Fabrication and eva‎luation of nickel-based core-shell nanostructure catalysts in biogas reforming

6/25/2023 12:00:00 AM

In dry reforming process, nickel is commonly used as the catalyst due to outstanding catalytic activity and acceptable price. The most critical challenge of Ni-based catalysts in the biogas reforming is coke deposition which leads to the inactivation of these catalysts. In this thesis, Ni-SiO2@SiO2 core-shell catalysts were prepared using the ammonia evaporated synthesis method, followed by encapsulation by a silica layer. The effect of nickel loading on catalytic activity was investigated in the biogas dry reforming reaction. The results showed that the catalytic activity improved and carbon deposition increased when nickel content increased from 2.5 to 15 wt.%. Ni-SiO2@SiO2 with 10 wt.% Ni loading exhibited stable and high methane and CO2 conversions with negligible carbon formation during 12 h time on stream at 700°C. Also, because of the high carbon resistance property of the prepared catalysts, the CH4 conversion over Ni-SiO2@SiO2 catalyst was remained constant at 52% for 12 h at a low reaction temperature of 600 °C. Compared with Ni-SiO2@SiO2 core-shell catalyst, Ni/SiO2 supported catalyst synthesized by impregnation method showed lower activity and stability. High stability and carbon deposition resistance properties of the Ni-SiO2@SiO2 catalyst were ascribed to the strong Ni-SiO2 interaction and coverage of the Ni particles by SiO2, which make them resistant against migration and sintering. In the second part of this study, the effect of adding promoter to the Ni-SiO2@SiO2 catalyst with 10 wt.% Ni loading was investigated. Catalyst with 1 wt.% cerium oxide showed higher activity and lower amount of carbon deposition dcompared to the unpromoted catalyst, which is attributed to the redox property of cerium oxide. In the third part of this study, the effect of silica shell thickness by controlling the amount of TEOS and the reaction time of shell formation on the core for Ni-SiO2@SiO2 catalyst was studied to investigate the effect of diffusion limited created by the silica shell. The results showed that carbon deposition decreased when TEOS increased from 0-2 ml and the reaction time of silica shell formation increased from 6 to19 h. Also, the formation of the silica shell on the Ni-SiO2 core doubled the specific surface area of this catalyst and significantly reduced the amount of carbon formed on the surface of the catalyst during 6 h time on stream. The chemical-physical properties of the prepared catalysts were eva‎luated using various analyses, including XRD, BET, TPR, FTIR, FESEM and EDX.

كاتاليست هسته-پوسته , ريفرمينگ خشك بيوگاز , مقاومت كربن , اكسيد سريم

Core-shell catalyst , Biogas dry reforming , Carbon resistance , Cerium oxide

maryam kaviani

mehran rezaei