Controllable Reduction Of Nitrobenzene For Value-added Utilization Of NOx

As important fine chemicals and organic intermediates,aniline and azoxybenzene have been extensively applied in the industry as dyes,medicine,agrochemicals,polymerization inhibitors and liquid crystal material with enormous marketing demand.At present,the main by-products of NOx utilization are nitrate/nitrite or concentrated nitric acid.Converting by-products of NOx recovery to aniline and azoxybenzene have a great attraction for both pollutant control and obtaining value-added products.On this basis,a new route of value-added utilization of NOx is provided.Specifically,NOx is absorbed and converted to concentrated nitric acid which could nitrify benzene to nitrobenzene,followed by controllable reduction of nitrobenzene to aniline and azoxybenzene.The industrial production of nitrobenzene is a mature and stable technology.Therefore,the controllable reduction of nitrobenzene is the key point in the route of value-added utilization of NOx.At present,high pressure,high temperature and solvents are required for the effective synthesis of aniline by catalytic nitrobenzene reduction,which increases energy consumption and discharges liquid waste.In addition,the base additives are necessary for azoxybenzene synthesis,which produces waste liquid and seriously endanger the ecological environment.Based on the above issues,the textural properties of catalysts were modified and optimized.The reaction mechanism about the influence of active hydrogen concentration on controllable nitrobenzene reduction has been elucidated.Moreover,the environmental and economic evaluations were carried out for catalysts synthesis and the controllable reduction of nitrobenzene.The primary research is summarized as follows:(1)To solve the problems of requiring high-temperature and high-pressure conditions in aniline synthesis,monodispersed Ni nanoparticles are synthesized and loaded on KIT-6 with high specific surface areas.According to characterization results,the effects of the pretreatment process on the structural properties of catalysts,including pore structure,valence states,specific surface area and dispersions of Ni nanoparticles were investigated.With the high concentration and high dispersion of Ni0 sites,Ni/KIT6cal+red exhibited 100%aniline yield under 90? and 1 MPa H2 conditions in ethanol solvent.To further improve the industrial application potential of the controllable reduction of nitrobenzene and produce aniline under solvent-free conditions,monodispersed Pd nanoparticles with high hydrogenation efficiency were synthesized and loaded on C-HNO3,GO and rGO.The characterization results indicated that the coupling of Pd nanoparticles and rGO nanosheets could inhibit the agglomeration of Pd nanoparticles during heat treatment.The high dispersion of Pd0 active sites on Pd/rGO enhances the dissociation of H2.Pd/rGO exhibited 100%aniline yield under solvent-free conditions under 1 MPa H2 and 90?.(2)To solve the challenges of azoxybenzene synthesis under base conditions that discharge environmentally hazardous waste liquid,four model CeO2 catalysts with modified exposed planes were synthesized to clarify the effects of different concentrations of coordination unsaturation(cus),Ce3+cations and oxygen vacancy defects on the controllable reduction of nitrobenzene.The results of DFT calculations and in-situ capping experiments suggested that oxygen vacancies and the present Ce3+cations are the key active site for nitrobenzene adsorption and activation,which affects the yields of azoxybenzene.Furthermore,seven CeO2 catalysts with various Ce3+proportions are synthesized.With optimal Ce3+proportion,the Rod-CeO2 produces 90.4%azoxybenzene yield under the base-free conditions with 150? and anhydrous toluene as the solvent.To further improve the industrial potential of azoxybenzene synthesis,the factors of strong metal-support interaction(SMSI)of Pd/CeO2 catalysts were tuned including different pretreatment calcination temperatures,various CeO2 morphologies and different Pd nanoparticles,which remarkably affect the surface electronic state of Pd species and influence azoxybenzene synthesis under solvent-free conditions.The results of the structure-activity relationship clarified that the PdOx proportion is the key factor for enhancing H2 dissociation.The desorption of azoxybenzene that happened once it was formed is the key step for azoxybenzene synthesis under solvent-free conditions.With calcination temperature of 450?,CeO2LP as supports,4.72 nm-Pd/CeO2 exhibited a yield of 70.9%for azoxybenzene synthesis under base-free and solvent-free conditions under 1 MPa H2 and 70?.(3)According to the above results,modifying strategy of controllable nitrobenzene reduction could be formed.The key factor for controllable nitrobenzene reduction is to adjust the concentration of hydrogen species on the surface of catalysts.Pd0 on the surface of nonreducible supports exhibits high activity for H2 dissociation,which promotes the rapid hydrogenation of nitrobenzene to aniline along the direct route.Proton hydrogen on the educible supports and O2-on the surface of the supports form Ce-O(H)-Ce structural units.The supports transmit several electrons to the metal,which catalyzes the reduction of nitrobenzene along the condensation route to form azoxybenzene.In addition,OpenLCA ReCiPe methods were used for evaluating the environmental and economic impacts.The route of value-added utilization of NOx exhibits satisfying environmental and economic benefits.