MOR zeolite has been effectively utilized for dimethyl ether(DME)carbonylation reaction due to its unique pore structure and acidity.During industrial production,the transformation of ammonium type MOR zeolite(NH_(4)-...MOR zeolite has been effectively utilized for dimethyl ether(DME)carbonylation reaction due to its unique pore structure and acidity.During industrial production,the transformation of ammonium type MOR zeolite(NH_(4)-MOR)into proton type MOR zeolite(H-MOR)causes inevitable dealumination.Therefore,understanding the influencing factors and dynamic evolution mechanism of zeolite dealumination is crucial.In this work,the stability of framework aluminum was studied by X-ray diffraction(XRD),Fourier transform infrared(FT-IR)spectroscopy,^(29)Si,^(27)Al,^(1)H magic angle spinning nuclear magnetic resonance(MAS NMR),and DME carbonylation performance evaluation.These results indicate that extra-framework cation Na^(+)and NH_(4)^(+)could better preserve the aluminum structure of the MOR zeolite framework compared to H^(+),primarily due to the different'attraction'of the framework to water.Furthermore,the impact of water on the zeolite framework aluminum at high temperature was studied by manipulating the humidity of the calcination atmosphere,revealing the formation of extra-framework six-coordinated aluminum(Al(Ⅵ)-EF)and the mechanism of water influence on the zeolite framework aluminum.展开更多
系统考察了4种不同模板剂(四乙基氢氧化铵、四丙基氢氧化铵、四丙基溴化铵、四丁基氢氧化铵)对HZSM-5分子筛织构性质、酸性、骨架铝分布和存在形态的影响,通过XRD、SEM、N_(2)吸附-脱附、XRF、FT-IR、NH_(3)-TPD、Py-IR、^(27)Al MAS NM...系统考察了4种不同模板剂(四乙基氢氧化铵、四丙基氢氧化铵、四丙基溴化铵、四丁基氢氧化铵)对HZSM-5分子筛织构性质、酸性、骨架铝分布和存在形态的影响,通过XRD、SEM、N_(2)吸附-脱附、XRF、FT-IR、NH_(3)-TPD、Py-IR、^(27)Al MAS NMR、UV-vis-DRS、TG等手段对HZSM-5分子筛进行表征,并研究了其催化乙醇制丙烯的性能。结果表明:模板剂影响HZSM-5的孔体积、比表面积、强酸量、骨架铝分布、铝对含量,导致HZSM-5催化乙醇制丙烯性能表现出较大差异;其中,以四丙基氢氧化铵为模板剂合成的HZSM-5-TP的孔体积和比表面积最大,强酸量和铝对含量最多,在常压、温度500℃时,其催化乙醇转化的丙烯选择性最高(29.72%),催化寿命最长(22.8 h);而以四乙基氢氧化铵为模板剂合成的HZSM-5-TE孔体积和比表面积最小,强酸量和铝对含量最少,所以其丙烯选择性最低(13.84%),催化寿命最短(1.6 h);相较HZSM-5-TE,HZSM-5-TP的内部硅烷醇基团密度更低,积炭速率更慢,催化寿命更长。展开更多
制备了不同Al含量的Al-MCM-41试样,其中Si/Al比值最小为3,即最高含铝量xAl=0.303.X射线粉末衍射（XPD）分析表明样品具有MCM-41的特征结构,氮气吸附研究表明,样品呈现Ⅳ型吸附等温线,具有孔径分布均一的中孔结构.文中还利用27Al MAS NM...制备了不同Al含量的Al-MCM-41试样,其中Si/Al比值最小为3,即最高含铝量xAl=0.303.X射线粉末衍射（XPD）分析表明样品具有MCM-41的特征结构,氮气吸附研究表明,样品呈现Ⅳ型吸附等温线,具有孔径分布均一的中孔结构.文中还利用27Al MAS NMR研究了试样中Al的化学环境,结果表明,即使在高铝含量的情况下,样品中的铝原子仍以四配位结合在MCM-41的硅骨架上,未能检测出骨架外六配位铝的存在.文中还就Al含量对孔结构的影响以及Al-MCM-41形成机理作了讨论.展开更多
采用27Al MAS NMR、N2吸附-脱附、IR等表征技术及XRD Rietveld结构精修的方法,通过清除和交换引入非骨架铝,探讨了USY沸石中非骨架铝的形态。结果表明,27Al MAS NMR化学位移为0的非骨架铝以游离在超笼中的非骨架铝为主,化学位移为30-50...采用27Al MAS NMR、N2吸附-脱附、IR等表征技术及XRD Rietveld结构精修的方法,通过清除和交换引入非骨架铝,探讨了USY沸石中非骨架铝的形态。结果表明,27Al MAS NMR化学位移为0的非骨架铝以游离在超笼中的非骨架铝为主,化学位移为30-50的非骨架铝与沸石骨架存在键合作用;晶体学可识别的离子态非骨架铝存在于方钠石笼的SⅠ′和SⅡ′位置,其中,SⅠ′位置的非骨架铝与沸石骨架3个O3原子及与其配位的三重轴的O形成不稳定的四配位结构,SⅡ′位置的Al不与沸石骨架O形成配位。超笼中未发现可识别的离子态非骨架铝。聚合态非骨架铝的存在将堵塞沸石孔道,影响微孔吸附性能,并掩盖B酸中心。清除非骨架铝后,可以使沸石孔道畅通,使B酸中心得到恢复。展开更多
Ce-or La-doped Cu/SSZ-13 catalysts were prepared by a hydrothermal method and Cu,Ce or La ions were incorporated through stepwise ion exchange,The catalyst activity was measured for the ammonia selective catalytic red...Ce-or La-doped Cu/SSZ-13 catalysts were prepared by a hydrothermal method and Cu,Ce or La ions were incorporated through stepwise ion exchange,The catalyst activity was measured for the ammonia selective catalytic reduction reaction.The structure and composition of catalyst were characterized by using X-ray diffraction,scanning electron microscopy,inductively coupled plasma mass spectrometry solid-state NMR,NH_(3)-TPD techniques,and the active components were examined by XPS and XANES.The results indicate that the Ce and La doping can both completely preserve the SCR activity of Cu/SSZ-13 above 300℃,but there is also a decrease of activity below 200℃.On the other hand,Ce doping is beneficial to the formation of framework aluminum,stabilizes molecular sieve framework and Cu active sites of Cu/SSZ-13,thereby improves the catalyst hydrothermal stability.But La doping will decrease the amount of framework aluminum and Cu active sites of Cu/SSZ-13 after hydrothermally aging,even destroy zeolite CHA structure.This is quite harmful to the catalyst hydrothermal stability.展开更多
基金support provided by the National Key Research and Development Program of China(No.2022YFE0116000)the National Natural Science Foundation of China(22241801,22022202,22032005,22288101,21972142,21991090,21991092,21991093)Dalian Outstanding Young Scientist Foundation(2021RJ01).
文摘MOR zeolite has been effectively utilized for dimethyl ether(DME)carbonylation reaction due to its unique pore structure and acidity.During industrial production,the transformation of ammonium type MOR zeolite(NH_(4)-MOR)into proton type MOR zeolite(H-MOR)causes inevitable dealumination.Therefore,understanding the influencing factors and dynamic evolution mechanism of zeolite dealumination is crucial.In this work,the stability of framework aluminum was studied by X-ray diffraction(XRD),Fourier transform infrared(FT-IR)spectroscopy,^(29)Si,^(27)Al,^(1)H magic angle spinning nuclear magnetic resonance(MAS NMR),and DME carbonylation performance evaluation.These results indicate that extra-framework cation Na^(+)and NH_(4)^(+)could better preserve the aluminum structure of the MOR zeolite framework compared to H^(+),primarily due to the different'attraction'of the framework to water.Furthermore,the impact of water on the zeolite framework aluminum at high temperature was studied by manipulating the humidity of the calcination atmosphere,revealing the formation of extra-framework six-coordinated aluminum(Al(Ⅵ)-EF)and the mechanism of water influence on the zeolite framework aluminum.
文摘系统考察了4种不同模板剂(四乙基氢氧化铵、四丙基氢氧化铵、四丙基溴化铵、四丁基氢氧化铵)对HZSM-5分子筛织构性质、酸性、骨架铝分布和存在形态的影响,通过XRD、SEM、N_(2)吸附-脱附、XRF、FT-IR、NH_(3)-TPD、Py-IR、^(27)Al MAS NMR、UV-vis-DRS、TG等手段对HZSM-5分子筛进行表征,并研究了其催化乙醇制丙烯的性能。结果表明:模板剂影响HZSM-5的孔体积、比表面积、强酸量、骨架铝分布、铝对含量,导致HZSM-5催化乙醇制丙烯性能表现出较大差异;其中,以四丙基氢氧化铵为模板剂合成的HZSM-5-TP的孔体积和比表面积最大,强酸量和铝对含量最多,在常压、温度500℃时,其催化乙醇转化的丙烯选择性最高(29.72%),催化寿命最长(22.8 h);而以四乙基氢氧化铵为模板剂合成的HZSM-5-TE孔体积和比表面积最小,强酸量和铝对含量最少,所以其丙烯选择性最低(13.84%),催化寿命最短(1.6 h);相较HZSM-5-TE,HZSM-5-TP的内部硅烷醇基团密度更低,积炭速率更慢,催化寿命更长。
文摘制备了不同Al含量的Al-MCM-41试样,其中Si/Al比值最小为3,即最高含铝量xAl=0.303.X射线粉末衍射（XPD）分析表明样品具有MCM-41的特征结构,氮气吸附研究表明,样品呈现Ⅳ型吸附等温线,具有孔径分布均一的中孔结构.文中还利用27Al MAS NMR研究了试样中Al的化学环境,结果表明,即使在高铝含量的情况下,样品中的铝原子仍以四配位结合在MCM-41的硅骨架上,未能检测出骨架外六配位铝的存在.文中还就Al含量对孔结构的影响以及Al-MCM-41形成机理作了讨论.
文摘采用27Al MAS NMR、N2吸附-脱附、IR等表征技术及XRD Rietveld结构精修的方法,通过清除和交换引入非骨架铝,探讨了USY沸石中非骨架铝的形态。结果表明,27Al MAS NMR化学位移为0的非骨架铝以游离在超笼中的非骨架铝为主,化学位移为30-50的非骨架铝与沸石骨架存在键合作用;晶体学可识别的离子态非骨架铝存在于方钠石笼的SⅠ′和SⅡ′位置,其中,SⅠ′位置的非骨架铝与沸石骨架3个O3原子及与其配位的三重轴的O形成不稳定的四配位结构,SⅡ′位置的Al不与沸石骨架O形成配位。超笼中未发现可识别的离子态非骨架铝。聚合态非骨架铝的存在将堵塞沸石孔道,影响微孔吸附性能,并掩盖B酸中心。清除非骨架铝后,可以使沸石孔道畅通,使B酸中心得到恢复。
基金the National Natural Science Foundation of China(21676288,21773230)Dalian National Laboratory for Clean Energy(DNL)Cooperation Fund,CAS(DNL 180406)+1 种基金QIBEBT(QIBEBT ZZBS 201805)Liaoning Revitalization Talents Program(XLYC1807207)。
文摘Ce-or La-doped Cu/SSZ-13 catalysts were prepared by a hydrothermal method and Cu,Ce or La ions were incorporated through stepwise ion exchange,The catalyst activity was measured for the ammonia selective catalytic reduction reaction.The structure and composition of catalyst were characterized by using X-ray diffraction,scanning electron microscopy,inductively coupled plasma mass spectrometry solid-state NMR,NH_(3)-TPD techniques,and the active components were examined by XPS and XANES.The results indicate that the Ce and La doping can both completely preserve the SCR activity of Cu/SSZ-13 above 300℃,but there is also a decrease of activity below 200℃.On the other hand,Ce doping is beneficial to the formation of framework aluminum,stabilizes molecular sieve framework and Cu active sites of Cu/SSZ-13,thereby improves the catalyst hydrothermal stability.But La doping will decrease the amount of framework aluminum and Cu active sites of Cu/SSZ-13 after hydrothermally aging,even destroy zeolite CHA structure.This is quite harmful to the catalyst hydrothermal stability.
