CO2 Methanation in the Presence of Ce-Promoted Alumina Supported Nickel Catalysts: H2S Deactivation Studies

Abstract

The performance of alumina supported unpromoted and cerium promoted nickel catalysts in CO 2 methanation reaction was investigated. It was found that the activity of catalysts in CO 2 methanation reaction at low reaction temperatures can be improved by the increase in nickel loading and introduction of cerium promoter. The catalysts showed high resistance for sintering and coking at high reaction temperatures. A few stages of catalysts deactivation by H 2 S in the methanation reaction carried out at 475 °C with the time on stream were identified. It was found that an introduction of H 2 S to the stream (8 ppm) did not induce rapid decrease of activity. Slight and then strong drop of CO 2 conversion and simultaneously the loss of methane selectivity was observed after specific time, depending on the catalysts composition. Deactivation of catalysts was related to the nickel content and the presence of cerium. X-ray diffraction studies indicated small changes of crystallite size with the time on stream. Raman spectroscopy studies pointed out that deactivation of catalysts was not connected with formation of carbon deposits. An in-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy studies showed that exposition of catalysts to the reaction mixture containing the traces of H 2 S led to the blocking of nickel active sites responsible for CO 2 and H 2 activation and successive transformation to carbonyl and formate species.

Direct Conversion of Carbon Dioxide to Methane over Ceria‐ and Alumina‐Supported Nickel Catalysts for Biogas Valorization

“…Three catalysts (denoted Ni20-CeO 2 , Ni20-Al 2 O 3 and Ni40-Al 2 O 3 ) for detailed investigation of durability in the feed streams of different composition were selected from the wider groups of catalysts, described earlier. [38,50] The properties of catalysts used in current studies are briefly summarized in the supporting information (Table 1S and Figures 3S-8S). The catalysts show high durability in the CO 2 methanation reaction in the feed stream containing CO 2 and H 2 with molar ratio equal 1/4.…”

“…We have evidenced in our former papers, that the activity of catalysts in CO 2 methanation reaction at low reaction temperatures performed in the presence of CO 2 À H 2 mixture can be strongly influenced by the nature of support and nickel loading. [38,50] It was observed in the studies of methanation reaction performed at different reaction temperatures, that the activity of Ni20-CeO 2 catalyst, regarded as CO 2 conversion at given temperature, in the range of 240-320°C in spite of the lower active surface area (S a = 6.8 m 2 g À 1 ), higher mean nickel crystallite size and lower nickel dispersion (Table 1S) was higher than the activity of Ni20-Al 2 O 3 catalyst (S a = 12.5 m 2 g À 1 ). [50] CO 2 conversion at 200°C over Ni20-CeO 2 was equal 4 % (Figure 7S).…”

“…Recently we have investigated the performance of alumina supported catalysts in the CO 2 methanation reaction carried out in the presence of the traces of H 2 S. [38] Three stages of catalyst deactivation were identified, i. e. (a) a stable operation with small drop of activity, (b) a strong drop of activity and simultaneous decrease of selectivity to methane, and (c) low activity for long operation time with high selectivity to carbon monoxide. We have indicated that the initial period of the operation of catalysts before the loss of activity was related to the active surface area of the catalysts, while the final activity was related to the presence of cerium promoter.…”

“…Recently we have indicated that the resistance of alumina supported nickel catalysts for H 2 S poisoning can be improved by the increase of the active surface area through the increase of nickel loading and introduction of promoters. [38] CO 2 methanation is a highly exothermic reaction. An uncontrolled increase in reaction temperature causes, apart from a decrease of CO 2 conversion originating from the thermodynamic equilibrium, a drop of selectivity towards methane, an increasing risk of carbon deposit formation, and it may accelerate sintering phenomena, leading either to structural changes of the catalysts or to decrease of the active surface area.…”

Container-Sized CO2 to Methane: Design, Construction and Catalytic Tests Using Raw Biogas to Biomethane

“…According to Hepola et al, sulfur's catalyst poisoning decreased along the catalyst bed [37]. Furthermore, before the reactor's daily startup, hydrogen treatment might have reactivated some of the nickel sites [38]. A complete mechanistic study of sulfur poisoning was not a part of this pilot plant test campaign.…”