Preparation And Optimization Of Molecular Sieve Catalyst

Nitrogen oxides are recognized as one of the major air pollutions in the world.They also cause damage to the water environment,soil and buildings,seriously harming human health and the natural environment.The nitrogen oxides emitted from the exhaust of motor vehicles are increasing day by day,and the resulting air pollution problem needs to be solved urgently.Selective catalytic reduction?SCR?technology is considered to be one of the effective methods for eliminating nitrogen oxides.The core of the technology is a stable and efficient catalyst.Molecular sieve catalysts are the current research hotspots and have a good application in the denitration of motor vehicle exhaust prospec.In this paper,two molecular sieves with chabazite?CHA?structure of SAPO-34and SSZ-13 were synthesized by hydrothermal method,and Cu modified molecular sieve catalyst was loaded by impregnation method.Evaluate its denitration performance and N₂ selectivity,use N₂ physical adsorption,X-ray diffraction?XRD?and scanning electron microscope?SEM?to characterize the sample,and optimize the preparation process and formulation of the two catalysts according to the characterization results.In the experiment of synthesizing SAPO-34 molecular sieve with silica sol as the silicon source,it was found that there was a problem that the raw material mixed slurry solidified in the early stage of synthesis and the magnetic stirrer could not rotate.Silica sol is relatively stable at pH=4¹0,and it is easy to coagulate outside this range.This problem can be solved by adjusting the feeding process,using slow dropwise addition,and adding aluminum sol first.Then the influence of crystallization time and crystallization temperature on the synthesis effect of SAPO-34 was investigated.After these molecular sieves were made into catalysts,the corresponding characterization was performed and their denitration performance was tested on an activity evaluation device.As a result,it was found that multiple groups of samples can achieve a denitration rate of 100%.Among them,the performance of the sample crystallized at 155?for 48h is more prominent,the active temperature window is 200⁴00?,which has good N2 selectivity,therefore,crystallized at 155?for 48h is a better synthesis condition.The synthesis of SSZ-13 introduces seed crystals on the basis of hydrothermal synthesis,which is equivalent to adding a large number of crystal nuclei to the crystallization reaction system,this method improves the growth rate of SSZ-13molecular sieve crystals and speeds up the preparation process of molecular sieve.Then the influence of the amount of template,sodium hydroxide and water in the synthesis components on the synthesis results of SSZ-13 molecular sieve was studied.After the molecular sieve is made into a catalyst,relevant characterization and performance tests are carried out.The results show that multiple groups of samples can achieve a denitrification rate of 100%.Among them,the template agent is 33.76g,NaOH is 1.4g,and the deionized water is 32g.The active temperature window of the sample is 200⁴50?,and within this range,the N₂ selectivity continues above 93%.Under the premise of ensuring the performance of the synthetic molecular sieve,the preparation conditions reduce the waste of raw materials and the amount of waste liquid generated,and reduce the production cost.Loaded metal modification is an important part of catalyst preparation.Next,the effect of impregnation on catalyst denitration performance was explored.It was found that in the process of catalyst modification by impregnation,ultrasonic treatment had a certain improvement in catalyst denitrification performance.The thesis explores the synthesis of two molecular sieves,SAPO-34 and SSZ-13.Under the premise of taking into consideration the performance,the preparation process and formula are optimized,reducing energy consumption,waste of raw materials and the amount of waste liquid generated,shortening the synthesis cycle,and reducing the preparation cost.And a simple study on the modification and denitrification performance,provides a certain reference for the industrial production of these two molecular sieve materials and commercial applications in the field of denitrification.