Effects of pretreatment on performance and structure of Ni-Co bimetallic catalyst for biogas reforming to hydrogen

Ni-Co bimetallic catalysts supported on gamma-Al2O3 pellets for biogas reforming to hydrogen were successfully prepared using the excessive impregnation method. The effects of pretreatment on the catalytic performance were investigated in a fixed-bed vertical quartz reactor under conditions of 850 degrees C, 0.1 MPa, and a gas hourly space velocity of 6000 mL gcat(-1) h(-1) (4 g of catalyst, 2.5-3.5 mm). The samples were characterized using X-ray diffraction, transmission electron microscopy, thermogravimetry coupled to differential scanning calorimetry, and emission scanning electron microscopy with energy-dispersive X-ray spectroscopy. The results showed that the catalyst pretreated with both H-2 and CO2 showed higher activity, and basically eliminated the long induction period of the biogas reforming reaction, compared with the catalyst pretreated with only H-2. In a 511 h stability test, the catalyst pretreated with both H-2 and CO2 exhibited excellent stability, with a very low carbon deposition rate, ca. 0.2 mg gcat(-1) h(-1). The average conversion of CH4 and CO2, selectivity for H-2 and CO, and ratio of H-2/CO were 96%, 97%, 98%, 99%, and 0.98, respectively. The characterization results showed that the catalyst pretreated with both H-2 and CO2 exhibited higher carbon formation resistance and better anti-sintering performance during reactions; this resulted in smaller metal particles and thus enhanced the stability of the catalyst. This new pretreatment route is very promising for enhancing the performance of biogas reforming catalysts. (C) 2013, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.