Catalytic hydrogenation of carbon dioxide by reverse water gas shift reaction (rWGS

Abstract

The growing concentration of CO2 in the atmosphere had increased the impact on the environment such as global warming and forcing a climate change. An innovative utilization technologies are greatly needed to reduce the CO2 released into the atmosphere. But, due to its thermodynamic and kinetic stability, CO2 is not used to fullest potential by utilization route. For any fruitful utilization of CO2 to high value and high volume useful chemicals, it is required to develop syngas platform from CO2. Therefore, catalytic hydrogenation of CO2 to syngas by reverse water gas shift (rWGS) reaction could be a promising route. Being rWGS a reversible reaction, catalysts active in the water gas shift (WGS) reaction are often active in the reverse reaction. In this work, four catalysts were evaluated at different temperatures (450-650 oC) at a constant CO2/H2 ratio (1:3 vol%) and space velocity (50 ml/gcat.min). Among these four catalysts, three catalysts were prepared in-house using Fe (III) as an active phase supported on commercial γ-alumina. With an objective to improve catalytic hydrogenation of CO2, few other components e.g. Co-, Ni- phases were incorporated with Fe/Al2O3 catalyst in order to assess effects of dopants. All these catalysts were prepared using co-impregnation method. The physico-chemical characterization e.g. BET surface area, pore volume, average particle size, X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), coke content, etc. were also performed to evaluate the catalysts properties and correlate with the catalytic activity. Textural properties of the catalysts suggested effective utilization of specific surface area and pore volume, which are predominant for catalytic activity. XRD analysis indicated homogeneous dispersion of Co and Ni with Fe2O3 phase on γ-Al2O3 support. ICP-OES results also indicated almost complete dispersion of the active components on the support material. Each set of the catalyst were tested under atmospheric pressure and temperature ranging from 450-650 oC in a fixed bed reactor. In comparison with Co-doped Fe/Al2O3 catalyst, Ni-doped catalyst showed slight less CO2 conversion as well as CO yield at 450-550 oC. Possibly, Ni-doped Fe-based catalysts would require higher temperature for higher yield of CO. The rWGS reaction with Co-doped Fe/Al2O3 at 550 oC confirms CO2 conversion and CO yield 53.3% and 42.6% respectively. The CO yield for all catalysts is approx. 79% of the equilibrium CO yield. The methane formation in rWGS reaction was limited to less than 0.1 mol%. Nevertheless, further improvements can be made to increase the yield of CO at lower temperature.