Methanation of Carbon Dioxide and Carbon Monoxide over Supported Ni-La₂O₃-Ru Catalysts

Abstract

Spherically granulated silica with bimodal macro- and micro-pore stucture was employed as the catalyst support. The content of Ni supported as the substrate of the catalyst was several percent. La₂O₃ and Ru were incorporated with Ni in atomic ratios of 0. 2 and 0. 1 (for one Ni), respectively. CO and CO₂ methanation over these catalysts was investigated by means of a continuous flow method at atmospheric pressure.
In CO methanation over the Ni catalyst, the selectivity for methane formation decreased due to CO₃ formation in higher temperature range where CO conversion was higher. On the other hand, when the Ni-La₂O₃ catalyst was used, the catalyst was activated at the tempera-ture several ten degrees lower than that for the Ni catalyst. Moreover, the selectivity for methane attained nearly 100% without CO₂ formation over the catalyst at higher temperatures (Fig. 1). In CO₂ methanation, methane was formed almost selectively, regardless of a variety of catalysts and reaction conditions, and all the catalysts gave an apparent activation energy of 19. 6 kcal/mol (Fig. 3 and Table 4).
Over the Ni catalyst, the methanation rate of CO was greater than that of CO₂ ; however, the reverse order in the rate was obtained with the catalyst containing La₂O₃, and with the Ru catalyst (Figs. 2 and 6). The activity of the Ni-La₂O₃-Ru catalyst far exceeded the sum of the activity of each single component catalyst (Fig. 3 and Table 4).
On the basis of the amount of adsorption of reactants on the catalyst (Table 3) and partial pressure dependences of methanation rates (Figs. 4, 5, and Table 2), the composite effects of these polygenous catalysts were estimated as follows. The rate of CO₂ methanation increases as a result of increase of H₂ and CO₂ uptakes owing to the combination of La₂O₃ with Ni, and in addition, as a result of the hydrogen-spillover effect consisting of Ni-La₂O₃ part as the hydrogen acceptor, and of Ru part as its porthole.