| FER zeolites have been widely concerned in the materials field due to the unique two-dimensional pore system consisting of 10-ring channels intersected by 8-ring channels and excellent chemical and hydrothermal stability in comparison with other zeolite catalysts.They are playing a very important role in the isomerization of n-butane, the key to improve the efficiency of isomerization is to improve the catalytic performance of the catalyst and the selectivity for the isobutune.In this paper, we treated the HFER catalyst by removing the aluminum processing with different degrees with different concentrations of HNO3 solution. Compared with the catalyst before modification, the performance of the modified catalysts obtained a certain degree of improvement.In addition,in order to further improve the catalytic efficiency, we modified the HFER catalyst by Pd and Pt,respectively,with different load quantity,and then,wo also loaded Co, Fe.etc common metal on the modified catalysts that have higher catalytic performance, thus we prepared a series of metal loaded molecular sieve catalysts. In this paper,we studied the influence of several factors including acid concentration, acid treatment time and the metal loading on the physical and chemical properties of HFER catalyst by a series of characterization methods,such as temperature-programmed desorption of ammonia(NH3-TPD), scanning electron microscope(SEM), transmission electron microscope(TEM),X-ray diffraction(XRD), Fourier-transform infrared spectroscopy(FTIR) and physical adsorption/desorption measurements of N2.The isomerization catalytic properties of the modified catalysts were evaluated in fixed bed reactor through the isomerization of n-butene.The main results are as follows:1. Influence of reaction temperature on catalytic properties of HFER catalyst were studied under the condition of constant pressure and the space velocity of 1.82h-1, the result shows 350℃ is th e best reaction temperature with the isobutene yield of 24.98% at 1440 min. The lower reaction temperature can effectively inhibit the speed of carbon formation, thus, the stability of the catalyst is improved. Besides, the lower temperature is favorable to the reaction in the thermodynamic equilibrium.2. The n-butene is mainly isomerized over plain Br?nsted acid sites. After HNO3 modification, some of the outside framework aluminum were removed, adjusting the distribution of zeolite acidity and acid site, which maked some strong acid center decreased and the quantity of plain Br?nsted acid sites increased, as a result, the cracking reaction is reduced and the catalytic efficiency is improved. The experiment result shows that the best effect occurs on the concentration of HNO3 with 4M and treat time for 6h, isobutene selectivity and yield reached 58% and 34.2%, respectively.3. Precious metals have a very high catalytic activity, along with the unique pore structure of FER catalyst, different precious metal loading can improve the specific surface area and pore volume, adjusting the acid strength of catalysts, then the catalytic performance is improved. Under the reaction condition of constant pressure 350℃ and the space velocity of 1.82h-1, Catalyst with Pd loading of 0.5% reached higher performance that isobutylene selectivity and yield are 54.22% and 35.91%, respectively.While under the same reaction conditions, catalyst with Pt loading of 0.3% reached the best performance, isobutylene selectivity and yield reached 53.41% and 34.84%, respectively.4. We loaded Co,Zn,Fe respectively with the same amount on Pd0.5-HFER catalyst and Pt0.3-HFER catalyst,which have the better catalytic effect in the reaction. The result shows that Co is helpful to improve the catalytic activity in the reaction, while Fe can in some degrees improve the selectivity. And all these results can provide certain data base for further research. |
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