MSc Thesis Title: Catalytic hydrogenation of CO2 over supported Ni and Ru catalysts
Tuesday 30 October 2018, at:9:30, Venue: Hall Κ2.A3
Examination Committee
- Assistant Professor Paraskevi Panagiotopoulou (advisor)
- Professor Ioannis Yentekakis
- Assistant Professor Nikolaos Xekoukoulotakis
Abstract:
Carbon dioxide (CO2) is one of the main greenhouse gases, which is responsible for global warming and therefore, considerable climate changes. Consequently, efforts have been made in order to develop efficient and environmental friendly technologies for CO2 elimination and utilization. Catalytic hydrogenation of CO2, which is one of the proposed utilization processes, is of great importance because it can create new ways for producing chemicals and fuels of high added value depending on the catalyst and reaction conditions employed. CO2 methanation offers certain advantages provided that hydrogen is generated from renewable energy sources. Specifically, methane produced can be used as synthetic substitute of natural gas in chemical and petrochemical industry and/or as energy carrier in power plants following well established methods for its storage and transfer.
In the present study, the effect of the nature of the support on catalytic activity and selectivity of supported nickel (Ni) and ruthenium (Ru) catalysts for the CO2 methanation reaction is investigated. In particular, the use of various metal oxides supports (Al2O3, CeO2, ZrO2, YSZ, TiO2) and the potential to improve catalytic performance of Ru/TiO2 and Ni/TiO2 by addition of small amounts (0.2 wt.%) of promoters (Ce, Zr, La, Ca, Ba) on TiO2 was studied. Furthermore, the use of bimetallic (Ni-Ru) catalysts supported on TiO2 and the effect of operating parameters of the reaction on the activity and selectivity of 5%Ni/CeO2 catalyst were investigated. Catalysts were synthesized employing the wet impregnation method and characterized with respect to their specific surface area and support crystallite size, employing nitrogen physisorption (BET) and X-ray diffraction (XRD), respectively. Catalytic performance was investigated in the temperature range 150-450 οC, using a feed stream consisting of 5%CO2 +20%H2 (in He).
Results showed that the nature of the support affects significantly the catalytic performance, which follows the order 5%Ni/CeO2>5%Ni/ZrO2>5%Ni/Al2O3~5%Ni/YSZ >5%Ni/TiO2. Both activity and selectivity toward CH4 of Ni catalysts do not seem to improve significantly by addition of promoters (0.2 wt. %) Νa and Zr on TiO2 support. In contrast, the addition of (0.2 wt. %) Ce, Zr, La, Ca and Ba promoters on TiO2 surface resulted in a significant increase of the activity of Ru catalysts, with the Ce-promoted sample (0.5%Ru/0.2%Ce-TiO2) presenting the optimal performance. Thus, the effect of Ce loading on catalytic performance was investigated, which did not seem to present any trend with respect to catalytic activity. The use of bimetallic Ni-Ru/TiO2 catalysts resulted in an increase of CO2 conversion toward CH4, which seemed to increase progressively with increasing Ru content from 0.25 to 1 wt.%. However, the monometallic catalyst 1%Ru/TiO2 presented significantly higher activity compared to that obtained over the bimetallic catalysts.
Finally, the effect of operating parameters was investigated with respect to catalytic activity of 5%Ni/CeO2 catalyst, and it was found that CO2 conversion to CH4 increases with decreasing space velocity and increasing Η2/CO2 molar ratio. Apart from high activity and selectivity, 5%Ni/CeO2 catalyst, , presented exceptional stability for more than 30 hours on stream, indicating that it is a promising catalyst for CO2 hydrogenation reaction.
