Performance Of Al₂O₃ Supported Ni-based Catalyst For Selective Methanation Of CO

Proton exchange membrane fuel cell(PEMFC) uses a purified H2-rich gas as fuel. The unpurified H2-rich gas is largely composed of 0.5~2vol%CO, 15~20vol%CO2, 70vol%H2 and 10vol% steam. It must be purified to CO content below 10 ppm over Pt anode catalyst or below 100 ppm over Pt-Ru catalyst to avoid poisoning of the anode by CO. Reaction of selective methanation of CO in H2-rich gas(CO-SMET) is an effective way to remove CO. CO-SMET reaction does not need any reactant gas supplied externally, reaction products of methane and water have no pollution to environment.Ni-based catalysts and Ru-based catalysts are widely used for CO-SMET. In this thesis, Al2O3 supported Ni-based catalysts were prepared for CO-SMET. The main results are summarized as follows:1. Four preparation methods were adopted to prepare samples 20%NiO/Al2O3, which were then reduced into 20%Ni/Al2O3 and used as catalysts for CO-SMET. It was found that the precipitation method with ammonium carbonate as precipitant produced the highest catalytic activity both for CO methanation and for CO2 methanation.2. The calcined samples x%NiO/Al2O3(x = 10, 20, 30, 40) with different Ni/Al atomic ratios were prepared by the precipitation method with ammonium carbonate as precipitant. The reduced samples x%Ni/Al2O3 were used as catalysts for CO-SMET. It was found that the Ni loading at x = 20 is optimal from viewpoints of catalytic activity and selectivity for CO-SMET reaction.3. The calcined samples 20%NiO/Al2O3 prepared with the precipitation method with ammonium carbonate as precipitant were reduced at the different temperatures of 400 oC, 500 oC, 600 oC and 800 oC, respectively. The reduced samples 20%Ni/Al2O3 were used for CO-SMET reaction. It was found that the catalytic activity was enhanced as reduction temperature was elevated from 400 oC to 800 oC.4. The samples 20%NiO/Al2O3 prepared by the precipitation method with ammonium carbonate as precipitant were calcined at different temperatures of 500 oC, 650 oC, 800 oC, respectively. Prior to catalytic reaction, the calcined samples were reduced and used for CO-SMET reaction. It was found that the lower calcination temperature is better for the catalytic activity.5. The calcined sample 20%NiO/Al2O3 prepared by the precipitation method with ammonium carbonate as precipitant was used as support and impregnated with Ru3+ solution, where the feed atomic ratio of Ru/Al was set at 1/100. Then it was calcined at 400 oC for 2h. The calcined sample was denoted as 1%RuO2-20%NiO/Al2O3, and reduced at either 500 oC or 400 oC for 2h. The so-obtained 1%Ru-20%Ni/Al2O3 was used as catalysts for CO-SMET reaction. It was found that 1%Ru-20%Ni/Al2O3 catalyst reduced at 500 oC had a superior catalytic performance, removing CO to ca.30 ppm with selectivity higher than 50% at reaction temperature of 220 oC.