Study On The Preparation And Catalytic Oxidation Of Nitric Oxide(NO)by Pure-silica Zeolite

NO_x causes the air pollution such as acid rain,haze,photochemical smog.In industry,the absorption of NO_x into aqueous solutions is carried out generally in packed columns or plate columns,outherwise,NO is not only difficult to be directly absorbed by water,acid or alkali,but also be removed by physical adsorption such as activated carbon or carbon fiber.Although NO and O₂ can be converted into NO₂ at normal temperature and pressure,it is well known that the NO_x absorption process is primarily affected by its oxidation degree.In order to achieve the oxidation degree of wet absorption,it is necessary to have a series of oxidation device.It is an ideal way to rapidly convert NO into NO₂ with the action of catalyst and O₂.Activated carbon and molecular sieves have been proved to be able to catalyze the conversion of NO and O₂ to NO₂.Although the specific surface area and pore volume of molecular sieves are lower than activated carbon,it has the better function of hydrophobicity.The objective of the study is to construct a better catalytic activity and hydrophobic composite catalyst,to adapt to NO oxidation into NO₂ under high-humidity environment.This paper intends to verify the catalytic oxidation of NO in dry gas and to study the conditions of NO oxidation into NO₂ in wet NO_x gas by Silicalite-1.It is investigated that the molding catalyst has activity and stability of NO oxidation in wet NO_x gas.It's prepared by hydrothermal synthesis with TEOS as silicon source and TPAOH as template for pure-silica zeolite at first.Then,Silicalite-1 and its molding are used in the study of NO oxidation at normal temperature.The results are as follows:1)The optimum synthesis conditions of pure-silica zeolite are as follows.SiO₂:TPAOH:H₂O=1:0.2:80,hydrothermal crystallization temperature is 180?,crystallization time is 24h.2)Through the comparison of Silicalite-1 and ZSM-5?commercial?for NO oxidation at low temperature,they both have good catalytic performance.The activity of Silicalite-1 is higher than ZSM-5 in wet gas,which shows that the better water resistance with improved ratio of Si/Al.3)The influenced factors of NO oxidation by Silicalite-1:the increase of temperature?15?⁵5??and relative humidity?0%¹00%?inhibited the reaction,therefore the NO oxidation efficiency decreased significantly.The increase of pressure can improve the reaction rate,which is conducive to the oxidation reaction.The conversion efficiency was still stable at64%and 55%in 38h when the reaction conditions are t=25?,C_NO=0.05%,C_O2=21%,GHSV=5000 h^-11 or 7500 h^-1,RH=100%.The results indicate that Silicalite-1 has excellent performance on NO oxidation,hydrophobicity and reaction stability.4)The formation of Silicalite-1 can reduce the oxidation efficiency of NO,but it can still transform stably in wet NO_x gas.The oxidation efficiency of NO is about 44%when the reaction conditions are t=25?,C_NO=0.05%,C_O2=21%,GHSV=5000h^-1,RH=100%,which has the prospect of industrial application.