A series of Ca-ZSM-5 catalysts with different loading amounts were prepared by ion exchange method.The catalytic performance of the catalysts for the preparation of cyanamide from urea dehydration was investigated in a fixed bed reactor.X-ray diffraction(XRD),N2 physical adsorption,scanning electron microscopy(SEM),ammonia temperature desorption(NH3-TPD)and pyridine infrared(Py-IR)were used to analyze the changes in the physical structure,microstructure and acidity of the catalysts before and after modification.The results showed that the physical structure of the modified catalyst was basically unchanged,but the specific surface area decreased with the increase of calcium load.After modification,the strength of weak acid and medium strong acid sites did not change significantly,but the strength of strong acid sites diminished,and the acid content of weak acid and medium strong acid increased significantly.In addition,the proportion of L-acid in the catalyst increased significantly,while the amount of B-acid decreased slightly,and thus the value of B/L decreased.When the reaction temperature was 550℃,urea feed rate was 0.2g/min,NH3 velocity was 3000h-1,condensate temperature was 0℃,and"0.1 Ca-ZSM-5"was used for a 30 min reaction,the urea conversion was 91.1％,the selectivity and yield of cyanamide were 40.5％ and 36.9％,respectively.
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