A series of different H-mordenites from acid leaching and steam calcination have beenmeasured with <sup>29</sup>Si NMR. Through analysis of these solid-state <sup>29</sup>Si NMR spectra, theres...A series of different H-mordenites from acid leaching and steam calcination have beenmeasured with <sup>29</sup>Si NMR. Through analysis of these solid-state <sup>29</sup>Si NMR spectra, theresults related to dealumination process of mordenite are obtained. It is shown that mor-denite is combined by four kinds of non-equivalent Si （or Al） via oxygen bridges. The deal-umination order is T（1）, T（2）, T（4） and T（3）. The dealuminated amount in the non-equivalentsites during different dealumination processes has also been discussed in detail.展开更多
Synthetic saponites have been intercalated with hydroxyl aluminium oligomers and characterized with several techniques. The basal 001 peak of the pillared saponite (PS) is 1. 8 nm. The amount of the aluminium in the t...Synthetic saponites have been intercalated with hydroxyl aluminium oligomers and characterized with several techniques. The basal 001 peak of the pillared saponite (PS) is 1. 8 nm. The amount of the aluminium in the tctrahedral sheet is correlative with cross-linking density. The sheet-to-pillar linkage mode may be Si-O-AlpⅥ. The acid sites in pillared saponite may locate either at surface of clay or at that of pillar. The cumene conversion is relative to accessible acid sites on the surface of PS. The pillar density in the PS has an effect on the pore structure which is correlative with shape selectivity during the reaction between ethanol and ammonia.展开更多
In this work,the thermal conductivity of alkaline earth borate melts was measured using hot-wire method from 1323 to 1623 K,and the thermal diffusivity was extrapolated from the thermal conductivity and heat capacity....In this work,the thermal conductivity of alkaline earth borate melts was measured using hot-wire method from 1323 to 1623 K,and the thermal diffusivity was extrapolated from the thermal conductivity and heat capacity.The compositional dependence of thermophysical properties was interpreted according to the structure in short-range and intermediate-range order.Based on the Raman spectroscopy,X-ray photoelectron spectroscopy(XPS),and 11B magic-angle spinning nuclear magnetic resonance(MAS-NMR)spectra,modifier cation with higher field strength prefers the formation of non-bridging oxygens(NBOs)for the charge compensation at high BO_(1.5)/MO ratios.A lower amount of covalent bond and greater isolation of large borate groups lead to a lower thermal conductivity in calcium borate melt compared with strontium and barium borates.But the large size of Ba^(2+)encounters difficulty in fitting around B^[4]-OB^[4]linkages inside the overcrowded large borate groups when BO_(1.5)/BaO=2.5,promoting the formation of NBOs on the edge of borate groups for the charge compensation of modifier cations and leading to the decline in the thermal conductivity.Thermal conductivity plays a major role in regulating the thermal diffusivity at a given temperature since the compositional dependence of volumetric heat capacity is relatively weak compared with that of thermal conductivity.展开更多
Five hydrotalcites with Mg/Al molar ratio range of 3–15 were prepared. The structure and basicity of Mg-Al mixed oxides (Mg(Al)O) transformed from hydrotalcites were investigated by TPD, XPS, XRD, FT-IR and NMR techn...Five hydrotalcites with Mg/Al molar ratio range of 3–15 were prepared. The structure and basicity of Mg-Al mixed oxides (Mg(Al)O) transformed from hydrotalcites were investigated by TPD, XPS, XRD, FT-IR and NMR techniques. The results of elemental analysis and XPS indicate that Al is enriched in the surface regions of Mg(Al)O, and its amount increases with the Mg/Al molar do and the Calcination temperature. 27Al-MAS-NMR results show that Al exists in two chemical environments: tetrahedral aluminium (Al(t)) and octahedral aluminium (Al(o)) in Mg(Al)O. The amount of Al(t) increases with the Mg/Al molar ratio and the calcination temperature. It is assumed that A(t) may be mainly from the surface Al. Temperature-programmed desorption (IPD) of CO2 shows that the number of basic sites of Mg(Al)0 samples increases with the Mg/Al molar ratio, and the maximum number of basic sites is obtained for hydrotalcite calcined at 773 K. Infrared spectra of adsorbed CO2 and B(OCH3)3 reveal that there are two kinds of basic sites: weak basic OH? sites and strong basic O2 sites on the Mg(Al)0 samples, the base strength depends on the Mg/Al molar do and calcination temperature.展开更多
文摘A series of different H-mordenites from acid leaching and steam calcination have beenmeasured with <sup>29</sup>Si NMR. Through analysis of these solid-state <sup>29</sup>Si NMR spectra, theresults related to dealumination process of mordenite are obtained. It is shown that mor-denite is combined by four kinds of non-equivalent Si （or Al） via oxygen bridges. The deal-umination order is T（1）, T（2）, T（4） and T（3）. The dealuminated amount in the non-equivalentsites during different dealumination processes has also been discussed in detail.
文摘Synthetic saponites have been intercalated with hydroxyl aluminium oligomers and characterized with several techniques. The basal 001 peak of the pillared saponite (PS) is 1. 8 nm. The amount of the aluminium in the tctrahedral sheet is correlative with cross-linking density. The sheet-to-pillar linkage mode may be Si-O-AlpⅥ. The acid sites in pillared saponite may locate either at surface of clay or at that of pillar. The cumene conversion is relative to accessible acid sites on the surface of PS. The pillar density in the PS has an effect on the pore structure which is correlative with shape selectivity during the reaction between ethanol and ammonia.
基金financially supported by the Ministry of Science and ICT(MSIT)through the National Research Foundation of Korea(NRF)(Grant No.2018R1A2B2006609)。
文摘In this work,the thermal conductivity of alkaline earth borate melts was measured using hot-wire method from 1323 to 1623 K,and the thermal diffusivity was extrapolated from the thermal conductivity and heat capacity.The compositional dependence of thermophysical properties was interpreted according to the structure in short-range and intermediate-range order.Based on the Raman spectroscopy,X-ray photoelectron spectroscopy(XPS),and 11B magic-angle spinning nuclear magnetic resonance(MAS-NMR)spectra,modifier cation with higher field strength prefers the formation of non-bridging oxygens(NBOs)for the charge compensation at high BO_(1.5)/MO ratios.A lower amount of covalent bond and greater isolation of large borate groups lead to a lower thermal conductivity in calcium borate melt compared with strontium and barium borates.But the large size of Ba^(2+)encounters difficulty in fitting around B^[4]-OB^[4]linkages inside the overcrowded large borate groups when BO_(1.5)/BaO=2.5,promoting the formation of NBOs on the edge of borate groups for the charge compensation of modifier cations and leading to the decline in the thermal conductivity.Thermal conductivity plays a major role in regulating the thermal diffusivity at a given temperature since the compositional dependence of volumetric heat capacity is relatively weak compared with that of thermal conductivity.
文摘Five hydrotalcites with Mg/Al molar ratio range of 3–15 were prepared. The structure and basicity of Mg-Al mixed oxides (Mg(Al)O) transformed from hydrotalcites were investigated by TPD, XPS, XRD, FT-IR and NMR techniques. The results of elemental analysis and XPS indicate that Al is enriched in the surface regions of Mg(Al)O, and its amount increases with the Mg/Al molar do and the Calcination temperature. 27Al-MAS-NMR results show that Al exists in two chemical environments: tetrahedral aluminium (Al(t)) and octahedral aluminium (Al(o)) in Mg(Al)O. The amount of Al(t) increases with the Mg/Al molar ratio and the calcination temperature. It is assumed that A(t) may be mainly from the surface Al. Temperature-programmed desorption (IPD) of CO2 shows that the number of basic sites of Mg(Al)0 samples increases with the Mg/Al molar ratio, and the maximum number of basic sites is obtained for hydrotalcite calcined at 773 K. Infrared spectra of adsorbed CO2 and B(OCH3)3 reveal that there are two kinds of basic sites: weak basic OH? sites and strong basic O2 sites on the Mg(Al)0 samples, the base strength depends on the Mg/Al molar do and calcination temperature.
