Abstract
Unsupported NiMo catalyst has high hydrogenation activity due to its high active site distribution. However, low specific surface area and pore distribution greatly limit the efficient utilization of the active components. The Y-zeolite nanoclusters were hydrothermally synthesized and introduced into the unsupported NiMo catalysts from a layered nickel molybdate complex oxide. The XRD, N2 adsorption-desorption, FT-IR, Py-IR, SEM, NH3-TPD, and TEM were used to characterize all catalysts. The dibenzothiophene (DBT) hydrodesulfurization (HDS) reaction was performed in a continuous high pressure microreactor. The results showed that the specific surface area, pore volume, and average pore size of the unsupported NiMo catalysts were greatly increased by the Y-zeolite nanoclusters, and a more dispersed structure was produced. Furthermore, the Lewis acid and total acid content of the unsupported NiMo catalysts were greatly improved by the Y-zeolite nanoclusters. The HDS results showed that the unsupported NiMo catalysts modified by the nanoclusters had the same high desulfurization efficiency as the unmodified catalyst, but had more proportion of direct desulfurization (DDS) products. The results offer an alternative to reducing hydrogen consumption and save cost in the production of ultra clean diesel.
Highlights
Unsupported hydrogenation catalysts, such as NiMo, CoMo, NiW, NiMoW, CoMoW, etc., have high activity which is 3-4 times greater in hydrodesulfurization (HDS) activity than commonly used industrial catalysts [1,2,3,4,5]
The ZSM-5 zeolite nanoclusters were used to modify the zeolite FDU-12 [29], the results showed that the introduction of the ZSM-5 zeolite nanoclusters resulted in the production of satisfactory pore properties, appropriate acidic properties, and preferable dispersed active components, which could be beneficial to the improvement of hydrodesulfurization activity
When the temperature was stabilized to 93 ◦ C, the ammonium hydroxide (28.8% NH3 ) was added under stirring until the mixture changed from a suspension to a clear solution and stopped dropping, the pH was about 12 for the clear solution, and the clear aqueous solution was heated at 93 ◦ C for 10 h under stirring to obtain the turbid liquid
Summary
Unsupported hydrogenation catalysts, such as NiMo, CoMo, NiW, NiMoW, CoMoW, etc., have high activity which is 3-4 times greater in hydrodesulfurization (HDS) activity than commonly used industrial catalysts [1,2,3,4,5]. The unsupported catalysts are usually synthesized by a co-precipitation method [9,10], and the catalyst precursors are mainly ammonium nickel molybdate crystals [11,12], which produce a lower specific surface area and have less pore distribution than the supported catalysts. The unsupported catalysts have only the weak Lewis acid site [18], and it can only be used for hydrogenation but not for isomerization and cracking reactions, which leads to great limitations. Y-zeolite nanoclusters were synthesized by hydrothermal method, and the Y-zeolite nanoclusters with different crystallization time were successfully introduced into the unsupported catalysts to improve the dispersion and the acidity of the unsupported catalysts. The effects of the Y-zeolite nanoclusters on the physic-chemical properties of unsupported catalyst were discussed systematically
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