Research On Embedded Catalysts For Syngas To Aromatics

As the feedstock for the production of dyes,medicines and synthetic rubber,aromatics are widely used in aerospace,pharmaceuticals,pesticides and polymer material synthesis industry.The catalytic reforming of naphtha is the traditional way to produce aromatics.However,with the depleting of oil resources and the deterioration of the global environment,it is urgent to find an environmentally benign process of aromatics production to alleviate the current situation of energy and environment.Recently,syngas to aromatics by Fischer-Tropsch synthesis becomes one of the most promising techniques utilizing the abundant coal and shale gas resources.Herein,an embedded Co-based metal zeolite catalyst（Co@HZSM-5）was prepared by hydrothermal synthesis method.Through XRD characterization,it was found that when TPAOH/Si=0.3 and the crystallization time was 96 h,the synthesized Co@HZSM-5 was highly crystalline with uniform metal distribution.With a Co loading at 10 wt%and Si/Al=40,syngas could be directly converted into aromatics under mild conditions.Under the reaction conditions of 260℃,1.0 MPa,H₂/CO=2 and GHSV=4500 m L·g^-1_cat·h^-1,76.3%CO conversion and 14.6%aromatic selectivity were achieved over Co@HZSM-5,the values were much higher than those of supported catalyst（Co/HZSM-5）.Combine with XRD,SEM-EDS and NH₃-TPD,it was shown that Co was evenly distributed in Co@HZSM-5 and the effect of acidity on the HZSM-5 was negligible.Moreover,N₂ adsorption-desorption and TG-DTA results showed that the embedded catalyst had a certain mesoporous structure,which could effectively promote the diffusion of products and inhibit the coke deposition.In order to further improve the selectivity of aromatics product,promoters such as Mo and Mn were added respectively to prepare bimetallic embedded zeolite catalysts.Under the same reaction conditions,5Mo10Co@HZSM-5 and 5Mn10Co@HZSM-5 catalysts exhibited aromatic selectivities of 31.9%and 32.8%at CO conversions of 59.1%and84.1%,respectively.Notably,both of which gave a high light aromatics selectivity over 95%.According to XRD,N₂ adsorption-desorption and NH₃-TPD characterization,the introduction of Mo and Mn had negligible effects on the structure and acidity of HZSM-5.