Oxidative CO2 reforming of methane over stable and active nickel-based catalysts modified with organic agents

Abstract

This study targeted the novel silica-supported nickel-based catalyst (Ni/SiO2) modified by organic agents. The synergic modification effect of ethylene glycol (EG) and citric acid (CA) on the nickel catalyst was investigated. EG was used to pretreat the silica support and CA was used in the impregnation solution to synthesize the nickel based catalysts with different CA loadings. NiCA-x/SiO2-EG (x: molar ratio of CA/Ni ranging from 0.25 to 1.5) catalysts achieved an excellent stability and higher catalytic activity than the catalysts without EG in oxidative CO2 reforming of methane (CH4/CO2/O2 = 40/20/10, total flow rate = 60 ml/min, reaction temperature = 750 °C, and reaction pressure = 1 atm). EG addition modified the surface properties of silica support. The use of CA in the impregnation solution had a clear effect on the dispersion of NiO and Ni in the silica matrix. For the catalysts with the same content of CA, the catalysts with EG modification showed the synergic effect of EG and CA by improving the chemical interaction between Ni and support, resulting in higher dispersion of nickel. The temperature programmed reduction revealed that the reduction peak shifted to higher temperature with increasing CA loading, which was attributed to the smaller metallic Ni size of the reduced catalysts. The transmission electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy confirmed that the addition of organic additive modified the silica surface and retained the metallic Ni species, and thus preventing the metal aggregation at high reaction temperature. The NiCA-1.5/SiO2-EG catalyst exhibited the highest activity, which was due to the small metallic metal size (4 nm) and the strong interaction between silica support and metal species.