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

Abstract

Ni-Co bimetallic catalysts supported on γ-Al 2 O 3 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 °C, 0.1 MPa, and a gas hourly space velocity of 6000 mL g cat −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 CO 2 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 CO 2 exhibited excellent stability, with a very low carbon deposition rate, ca. 0.2 mg g cat −1 h −1 . The average conversion of CH 4 and CO 2 , 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 CO 2 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. A novel pretreatment route, using both H 2 and CO 2 , for a Ni-Co bimetallic biogas reforming catalyst was designed. The new route significantly improved the performance of the catalyst and basically eliminated the long induction period. The carbon deposition resisitance, anti-sintering ability, and stability of the catalyst were also enhanced by the pretreatment.