Study On Submicron And Hollow Cu-SSZ-13 Catalysts For Selective Catalytic Reduction Of NO_x By Ammonia

With the rapid development of society and economy,the issue of environmental protection has attracted widespread attention.As one of the most serious air pollutants,nitrogen oxides can cause many environmental pollution problems,such as acid rain and photochemical smog,and seriously harm human health and the natural environment.The selective catalytic reduction of NOx by NH3 has attracted much attention because of its ability to remove nitrogen oxides economically and efficiently.And the catalyst plays a key role in this technique.Cu exchanged SSZ-13 stands out among many denitration catalysts owing to its superior catalytic performance and stability.Due to its extremely small microporous structure,SSZ-13 has the advantages of larger specific surface area,higher hydrothermal stability,and more acidic sites.However,microporous structure also brings a large diffusion limitation,which reduces the utilization efficiency of catalyst active sites,and the reactants and products transport slowly on the catalyst,thereby reducing catalytic performance.In this paper,in order to improve the catalytic performance of selective catalytic reduction of NOx with NH3 by reducing the intracrystalline diffusion restriction,Cu-SSZ-13 zeolites with submicron size and hollow morphology were prepared.At the same time,a variety of characterization methods were used to analyze and test the prepared catalyst and evaluate the activity.The main research content is as follows:The grain size of SSZ-13 synthesized by conventional hydrothermal method is mostly in the micron level.Herein,the size of the SSZ-13 zeolite was successfully adjusted by the growth regulator,and submicron-sized crystal particles were synthesized.Through liquid ion exchange,copper ions were loaded on SSZ-13 zeolite,and a series of Cu-SSZ-13 zeolite catalysts with different particle sizes were synthesized.The catalytic performance test results show that with the decrease of crystal size from micron to submicron,the active temperature window of NOx conversion >90% increased from 200-450 ? to 200-550 ?.This is mainly because the small-sized crystal can decrease the average diffusion length of molecules in the catalyst and reduce the diffusion limitation of the reactant and product gas molecules in the catalyst.Through the thin-walled shell,hollow zeolite can also reduce diffusion restrictions and accelerate molecular transport.In this work,Al-zone was formed by adjusting the distribution of aluminum elements throughout the SSZ-13 crystal particles,and the cavity was formed by selective desiliconization.Furthermore,Cu-loaded hollow SSZ-13 zeolite was prepared.And some characteristics of solid and hollow Cu-SSZ-13 zeolites were compared,such as acid site,Cu active site,catalytic activity and catalytic kinetics.The results show that compared with solid samples,hollow Cu-SSZ-13 catalyst exists stronger capacity of acid adsorption,and the NOx conversion of selective catalytic reduction of NOx by ammonia in the low temperature(150-200 ?)and high temperature(450-500 ?)than the solid sample improves about 20%,the temperature window of best conversion activity increased almost 150 ?,catalytic activity received a significant boost.