Development of nickel based catalysts for hydrogen production from biogas

Within the scope of this master's thesis, the effects of manganese incorporation on the activity of nickel-based alumina supported catalysts in dry reforming reaction of biogas were investigated in the presence of H2S. Monometallic (Ni) and bimetallic (Ni-Mn) catalysts were synthesized by using alumina support prepared by sol-gel method. XRD, N2 adsorption-desorption, XPS, ATR-IR, DRIFTS, TGA-DTA and SEM-EDX techniques were used to explain the performances of the catalysts in activity tests. N2 adsorption-desorption and XRD analyses showed that synthesized monometallic and bimetallic catalysts have a mesoporous structure, mainly containing metallic nickel and γ-Al2O3 phases. Catalytic activity tests of the catalysts were performed in a tubular fixed-bed reactor at 750°C and atmospheric pressure in the presence of 0, 2 and 50 ppm H2S. The gases at the reactor exit stream were analyzed by using a gas chromatography equipment. Monometallic and bimetallic catalysts showed stable activity in dry reforming of biogas reaction in the presence of 0 ppm H2S. Mn incorporation into the catalyst structure decreased the activity of Ni-based catalysts in terms of CH4 conversion; however, increased CO2/CH4 ratio due to the enhancement of reverse water gas shift reaction. In the catalytic activity tests performed in the presence of 2 ppm H2S, the activity of mono- and bimetallic catalysts decreased slightly within the reaction time of 4 hours. In order to explain the effects of H2S in the feed stream on the catalytic activity for dry reforming reaction of biogas, reaction tests were performed with FTIR spectrometer by using different gas mixtures (10 000 ppm H2S + He, 10 000 ppm H2S + CO2 + He, and 10 000 ppm H2S + CO2 + CH4 + He). In the reaction tests performed by using FTIR equipment, different sulfur components, such as H2S, COS, elemental S, SO2, and water vapor were observed at the exit stream of the tubular fixed-bed reactor. In the case of the presence of H2S in the feed stream, the formation of COS and H2O were predominantly observed. Even though Mn incorporation decreased the coke deposition of the Ni based catalysts, it did not enhance the sulfur resistance of Ni catalyst due to the formation of sulfate species on the catalyst surface.