α-氧化鐵觸媒同步還原NO /氧化CO之研究

Abstract

Ferrite is a porous material, which is a common catalyst in many chemical processes. α-Fe2O3(d=5μm) was used to oxidize CO in novel, and CO could be oidized to CO2. Commercial α-Fe2O3 (d < 45μm, RdH) was used in this study to evaluate the efficiencies of simultaneous reducing NO and oxidizing CO by packed bed reactor. There were four reaction parameters in this study： reaction temperature、NO influent、CO influent and α-Fe2O3 dosage. Possible reaction steps were investigated by reacted Fe2O3XRD spectrum. The NO removal efficiency was low in the initial, but NO removal efficiency increased when the reduced iron site by CO increased on the ferrite’s surface. NO and CO removal efficiencies would achieve steady states until operating for awhile. CO reacted efficiency was linearly correlated with reaction temperature. Reaction temperature from 623 K increased to 773 K, CO reacted efficiency from 19% increased to 55%. NO removal efficiency was linearly correlated with reaction temperature only in 623~673 K. The ratio of CO removal molar rate and NO removal molar rate (RNO/RCO) remained constant in 648~773 K, RCO was the major parameter of NO removal efficiency. NO removal efficiency were over 95% in NO influents 240~720 ppmv, and CO reacted efficiency increased to 73% from 55%. NO influent over 720 ppmv, NO removal efficiency decreased but CO reacted efficiency didn’t change. The ratio of CO conversion and NO conversion (XCO/XNO) was linearly correlated with NO influent. NO removal efficiency was only 4.45% in CO influent 955 ppmv, it was assumed the reduced iron site by CO was not sufficient to provide NO reducing in low CO influent environment. NO efficiency increased to 95% when CO influent increased to 1910 ppmv or above. RCO was higher in higher CO influent, but RNO remained stable. It could be considered the increasing reduced iron by CO oxidized didn’t participate NO reduction reaction, the reduced iron must have another reaction steps in the system. XCO was 27.67% and XNO was 58.61% at α-Fe2O3 dosage 0.5g, there were no sufficient sites for rteactions in this dosage obviosly. The dosage increased from 2g to 3g, XCO remained 53% ~55%, XNO both were 96%. α-Fe2O3 dosage over 2g was excess in the system, the efficiencies could not be increased when dosage increased. XRD (X-Ray Diffraction) was conducted to analyze the crystal structure and oxidation state of the reacted Fe2O3. It is considered carbon monoxide reduced Fe3+ ion of Fe2O3 to Fe2+, nitric oxide oxidized Fe2+ back to Fe3+ ion, Fe2O3 is a catalyst in the reaction. But the molar rate of carbon monoxide and nitric oxide were not equal, carbon monoxide also consumed a part of Fe2+ to Fe0.