In order to investigate the rules on preparation of titanium silicalite （TS-1） the ^1H →^13C CP/ MAS NMR spectrometers were applied to track the function of template TPAOH in the process of crystallization of titan...In order to investigate the rules on preparation of titanium silicalite （TS-1） the ^1H →^13C CP/ MAS NMR spectrometers were applied to track the function of template TPAOH in the process of crystallization of titanium silicalite. The research results revealed that at the initial stage of crystallization the TPA＋ ions acting as the template could predominantly absorb the polymers of negatively charged silicatitania sol and the interactions between silica sol and titania sol could gradually lead to the formation of tiny crystal nuclei that could slowly grow up to form molecular sieves. Upon investigating the course of crystallization of titanium silicalite the ^1H →^13C CP/MAS NMR spectrometers were applied to effectively enhance the resolution of 29Si signals in the titanium silicalite. Study results have shown that during the formation of tiny crystal nuclei upon interaction between titania sol and silica sol the influence of titania sol on the silica sol was insignificant. However, when tiny crystal nuclei broke out into molecular sieves the titania sol could enter the zeolite framework that could apparently impose an enhanced effect on the silica sol.展开更多
In order to investigate the rules on formation of zeolite during crystallization of titanium silicalite zeolite(TS-1)the X-ray diffractometry and Foulier transform infra-red spectrometry were applied to track the proc...In order to investigate the rules on formation of zeolite during crystallization of titanium silicalite zeolite(TS-1)the X-ray diffractometry and Foulier transform infra-red spectrometry were applied to track the process of crystallization of titanium silicalite zeolite.The research results revealed that at the initial stage of crystallization the interactions between silica gel and titania gel in the polymer blend could gradually lead to the formation of tiny crystal nuclei with complicated structure that could slowly grow up to form molecular sieves.Quite different from the conventional zeolites that use the acid sites as the catalytically active centers,the oxidative reactivity of the titanium silicalite zeolite was not proportional to its crystallinity and is associated with the oxidative centers of titanium contained in the zeolite.展开更多
The oxidation of thiophene by H_(2)O_(2)under mild conditions was difficult in the past,and it appears again with the proposed oxidative deep desulfurization(ODS)process to obtain ultralow sulfur fuel for fuel cell in...The oxidation of thiophene by H_(2)O_(2)under mild conditions was difficult in the past,and it appears again with the proposed oxidative deep desulfurization(ODS)process to obtain ultralow sulfur fuel for fuel cell industry and for environmental protection[1,2].The ODS process is very efficient in reducing ben-zothiophene,di-benzothiophene and their corresponding alkyl derivatives[1.2].However,thiophene and its alkyl derivatives,most of which exist in gasoline,are not removed in this process.展开更多
A simple, quick, sensitive, accurate and precise method has been developed for evaluating the catalytic active sites of titanium silicalite-1 (TS-1). The catalytic active sites of titanium silicalite zeolite depend on...A simple, quick, sensitive, accurate and precise method has been developed for evaluating the catalytic active sites of titanium silicalite-1 (TS-1). The catalytic active sites of titanium silicalite zeolite depend on the effectively active species (EAS) in TS-1 which react with specific substrates quickly. However, the EAS was hard to be evaluated with conventional instruments and techniques in the past. In this paper, the EAS was formed in TS-1 upon interaction with H2O2, and its presence could be confirmed by UV-vis spectroscopy which has an absorption peak at 385 nm. The absorbance at 385 nm was found to be linearly related to time, and when the absorbance and the increasing rate of absorbance (k) increased, the catalytic performance of TS-1 enhanced.展开更多
Unique sheet-like Silicalite-1 single crystals containing intracrystalline macropores(HMS-Silicalite-1)were prepared by urea-assisted,dry-gel synthesis,which uses mesoporous silica spheres(MSSs)as both the silica prec...Unique sheet-like Silicalite-1 single crystals containing intracrystalline macropores(HMS-Silicalite-1)were prepared by urea-assisted,dry-gel synthesis,which uses mesoporous silica spheres(MSSs)as both the silica precursor and the macropore template.Urea was found to inhibit crystal growth in the b-axis direction and,therefore,play a pivotal role in the formation of the sheet-like crystals.Zeolite growth occurred via“dissolution-crystallization”transformation of MSSs to produce macro/microporous Silicalite-1 crystals.Systematic studies revealed that the urea/SiO_(2) and H_(2)O/SiO_(2) ratios affect the morphology of the resulting Silicalite-1 zeolites and that the thickness of HMS-Silicalite-1 platelets can be tuned between 190 nm and 400 nm.It was also found that the H_(2)O/SiO_(2) and urea/SiO_(2) ratios can be modulated to match the“inhibition”and“dissolution-crystallization”processes.HMS-Silicalite-1 was assessed as a catalyst for the Beckmann rearrangement of cyclohexanone oxime toε-caprolactam and found to exhibit significantly greater resistance to deactivation than conventional Silicalite-1 and hierarchical macro/microporous Silicalite-1.The superior performance of HMS-Silicalite-1 is attributed to the presence of crystals of Silicalite-1 that are thin in the direction of the b-axis and contain significant macropores(150 to 400 nm in size).The results of this study offer a novel,yet simple,method for simultaneous control of the zeolite crystal aspect ratio and macropore content to produce catalysts that are highly efficient for diffusion-limited reactions involving large reactant molecules.展开更多
Pure silica zeolite MFI(silicalite-1)has been widely used in gas separation and volatile organic compounds(VOCs)adsorption.The molar ratio of tetrapropylammonium(TPA^(+))and SiO_(2)(TPA^(+)/SiO_(2))included in the fra...Pure silica zeolite MFI(silicalite-1)has been widely used in gas separation and volatile organic compounds(VOCs)adsorption.The molar ratio of tetrapropylammonium(TPA^(+))and SiO_(2)(TPA^(+)/SiO_(2))included in the framework of silicalite-1 is 0.042.Reducing the utilization of TPA^(+)will not only benefit the environment but also reduce the cost of silicalite-1.Herein,we reported the synthesis of highly crystalline silicalite-1 from a reaction mixture with a TPA^(+)/SiO_(2)molar ratio of 0.035 and a seed loading of 5 wt%or 0.01 and a seed loading of 10 wt%.展开更多
The oxidative dehydrogenation of propane by CO_(2)(CO_(2)-ODHP)is an attractive and sustainable process that can simultaneously produce propylene and reduce CO_(2),but C3H8 and CO_(2)are relatively inert at low temper...The oxidative dehydrogenation of propane by CO_(2)(CO_(2)-ODHP)is an attractive and sustainable process that can simultaneously produce propylene and reduce CO_(2),but C3H8 and CO_(2)are relatively inert at low temperatures.Herein,we developed a novel approach for oxidative dehydrogenation of propane with CO_(2)by microwave catalysis at low temperature.A novel microwave catalyst,cobalt-promoted Zn encapsulated within silicalite-1(Zn8Co1@S-1+SiC),has been synthesized by confining Zn and Co species within a silicalite-1 zeolite via a hydrothermal method.This microwave catalyst achieved C3H8 conversion of 68%,CO_(2)conversion of 16%,and C3H6 selectivity of 88%under microwave irradiation at a low temperature of 500℃.In comparison,in the conventional reaction mode of the identical conditions,it shows only C3H8 conversion of 14%and CO_(2)conversion of 5%.Characterization studies showed that encapsulating Zn and Co species within the silicalite-1 zeolite inhibits metal loss and generates more Lewis acid sites,thereby enhancing the dehydrogenation activity.The combination of zinc and cobalt demonstrated a synergistic effect.The carbon deposition on the Zn8Co1@S-1 catalyst was reduced from 5.75%to 4.62%by introducing CO_(2)into the propane dehydrogenation to propylene.In addition,the activation energy of oxidative propane dehydrogenation with CO_(2)under microwave irradiation was reduced(85.05 kJ mol^(-1)→46.54 kJ mol^(-1)).The superior catalytic performance under microwave irradiation at low temperatures can provide guidelines for propane dehydrogenation with microwave catalyst design and process enhancement.展开更多
Two kinds of radiolarian silicalites at the bottom and top of the ophiolite in the Mount (Mt.) Ailao belt, Yunnan Province, are dealt with in this work in terms of geology, micro-paleontology, isotope and REE. The fir...Two kinds of radiolarian silicalites at the bottom and top of the ophiolite in the Mount (Mt.) Ailao belt, Yunnan Province, are dealt with in this work in terms of geology, micro-paleontology, isotope and REE. The first kind of silicalite was defined as the turbidite formation. In this category, the radiolarian species lived in the Late Devonian (D3). The corresponding ecologic assemblage, composed of δ30Si (0.4‰-0.5‰, average 0.03‰), δCe (0.77-0.97, average 0.85) and LaN/YbN (0.77-1.06, average 0.96) of silicalite, shows that it occurred in the abyssal environment. The second kind of silicalite was defined as the mud-siliceous formation. Contacting conformably with the basalt of the ophiolite suit, the radiolarian silicalite at the top of ophiolite was in the category of the component units of the ophiolite in the Mt. Ailao belt. In this category, the radiolarian species lived in the Early Carboniferous (C1). The corresponding ecologic assemblage, composed of δ30Si (0.2‰-1.3‰averaging 0.7‰), ?展开更多
THE Dajiangping pyrite ore deposit located in the Yunfu County of Guangdong Province is asuper-large pyrite ore deposit. Its age has not been defined so far because of the absence of fos-sil. This note is to use Rb-Sr...THE Dajiangping pyrite ore deposit located in the Yunfu County of Guangdong Province is asuper-large pyrite ore deposit. Its age has not been defined so far because of the absence of fos-sil. This note is to use Rb-Sr isotope dating of silicalite to constrain the age of the ore depositand place special emphasis on its geological significance.展开更多
Silicalite-1/ceramic composite membrane was prepared on the outer surface of the α-Al2O3 tubular support byin-situ hydrothermal synthesis. The membrane was characterized by X-ray diffraction (XRD) and scanning electr...Silicalite-1/ceramic composite membrane was prepared on the outer surface of the α-Al2O3 tubular support byin-situ hydrothermal synthesis. The membrane was characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The pure gas permeances of H2, N2, Ar, CH4, C2H4, C2H6, C3H8, n-C4H10 and i-C4H10 were measured as a function of the pressure difference at 298 and 473 K. The permeances of H2, N2 and Ar showed little dependence on the pressure differences; the permselectivities of H2/i-C4H10 were 249 and 36.2 at 298 and 473 K respectively, which is a characteristic of molecular transport in silicalite-1 channels. The permeances of light alkanes decreased in the following order: CH4】C2H6】C3H8】n-C4H10】i-C4H10. The permselectivity of n-C4H10/i-C4H10 was above 15 at 298 K. As the temperature increased, the permeances of all gases increased except those of N2 and Ar, and a significant increment was found for alkanes. The permselectivity ofn-C4H10/i-C4H10 decreased to about 9 at 473 K. The gas permeation results showed that the silicalite-1/ceramic composite membrane was defect-free.展开更多
Titanium silicalite-1 (TS-1) was easily synthesized using inorganic silicon and titanium source, tetrapropylammonium bromide (TPABr) or TPAOH as templating molecule, NH3H2O, HDA or TEAOH etc. as base sources. In this ...Titanium silicalite-1 (TS-1) was easily synthesized using inorganic silicon and titanium source, tetrapropylammonium bromide (TPABr) or TPAOH as templating molecule, NH3H2O, HDA or TEAOH etc. as base sources. In this system, TPA+ cations (come from TPABr or TPAOH) served as templating agents to direct the MFI structure. NH3H2O, TEAOH or HDA etc. provides the alkalinity necessary for crystallization. X-ray diffraction, UV-Vis, IR spectroscopies, SEM, 29Si MAS NMR showed that the zeolites obtained possessed all the structural characteristics of TS-1, and titanium atoms were introduced into the framework in TS-1. This material was proved to have high crystallinity and high catalytic activity to allyl chloride epoxidation and propylene epoxidation. All the samples synthesized had similar catalytic properties with a standard TS-1 through compared inorganic reactant system with organic synthesis system using propylene epoxidation. The effects of silicon source and TPABr/SiO2 ratio were discussed.展开更多
Au-Ag bimetallic nanoparticle‐supported microporous titanium silicalite‐1catalysts were prepared via a hydrothermal‐immersion method,and their structures were examined.These materials serve as efficient catalysts f...Au-Ag bimetallic nanoparticle‐supported microporous titanium silicalite‐1catalysts were prepared via a hydrothermal‐immersion method,and their structures were examined.These materials serve as efficient catalysts for the photosynthesis of propylene oxide via the epoxidation of propene.The Au/Ag mass ratio and reaction temperature were demonstrated to have significant effects on the catalytic activity and selectivity of propylene oxide.The optimal formation rate(68.3μmol/g·h)and selectivity(52.3%)toward propylene oxide were achieved with an Au:Ag mass ratio of4:1.Notably,the strong synergistic effect between Au and Ag resulted in superior photocatalysis of the bimetallic systems compared with those of the individual systems.A probable reaction mechanism was proposed based on the theoretical and experimental results.展开更多
An intrinsic kinetics of cyclohexanone ammoximation in the liquid phase over titanium silicate molecular sieves is investigated in an isothermal slurry reactor at different initial reactant concentrations, catalyst lo...An intrinsic kinetics of cyclohexanone ammoximation in the liquid phase over titanium silicate molecular sieves is investigated in an isothermal slurry reactor at different initial reactant concentrations, catalyst loading, and reaction temperature. The rate equations are developed by analyzing data of kinetic measurements. More than 10 side reactions were found. H2O2 decomposition reaction must be considered and other side reactions can be neglected in the kinetic modeling. The predicted values of reaction rates based on the kinetic models are almost consistent with experimental ones. The models have guidance to the selection of reactor types and they are useful to the design and operation of reactor used.展开更多
The toluene oxidative bromination reaction catalyzed by hollow titanium silicalite(HTS)zeolite in aqueous medium was investigated by employing H2O2 and HBr under mild conditions without the need for organic solvent.A ...The toluene oxidative bromination reaction catalyzed by hollow titanium silicalite(HTS)zeolite in aqueous medium was investigated by employing H2O2 and HBr under mild conditions without the need for organic solvent.A high toluene conversion(90.7%)and high selectivity of mono-bromotoluene(99.0%)was achieved under the optimal reaction conditions.The UV-Raman spectroscopy was applied for the mechanism study and the result reveals that HTS is efficient for catalyzing the oxidation reaction of HBr with H2O2 to produce abundant active bromine species,which can further facilitate the toluene electrophilic bromination reaction.A two-step toluene bromination reaction mechanism involving the HTS catalyzed active bromine species“generation-conversion-utilization”process is proposed based on the UV-Raman spectroscopy analysis.展开更多
Controlling selectivity in the hydrogenation of compounds with several functional groups remains a challenging task in heterogeneous catalysis.We report herein the design and use of simple catalysts composed of Pt nan...Controlling selectivity in the hydrogenation of compounds with several functional groups remains a challenging task in heterogeneous catalysis.We report herein the design and use of simple catalysts composed of Pt nanoparticles confined in Silicalite-1(S-1,MFI type zeolite)for the inversion of the inherent C[double bond,length as m-dash]O selective hydrogenation of cinnamaldehyde over Pt.The encapsulated catalyst achieved an unconventional 98%hydrocinnamaldehyde selectivity at high conversion levels(88%),which bypasses the inherent selectivity of Pt for C[double bond,length as m-dash]O versus C[double bond,length as m-dash]C hydrogenation.This high selectivity originates from the combination of the low polarity of the S-1 support and the toluene solvent that favor interaction of the catalyst with the C[double bond,length as m-dash]C over the C[double bond,length as m-dash]O group,and to the efficient encapsulation of the platinum in the zeolite channels which restricts the growth of the nanoparticles and consequently decreases the number of undesirable Pt(111)facets active for C[double bond,length as m-dash]O hydrogenation.展开更多
Using a prototypical family of hierarchical zeolites,we show how adsorption-based characterization can be extended to provide morphological and topological assessment beyond state-of-the-art tools.The well-controlled ...Using a prototypical family of hierarchical zeolites,we show how adsorption-based characterization can be extended to provide morphological and topological assessment beyond state-of-the-art tools.The well-controlled materials under study consist of submicron-sized zeolite crystals(silicalite-1)that exhibit large nanoporous cavities in addition to their intrinsic microporosity.Such zeolites nanoboxes can be prepared with a single large cavity,with several independent cavities or with several interconnected cavities depending on synthesis conditions.It is shown that analysis of the adsorption/desorption branches using the Derjaguin model allows determining the cavity size distributions in these materials but also the fraction of pores directly connected to the external surface for each cavity size.Moreover,using the independent domain theory,we illustrate how scanning the capillary hysteresis provides a means to determine whether pores behave independently from each other or are connected to each other.All our findings are found to be consistent with additional electron microscopy data including electron tomography data.展开更多
Titanium silicalite-1 (TS-1) zeolite,as a promising shape-selective catalyst,has excellent catalytic activity in many oxidation reactions.However,there are still challenges to rapidly synthesize TS-1 and achieve a hig...Titanium silicalite-1 (TS-1) zeolite,as a promising shape-selective catalyst,has excellent catalytic activity in many oxidation reactions.However,there are still challenges to rapidly synthesize TS-1 and achieve a high content of Ti in TS-1 without anatase TiO_(2).In this work,a high-efficiency strategy has been proposed by using 1,3,5-benzenetricarboxylic acid (H_(3)BTC) as a crystallization modifier to rapidly synthesize enhanced-Ti TS-1 zeolite without extra-framework anatase TiO_(2).In such a synthetic system,a mixed liquid–solid precursor phase is formed within 4.5 hours,and then TS-1 crystals can be produced within one day based on the special combination mechanism of liquid-phase and solid-phase conversion.Ti species enter into the TS-1 framework by the transformation from the liquid phase to crystals as well as by the in situ transformation of the solid phase,which makes the content of framework Ti increase significantly,and the Si/Ti ratio can reach 48.5 without any anatase TiO_(2).In the epoxidation of 1-hexene with H_(2)O_(2) as an oxidant,the conversion of alkene over the synthesized TS-1 was improved by 8.01% compared to the traditional TS-1 (18.11% vs.10.10%).The high-efficiency strategy reported in this paper will provide new opportunities for further promoting the industrial application of TS-1 zeolite.展开更多
Metal catalysts confined inside zeolite micropores or crystals are widely applied in the chemical industry because of their distinctive catalytic functions,especially with regard to the conversion of small and stable ...Metal catalysts confined inside zeolite micropores or crystals are widely applied in the chemical industry because of their distinctive catalytic functions,especially with regard to the conversion of small and stable alkane molecules[1,2].Silicalite-1(S-1),a pure silica zeolite with an MFI topology,has a robust framework capable of withstanding harsh thermal and chemical conditions.展开更多
文摘In order to investigate the rules on preparation of titanium silicalite （TS-1） the ^1H →^13C CP/ MAS NMR spectrometers were applied to track the function of template TPAOH in the process of crystallization of titanium silicalite. The research results revealed that at the initial stage of crystallization the TPA＋ ions acting as the template could predominantly absorb the polymers of negatively charged silicatitania sol and the interactions between silica sol and titania sol could gradually lead to the formation of tiny crystal nuclei that could slowly grow up to form molecular sieves. Upon investigating the course of crystallization of titanium silicalite the ^1H →^13C CP/MAS NMR spectrometers were applied to effectively enhance the resolution of 29Si signals in the titanium silicalite. Study results have shown that during the formation of tiny crystal nuclei upon interaction between titania sol and silica sol the influence of titania sol on the silica sol was insignificant. However, when tiny crystal nuclei broke out into molecular sieves the titania sol could enter the zeolite framework that could apparently impose an enhanced effect on the silica sol.
基金supported by the NationalScience Foundation of China(2006CB202508)wewould like to extend our heartfelt thanks to the RIPP’s labo-ratories engaging in XRD and FT-IR analyses for theirenergetical support and warm assistance provided to thisresearch work.
文摘In order to investigate the rules on formation of zeolite during crystallization of titanium silicalite zeolite(TS-1)the X-ray diffractometry and Foulier transform infra-red spectrometry were applied to track the process of crystallization of titanium silicalite zeolite.The research results revealed that at the initial stage of crystallization the interactions between silica gel and titania gel in the polymer blend could gradually lead to the formation of tiny crystal nuclei with complicated structure that could slowly grow up to form molecular sieves.Quite different from the conventional zeolites that use the acid sites as the catalytically active centers,the oxidative reactivity of the titanium silicalite zeolite was not proportional to its crystallinity and is associated with the oxidative centers of titanium contained in the zeolite.
文摘The oxidation of thiophene by H_(2)O_(2)under mild conditions was difficult in the past,and it appears again with the proposed oxidative deep desulfurization(ODS)process to obtain ultralow sulfur fuel for fuel cell industry and for environmental protection[1,2].The ODS process is very efficient in reducing ben-zothiophene,di-benzothiophene and their corresponding alkyl derivatives[1.2].However,thiophene and its alkyl derivatives,most of which exist in gasoline,are not removed in this process.
文摘A simple, quick, sensitive, accurate and precise method has been developed for evaluating the catalytic active sites of titanium silicalite-1 (TS-1). The catalytic active sites of titanium silicalite zeolite depend on the effectively active species (EAS) in TS-1 which react with specific substrates quickly. However, the EAS was hard to be evaluated with conventional instruments and techniques in the past. In this paper, the EAS was formed in TS-1 upon interaction with H2O2, and its presence could be confirmed by UV-vis spectroscopy which has an absorption peak at 385 nm. The absorbance at 385 nm was found to be linearly related to time, and when the absorbance and the increasing rate of absorbance (k) increased, the catalytic performance of TS-1 enhanced.
基金supported by the National Natural Science Foundation of China(No.22302025)the Fundamental Research Funds for the Central Universities of Dalian Maritime University in China(No.3132023161 and No.3132023520)A.T.B.acknowledges the support from the Office of Science,Office of Basic Energy Sciences,of the U.S.Department of Energy(DOE)(No.DE-AC02-05CH11231).
文摘Unique sheet-like Silicalite-1 single crystals containing intracrystalline macropores(HMS-Silicalite-1)were prepared by urea-assisted,dry-gel synthesis,which uses mesoporous silica spheres(MSSs)as both the silica precursor and the macropore template.Urea was found to inhibit crystal growth in the b-axis direction and,therefore,play a pivotal role in the formation of the sheet-like crystals.Zeolite growth occurred via“dissolution-crystallization”transformation of MSSs to produce macro/microporous Silicalite-1 crystals.Systematic studies revealed that the urea/SiO_(2) and H_(2)O/SiO_(2) ratios affect the morphology of the resulting Silicalite-1 zeolites and that the thickness of HMS-Silicalite-1 platelets can be tuned between 190 nm and 400 nm.It was also found that the H_(2)O/SiO_(2) and urea/SiO_(2) ratios can be modulated to match the“inhibition”and“dissolution-crystallization”processes.HMS-Silicalite-1 was assessed as a catalyst for the Beckmann rearrangement of cyclohexanone oxime toε-caprolactam and found to exhibit significantly greater resistance to deactivation than conventional Silicalite-1 and hierarchical macro/microporous Silicalite-1.The superior performance of HMS-Silicalite-1 is attributed to the presence of crystals of Silicalite-1 that are thin in the direction of the b-axis and contain significant macropores(150 to 400 nm in size).The results of this study offer a novel,yet simple,method for simultaneous control of the zeolite crystal aspect ratio and macropore content to produce catalysts that are highly efficient for diffusion-limited reactions involving large reactant molecules.
基金support from the National Natural Science Foundation of China(U1967215,21835002,21621001,and 21875221)the 111 Project of China(B17020).
文摘Pure silica zeolite MFI(silicalite-1)has been widely used in gas separation and volatile organic compounds(VOCs)adsorption.The molar ratio of tetrapropylammonium(TPA^(+))and SiO_(2)(TPA^(+)/SiO_(2))included in the framework of silicalite-1 is 0.042.Reducing the utilization of TPA^(+)will not only benefit the environment but also reduce the cost of silicalite-1.Herein,we reported the synthesis of highly crystalline silicalite-1 from a reaction mixture with a TPA^(+)/SiO_(2)molar ratio of 0.035 and a seed loading of 5 wt%or 0.01 and a seed loading of 10 wt%.
基金supported by the National Natural Science Foundation of China(No.22178295,21706225)the Natural Science Foundation of Hunan Province(No.2020JJ4572,2021JJ30665)the Hunan Collaborative Innovation Center of New Chemical Technologies for Environmental Benignity and Efficient Resource Utilization.
文摘The oxidative dehydrogenation of propane by CO_(2)(CO_(2)-ODHP)is an attractive and sustainable process that can simultaneously produce propylene and reduce CO_(2),but C3H8 and CO_(2)are relatively inert at low temperatures.Herein,we developed a novel approach for oxidative dehydrogenation of propane with CO_(2)by microwave catalysis at low temperature.A novel microwave catalyst,cobalt-promoted Zn encapsulated within silicalite-1(Zn8Co1@S-1+SiC),has been synthesized by confining Zn and Co species within a silicalite-1 zeolite via a hydrothermal method.This microwave catalyst achieved C3H8 conversion of 68%,CO_(2)conversion of 16%,and C3H6 selectivity of 88%under microwave irradiation at a low temperature of 500℃.In comparison,in the conventional reaction mode of the identical conditions,it shows only C3H8 conversion of 14%and CO_(2)conversion of 5%.Characterization studies showed that encapsulating Zn and Co species within the silicalite-1 zeolite inhibits metal loss and generates more Lewis acid sites,thereby enhancing the dehydrogenation activity.The combination of zinc and cobalt demonstrated a synergistic effect.The carbon deposition on the Zn8Co1@S-1 catalyst was reduced from 5.75%to 4.62%by introducing CO_(2)into the propane dehydrogenation to propylene.In addition,the activation energy of oxidative propane dehydrogenation with CO_(2)under microwave irradiation was reduced(85.05 kJ mol^(-1)→46.54 kJ mol^(-1)).The superior catalytic performance under microwave irradiation at low temperatures can provide guidelines for propane dehydrogenation with microwave catalyst design and process enhancement.
文摘Two kinds of radiolarian silicalites at the bottom and top of the ophiolite in the Mount (Mt.) Ailao belt, Yunnan Province, are dealt with in this work in terms of geology, micro-paleontology, isotope and REE. The first kind of silicalite was defined as the turbidite formation. In this category, the radiolarian species lived in the Late Devonian (D3). The corresponding ecologic assemblage, composed of δ30Si (0.4‰-0.5‰, average 0.03‰), δCe (0.77-0.97, average 0.85) and LaN/YbN (0.77-1.06, average 0.96) of silicalite, shows that it occurred in the abyssal environment. The second kind of silicalite was defined as the mud-siliceous formation. Contacting conformably with the basalt of the ophiolite suit, the radiolarian silicalite at the top of ophiolite was in the category of the component units of the ophiolite in the Mt. Ailao belt. In this category, the radiolarian species lived in the Early Carboniferous (C1). The corresponding ecologic assemblage, composed of δ30Si (0.2‰-1.3‰averaging 0.7‰), ?
文摘THE Dajiangping pyrite ore deposit located in the Yunfu County of Guangdong Province is asuper-large pyrite ore deposit. Its age has not been defined so far because of the absence of fos-sil. This note is to use Rb-Sr isotope dating of silicalite to constrain the age of the ore depositand place special emphasis on its geological significance.
文摘Silicalite-1/ceramic composite membrane was prepared on the outer surface of the α-Al2O3 tubular support byin-situ hydrothermal synthesis. The membrane was characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The pure gas permeances of H2, N2, Ar, CH4, C2H4, C2H6, C3H8, n-C4H10 and i-C4H10 were measured as a function of the pressure difference at 298 and 473 K. The permeances of H2, N2 and Ar showed little dependence on the pressure differences; the permselectivities of H2/i-C4H10 were 249 and 36.2 at 298 and 473 K respectively, which is a characteristic of molecular transport in silicalite-1 channels. The permeances of light alkanes decreased in the following order: CH4】C2H6】C3H8】n-C4H10】i-C4H10. The permselectivity of n-C4H10/i-C4H10 was above 15 at 298 K. As the temperature increased, the permeances of all gases increased except those of N2 and Ar, and a significant increment was found for alkanes. The permselectivity ofn-C4H10/i-C4H10 decreased to about 9 at 473 K. The gas permeation results showed that the silicalite-1/ceramic composite membrane was defect-free.
基金Project (No. 29792070) supported by the National Natural Science Foundation of China.Present address: Department of Chemical Engineering,Xiangtan University, Xiangtan, Hunan 411105, China.
文摘Titanium silicalite-1 (TS-1) was easily synthesized using inorganic silicon and titanium source, tetrapropylammonium bromide (TPABr) or TPAOH as templating molecule, NH3H2O, HDA or TEAOH etc. as base sources. In this system, TPA+ cations (come from TPABr or TPAOH) served as templating agents to direct the MFI structure. NH3H2O, TEAOH or HDA etc. provides the alkalinity necessary for crystallization. X-ray diffraction, UV-Vis, IR spectroscopies, SEM, 29Si MAS NMR showed that the zeolites obtained possessed all the structural characteristics of TS-1, and titanium atoms were introduced into the framework in TS-1. This material was proved to have high crystallinity and high catalytic activity to allyl chloride epoxidation and propylene epoxidation. All the samples synthesized had similar catalytic properties with a standard TS-1 through compared inorganic reactant system with organic synthesis system using propylene epoxidation. The effects of silicon source and TPABr/SiO2 ratio were discussed.
基金supported by the National Natural Science Foundation of China(21576050)the Natural Science Foundation of Jiangsu Province(BK20150604)~~
文摘Au-Ag bimetallic nanoparticle‐supported microporous titanium silicalite‐1catalysts were prepared via a hydrothermal‐immersion method,and their structures were examined.These materials serve as efficient catalysts for the photosynthesis of propylene oxide via the epoxidation of propene.The Au/Ag mass ratio and reaction temperature were demonstrated to have significant effects on the catalytic activity and selectivity of propylene oxide.The optimal formation rate(68.3μmol/g·h)and selectivity(52.3%)toward propylene oxide were achieved with an Au:Ag mass ratio of4:1.Notably,the strong synergistic effect between Au and Ag resulted in superior photocatalysis of the bimetallic systems compared with those of the individual systems.A probable reaction mechanism was proposed based on the theoretical and experimental results.
文摘An intrinsic kinetics of cyclohexanone ammoximation in the liquid phase over titanium silicate molecular sieves is investigated in an isothermal slurry reactor at different initial reactant concentrations, catalyst loading, and reaction temperature. The rate equations are developed by analyzing data of kinetic measurements. More than 10 side reactions were found. H2O2 decomposition reaction must be considered and other side reactions can be neglected in the kinetic modeling. The predicted values of reaction rates based on the kinetic models are almost consistent with experimental ones. The models have guidance to the selection of reactor types and they are useful to the design and operation of reactor used.
基金The author thanks for the financial support of SINOPEC Corporation(S413108).
文摘The toluene oxidative bromination reaction catalyzed by hollow titanium silicalite(HTS)zeolite in aqueous medium was investigated by employing H2O2 and HBr under mild conditions without the need for organic solvent.A high toluene conversion(90.7%)and high selectivity of mono-bromotoluene(99.0%)was achieved under the optimal reaction conditions.The UV-Raman spectroscopy was applied for the mechanism study and the result reveals that HTS is efficient for catalyzing the oxidation reaction of HBr with H2O2 to produce abundant active bromine species,which can further facilitate the toluene electrophilic bromination reaction.A two-step toluene bromination reaction mechanism involving the HTS catalyzed active bromine species“generation-conversion-utilization”process is proposed based on the UV-Raman spectroscopy analysis.
基金Funding for this work was provided by baseline grant(BAS/1/1402-01-01)from King Abdullah University of Science and Technology(KAUST).
文摘Controlling selectivity in the hydrogenation of compounds with several functional groups remains a challenging task in heterogeneous catalysis.We report herein the design and use of simple catalysts composed of Pt nanoparticles confined in Silicalite-1(S-1,MFI type zeolite)for the inversion of the inherent C[double bond,length as m-dash]O selective hydrogenation of cinnamaldehyde over Pt.The encapsulated catalyst achieved an unconventional 98%hydrocinnamaldehyde selectivity at high conversion levels(88%),which bypasses the inherent selectivity of Pt for C[double bond,length as m-dash]O versus C[double bond,length as m-dash]C hydrogenation.This high selectivity originates from the combination of the low polarity of the S-1 support and the toluene solvent that favor interaction of the catalyst with the C[double bond,length as m-dash]C over the C[double bond,length as m-dash]O group,and to the efficient encapsulation of the platinum in the zeolite channels which restricts the growth of the nanoparticles and consequently decreases the number of undesirable Pt(111)facets active for C[double bond,length as m-dash]O hydrogenation.
基金supported by the French Research Agency(ANR CATCALL(ANR-19-CE07-0025))Numerical calculations in this paper were performed using the Froggy platform of the GRICAD infrastructure(https://www.gricad.univ-grenoblealpes.fr),which is supported by the Rhône-Alpes region(GRANT CPER07-13 CIRA)the Equip@Meso project(reference ANR-10-EQPX-29-01)of the program Investissements d’Avenir supervised by the French Research Agency.
文摘Using a prototypical family of hierarchical zeolites,we show how adsorption-based characterization can be extended to provide morphological and topological assessment beyond state-of-the-art tools.The well-controlled materials under study consist of submicron-sized zeolite crystals(silicalite-1)that exhibit large nanoporous cavities in addition to their intrinsic microporosity.Such zeolites nanoboxes can be prepared with a single large cavity,with several independent cavities or with several interconnected cavities depending on synthesis conditions.It is shown that analysis of the adsorption/desorption branches using the Derjaguin model allows determining the cavity size distributions in these materials but also the fraction of pores directly connected to the external surface for each cavity size.Moreover,using the independent domain theory,we illustrate how scanning the capillary hysteresis provides a means to determine whether pores behave independently from each other or are connected to each other.All our findings are found to be consistent with additional electron microscopy data including electron tomography data.
基金supported by the National Natural Science Foundation of China(Grant No.21671075 and 21621001)the 111 Project(No.B17020).
文摘Titanium silicalite-1 (TS-1) zeolite,as a promising shape-selective catalyst,has excellent catalytic activity in many oxidation reactions.However,there are still challenges to rapidly synthesize TS-1 and achieve a high content of Ti in TS-1 without anatase TiO_(2).In this work,a high-efficiency strategy has been proposed by using 1,3,5-benzenetricarboxylic acid (H_(3)BTC) as a crystallization modifier to rapidly synthesize enhanced-Ti TS-1 zeolite without extra-framework anatase TiO_(2).In such a synthetic system,a mixed liquid–solid precursor phase is formed within 4.5 hours,and then TS-1 crystals can be produced within one day based on the special combination mechanism of liquid-phase and solid-phase conversion.Ti species enter into the TS-1 framework by the transformation from the liquid phase to crystals as well as by the in situ transformation of the solid phase,which makes the content of framework Ti increase significantly,and the Si/Ti ratio can reach 48.5 without any anatase TiO_(2).In the epoxidation of 1-hexene with H_(2)O_(2) as an oxidant,the conversion of alkene over the synthesized TS-1 was improved by 8.01% compared to the traditional TS-1 (18.11% vs.10.10%).The high-efficiency strategy reported in this paper will provide new opportunities for further promoting the industrial application of TS-1 zeolite.
基金supported by the National Key R&D Program of China(Nos.2022YFE0116000 and 2021YFA1502600)the National Natural Science Foundation of China(No.22241801).
文摘Metal catalysts confined inside zeolite micropores or crystals are widely applied in the chemical industry because of their distinctive catalytic functions,especially with regard to the conversion of small and stable alkane molecules[1,2].Silicalite-1(S-1),a pure silica zeolite with an MFI topology,has a robust framework capable of withstanding harsh thermal and chemical conditions.
