Effect of CO2 Pretreatment Operation Conditions on the Catalytic Performance and Structure of Ni-Co Bimetallic Catalyst

The performance of the Ni-Co bimetallic catalyst was significantly improved by a novel H-2 and CO2 (HCD) pretreatment in the dry reforming of methane compared with traditional H-2 pretreatment. The effects of the HCD pretreatment operating conditions, such as pretreatment time, temperature, gas feeding ratio, and gas flow rate, on the catalytic performance of Ni-Co bimetallic catalyst were investigated. The optimal pretreatment time, temperature, gas feeding ratio (CH4/CO2), and gas flow rate were 0.5-1 h, 780-800 degrees C, 0:10, and 175-200 mL.min(-1), respectively. Biogas was simulated with CH4 and CO2 in a volume ratio of 1 and without any other diluted gas. The catalyst was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and thermogravimetry (TG) coupled to differential scanning calorimetry (DSC). In a 511 h stability test under the optimized operating conditions, the catalyst pretreated with both H-2 and CO2 exhibited excellent stability. The average conversions of CH4 and CO2, selectivities for H-2 and CO, and volume ratio of H-2/CO were 96%, 97%, 98%, 99%, and 0.98, respectively. The average carbon deposition rate over the Ni-Co bimetallic catalyst was only about 0.2 mg.g(-1).h(-1). The characterization results revealed that the sintering speed of the metal greatly decreased with testing time, and the metal particle will not greatly sinter with further testing time. The amount of deposited carbon on the catalyst gradually decreased and growth of filamentous carbon over the surface of the catalyst could be inhibited. Thereby, great catalytic activity and stability could be obtained during the dry reforming of methane reaction.