Aluminosilicate zeolites as one of the most important catalytic materials are widely applied in industrial reactions,and understanding of their synthetic mechanism is one of key factors in this field.27Al and 29Si NMR...Aluminosilicate zeolites as one of the most important catalytic materials are widely applied in industrial reactions,and understanding of their synthetic mechanism is one of key factors in this field.27Al and 29Si NMR techniques are one of powerful tools for characterization of zeolite synthesis,but unfortunately the study on 27Al NMR spectra of aluminosilicate solutions is still argumentative,and the assignment of aluminosi-licate species in the solutions are challengeable.In this work,we have carefully compared 27Al NMR spectra of various aluminosilicate solutions,harmonizing the assignments reported previously.Furthermore,we assigned 29Si NMR spectra related to Al species.The peaks at δ:-75.1 and-82.5 in 29Si NMR spectrum are related to Q2 Al species,the peaks at δ:-84.5 and-90.8 are related to Q3 and Q4 Al species in aluminosilicate solutions,respectively.展开更多
The microstructural study was conducted on cement and cement-slag pastes immersed in different concentrations of Mg（NO3）2 solutions utilizing ^29Si, ^27Al NMR spectroscopy and XRD techniques. The results show that t...The microstructural study was conducted on cement and cement-slag pastes immersed in different concentrations of Mg（NO3）2 solutions utilizing ^29Si, ^27Al NMR spectroscopy and XRD techniques. The results show that the hydration of both the cement and cement-slag pastes is delayed when the pastes are cured in Mg（NO3）2 solutions as compared to the pastes cured in water. Moreover, Mg^2＋ ions also exhibit an decalcifying and dealuminizing effect on the C-A-S-H in cement and cement-slag pastes, and thereby decrease Ca/Si and Al[4]/Si ratios of the C-A-S-H. The dealuminization of C-A-S-H is mitigated for cement-slag paste as compared to pure cement paste. The depolymerized calcium and aluminum ions from C-A-S-H gel mainly enter the pore solution to maintain the pH value and form Al^[6] in TAH, respectively. On the other hand, Mg^2＋ ions exert an impact on the intra-transition between Al^[6] species, from AFm and hydrogarnet to hydrotalcite-like phase. NO3^-ions are interstratified in the layered Mg-Al structure and formed nitrated hydrotalcite-like phase（Mg1-xAlx（OH）2（NO3）x·nH2O）. Results from both ^27Al NMR and XRD data show that ettringite seems not to react with Mg^2＋ ions.展开更多
Ca-montmorillonite samples from Choushan treated at various acid concentrations were studied using chemical analysis, XRD, 29Si and 27A1 MAS NMR, to investigate the microstructure of the activated montmorillonites. Wi...Ca-montmorillonite samples from Choushan treated at various acid concentrations were studied using chemical analysis, XRD, 29Si and 27A1 MAS NMR, to investigate the microstructure of the activated montmorillonites. With the increase of acid concentration and dissolution of cations of montmorillonite, the intensity of d(001) decreased obviously and significant changes of the microstructure of Si and Al occurred. There were two new types of structural units of Si atoms formed: (SiO)3SiOH units and Q4(0A1) units. For Al atoms, in the course of activation, the removal of one of a pair of octahedral aluminium atoms from montmorillonite removed two hydroxyl groups and left the other aluminum of the pair in the four-fold coordination. The 27A1 signal at 5 54.0 corresponding to AlIV arose from the four-coordinated Al in the octahedral sheet. This study first confirmed, by 29Si and 27A1 MAS NMR spectra, that the model of microstructural evolution for activated montmorillonite postulated by Thomas et al. (1950)展开更多
Adularia sample was collected from epithermal Au-, Ag-bearing quartz-adularia veins from Hishikari, Japan. This adularia is rich in K, Or=94.63, clear, transparent, fine-grained and closely associated with quartz. In ...Adularia sample was collected from epithermal Au-, Ag-bearing quartz-adularia veins from Hishikari, Japan. This adularia is rich in K, Or=94.63, clear, transparent, fine-grained and closely associated with quartz. In this study, it was determined by XRD, IR and 29Si, 27A1 MAS NMR methods. The adularia studied is of high sanidine with triclinic domains in it. The occupancy of Al 2t1=0.60, IR ordering θ=0.15.29Si NMR spectrum of this adularia shows a broad triplet peak, i.e. 3 poorly separated peaks at -94.9, -96.7, -99.9. This kind 29Si NMR spectrum for natural high sanidine has never been reported before. And the 27A1 NMR spectrum gives an asymmetry peak with chemical shift at 58.7 extending slightly to the low frequency. Under a violent boiling environment, Hishikari adularia rapidly crystallized from a supersaturated solution.展开更多
A natural CXN zeolite (stilbite, type code-STI) discovered in China was modified with +4NH exchange by using ammonium salt and calcinations (procedure I), or with +4NH exchange followed by treatment with acid (procedu...A natural CXN zeolite (stilbite, type code-STI) discovered in China was modified with +4NH exchange by using ammonium salt and calcinations (procedure I), or with +4NH exchange followed by treatment with acid (procedure II). The coordination state of Si and Al atoms in the framework, the property of ion exchange, and the adsorption of the H-STI zeolite samples prepared by different modification procedure were investigated with XRD, EDX, 29Si and 27Al MAS NMR, Ag+ ion exchange and N2 adsorption. The results of the investigations indicate that different procedure of the modification made variety on the distribution of the framework Si atoms and Al atoms, the content of non-framework aluminum, and the blocking channels and the shielding effect to the positions of the exchangeable cations. The H-STI zeolite prepared by the procedure II possesses high ion exchange capacity, open and perfect pore system, and high thermal stability.展开更多
文摘Aluminosilicate zeolites as one of the most important catalytic materials are widely applied in industrial reactions,and understanding of their synthetic mechanism is one of key factors in this field.27Al and 29Si NMR techniques are one of powerful tools for characterization of zeolite synthesis,but unfortunately the study on 27Al NMR spectra of aluminosilicate solutions is still argumentative,and the assignment of aluminosi-licate species in the solutions are challengeable.In this work,we have carefully compared 27Al NMR spectra of various aluminosilicate solutions,harmonizing the assignments reported previously.Furthermore,we assigned 29Si NMR spectra related to Al species.The peaks at δ:-75.1 and-82.5 in 29Si NMR spectrum are related to Q2 Al species,the peaks at δ:-84.5 and-90.8 are related to Q3 and Q4 Al species in aluminosilicate solutions,respectively.
基金Funded by National Natural Science Foundation of China(Nos.51778513,51402003,51578004)China Ministry of Science and Technology(No.2015CB655101)
文摘The microstructural study was conducted on cement and cement-slag pastes immersed in different concentrations of Mg（NO3）2 solutions utilizing ^29Si, ^27Al NMR spectroscopy and XRD techniques. The results show that the hydration of both the cement and cement-slag pastes is delayed when the pastes are cured in Mg（NO3）2 solutions as compared to the pastes cured in water. Moreover, Mg^2＋ ions also exhibit an decalcifying and dealuminizing effect on the C-A-S-H in cement and cement-slag pastes, and thereby decrease Ca/Si and Al[4]/Si ratios of the C-A-S-H. The dealuminization of C-A-S-H is mitigated for cement-slag paste as compared to pure cement paste. The depolymerized calcium and aluminum ions from C-A-S-H gel mainly enter the pore solution to maintain the pH value and form Al^[6] in TAH, respectively. On the other hand, Mg^2＋ ions exert an impact on the intra-transition between Al^[6] species, from AFm and hydrogarnet to hydrotalcite-like phase. NO3^-ions are interstratified in the layered Mg-Al structure and formed nitrated hydrotalcite-like phase（Mg1-xAlx（OH）2（NO3）x·nH2O）. Results from both ^27Al NMR and XRD data show that ettringite seems not to react with Mg^2＋ ions.
基金This wok was supported by the National Natural Science Foundation of China (Grant No. 49972018)the Natural Science Foundation of Guangdong Province (Grant No. 990522).
文摘Ca-montmorillonite samples from Choushan treated at various acid concentrations were studied using chemical analysis, XRD, 29Si and 27A1 MAS NMR, to investigate the microstructure of the activated montmorillonites. With the increase of acid concentration and dissolution of cations of montmorillonite, the intensity of d(001) decreased obviously and significant changes of the microstructure of Si and Al occurred. There were two new types of structural units of Si atoms formed: (SiO)3SiOH units and Q4(0A1) units. For Al atoms, in the course of activation, the removal of one of a pair of octahedral aluminium atoms from montmorillonite removed two hydroxyl groups and left the other aluminum of the pair in the four-fold coordination. The 27A1 signal at 5 54.0 corresponding to AlIV arose from the four-coordinated Al in the octahedral sheet. This study first confirmed, by 29Si and 27A1 MAS NMR spectra, that the model of microstructural evolution for activated montmorillonite postulated by Thomas et al. (1950)
文摘Adularia sample was collected from epithermal Au-, Ag-bearing quartz-adularia veins from Hishikari, Japan. This adularia is rich in K, Or=94.63, clear, transparent, fine-grained and closely associated with quartz. In this study, it was determined by XRD, IR and 29Si, 27A1 MAS NMR methods. The adularia studied is of high sanidine with triclinic domains in it. The occupancy of Al 2t1=0.60, IR ordering θ=0.15.29Si NMR spectrum of this adularia shows a broad triplet peak, i.e. 3 poorly separated peaks at -94.9, -96.7, -99.9. This kind 29Si NMR spectrum for natural high sanidine has never been reported before. And the 27A1 NMR spectrum gives an asymmetry peak with chemical shift at 58.7 extending slightly to the low frequency. Under a violent boiling environment, Hishikari adularia rapidly crystallized from a supersaturated solution.
文摘A natural CXN zeolite (stilbite, type code-STI) discovered in China was modified with +4NH exchange by using ammonium salt and calcinations (procedure I), or with +4NH exchange followed by treatment with acid (procedure II). The coordination state of Si and Al atoms in the framework, the property of ion exchange, and the adsorption of the H-STI zeolite samples prepared by different modification procedure were investigated with XRD, EDX, 29Si and 27Al MAS NMR, Ag+ ion exchange and N2 adsorption. The results of the investigations indicate that different procedure of the modification made variety on the distribution of the framework Si atoms and Al atoms, the content of non-framework aluminum, and the blocking channels and the shielding effect to the positions of the exchangeable cations. The H-STI zeolite prepared by the procedure II possesses high ion exchange capacity, open and perfect pore system, and high thermal stability.
