Preparation And Application Of Beta Molecular Sieve Using Diatomite As Silicon Source

Beta molecular sieve is a high silica zeolite molecular sieve with three-dimensional and 12-membered ring-hole structure,which has excellent acid catalytic properties,pore structure characteristics and hydrothermal stability.Its unique structural characteristics make it widely used as a catalytic material in industrial catalysis such as petroleum processing and environmental management.Natural mineral diatomite is rich in resources,low in price,and diatomite has a high content of SiO2.It is of great research significance to make full use of the chemical constituents in diatomite as raw materials to prepare molecular sieves.In this paper,the natural mineral diatomite from different producing areas was selected as the whole silicon source to prepare molecular sieves.The Beta molecular sieve was synthesized by hydrothermal crystallization one-step method.The effects of various factors on the synthesis of Beta molecular sieves prepared by diatomite as a silicon source were investigated in detail,and the crystallization process was analyzed.Finally,catalytic activity of N2O was used as a reaction model to evaluate the activity of Beta molecular sieves and to study its catalytic activity center.Beta molecular sieves were prepared by hydrothermal crystallization of diatomaite from Changbai County,Inner Mongolia and Jilin Yuantong.The SiO2 content of diatomite in Changbai County and Yuantong County of Jilin Province can reach more than 95%after roasting at 500? and pickling,and the SiO2 content of diatomite in Inner Mongolia has increased from 75%to 93%.At the same time Processing remove a lot of metal oxide,quartz sand and other inert impurities.The study found that the process of Beta molecular sieve formation is as follows:the diatomite continuously dissolves in the alkaline environment to release the active silicon source to form the aluminosilicate and then transform into the small crystal nucleus of the molecular sieve.The crystal nucleus grows evenly on the surface of the diatom structure to further promote the release of the active silicon source to form aluminosilicate condensation.The gel re-transforms the nucleus and finally forms a Beta molecular sieve.The addition of too much aluminum source during the synthesis process will inhibit the release of the active silicon source on the surface of the diatomite.The optimal synthesis conditions were investigated for crystallization at 150? for 72-96 hours to obtain a Beta molecular sieve with a microporous structure,a high specific surface area and a high crystallinity.Beta molecular sieve prepared by using diatomite has excellent catalytic decomposition of N2O properties.This synthetic method does not need any additives and has obvious economic advantages.The diatomaite pretreated with strong acid has less Fe content and less Fe-Beta active center.Therefore,the dilute acid was used to pretreat the diatomite from Changbai to retain a large amount of Fe.The Fe-Beta molecular sieve with higher relative crystallinity was finally prepared to completely decompose N2O at 480?.Characterization of the molecular sieves revealed that the surface contained a small amount of Fe2O3 particles,and most of the Fe was in the form of isolated Fe3+.