalyst for dynamic photocatalytic H2 and hydrocarbons production from ethanol-water mixture under UV-light

Abstract

Photocatalytic H2 evolution from ethanol-water mixture over Ni and montmorillonite (MMT)-loaded TiO2 nanocomposite has been investigated. The samples, prepared by a single step sol-gel method, were characterized by XRD, SEM, TEM, FTIR, XPS, UV–Vis and PL spectroscopy. The TiO2 crystal growth was controlled by Ni/MMT, thus produced anatase phase TiO2. The nickel presented over the TiO2 as Ni2+, thus promoted charges separation. The photocatalytic H2 production activity was conducted in a gas phase continuous flow photoreactor system under UV-light. A significant enhancement in photoactivity of Ni-promoted MMT/TiO2 catalyst was detected for selective H2 production with appreciable amounts of C1-C3 hydrocarbons. The highest amount of H2 evolved over 3 wt% Ni-10 wt% MMT/TiO2 composite was 3470 μmole g-cat. −1 h−1 at selectivity 99%, 2.62 order of magnitude higher than pure Ni/TiO2, 6.48 fold more than MMT/TiO2 and 6.45 times the amount of H2 produced the over the pure TiO2 catalyst. Among the hydrocarbons, MMT promoted CH4/C2H6 production, while Ni/MMT was favorable for CH4/C3H6 production. The activity and selectivity of Ni-MMT/TiO2 was reduced at higher catalyst loading due to mass transfer limitations. In addition, significantly improved and stable cyclic performance was detected over the irradiation time for dynamic and selective H2 evolution. The enhanced performance of the Ni-MMT/TiO2 composite for H2 production is mainly associated with efficient charges separation due to synergistic effect of Ni/MMT and appropriate redox potentials. The reaction mechanism to understand the production of H2 and hydrocarbons in a gas phase system is critically deliberated.