Plasma-enhanced Selective Reduction Of CO₂ To CO Over Cu/ZnO/Al₂O₃ Catalyst

Hydrogenation reduction of CO₂,as a kind of greenhouse gas and renewable carbon source,into CO and then conversion into high value-added chemicals are of great significance.Due to the disadvantage of thermodynamics of the hydrogenation reduction of CO₂ to CO,the conventional thermal catalysis requires high reaction temperature.Compared with the thermal catalysis,the plasma method can be performed at lower temperature,due to the activation of CO₂ molecules by electron excitation.In this paper,plasma alone and the combination of plasma and catalyst are used to study the reaction process of hydrogenation reduction of CO₂into to CO.The main results are as follows:（1）The thermal effect of dielectric barrier discharge（DBD）was studied The effects of N₂ gas flow rate and input power on the wall temperature of the reactor and rotational temperature of N₂ were investigated,respectively.As increasing of gas flow rate from 400SCCM to 1000 SCCM under the input power of 23 W,the wall temperature of reactor and rotational temperature of N₂ decrease from 397 K to 376 K and from 680 K to 640 K,respectively.Meanwhile,with the increase of input power from 23 W to 29 W under the gas flow rate of 200 SCCM,the rotational temperature of N₂ increases from 700 K to 850 K,and the wall temperature of reactor has risen by 30 K.After wrapping the outer wall of reactor with insulation material,the wall temperature of reactor and rotational temperature all increase about 100-200 K.Furthermore,under the constant total gas flow rate and input power,the variation of the ratio of CO₂/N₂ has no effect on the wall temperature of reactor and rotational temperature.（2）Catalysis alone and combination between the plasma and catalysis were studied for the process of hydrogenation reduction of CO₂ into CO.The effects of input power,gas flow rate,temperature and the molar ratio of CO₂/H₂ on the CO₂conversion were investigated.The synergistic effect of plasma and catalysis was also investigated based on reaction rate.The results of the effects of plasma alone and combination of plasma and filling Al₂O₃ beads on the CO₂ conversion indicate that the filling of Al₂O₃ beads promotes the CO₂ conversion.With the gas flow rate of 50 SCCM,the CO₂/H₂molar ratio of 1/1 and the input power of 35W,the CO₂ conversions for the plasma alone and the combination between plasma and filling Al₂O₃ beads are 10%and 21.3%,respectively.Furthermore,it is indicated that the increasing of the temperature and decreasing of gas flow rate and molar ratio of CO₂/H₂ all are in favor of the conversion of CO₂.When the reaction temperature is lower than 473 K,there is no activity for the thermal catalysis.With the decrease of the molar ratio of CO₂/H₂（gas flow rate 50 SCCM）from 2/1,1/1 to 1/2,the CO₂ conversion increases 17.8%,23.3%to 27.6%,respectively,at the reaction temperature of 673 K.Furthermore,with the increase of gas flow rate（molar ratio of CO₂/H₂ is 1/1）from 50 SCCM to 400 SCCM,the CO₂ conversion decreases from 23.3%to 4.4%,respectively.The results of combination between the plasma and catalyst indicate that both increasing of the input power and decreasing of molar ratio of CO₂/H₂ can improve the conversion of CO₂.When the total flow rate is 200 SCCM and the molar ratio of CO₂/H₂ is 1/1,As increasing of the wall temperature of reactor from 523 K to573 K,the CO₂ conversion increases from 12.4%to 19.3%with gas flow rate of 200 SCCM and the molar ratio of CO₂/H₂ of 1/1,respectively.It is much larger than that of the 1.5%and6.2%of the thermal catalysis alone at the same temperature.With the increase of reaction temperature from 473 K to 573 K,compared with the conditions of plasma alone and thermal catalysis alone,the combination between the plasma and catalyst significantly boosts the conversion of CO₂,which indicates the synergistic effect of plasma and catalyst.This synergy effect,however,are gradually weakened by the increase of the conversion of CO₂ of thermal catalysis due to the rising of the temperature.