| Motor vehicle exhaust pollution has seriously jeopardized the ecological environment in China.At present,automobile exhaust gas purification technology cannot fundamentally solve the problem of pollution caused by sulfides.In order to meet increasingly stringent fuel standards,ultra-deep desulfurization of the oil must be implemented.Therefore,the dibenzothiophene?DBT?and its derivatives?such as4,6-DMDBT?that are most difficult to deal with in the diesel fraction must be removed.This requires that the novel hydrodesulfurization?HDS?catalysts have higher catalytic activities than conventional catalysts.Therefore,this dissertation aims to develop a high efficiency HDS catalyst of diesel oil.Micro-mesoporous material ZSM-5-KIT-6?denoted as ZK?was directionally design and synthesized under hydrothermal condition using ZSM-5 microcrystalline emulsion as precursor,triblock copolymer P123 together with n-butanol as mesoporous templates.And then,catalysts with different pore structure and acidity were prepared by loading active metals Ni and Mo.The effects of crystallization temperature,the addition amount of templating agent and the molar ratio of SiO2/Al2O3 on the composites were investigated in detail.The materials and their corresponding catalysts were characterized by X-ray diffraction?XRD?,Fourier transform infrared spectroscopy?FTIR?,transmission electron microscopy?TEM?,nitrogen adsorption-desorption,pyridine adsorption infrared spectroscopy?Py-FTIR?,Raman spectroscopy?Raman?,high resolution transmission electron microscopy?HRTEM?techniques.The results showed that with the increasing of crystallization temperature,the pore size of ZK composites increased,but the specific surface area decreased,besides,the crystallinity and the degree of structural order became worse in the studied temperature range.Its application for HDS reaction of diesel showed that the NiMo catalysts with ZK composites as supports showed better HDS activities,NiMo/ZK-100 had the highest HDS catalytic activity,and the desulfurization rate was 96.4%.The modification of the pore structure was achieved by changing the molar ratio of BuOH/P123.The composite ZK-B3 had a larger specific surface area and an excellent pore structure when BuOH/P123=100.Therefore,NiMo/Al-ZK-B3 exhibited good catalytic activity in the hydrodesulfurization reaction of diesel,and the conversion rate of S reached up to 95.6%.Based on the front researches,the acidity modulation of the catalyst was achieved by changing the molar ratio of SiO2/Al2O3.NiMo/Al-ZK-80 had a suitable acidity and acid distribution when SiO2/Al2O3=80,and the desulphurization rate of diesel oil on the catalyst NiMo/Al-ZK-80 was 97.2%.DBT and 4,6-DMDBT were used as model compounds to investigate the HDS route.DBT had the highest conversion rate on NiMo/ZK-B3 when the LHSV=20 h-1,and the direct desulfurization product biphenyl?BP?selectivity reached 72.1%,NiMo/ZK-80exhibited the highest catalytic activity in the HDS reaction of 4,6-DMDBT,and the selectivity of isomerization pathway reached 68.1%when LHSV=10 h-1.Therefore,within the scope of the experimental conditions,the optimum crystallization temperature was 100°C,the molar ratio of BuOH/P123 and SiO2/Al2O3were 100 and 80,respectively.A possible reaction network for the HDS of 4,6-DMDBT over the series of NiMo/ZK catalysts was proposed.These results are meaningful for the development of efficient industrial HDS catalysts. |
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