Design Of Carbon-based Catalyst For Low-temperature Oxidation Of High Concentration NO And Study On Its Dual Oxidation Paths

The high concentration NOx flue gas from glass,cement and coal mine associated gas power generation industries is highly polluted and difficult to meet emission standards.The demand side is mostly small or micro enterprises with poor economic affordability.Therefore,the low-temperature and low-cost emission reduction technology for high-concentration NOx is a research difficulty and focus of current research in the field of flue gas treatment.Carbon-based catalysts have the natural advantage of low-temperature NO oxidation.The high concentration NOx oxidation products are easy to be absorbed by liquid and turned into nitric acid,nitrate,etc.Besides,NO2 is easily converted into harmless N2 by reducing agents such as NH3.ACF was selected as a flexible carbon-based catalyst substrate in this study,the unique reaction pathway of ACF catalytic oxidation of NO was explored.According to the research idea of theory guiding practice,the method of functional group modification and in-situ growth to support MnO2 to improve the catalyst activity were emphatically designed and optimized.The low-temperature catalytic oxidation of high-concentration NO over ACF is accomplished through a dual way parallel mechanism:the quasi-homogeneous NO oxidation path and the chemical catalytic reaction pathway.In the quasihomogeneous NO oxidation pathway,the microporous structure relies on the van der Waals interaction to constrain the NO oxidation transition state,which accelerates the transfer of gaseous reactants to the transition state.Therefore,ACF catalysis increases the NO oxidation rate at room temperature by about 1000 times.That is,the negative enthalpy stabilization effect.At the same time,the kinetic properties of the transition state are restricted,and the negative entropy barrier effect of the transition state appears,which is the main reason for the decrease in the catalytic activity of ACF for NO oxidation due to temperature increase.In the chemical catalytic reaction pathway,pyridine(N-6)and quaternary nitrogen(N-Q)are the main catalytically active sites,and the excess π electrons generated by the N substitution of C on the aromatic ring are transferred from original position to the adsorbate,promoting adsorption of NO and O2,forming-NO2 groups,and finally released in the form of NO2 gas.This process is synergistic with the quasihomogeneous NO oxidation pathway.The dual oxidation pathways occur simultaneously and are selective to the reaction temperature.ACF(NH3)catalyst prepared by nitrogen doping method has widened micropore pore size,increased[N-Q+N-6]%ratio,sufficient innate accumulation of-NO2 groups,and increased number of activated carbon atoms.It showed a better catalytic oxidation activity in the whole temperature range.At 25℃,the NO oxidation rate was 51.06%。For the ACF(NH3)catalyst,the selectivity of the dual oxidation pathway at each temperature was quantitatively analyzed by transition state theory calculations.These data verify the synergistic effect and temperature driven law of the dual oxidation pathway.And extract a catalyst design idea that enhancing the activity of the chemical catalytic reaction pathway can effectively compensate for the negative entropy barrier of the quasi-homogeneous NO oxidation pathway.MnO2/ACF catalysts were prepared by a pore-constrained insitu growth method.The method is efficient and convenient,saving energy and investment costs.The obtained catalysts have high mechanical strength and flexibility,and thus have excellent industrial application prospects.MnO2/ACF can significantly improve the NO oxidation rate at high temperature due to its higher content of adsorbed active oxygen Oα and Mn4+/Mn3+ratio on its surface.Compared with ACF,the NO oxidation rate of MnO2/ACF-O2-NTP was enhanced by 1.32×104 mol·L-1·s-1 at 25℃.The flue gas purification effect of removing 90.5%of NOx at 25℃ can be preliminarily achieved.This study will provide new ideas for the design and development of green and efficient high concentration NO oxidation catalysts,and provide technical support for the application and promotion of flexible denitrification catalysts.