Transition metal free dual functional materials (Na/Al2O3) were used for ICCU-RWGS and the influence of hydrogen flow rate (25, 50, 100, 200 and 500 ml/min) was investigated (https://doi.org/10.1016/j.jcou.2022.102049). The influence of hydrogen flow rate was studied at different temperatures also.
As shown in the two figures below, hydrogen flow rate showed little influence at higher reaction temperatures (e.g. 500 °C). However, at 350°C, the increase of hydrogen flow rate resulted in the reduction of CO2 conversion and the increase of CO selectivity. The lower selectivity to CO at lower temperatures was due to enhanced selectivity to CH4, which was favoured at lower temperatures, ascribed to the exothermic reaction of methane formation.
In general, the selectivity of CO was very high (close to 100%) at low reaction temperatures. And the flow rate of hydrogen had no effect on CO selectivity at 350 °C. It is also clear that at 450 °C, the increase of H2 flow reduced the production of CO. This might be related to the reduction of reaction time between H2 and the captured CO2.
“Figure – Concentration profiles during ICCC using Na/Al2O3 at 450 °C and an H2 flow rate of 25–500 mL/min.”(https://doi.org/10.1016/j.jcou.2022.102049)
“Figure – Effect of H2 flow rate and reaction temperature on (a) CO2 conversion and (b) CO selectivity of Na/Al2O3.”