Methanation of CO2 is a promising reaction in the “power to gas” (P2G) concept, which aims at overcoming fluctuations in the supply of energy from renewable sources. This way H2 produced from surplus electrical energy can be converted to CH4, which is easily stored and distributed using the natural gas grid.[1] Supported Ru catalysts are among the most active catalysts for the methantion of carbon oxides, especially for CO at low temperatures (&lt;200°C) and for CO2 at slightly higher temperatures (200-350°C).[2] A major drawback for large scale applications of CO2 methanation is, however, the parallel consumption of H2 via the RWGS reaction.[3] Recent studies revealed that the specific surface area (SA) strongly affects the activity and selectivity of Ru/TiO2 for both reactions.[3] While Ru/TiO2 catalysts with SAs below 200 m2g-1 are only active for methanation over a wide range of temperatures (190°C-350°C), Ru/TiO2 with high surface area (&gt; 200 m2g-1) start to catalyze RWGS at about 230°C. Here the RWGS even becomes dominant for higher temperatures and, in parallel, COx methanation is suppressed.[3] Interestingly, when going back to 190°C after reaction at elevated temperatures the high SA catalyst is even active for the RWGS at such low temperatures. This clearly indicates permanent structural changes of the Ru/TiO2 catalysts during reaction at elevated temperatures, which strongly affect their catalytic performance. Based on kinetic and in situ infrared measurements in combination with detailed catalyst characterization by HR-TEM; XPS and XRD (before and after reaction at different temperatures), we will discuss how these structural changes are related to the adsorption properties, which in turn control the catalysts selectivity towards CO2 methanation.

Competition between Reverse Water Gas Shift (RWGS) reaction and CO2 methanation on Ru/TiO2: Temperature induced structural changes

253rd National Meeting (2017)

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