Abstract
SAPO-11 molecular sieves were modified with different Ni contents by the in situ modification method. The Ni-modified SAPO-11 molecular sieves were used as the supports to prepare the corresponding NiW-supported catalysts for the hydroisomerization of n-hexadecane. The Ni-modified SAPO-11 and the corresponding NiW-supported catalysts were characterized by X-ray diffraction, scanning electron microscopy, N2 adsorption–desorption, NH3-temperature-programmed desorption, pyridine adsorbed infrared, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. The results showed that Ni in situ modification preserved the crystal structure of SAPO-11; increased the BET specific surface area, mesopore volume, and medium and strong Brønsted acid amount of SAPO-11; and increased the stacking number of the active phase of the catalysts. 3Ni-SAPO-11 possessed the largest BET specific surface area, mesopore volume, and medium and strong Brønsted acid amount. NiW/3Ni-SAPO-11 possessed the highest dispersion of the active phase and the highest sulfidation degree of the active metals. The results of the hydroisomerization of n-hexadecane showed that Ni in situ modification improved the catalytic activity and selectivity of the catalysts for the hydroisomerization of n-hexadecane to varying degrees. Especially, NiW/3Ni-SAPO-11 had the highest catalytic activity and isomer selectivity, and the maximum yield of isomeric hexadecane could reach 71.18%.
Highlights
In order to meet the utilization standards of oil products in cold regions, diesel oil is required to have a low freezing point, and lubricant base oil has good low-temperature fluidity
The results showed that the dispersion degree of tungsten species on different catalysts decreased in the order of NiW/3Ni-SAPO-11 > NiW/2Ni-SAPO-11 > NiW/4Ni-SAPO-11 ≈ NiW/1Ni-SAPO11 > NiW/SAPO-11, which was completely consistent with the results reflected by the length and stacking number of WS2 slabs
SAPO-11 molecular sieves were modified with different Ni contents by the in situ modification method, and the Ni in situ modified SAPO-11 molecular sieves were used as the supports to prepare the NiW-supported catalysts for the hydroisomerization of n-hexadecane
Summary
In order to meet the utilization standards of oil products in cold regions, diesel oil is required to have a low freezing point, and lubricant base oil has good low-temperature fluidity. Finding metal components with low cost and high dehydrogenation/ hydrogenation activity is the research focus of developing a new SAPO-11 molecular sieve-based hydroisomerization catalyst. There are few reports about the application of NiWS and NiMoS active phases in the SAPO-11 molecular sieve-based hydrocarbon hydroisomerization catalyst. The properties of the active phase, such as slab length, stacking number, and dispersion, are closely related to the catalytic performance of the catalyst. SAPO-11 molecular sieves were modified with different percentages of Ni content by the in situ modification method, and NiW supported catalysts were prepared for the hydroisomerization of n-hexadecane with the Ni in situ modified. The solid products collected by filtration were washed to neutrality with deionized water, dried at 110°C overnight, and calcined at 600°C for 6 h to obtain the Ni-modified SAPO-11 molecular sieves. Where Vfeed is the feed flow rate of the reactant n-C16 in mol/h, x is the conversion of n-C16 at 340°C, nw is the amount of W atoms of the catalyst in mol, and fW is the dispersion degree of W species
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