Catalytic Conversion of CO2 to CH4 with a Ru Catalyst: Application at Vehicle Exhaust

For the first time, catalytic conversion of CO2 to CH4 (Sabatier reaction) has been studied on real vehicle exhaust. Preliminary tests were carried out on model gas mixtures using as reactants a N2/CO2 gas mixture (CO2 = 9.5 vol% concentration similar to that of road vehicle exhaust) and pure hydrogen. Ruthenium powder (5 wt%) on alumina was used as catalyst, in a fixed bed cylindrical reactor. The operating conditions investigated are P = 1 atm, temperature in the range 160-320 °C, contact time 0.6-1.29 s, and H2/CO2 ratio 2.75- 4.11. Experimental conditions were varied to study the effect of temperature, contact time, and H2/CO2 ratio on conversion, yield, and selectivity of the process. Once evaluated the performance of the catalytic process and identified the best operating conditions, real exhausts of a two-wheel motorcycle and a fourwheel gasoline vehiclewere treated with the same experimental apparatus. Analyses of physical and chemical characterization of catalyst samples before and after the use were also performed. Results show that, even though best performances are generally obtained with model mixtures, high CO2 conversion together with high yield and selectivity in CH4 can be obtained with real vehicle exhausts too. Moreover, phenomena causing the deactivation of catalyst have not been observed. Results seem to indicate good opportunities for the development of the process.