Bifunctional Syngas-to-Aromatics Catalyst Developed by SRIPT

Recently, the directionally distributed two‐component Cr2O3/ZSM‐5 catalyst, which was cooperatively developed by the SINOPEC Shanghai Research Institute of Petrochemical Technology (SRIPT) and the University of Science and Technology of China (USTC), has been applied in the coupling and serially connected process for syngas‐to‐aromatics catalysis to effectively utilize the anisotropy of ZSM‐5 channels by constructing the spatial path of orderly diffusion reaction for serially connected reaction intermediates,which can significantly enhance the STA reaction efficiency.In the early stage of study the research team has discovered that different channels of ZSM‐5 zeolite have obvious impact on the formation of aromatic compounds,and the straight channels of b-axis are the main ones for the formation and diffusion of aromatics.Hence, in a bifunctional catalytic system, the establishment of an oxide‐zeolite orientated distribution pattern can optimize the diffusion and transfer in the spatial path of C1intermediate to improve the catalytic reaction efficiency.Hereby, the research team has prepared the bifunctional Cr2O3/ZSM‐5 catalyst with directionally distributed ingredients that can match up to the orientation of zeolite channels, leading to the establishment of STA ordered spatial reaction path for improving the reaction efficiency.Starting from the mixed catalyst of oxide and zeolite powder,through adding binder, extrusion, molding, and then by means of secondary crystallization in an organic template atmosphere, the research team has prepared a bifunctional catalyst CrZ‐Recry with Cr2O3components directionally distributed on the specific crystal plane of ZSM‐5 zeolite.Being different from the disordered distribution of the components in the catalyst formed thereby, the Cr2O3components in the CrZ‐Recry samples are selectively distributed on the (100) and (101) crystal planes of ZSM‐5 zeolite, and the degree of exposure of the b‐axis straight channels, which function as the main diffusion channels of the aromatic components, is improved.

In the bifunctional catalyst system with directional distribution of components, the C1intermediate formed by hydrogenation of CO on the oxide surface can diffuse to the inside of ZSM‐5 zeolite through adjacent sinusoidal channels, and the aromatization reaction takes place under the action of acidic sites inside the channels to generate aromatics, and the aromatic products are then diffused to the gas phase through the straight channels.The construction of the ordered spatial path can promote the diffusion of reaction intermediates and products to improve the reaction efficiency and reduce the probability of side reactions.

Compared with the catalyst with disordered distribution of its components, the directionally distributed bifunctional catalyst can improve the reaction efficiency of syngas conversion.Under conditions covering a reaction temperature of 395℃,a H2/CO ratio of 1, a reaction pressure of 7.0 MPa, and a volume hourly space velocity of 1000 h‐1, the CO conversion over the directionally distributed bifunctional catalyst can reach 49.4%, which is much higher than that achieved by the conventionally formed catalyst.Meanwhile, the aromatics selectivity of the directionally distributed catalyst remains high on the basis of the high CO conversion rate, and the formation of C10+ aromatics is effectively inhibited.

The strategy of establishing orderly diffusion‐spatial path of reaction proposed by this study can provide a new idea for the design of bifunctional catalytic system for catalyzing the coupled and serially connected reactions.