A series of 3.0Mo/MCM-22-Al2O3 catalysts with γ-Al2O3 contents in the range of 0-100 wt% were prepared and applied in the metathesis reaction of ethene and butene-2. Addition of γ-Al2O3did not affect the structure o...A series of 3.0Mo/MCM-22-Al2O3 catalysts with γ-Al2O3 contents in the range of 0-100 wt% were prepared and applied in the metathesis reaction of ethene and butene-2. Addition of γ-Al2O3did not affect the structure of MCM-22 zeolite as evidenced by XRD and N2 adsorption measurements. It was deduced from TPR experiments that γ-Al2O3 phase favored the formation of polymolybdate or multilayered Mo oxide, while more Al2（MoO4）3 species were generated over MCM-22 zeolites. Alumina content in the support was directly related to the metathesis activity of ethene and butene-2 to propene. Mo species with higher valence （Mo6＋or Mo5＋） contributed more to the excellent performance of catalyst than metallic Mo. The best catalyst activity and stability was obtained over 3.0Mo/（MCM-22-30%Al2O3） under the reaction condition of 1.0 MPa and 125℃ using N2 as the pretreatment gas.展开更多
In this study,we investigated Mo-impregnated H-MCM-22 catalysts(denoted Mo/M)for methanedehydroaromatization(MDA)to produce aromatics such as benzene and toluene(BT).We attemptedto improve the performance of the MDA c...In this study,we investigated Mo-impregnated H-MCM-22 catalysts(denoted Mo/M)for methanedehydroaromatization(MDA)to produce aromatics such as benzene and toluene(BT).We attemptedto improve the performance of the MDA catalysts by reducing the amount of Brönsted acidsites(BAS)of the H-MCM-22 supports via hydrothermal dealumination.Among the prepared catalysts,an optimal hydrothermal treatment(HT)of H-MCM-22 supports at 400℃,followed by Moimpregnation(denoted Mo/M_400),resulted in a reduced and optimal amount of BAS,along with acomparable Mo distribution to Mo/M.Further,Mo/M_400 enhanced BT formation rates(maximumBT formation rate of 5.23 vs.4.73 mmolBT·g^(−1)·h^(−1) for Mo/M);it appears that dealumination-inducedreduction in the quantity of BAS altered their spatial interaction with active Mo species,promotingBT and naphthalene formation.Interestingly,the lifetime of intermediate C_(2)(ethane and ethylene)formation was also improved for Mo/M_400.Rigorous coke analyses revealed that the decreasedcoke content in the aromatic-selective 10-membered-ring(10-MR)pores,as well as the ability ofthe 12-MR pores to accommodate coke deposits over a longer reaction time,improved the stabilityof Mo/M_400.Nonetheless,for all catalysts,the deactivations of BAS,and subsequently,the activeMo sites were mainly ascribed to coke deposition.The overall enhancement in MDA performance byMo/M_400 was attributed to the advantages of the optimally reduced BAS,allowing such performanceto surpass those of previously reported Mo-based catalysts.展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 20903088 and 20773120)the Ministry of Science and Technology of China through the National Key Project of Fundamental Research (Grant No.2009CB623507)
文摘A series of 3.0Mo/MCM-22-Al2O3 catalysts with γ-Al2O3 contents in the range of 0-100 wt% were prepared and applied in the metathesis reaction of ethene and butene-2. Addition of γ-Al2O3did not affect the structure of MCM-22 zeolite as evidenced by XRD and N2 adsorption measurements. It was deduced from TPR experiments that γ-Al2O3 phase favored the formation of polymolybdate or multilayered Mo oxide, while more Al2（MoO4）3 species were generated over MCM-22 zeolites. Alumina content in the support was directly related to the metathesis activity of ethene and butene-2 to propene. Mo species with higher valence （Mo6＋or Mo5＋） contributed more to the excellent performance of catalyst than metallic Mo. The best catalyst activity and stability was obtained over 3.0Mo/（MCM-22-30%Al2O3） under the reaction condition of 1.0 MPa and 125℃ using N2 as the pretreatment gas.
文摘In this study,we investigated Mo-impregnated H-MCM-22 catalysts(denoted Mo/M)for methanedehydroaromatization(MDA)to produce aromatics such as benzene and toluene(BT).We attemptedto improve the performance of the MDA catalysts by reducing the amount of Brönsted acidsites(BAS)of the H-MCM-22 supports via hydrothermal dealumination.Among the prepared catalysts,an optimal hydrothermal treatment(HT)of H-MCM-22 supports at 400℃,followed by Moimpregnation(denoted Mo/M_400),resulted in a reduced and optimal amount of BAS,along with acomparable Mo distribution to Mo/M.Further,Mo/M_400 enhanced BT formation rates(maximumBT formation rate of 5.23 vs.4.73 mmolBT·g^(−1)·h^(−1) for Mo/M);it appears that dealumination-inducedreduction in the quantity of BAS altered their spatial interaction with active Mo species,promotingBT and naphthalene formation.Interestingly,the lifetime of intermediate C_(2)(ethane and ethylene)formation was also improved for Mo/M_400.Rigorous coke analyses revealed that the decreasedcoke content in the aromatic-selective 10-membered-ring(10-MR)pores,as well as the ability ofthe 12-MR pores to accommodate coke deposits over a longer reaction time,improved the stabilityof Mo/M_400.Nonetheless,for all catalysts,the deactivations of BAS,and subsequently,the activeMo sites were mainly ascribed to coke deposition.The overall enhancement in MDA performance byMo/M_400 was attributed to the advantages of the optimally reduced BAS,allowing such performanceto surpass those of previously reported Mo-based catalysts.
