Synthesis Of Ni-Mo-N Catalyst And Its Hydrogenation Performance Of Thiophene-Containing Benzene

Coal is the main energy in our country.Coal liquefaction technology is of great significance to reduce oil external dependency.However,the coal direct liquefaction oil contains rich aromatics and oxygen,nitrogen,and sulfur impurity atoms,which seriously affected the quality of the product.Therefore,hydrogenation is to obtain product that conforms to the national standard,and the most critical problem in the process of hydrofining is eliminate the influence of impurity atoms on the catalyst.This thesis choose benzene as the model compounds and thiophene as poisons were determined by the composition of coal direct liquefaction oil and the characteristics of aromatic hydrogenation.Since the first report on the preparation of high surface area carbide and nitride materials by temperature programmed reaction,transition metal carbides and nitrides have attracted constant interest of researchers.Recently it has been shown that the Mo-based nitrides have been identified as potential catalysts for many applications.In particular,the bimetallic molybdenum nitrides have shown higher activities in catalyticreactionssuchasisomerization,hydrodesulfurization,hydrodenitrogenation,andammoniasynthesis,especiallyin hydrodearomatization.They are used as cheaper alternative catalysts to replace conventional hydrotreating catalysts due to their similar catalytic activity and higher sulfur and nitrogen tolerance.But Mo-based nitrides on the preparation of single and difficulties may be its hard to realize industrial production.The bimetallic nitrides Ni₂Mo₃N were chosen as hydrogenation catalyst,first,the prepared method of complex decomposition method and hydrogen reduction method affected the formation of Ni₂Mo₃N were investigated.Then the loading of Ni₂Mo₃N were prepared,the impregnation method and support effects on catalytic properties were investigated.In addition,according to the design principle of sulfur-resistant catalysts,the introduction of boron to improve the sulfur resistant of catalyst was investigated.The main results and conclusions are as follows.First,the complex decomposition method and hydrogen reduction method prepared Ni₂Mo₃N have the same formation mechanism,the compound of Ni and Mo₂N were formed,and then Ni₂Mo₃N is formed by solid-solid reaction.However,there are some differences in the synthesis process between the hydrogen reduction method and the complex decomposition method.One is that the preparation temperatures are different.In the hydrogen reduction method,Ni₂Mo₃N is formed at 600oC,while a preparation temperature of at least 650oC is needed for the complex decomposition method.Second is that the nitrogen source is different.In the hydrogen reduction method,inorganic ammonium groups contained in the solid precursor are employed as the N source to form Ni₂Mo₃N,while hexamethylenetetramine as the N source for the complex decomposition method.Third is that the composition of bimetal nitride is different.In the hydrogen reduction method,the composition of catalysts is Ni₂Mo₃N and Mo,while the composition of catalysts is Ni₂Mo₃N,Ni and MoO₂ for the complex decomposition method.Compared to the complex decomposition method,hydrogen reduction method is more suitable for the preparation of Ni₂Mo₃N catalyst.Second,when the loading of Ni₂Mo₃N is 25 wt.%,Ni?CH₃COO?₂,?NH₄?₆Mo₇O₂₄ and HMT with a molar ratio of 14:3:27 and 14:3:34,Ni₂Mo₃N/?-Al₂O₃ catalysts have an obvious peak of Ni₂Mo₃N.The content of Ni₂Mo₃N is up to 94.09%with prepared by hydrogen reduction method,and the average grain size of Ni₂Mo₃N is 5.7 nm,while the content of Ni₂Mo₃N has only 34.80%for the complex decomposition method.Therefore,the hydrogen reduction method is a kind of feasible industrial prepared method of bimetallic nitride.The support of?-Al₂O₃ and HZSM-5 were used to load Ni₂Mo₃N,the support acid on the influence of sulfur resistance was researhed.The result show that strongly acidic has disadvantage of sulfur resistance.Third,the catalysts of Ni₂Mo₃N/?-Al₂O₃ has not difference of composition,crystal structure,surface area,and bore diameter with prepared by different impregnation method.But the hydrogen reduction temperature and the metal dispersion were changed,hydrogen reduction temperature shift to lower temperature and improved the metal dispersion with multiple-impregnation method.First impregnation Mo,then Ni is the best way to promote the active metal dispersion and possessed best activity and stability,this is because Mo laoded on?-Al₂O₃ at the first stage can weaken the interaction between Ni and supporter,to promote the activation of metals.Fourth,adding boron did not change the original phase of the Ni₂Mo₃N,but its electronic structure has changes,then the sulfur resistance of the catalyst has improved.When the boron content is 0.1wt.%,under the condition of 250oC and3 MPa with the content of thiophene is 100 ppm,benzene hydrogenation activity is keep up with 93%after 16 hours.