Ni-CeO2/TS-1 catalyze methane dry reforming: Improving catalytic performance and stability by modulating the amount and strength of Ni-O-X species

In this study, a series of Ni-CeO2/TS-1 (Titanium Silicalite-1) catalysts were synthesized for dry reforming of methane (DRM). Among them, 5Ni-10CeO2/TS-1 exhibited the highest catalytic performance with 89 % CH4 and 93 % CO2 conversions, 4.81 molCH4·gNi-1·h−1 and 4.99 molCO2·gNi-1·h−1 specific activities, 95.5 % H2/CO ratio after 50 h, accompanied by the good stability with 2.9 % CH4 and 2.3 % CO2 activity loss within 100 h. Combined with various characterizations, the structure–function relationship was also investigated. For the physical and morphological analysis, it was indicated that the appropriate CeO2 content could effectively diminish, disperse the Ni nanoparticles, and maintain MFI backbone structure. For the electronic structure, the introduced CeO2 could improve the amount and strength of the surface Ni-O-X (Ti or Ce) species by changing the interaction among Ni nanoparticles, TS-1 and CeO2. It led to more Ni nanoparticles in stronger electron-deficient state, as well as more medium-strength basic sites, favoring for the activation of CH4 and CO2. However, Ni nanoparticles would be covered when excessive CeO2 was introduced, preventing the exposure of the active sites. Therefore, only the suitable CeO2 in the catalysts could significantly improve catalytic performance for DRM with long-term stability. Furthermore, the good anti-sintering and anti-coking properties of 5Ni-10CeO2/TS-1 were mainly dependent on the optimal amount of surface Ni-O-X species with high strength. In-situ DRIFTS (diffuse reflectance infrared spectroscopy) analysis demonstrated that the introduced CeO2 could help catalyst favor for activating CH4 and CO2 molecules, and inhibiting the CH4 overcracking and carbon accumulation, confirmed by the long-term measurement and structure analysis of spent catalysts.