The Loading Of Pt-based Nanoclusters On HZSM-5 Zeolite For Catalytic Cracking Of N-Butane To Light Olefins

Ethylene and propylene are important chemical raw materials,and steam cracking of hydrocarbons is the major source of light olefins.The disadvantages of steam cracking are high energy consumption and low selectivity of low carbon olefins.In contrast,the catalytic cracking process can effectively reduce energy consumption,control the ratio of propylene/ethylene,improve the yield of propylene.Furthermore,C4 hydrocarbon raw materials in China is relatively surplus.So,the use of C4 alkanes catalytic cracking to produce low carbon olefins is of great significance.This paper is mainly focused on the preparation of a new catalyst for the catalytic cracking of n-butane.From the view point of improving the conversion of alkanes and the yield of olefins,aiming at alkane dehydrogenation first and then cracking for the conversion of alkane,the combination of HZSM-5 molecular sieve with cracking function and Pt nanoclusters with dehydrogenation function for n-butane catalytic cracking reaction is put forward.The stability of Pt cluster was further improved by coating alumina layers and introduction of Sn.The Pt/HZSM-5 catalyst with different Pt cluster loadings,the Al₂O₃/Pt/HZSM-5 catalysts with different layers of alumina by using ALD technique and PtSn/HZSM-5 catalyst with different PtSn loading amount were prepared.The physical properties of various catalysts were characterized.The results show that the as-prepared Pt nanoclusters are uniform,with a high degree of dispersion,while the average particle size is 1.8 nm,and the valence state is zero.The anti-sintering stability of Pt clusters is greatly enhanced after the coating of alumina.The as-synthesized PtSn clusters with uniform particle size?2 nm?possess well anti-sintering stability.The introduction of the clusters does not destroy the structure of HZSM-5,and it does not caused a serious pore blockage.The catalytic performance of Pt/HZSM-5 catalysts with different Pt loadings showed that the conversion of n-butane and the yield of the low carbon olefin increased with the increasing of the temperature and Pt loading.At 625 ?,the 1.0%Pt/HZSM-5 catalyst?The actual loading is 0.767%?showed the best performance.Compared with the HZSM-5,the conversion of the n-butane increased by 17%,and the yield of ethylene and propylene increased by 7% and 5% respectively.Among the Al₂O₃/Pt/HZSM-5 series catalysts with different alumina layers,the activity of the 20 Al₂O₃/Pt/HZSM-5 catalyst with 20 layer alumina showed the best performance,because of the low layers of coated aluminum,no serious pore blockage occured and the anti-sintering stability of Pt clusters was enhanced.At 625 ?,compared with Pt/HZSM-5 catalyst without coated alumina layer,the n-butane conversion was increased by 6 %,and the yield of ethylene and propylene was both increased by 3%.The study on the performance of PtSn/HZSM-5 catalysts with different PtSn nanocluster loadings for the catalytic cracking of n-butane were all showed that the conversion of n-butane and the yield of the low carbon olefin increased with the increasing of the temperature and loading.Due to the introduction of Sn,the activity of Pt catalyst was reduced,and the anti-sintering stability of Pt was improved.Compared with the HZSM-5,at 625 ?,1.0%PtSn/HZSM-5 catalyst showed the best performance.The n-butane conversion was increased by 12%,and the yield of ethylene and propylene was increased by 5% and 3% respectively.