The direct oxidation of cyclohexane to adipic acid(AA)without the use of HNO_(3)is important but still challenging.Herein,hierarchical manganese-containing TS-1 zeolite(HMTS)was prepared using an improved direct synth...The direct oxidation of cyclohexane to adipic acid(AA)without the use of HNO_(3)is important but still challenging.Herein,hierarchical manganese-containing TS-1 zeolite(HMTS)was prepared using an improved direct synthesis method,in which titanium and manganese coexist within the zeolite matrix,as characterized by X-ray diffraction,X-ray photoelectron spectroscopy,transmission electron microscopy,ultraviolet,extended X-ray absorption fine structure etc.The introduction of matrix Mn species(Mn^(3+),Mn^(4+))not only increased the surface oxygen vacancies,but also generated medium-strong acid sites,which endowed HMTS catalysts with the ability to efficiently activate oxygen and facilitate substrate coordination.On HMTS-3,one-pot oxidation of cyclohexane at 140℃and 2 MPa O_(2)gave 81.6%conversion and 71.5%AA selectivity,the highest value obtained at present.Control experiments with single-component samples confirmed that matrix Ti^(4+)catalyzed the conversion of cyclohexane to a mixture of cyclohexanone and cyclohexanol(KA oil),and matrix Mn favored the conversion of KA oil to AA.The synergy between matrix Ti and Mn inside the hierarchical structure were the key factor for the superior activity.Specifically,the matrix Ti^(4+)might activate oxygen to form Ti-O_(2)2-which facilitated the activation of the C-H bond of cyclohexane.The activation of O_(2)on matrix Mn^(3+)formed Mn^(4+)-O_(2)-favoring the breaking of the C-C bond of cyclohexanone.The hierarchical structure not only exposed more active sites and promoted mass transfer,but also provided a better microenvironment for the matrix Mn to synergize with the matrix Ti,which facilitated the overall reaction.This work demonstrated the practical application potential of HMTS and provided useful insights into the direct oxidation of cyclohexane to AA.展开更多
Coordinating the ratio of Bronsted to Lewis acid sites in zeolite catalyst is crucial for the efficient conversion of dihydroxyacetone(DHA)to methyl lactate(ML)in methanol media due to the different acidic requirement...Coordinating the ratio of Bronsted to Lewis acid sites in zeolite catalyst is crucial for the efficient conversion of dihydroxyacetone(DHA)to methyl lactate(ML)in methanol media due to the different acidic requirements of the four fundamental reactions.Herein,we couple Sn-MFI and TS-1 zeolites with different abilities to induce methanol dissociation to rationally regulate the ratio of Bronsted and Lewis acid sites in methanol,thus facilitating the yield of DHA to ML.It is found that framework Sn sites with low dissociation energy(39.2 kJ/mol)induce methanol to release hydrogen protons,creating Bronsted acid sites to enable DHA dehydration to PA.Ti sites in TS-1 zeolite possess high methanol dissociation energy(73.5 kJ/mol),maintaining Lewis acidity in methanol,which provides sufficient active sites for cooperatively intensifying PA addition to HA and subsequent HA isomerization to ML.The synergistic effect of the two zeolites mitigates the side reaction while achieving high DHA conversion,thus steering the reaction toward ML generation.Consequently,ML yield increases by over 25% compared with that of single Sn-MFI zeolite,which offers a promising pathway to promote the synthesis of DHA to ML under mild conditions.展开更多
文摘The direct oxidation of cyclohexane to adipic acid(AA)without the use of HNO_(3)is important but still challenging.Herein,hierarchical manganese-containing TS-1 zeolite(HMTS)was prepared using an improved direct synthesis method,in which titanium and manganese coexist within the zeolite matrix,as characterized by X-ray diffraction,X-ray photoelectron spectroscopy,transmission electron microscopy,ultraviolet,extended X-ray absorption fine structure etc.The introduction of matrix Mn species(Mn^(3+),Mn^(4+))not only increased the surface oxygen vacancies,but also generated medium-strong acid sites,which endowed HMTS catalysts with the ability to efficiently activate oxygen and facilitate substrate coordination.On HMTS-3,one-pot oxidation of cyclohexane at 140℃and 2 MPa O_(2)gave 81.6%conversion and 71.5%AA selectivity,the highest value obtained at present.Control experiments with single-component samples confirmed that matrix Ti^(4+)catalyzed the conversion of cyclohexane to a mixture of cyclohexanone and cyclohexanol(KA oil),and matrix Mn favored the conversion of KA oil to AA.The synergy between matrix Ti and Mn inside the hierarchical structure were the key factor for the superior activity.Specifically,the matrix Ti^(4+)might activate oxygen to form Ti-O_(2)2-which facilitated the activation of the C-H bond of cyclohexane.The activation of O_(2)on matrix Mn^(3+)formed Mn^(4+)-O_(2)-favoring the breaking of the C-C bond of cyclohexanone.The hierarchical structure not only exposed more active sites and promoted mass transfer,but also provided a better microenvironment for the matrix Mn to synergize with the matrix Ti,which facilitated the overall reaction.This work demonstrated the practical application potential of HMTS and provided useful insights into the direct oxidation of cyclohexane to AA.
基金the SINOPEC Project(411058,413025)the National Key R&D Program of China(2017YFB0306800)the National Natural Science Foundation of China(21808244,22278441,and 22478452)for funding this research.
文摘Coordinating the ratio of Bronsted to Lewis acid sites in zeolite catalyst is crucial for the efficient conversion of dihydroxyacetone(DHA)to methyl lactate(ML)in methanol media due to the different acidic requirements of the four fundamental reactions.Herein,we couple Sn-MFI and TS-1 zeolites with different abilities to induce methanol dissociation to rationally regulate the ratio of Bronsted and Lewis acid sites in methanol,thus facilitating the yield of DHA to ML.It is found that framework Sn sites with low dissociation energy(39.2 kJ/mol)induce methanol to release hydrogen protons,creating Bronsted acid sites to enable DHA dehydration to PA.Ti sites in TS-1 zeolite possess high methanol dissociation energy(73.5 kJ/mol),maintaining Lewis acidity in methanol,which provides sufficient active sites for cooperatively intensifying PA addition to HA and subsequent HA isomerization to ML.The synergistic effect of the two zeolites mitigates the side reaction while achieving high DHA conversion,thus steering the reaction toward ML generation.Consequently,ML yield increases by over 25% compared with that of single Sn-MFI zeolite,which offers a promising pathway to promote the synthesis of DHA to ML under mild conditions.
