Application Study Of MoS₂-based Catalysts For Selective Hydrogenation And Hydrodesulfuration

Hydrodesulfurization?HDS?is the one of the most important process in oil refining and coal tar processing.The main purpose is removing the sulfur impurities,reducing environmental pollution and improving the quality of product.Moreover,HDS is multiple reaction process,involved in hydrodenitrification,hydrodeoxidization,demealization,dearomatization and deolefins,etc.,so the process is also called as hydrorefining.In recent years,environmental laws and regulations are more and more strict with the limitation of sulfur content in petroleum.In the latest V standard,the content of olefins and aromatics in gasoline is also more stringent restriction and the content of polyaromatic hydrocarbons?PAHs?in the diesel needs to be further reduced.Currently,oil processing is not only to solve the problem of ultra deep desulfurization,but also to ensure the quality of product,meeting the requirements of other compulsive indicators,thus the more strict requirement for the design of catalysts is put forward.For gasoline desulfurization catalysts,it is not allowed that the octane number is decreased obviously when the deep desulfurization is proceeding.There are two methods in common:the one is to avoid excessive hydrogenation of high octane number and olefins.The other words,it needs to improve the ability of selective hydrogenation of catalysts.The other one is to recover octane number by isomerization.The other words,it needs to be proper coupling desulfurization and isomerization reaction.For desulfurization of diesel,in order to improve the cetane number,deep desulfurization is required to promote the hydrogenation of PAHs.Therefore,it is necessary to simultaneously improve the hydrogenation capacity of catalysts.MoS₂-based HDS catalysts are the most commonly used catalysts in the refining industry,generally adding Co or Ni promotors to improve the reaction performance.In recent years,HDS catalysts have been prepared by the addition of complexes,resulting in a relatively large improvement in catalytic activity and selectivity.In order to reveal the effect of complexes,in this paper,we select four bidentatecoordinationmoleculeswithdifferentcoordinationgroups,ethylenediamine?EN?,ethanolamine?EA?,ethylene glycol?EG?and malonic acid?MA?and modify CoMo/?-Al₂O₃ catalyst.The role of coordination groups in the formation of active structures is elucidated by characterizing and comparing the effects of hydrogenation and desulfurization of dibenzothiophene?DBT?.Subsequently,NiMoS₂/?-Al₂O₃ selective hydrogenation catalyst is prepared by studying hydrogenation selectivity of MoS₂-based catalyst to aromatic nitro compouds.Through the above research,the main conclusions are the following:?1?Compared with the contrast roasting CoMo catalyst,adopting to step by step impregnation method,without calcined catalysts increased HDS activity with different degrees and the catalytic activity was observed in the sequence of CoMo?EN?>CoMo?EA?>CoMo?EG??CoMo?MA?>CoMo.For all catalysts,the direct desulfurization route is dominated,but with the increase of reaction temperature,desulfurization by hydrogenation route become more apparent.?2?Coordination groups were studied by a series of characterization method for the regulation of the structure and properties.Results showed that NH₂ group has strong complexing interaction with Co²⁺.COOH group mainly shows electrostatic interaction with cobalt ion.Meanwhile OH group hardly interact with Co²⁺.It notes that the HDS activity is directly related with the interaction between coordinating groups and Co²⁺.The combination of coordinating molecules with Co²⁺leads to the effective formation of Co-Mo-S active centre,and the carbonization of chelating decreases the interaction of support with active phases,facilitating the formation of type II active phases which has higher intrinsic catalytic activity.?3?The selective hydrogenation of 4-nitrostyrene as the model reaction,adopting to step by step impregnation method,Ni?Co,Fe?-MoS₂/?-Al₂O₃ catalyst was prepared using different promoters.Under the same sulfuration and reaction,the effects of promoters on the selective hydrogenation were studied.The results showed that Ni-MoS₂/?-Al₂O₃ catalyst has the best selective hydrogenation performance and the synergistic effect between Ni and Mo promotes this reaction.?4?In order to study the application of Ni-MoS₂/?-Al₂O₃,we evaluate a series of aromatic nitro compounds.The results showed that Ni-MoS₂/?-Al₂O₃ catalyst has good catalytic activity,selectivity and stability.Meanwhile,the mechanism was boldly speculated and discussed through many characterizations,largely expanding the application range of MoS₂-based catalysts.