CO2-CH4 reforming over NiO/γ-Al2O3 in fixed-bed/fluidized-bed switching mode

CO2 reforming of methane was conducted over 13 wt.% NiO/gamma-Al2O3 in a micro quartz reactor in fixed-bed/fluidized-bed switching modes under the condition of 1 atm, a fixed furnace temperature of 800degreesC and a fixed CO2/CH4 molar ratio of 1.5. In the fluidized-bed mode, CH4 conversion at steady state was always as high as about 92%, while in the fixed-bed reforming, it depended strongly on the starting mode. As the reforming was started directly from the fixed-bed, CH4 conversion was only 48%, while it increased to about 75% as the catalyst was first applied to fluidized-bed reforming and then the fixed-bed operation. To understand the causes of such better catalytic performance of the catalyst in the fluidized-bed reforming, TPO and H-2-TPR techniques were then applied to the spent samples recovered from the mode-switching reforming tests ended at the different times of different modes. The results showed that fluidized-bed operation could not only suppress carbon accumulation over the catalyst but also remove some of the carbon deposited on it in the preceding fixed-bed reforming already, thus leading to recovery of the catalyst activity. It was also found that the extent of reduction of the catalyst after the fluidized-bed mode reforming was larger than that of the sample experiencing the fixed-bed operation only. Possible reasons for all these observations were also explored and discussed in the paper. (C) 2004 Elsevier B.V. All rights reserved.