Toluene Catalytic Oxidation Mechanism Over Pt/CeO₂ And Numerical Simulation Of Flow Field In The Reactor

In recent years,with the rapid development of my country’s social economy,a large number of pollutants generated by energy consumption are discharged into the atmospheric environment,which leads to the continuous outbreak of air pollution events such as smog in various regions of the country.Currently,PM_2.5and ozone（O₃）are the main pollutants in the atmospheric environment.Volatile organic compounds（VOCs）are key precursors for the formation of PM_2.5and O₃.Therefore,the emission control of VOCs pollutants is one of the important ways to solve the problem of air pollution.At present,thermal combustion and catalytic oxidation are widely used as efficient technologies to solve VOCs pollution emissions.The representative equipment of thermal combustion is regenerative thermal combustion（RTO）reactor,and the representative equipment of catalytic oxidation is regenerative catalytic oxidation（RCO）reactor.Among them,RCO reactor combines catalysis and heat storage to improve the heat recovery efficiency and reduce the energy required for the reaction.The main factors affecting the catalytic effect of RCO reactor are catalyst and equipment structure.The in-depth study of the reaction mechanism of catalyst catalytic oxidation of VOCs and the structural optimization of RCO reactor model has certain guiding significance for the development of high-performance catalyst,improving the heat transfer efficiency of the reactor and the stable operation of the reaction.In this paper,CeO₂support materials with exposed different crystal planes were prepared by hydrothermal method:nanorods（1 1 0）,nano-octahedrons（1 1 1）,nanocubes（1 0 0）,and the same content was supported by deposition precipitation method.The Pt nanoparticles were analyzed for their catalytic performance in the oxidation of toluene.By characterizing and analyzing the physicochemical properties of the catalysts,the reasons why the Pt/CeO₂catalysts with different morphologies showed different catalytic activities for toluene were investigated.At the same time,the reaction mechanism of toluene on the surface of Pt/CeO₂catalyst was studied by in-situ DRIFT combined with kinetic experiments.Then,the RCO reactor was simulated through its working principle,main parameters and the theoretical basis of numerical simulation.At the same time,the internal flow field characteristics of the rotary RCO reactor were analyzed under the conditions of different exhaust gas concentration and inlet velocity,and the reactor structure was optimized.The results show:（1）Characterizations reveals that the（1 1 0）plane of CeO₂are more conducive to the dispersion of Pt species,followed by（1 1 1）plane.The improved dispersion of Pt species could enhance the metal-supports interaction,which promotes the electron transfer from CeO₂to Pt nanoparticles and the adsorption-activation of oxygen,thereby facilitating to the total oxidation of toluene via Langmuir-Hinshelwood（L-H）mechanism.Therefore,Pt/CeO₂-r（nanorods）catalyst displays the best catalytic activity of toluene oxidation.（2）Through in-situ DRIFT and kinetic experiments,it can be inferred that the toluene reaction mechanism on the Pt/CeO₂surface is that O₂adsorbs on the Pt site to generate active oxygen species,and then reacts with the adsorbed toluene.The toluene can be oxidized to CO₂and H₂O,in which the adsorption-activation of O₂is the control step of the reaction.Meanwhile,the reaction process of toluene on the surface of Pt/CeO₂-r is toluene→benzyl alcohol→benzaldehyde→phenyl formic acid→CO₂and H₂O.（3）Part of the gas will accumulate at the bottom of the reactor when the reaction gas enters the RCO reactor,which is not conducive to the stable operation of the reaction.A deflector is arranged at the bottom of the reactor to prevent the accumulation of reaction gas.The setting of the deflector makes the reaction gas enter the regenerator along the deflector,which effectively prevents the accumulation of reaction gas at the bottom of the reactor.At the same time,the setting of the deflector can reduce the inlet velocity non-uniformity coefficient at the first heat storage layer,which is conducive to the uniform heating of the reaction gas through the heat storage body.And the inlet velocity nonuniformity coefficient is the lowest when the number of deflectors is 5,which is most conducive to the stability of the reaction.（4）The toluene conversion at the outlet of the reactor decreases gradually with the increase of the inlet gas flow rate.Under the condition of constant inlet gas flow rate,the outlet temperature of the first catalyst layer increases with the raise of toluene mass fraction at the inlet.Then,in the process of the reaction gas passing through the second catalyst layer,the toluene conversion at the outlet of the second catalyst layer increases due to the raise of the reaction temperature.Finally,the toluene conversion at the outlet of the reactor increases.