Alkali leaching was employed to investigate the separation of alumina and silica in roasted kaolin obtained by roasting kaolin alone in air at 1273 K for 60 min and in clinker prepared by roasting the mixed raw meal o...Alkali leaching was employed to investigate the separation of alumina and silica in roasted kaolin obtained by roasting kaolin alone in air at 1273 K for 60 min and in clinker prepared by roasting the mixed raw meal of kaolin,ferric oxide and coal powder with Fe2O3/Al2O3/C molar ratio of 1.2:2.0:1.2 in reducing atmosphere at 1373 K for 60 min.The thermodynamic analyses and alkali leaching results show that the composition of the Al-Si spinel in roasted kaolin is close to that of 3Al2O3·2SiO2 and the spinel is dissolved with increasing leaching time,resulting in difficulty in deeply separating alumina and silica in kaolin by the traditional roasting-leaching process.On the contrary,the efficient separation of alumina and silica in kaolin can be reached by fully converting kaolinite into insoluble hercynite and soluble free silica,namely quartz solid solution and cristobalite solid solution,during reduction roasting,followed by alkali leaching of the obtained clinker.Furthermore,experimental results from treating high-silica diasporic bauxite indicate that the reduction roasting-alkali leaching process is potential to separate silica and alumina in aluminosilicates.展开更多
This paper reviews high temperature sensing applications based on fiber Bragg gratings fabricated by use of femtosecond laser. Type II fiber Bragg gratings fabricated in the silica fiber can sustain up to 1200 ℃ whil...This paper reviews high temperature sensing applications based on fiber Bragg gratings fabricated by use of femtosecond laser. Type II fiber Bragg gratings fabricated in the silica fiber can sustain up to 1200 ℃ while that fabricated in the sapphire fiber have the good thermal stability up to 1745 ℃.展开更多
Ultra-pure mesoporous silica microspheres with good monodispersity were synthesized in two steps： nanometer-sized silica sol was produced by the sol-gel process, then micrometer-sized silica microspheres were synthes...Ultra-pure mesoporous silica microspheres with good monodispersity were synthesized in two steps： nanometer-sized silica sol was produced by the sol-gel process, then micrometer-sized silica microspheres were synthesized by polymerization-induced colloid aggregation of the silica sol. The total metal content of the microspheres was extremely low, which eliminated the tailing of chromatographic peaks by chelating reagents. The pore structure of the silica microspheres could be controlled by altering the sol-gel conditions. The silica microsphere particle size could be adjusted by using different polymerizationinduced colloid aggregation conditions.展开更多
Well-crystallized high-silica NaY zeolites （Si/Al〉2.5） were prepared from a reaction mixture consisting of metakaolin, sodium silicate solution and seed solution via optimization of the mixture composition and reac...Well-crystallized high-silica NaY zeolites （Si/Al〉2.5） were prepared from a reaction mixture consisting of metakaolin, sodium silicate solution and seed solution via optimization of the mixture composition and reaction conditions. The transformation from kaolin to high-silica NaY zeolite was confirmed by XRD, SEM and IR techniques. Subsequently, the influence of synthesis parameters, i.e. initial SIO2/Al2O3, initial Na2O/SiO2, initial H2O/SiO2, aging time of the seed solution, crystallization temperature and crystallization time, on the NaY growth was investigated in terms of crystallinity and Si/Al ratio. The results showed that the effects of initial SiO2/Al2O3, initial Na2O/SiO2 and initial H2O/ SiO2 on the crystaIlinity and Si/Al ratio of NaY zeolite are similar to those observed in the conventional syntheses of NaY zeolites only using sodium silicate solution as silicon source. However, due to the use of metakaolin as the main silicon and aluminum sources in the present study, a long crystallization induction period of 20 h was achieved, which can be attributed to the dissolution of metakaolin. In addition, different from the conventional syntheses of zeolite NaY, pure NaY zeolites （i.e. without NaP zeolite impurity） were still obtained even at 120℃ because of the use of a large quantity of seed solution （23 wt%） in the reaction mixture. As the aging time of the seed solution increased from 3.5 h to 22 h, the relative crystallinity of the NaY zeolite first increased sharply and then reached a plateau, while the Si/Al ratio first increased rapidly up to a maximum value of 2.75 corresponding to an aging time of 6.5 h, and then decreased sharply with the aging time.展开更多
In this work,we show for the first time that high-silica zeolites(MFI,TON,MTT,and*MRE)could be synthesized from a combined strategy of both zeolite seeding and alcohol filling in the absence of organic structure-direc...In this work,we show for the first time that high-silica zeolites(MFI,TON,MTT,and*MRE)could be synthesized from a combined strategy of both zeolite seeding and alcohol filling in the absence of organic structure-directing agents(OSDAs).High-silica ZSM-5 zeolites with Si/Al ratios ranging from 38 to 240(TF-Al-ZSM-5)could be synthesized via this route.The key to the success of this technique was the employment of an aluminosilicate precursor with a fully 4-coordinated aluminum species as the initial source,wherein the rearrangement and condensation of the silicate species,rather than the aluminate species,occurred during zeolite crystallization.In addition,heteroatoms,such as Fe and B,could be incorporated into the zeolite frameworks.Catalytic tests for the methanol-to-propylene(MTP)reaction exhibited good catalytic performance for TF-Al-ZSM-5,which was comparable to that of the aluminosilicate ZSM-5 zeolite synthesized with OSDAs.Hence,this method offers viable opportunities for the industrial production and catalytic application of high-silica zeolites in the future.展开更多
It was found that silica fume can reduce the maximum hydration heat release rate of cement by microcalorimetry,inhibit CAH_(10),promote the generation of C_(3)AH_(6)and strätlingite C_(2)ASH_(8),or promote the co...It was found that silica fume can reduce the maximum hydration heat release rate of cement by microcalorimetry,inhibit CAH_(10),promote the generation of C_(3)AH_(6)and strätlingite C_(2)ASH_(8),or promote the conversion of CAH_(10)to C_(3)AH_(6).Sodium tripolyphosphate can retard the early hydration of cement,have a slight effect on 1 d hydration products of cement and inhibit the generation hydration products.Sodium tripolyphosphate and silica fume can promote the early hydration of cement,advance the formation of C_(2)ASH_(8)or the conversion from CAH_(10)to C_(3)AH_(6)at 1 d.展开更多
With rapid development of the pellet production under the background of green development,high-quality iron concentrates were gradually exhausted;thus,using high-silica iron concentrates was expected to be a promising...With rapid development of the pellet production under the background of green development,high-quality iron concentrates were gradually exhausted;thus,using high-silica iron concentrates was expected to be a promising way to relieve resource pressure for pellet production.However,increasing the proportion of high-silica acid pellets into the furnace led to worse blast furnace slag,and the metallurgical properties of high-silica pellets were imperfect.To understand the reciprocal effects of basicity(CaO/SiO_(2))and MgO content on the properties of the high-silica pellets,the phase compositions and microstructure were investigated using X-ray diffraction and scanning electron microscope,equipped with energy dispersive X-ray spectrometry.The results indicated that simply increasing MgO content from O to 2.50 wt.%could decrease the reduction swelling index,but the compressive strength rapidly declined due to the formation of magnesioferrite.However,adding CaO to 2.50 wt.%MgO pellets greatly improved the pellet qualities,which could be attributed to a substantial increase in the amount of high-melting-point silicate liquid phase.展开更多
Zeolite-encapsulated metal nanoclusters are at the heart of bifunctional catalysts,which hold great potential for petrochemical conversion and the emerging sustainable biorefineries.Nevertheless,efficient encapsulatio...Zeolite-encapsulated metal nanoclusters are at the heart of bifunctional catalysts,which hold great potential for petrochemical conversion and the emerging sustainable biorefineries.Nevertheless,efficient encapsulation of metal nanoclusters into a high-silica zeolite Y in particular with good structural integrity still remains a significant challenge.Herein,we have constructed Ru nanoclusters(~1 nm)encapsulated inside a high-silica zeolite Y(SY)with a SiO_(2)/Al_(2)O_(3) ratio(SAR)of 10 via a cooperative strategy for direct zeolite synthesis and a consecutive impregnation for metal encapsulation.Compared with the benchmark Ru/H-USY and other analogues,the as-prepared Ru/H-SY markedly boosts the yields of pentanoic biofuels and stability in the direct hydrodeoxygenation of biomass-derived levulinate even at a mild temperature of 180℃,which are attributed to the notable stabilization of transition states by the enhanced acid accessibility and properly sized constraints of zeolite cavities owing to the good structural integrity.展开更多
Zeolite synthesis in contemporary chemical industries is predominantly conducted using organic structure‐directing agents(OSDAs),which are chronically hazardous to humans and the environment.It is a growing trend to ...Zeolite synthesis in contemporary chemical industries is predominantly conducted using organic structure‐directing agents(OSDAs),which are chronically hazardous to humans and the environment.It is a growing trend to develop an eco‐friendly and nuisanceless OSDA for zeolite synthesis.Herein,choline is employed as a non‐toxic and green OSDA to synthesize high silica Y zeolite with SiO2/Al2O3 ratios of 6.5–6.8.The prepared Y zeolite samples exhibited outstanding(hydro)thermal stability at ultrahigh temperature owing to the higher SiO2/Al2O3 ratio.The XRF,SEM,29Si‐NMR and 13Na+results suggested that choline plays a structure‐directing role in the synthesis of Y zeolite,while the feed molar fraction of Na+is a crucial determinant for the framework SiO2/Al2O3 ratio and the crystal morphology.展开更多
基金Project(51604309) supported by the National Natural Science Foundation of China
文摘Alkali leaching was employed to investigate the separation of alumina and silica in roasted kaolin obtained by roasting kaolin alone in air at 1273 K for 60 min and in clinker prepared by roasting the mixed raw meal of kaolin,ferric oxide and coal powder with Fe2O3/Al2O3/C molar ratio of 1.2:2.0:1.2 in reducing atmosphere at 1373 K for 60 min.The thermodynamic analyses and alkali leaching results show that the composition of the Al-Si spinel in roasted kaolin is close to that of 3Al2O3·2SiO2 and the spinel is dissolved with increasing leaching time,resulting in difficulty in deeply separating alumina and silica in kaolin by the traditional roasting-leaching process.On the contrary,the efficient separation of alumina and silica in kaolin can be reached by fully converting kaolinite into insoluble hercynite and soluble free silica,namely quartz solid solution and cristobalite solid solution,during reduction roasting,followed by alkali leaching of the obtained clinker.Furthermore,experimental results from treating high-silica diasporic bauxite indicate that the reduction roasting-alkali leaching process is potential to separate silica and alumina in aluminosilicates.
文摘This paper reviews high temperature sensing applications based on fiber Bragg gratings fabricated by use of femtosecond laser. Type II fiber Bragg gratings fabricated in the silica fiber can sustain up to 1200 ℃ while that fabricated in the sapphire fiber have the good thermal stability up to 1745 ℃.
基金Financial support was granted by China National Natural Science Foundation(No.51242001)the Doctor Scientific Research Foundation of Henan University of Technology (2013BS029)
文摘Ultra-pure mesoporous silica microspheres with good monodispersity were synthesized in two steps： nanometer-sized silica sol was produced by the sol-gel process, then micrometer-sized silica microspheres were synthesized by polymerization-induced colloid aggregation of the silica sol. The total metal content of the microspheres was extremely low, which eliminated the tailing of chromatographic peaks by chelating reagents. The pore structure of the silica microspheres could be controlled by altering the sol-gel conditions. The silica microsphere particle size could be adjusted by using different polymerizationinduced colloid aggregation conditions.
基金supported by Beijing Natural Science Foundation (Grant No.2093043)the National Natural Science Foundation of China (Grant No.20606038)
文摘Well-crystallized high-silica NaY zeolites （Si/Al〉2.5） were prepared from a reaction mixture consisting of metakaolin, sodium silicate solution and seed solution via optimization of the mixture composition and reaction conditions. The transformation from kaolin to high-silica NaY zeolite was confirmed by XRD, SEM and IR techniques. Subsequently, the influence of synthesis parameters, i.e. initial SIO2/Al2O3, initial Na2O/SiO2, initial H2O/SiO2, aging time of the seed solution, crystallization temperature and crystallization time, on the NaY growth was investigated in terms of crystallinity and Si/Al ratio. The results showed that the effects of initial SiO2/Al2O3, initial Na2O/SiO2 and initial H2O/ SiO2 on the crystaIlinity and Si/Al ratio of NaY zeolite are similar to those observed in the conventional syntheses of NaY zeolites only using sodium silicate solution as silicon source. However, due to the use of metakaolin as the main silicon and aluminum sources in the present study, a long crystallization induction period of 20 h was achieved, which can be attributed to the dissolution of metakaolin. In addition, different from the conventional syntheses of zeolite NaY, pure NaY zeolites （i.e. without NaP zeolite impurity） were still obtained even at 120℃ because of the use of a large quantity of seed solution （23 wt%） in the reaction mixture. As the aging time of the seed solution increased from 3.5 h to 22 h, the relative crystallinity of the NaY zeolite first increased sharply and then reached a plateau, while the Si/Al ratio first increased rapidly up to a maximum value of 2.75 corresponding to an aging time of 6.5 h, and then decreased sharply with the aging time.
文摘In this work,we show for the first time that high-silica zeolites(MFI,TON,MTT,and*MRE)could be synthesized from a combined strategy of both zeolite seeding and alcohol filling in the absence of organic structure-directing agents(OSDAs).High-silica ZSM-5 zeolites with Si/Al ratios ranging from 38 to 240(TF-Al-ZSM-5)could be synthesized via this route.The key to the success of this technique was the employment of an aluminosilicate precursor with a fully 4-coordinated aluminum species as the initial source,wherein the rearrangement and condensation of the silicate species,rather than the aluminate species,occurred during zeolite crystallization.In addition,heteroatoms,such as Fe and B,could be incorporated into the zeolite frameworks.Catalytic tests for the methanol-to-propylene(MTP)reaction exhibited good catalytic performance for TF-Al-ZSM-5,which was comparable to that of the aluminosilicate ZSM-5 zeolite synthesized with OSDAs.Hence,this method offers viable opportunities for the industrial production and catalytic application of high-silica zeolites in the future.
基金Funded by the National Natural Science Foundation of China(No.51802235)Hubei Science and Technology Innovation Talent Project,China(No.2023DJC087)。
文摘It was found that silica fume can reduce the maximum hydration heat release rate of cement by microcalorimetry,inhibit CAH_(10),promote the generation of C_(3)AH_(6)and strätlingite C_(2)ASH_(8),or promote the conversion of CAH_(10)to C_(3)AH_(6).Sodium tripolyphosphate can retard the early hydration of cement,have a slight effect on 1 d hydration products of cement and inhibit the generation hydration products.Sodium tripolyphosphate and silica fume can promote the early hydration of cement,advance the formation of C_(2)ASH_(8)or the conversion from CAH_(10)to C_(3)AH_(6)at 1 d.
基金the National Natural Science Foundation of China(Nos.U1960114 and 51574283)the Fundamental Research Funds for theCentraUlniversities(2021XQLH029).
文摘With rapid development of the pellet production under the background of green development,high-quality iron concentrates were gradually exhausted;thus,using high-silica iron concentrates was expected to be a promising way to relieve resource pressure for pellet production.However,increasing the proportion of high-silica acid pellets into the furnace led to worse blast furnace slag,and the metallurgical properties of high-silica pellets were imperfect.To understand the reciprocal effects of basicity(CaO/SiO_(2))and MgO content on the properties of the high-silica pellets,the phase compositions and microstructure were investigated using X-ray diffraction and scanning electron microscope,equipped with energy dispersive X-ray spectrometry.The results indicated that simply increasing MgO content from O to 2.50 wt.%could decrease the reduction swelling index,but the compressive strength rapidly declined due to the formation of magnesioferrite.However,adding CaO to 2.50 wt.%MgO pellets greatly improved the pellet qualities,which could be attributed to a substantial increase in the amount of high-melting-point silicate liquid phase.
基金supported by the National Natural Science Foundation of China (22288101,21991090,21991091,22078316,22272171 and 22109167)the Sino-French International Research Network (Zeolites)+2 种基金the BL01B1 beamline of SPring-8 and the 1W1B station of Beijing Synchrotron Radiation Facility (BSRF)for the support of XAS measurementsthe Division of Energy Research Resources of Dalian Institute of Chemical Physics for the support of iDPC-STEM measurementsthe support of the Alexander von Humboldt Foundation (CHN 1220532 HFST-P)。
文摘Zeolite-encapsulated metal nanoclusters are at the heart of bifunctional catalysts,which hold great potential for petrochemical conversion and the emerging sustainable biorefineries.Nevertheless,efficient encapsulation of metal nanoclusters into a high-silica zeolite Y in particular with good structural integrity still remains a significant challenge.Herein,we have constructed Ru nanoclusters(~1 nm)encapsulated inside a high-silica zeolite Y(SY)with a SiO_(2)/Al_(2)O_(3) ratio(SAR)of 10 via a cooperative strategy for direct zeolite synthesis and a consecutive impregnation for metal encapsulation.Compared with the benchmark Ru/H-USY and other analogues,the as-prepared Ru/H-SY markedly boosts the yields of pentanoic biofuels and stability in the direct hydrodeoxygenation of biomass-derived levulinate even at a mild temperature of 180℃,which are attributed to the notable stabilization of transition states by the enhanced acid accessibility and properly sized constraints of zeolite cavities owing to the good structural integrity.
基金supported by the National Natural Science Foundation of China(Grant No.21802136)~~
文摘Zeolite synthesis in contemporary chemical industries is predominantly conducted using organic structure‐directing agents(OSDAs),which are chronically hazardous to humans and the environment.It is a growing trend to develop an eco‐friendly and nuisanceless OSDA for zeolite synthesis.Herein,choline is employed as a non‐toxic and green OSDA to synthesize high silica Y zeolite with SiO2/Al2O3 ratios of 6.5–6.8.The prepared Y zeolite samples exhibited outstanding(hydro)thermal stability at ultrahigh temperature owing to the higher SiO2/Al2O3 ratio.The XRF,SEM,29Si‐NMR and 13Na+results suggested that choline plays a structure‐directing role in the synthesis of Y zeolite,while the feed molar fraction of Na+is a crucial determinant for the framework SiO2/Al2O3 ratio and the crystal morphology.
