Nickel-containing zeolite samples were prepared by dry mechanical mixing of ZSM-5 zeolite (silica modulus 40) and nickel powder with the average particle size of 50 nm in the amount of 0.5 mass %. The samples were mechanically treated in a ball mill for 24-120 h. The crystallinity of the initial zeolite and mechanically treated nickel-containing zeolites was determined by means of IR spectroscopy and XRS. The degree of zeolite crystallinity was revealed to decrease due to loosening of the structure of both the polycrystalline units and primary crystallites as a result of mechanical treatment. The analysis of the state of nanosized nickel in zeolite catalysts by means of UV spectroscopy and XPS revealed almost complete absence of the oxidation of nickel particles. The morphology of the crystals of the initial and mechanically treated zeolites was studied by means of the high resolution transmission electron microscopy. Mechanical treatment was determined to cause a decrease in the particle size of initial ZSM-5 and partial migration of nickel from the surface into zeolite pores. The size of nickel particles decreases during the initial period of mechanical treatment, while a longer mechanical impact, on the contrary, contributes to the agglomeration of nickel particles. The particles of ZSM-5 zeolite in the initial sample look like coarse agglomerates with the overall size of several micrometres. The agglomerates are composed of smaller polycrystalline units 0.5-1.0 mu m in size. However, the primary particles are zeolite crystals 50-100 nm in size. Mechanical treatment causes disintegration of coarse zeolite agglomerates into smaller polycrystalline units less than 1 mu m in size; primary crystallites comprising the polycrystalline structure are dispersed, too, decreasing in size to similar to 50 nm. According to the data of low-temperature desorption of nitrogen, mechanical pretreatment of nickel-containing zeolite causes a decrease in its specific surface area and pore volume. The changes in the physicochemical properties of the Ni/ZSM-5 catalyst caused by mechanical treatment should promote selective conversion of feedstock components and flexibility of the regulation of selective formation of target products in oil refining processes.
|Журнал||Химия в интересах устойчивого развития|
|Состояние||Опубликовано - 2020|