The roles of acidity and micropore structure of zeolite were studied in the hydrolysis of the model oligosaccharide of cellulose–cellobiose. HZSM-5, HY, HMOR and Hβ zeolites were selected as model catalysts for the ...The roles of acidity and micropore structure of zeolite were studied in the hydrolysis of the model oligosaccharide of cellulose–cellobiose. HZSM-5, HY, HMOR and Hβ zeolites were selected as model catalysts for the hydrolysis of cellobiose. The effect of acidity of zeolite, including the strength, type and location, on its catalytic activity was investigated. The strong Br?nsted acid sites located in micropores are the active sites for the hydrolysis of cellobiose to glucose. Meanwhile, the catalytic performance of zeolite is also dependent on the micropore size of zeolite.展开更多
The catalytic transformation of methylcyclohexane as an accepted probe reaction to evaluate zeolitic acidity(concentration,strength,and accessibility)is employed to study the acidity and the reactivity of three commer...The catalytic transformation of methylcyclohexane as an accepted probe reaction to evaluate zeolitic acidity(concentration,strength,and accessibility)is employed to study the acidity and the reactivity of three commercial dealuminated Y zeolites(DAY)with different Si/Al ratios and meso/microporosities,with their properties analyzed by N_(2) adsorption/desorption,pyridine-IR,and hydroxyl-IR spectroscopy technologies.The global activity(conversion)is largely dependent on the concentration of the acid sites,and the activity of the protonic sites in terms of turnover frequency(TOF)reflects the accessibility of acid sites.The products of aromatics and isomers,and the yield of cracking products increase with the increase of concentration of strong protonic sites in zeolite micropores.Moreover,the decrease of aromatics with the reduction of the concentration of acid sites and the diffusion length within DAY zeolites are observed due to the decrease of the secondary reaction.For the same reason,it results in the increasing of C_(7)products and alkenes/alkanes ratios in the cracking products.The high i-C_(4)product selectivity is a unique reflection of the high percentage of very strong acid sites,which is characterized by the hydroxyl-IR band at 3600 cm^(-1).展开更多
The adsorb model of formic acid on NaX derived from TPD was discussed. It was showed that the adsorb sites were various exposed framework O2- centers bearing different basic intensity and spatial resistance. The h-pea...The adsorb model of formic acid on NaX derived from TPD was discussed. It was showed that the adsorb sites were various exposed framework O2- centers bearing different basic intensity and spatial resistance. The h-peak was attributed to O2- near S-III in supercage and l-peak to O2- near S-II in beta-cage of faujusite zeolite. The model can explain the experimental results. Meanwhile, a relative standard of basic intensity based on TPD of formic acid was founded.展开更多
In this paper the effect of ion-exchange simplified as water handling on basic zeolitewas studied.It was foond that the interaction between chemisorbed water and Na+-O2- couplewould increase the total number of basic ...In this paper the effect of ion-exchange simplified as water handling on basic zeolitewas studied.It was foond that the interaction between chemisorbed water and Na+-O2- couplewould increase the total number of basic sites, while weaken the intensity of each basic sites.Theprocess can be explained by the adsorb model of organic acid on NaX presented before.展开更多
The stability of beta zeollie in acid solution and the effect of acid treatment on the polymorphs in beta zeolite were studied. This zeolite is easily dealuminated by HCI treatment but its framework highly resistent t...The stability of beta zeollie in acid solution and the effect of acid treatment on the polymorphs in beta zeolite were studied. This zeolite is easily dealuminated by HCI treatment but its framework highly resistent to acidity.In β zeolite, polymorph A is less stable than polymorph B.The chirality of β zeolite can be modified by the method of acid treatment.展开更多
Avery wide range of the C3^=/C2^= ratio from 0.72 to 7.56 with high C2^= + C3^= selectivity of around 66%in the methanol-to-hydrocarbons process can be realized over ZSM-5 catalyst in a fixed-bed reactor.We firstly c...Avery wide range of the C3^=/C2^= ratio from 0.72 to 7.56 with high C2^= + C3^= selectivity of around 66%in the methanol-to-hydrocarbons process can be realized over ZSM-5 catalyst in a fixed-bed reactor.We firstly conduct a single factor experiment of acidity,demonstrating that the acidity control of MTH catalyst is crucial to adjusting light olefins selectivity.Weak Bronsted acid sites favor to high C3^= selectivity(59.0%)due to the suppression of the conversion reactions from the alkene-based to arene-based cycle,while Lewis acid sites conduce to high C2^= selectivity(39.6%) due to the promotion of the conversion reactions for the aromatics formation and steric constraints of Lewis acid sites making the aromatics crack more efficiently to C2^=.展开更多
Liquid fuel intermediates could be produced via aldol condensation reaction between furfural or 5-hydroxymethylfurfural(HMF)and acetone.It was found that iron-modified MCM-41 zeolite can be an effective Lewis acid cat...Liquid fuel intermediates could be produced via aldol condensation reaction between furfural or 5-hydroxymethylfurfural(HMF)and acetone.It was found that iron-modified MCM-41 zeolite can be an effective Lewis acid catalyst for C-C bond formation via aldol condensation of furfural or HMF with acetone.The 4-(2-furyl)-3-buten-2-one and 1,5-di-2-furanyl-1,4-pentadien-3-one(FAc and F_(2)Ac),or 1,5-di-2-furanyl-1,4-pentadien-3-one and 1,5-bis[(5-hydroxlmethyl)-2-furanyl]-1,4-pentadien-3-one(HAc and H_(2)Ac),as two main condensation products of furfural with acetone or HMF with acetone,were observed.After 24 h at 160℃,86.9%conversion of furfural with 60.0%yield of the FAc as well as 7.5%yield of the F_(2)Ac and 88.9%conversion of the HMF with 41.1%yield of the HAc as well as 3.5%yield of the H_(2)Ac were achieved.Although furfural or HMF conversion was almost same after 24 h at 160℃,iron-modified MCM-41 zeolite catalyst displayed an enhanced selectivity to condensation products of furfural with acetone.In addition,catalysts showed an improved selectivity to the F_(2)Ac and H_(2)Ac at higher reaction temperature.The reusability and regeneration studies showed that iron-modified MCM-41 zeolite catalyst could not be reused directly,but could be regenerated by calcination in air,and the catalytic perfor-mance of regenerated catalyst was acceptable.展开更多
Zeolites are typically synthesized in alkaline or fluoride-containing near-neutral media.Sophisticated organic structure-directing agents have been investigated for such systems with the aim of discovering materials w...Zeolites are typically synthesized in alkaline or fluoride-containing near-neutral media.Sophisticated organic structure-directing agents have been investigated for such systems with the aim of discovering materials with unprecedented structures and properties for novel technical applications.In contrast,zeolite crystallization in strongly acidic media has yet to be explored.This study demonstrates that a zeolitic silicate phase crystallizes from acidic gels using trimethylamine as an organic additive with the composition 1 SiO_(2):0.3 TMA:0.3 HCl:0.15 HF:55 H_(2)O:(0.1-0.4)GeO_(2).This phase has an interrupted four-connected framework analog to the octahedron/tetrahedron-mixed framework of the mineral family pharmacosiderite.In comparison to the pharmacosiderite-type HK_(3)(Ge_(7)O_(16))(H_(2)O)_(4),the four GeO_(6)-octahedra forming the central[HGe_(4)O_(4)O_(12)]-cluster are replaced by four SiO_(4)-tetrahedra in a[Si_(4)O_(6)(OH)2.89]-unit in the new phase.However,the structure is distorted and may contain connectivity and point defects;thus,healing by the occasional incorporation of GeO_(6)-units is necessary.The refined unit cell has a cubic symmetry,space group P-43m(#215),with a=7.7005(1)Å.Acidic-medium synthesis is a useful way to find new zeolites that move in a fundamentally different direction from sophisticated organic structure-directing agents.展开更多
基金supported by the National Natural Science Foundation of China(Grant:U1304209,J1210060)the Undergraduate Innovation Education Project of Zhengzhou University for the financial support(Grant:2014sjxm008)
文摘The roles of acidity and micropore structure of zeolite were studied in the hydrolysis of the model oligosaccharide of cellulose–cellobiose. HZSM-5, HY, HMOR and Hβ zeolites were selected as model catalysts for the hydrolysis of cellobiose. The effect of acidity of zeolite, including the strength, type and location, on its catalytic activity was investigated. The strong Br?nsted acid sites located in micropores are the active sites for the hydrolysis of cellobiose to glucose. Meanwhile, the catalytic performance of zeolite is also dependent on the micropore size of zeolite.
基金This work was financially supported by the National Natural Science Foundation of China(Grant No.21978192)the SINOPEC Technology Project(No.117009-1)the Shanxi Province Key Innovative Research Team in Science and Technology(No.2014131006).
文摘The catalytic transformation of methylcyclohexane as an accepted probe reaction to evaluate zeolitic acidity(concentration,strength,and accessibility)is employed to study the acidity and the reactivity of three commercial dealuminated Y zeolites(DAY)with different Si/Al ratios and meso/microporosities,with their properties analyzed by N_(2) adsorption/desorption,pyridine-IR,and hydroxyl-IR spectroscopy technologies.The global activity(conversion)is largely dependent on the concentration of the acid sites,and the activity of the protonic sites in terms of turnover frequency(TOF)reflects the accessibility of acid sites.The products of aromatics and isomers,and the yield of cracking products increase with the increase of concentration of strong protonic sites in zeolite micropores.Moreover,the decrease of aromatics with the reduction of the concentration of acid sites and the diffusion length within DAY zeolites are observed due to the decrease of the secondary reaction.For the same reason,it results in the increasing of C_(7)products and alkenes/alkanes ratios in the cracking products.The high i-C_(4)product selectivity is a unique reflection of the high percentage of very strong acid sites,which is characterized by the hydroxyl-IR band at 3600 cm^(-1).
文摘The adsorb model of formic acid on NaX derived from TPD was discussed. It was showed that the adsorb sites were various exposed framework O2- centers bearing different basic intensity and spatial resistance. The h-peak was attributed to O2- near S-III in supercage and l-peak to O2- near S-II in beta-cage of faujusite zeolite. The model can explain the experimental results. Meanwhile, a relative standard of basic intensity based on TPD of formic acid was founded.
文摘In this paper the effect of ion-exchange simplified as water handling on basic zeolitewas studied.It was foond that the interaction between chemisorbed water and Na+-O2- couplewould increase the total number of basic sites, while weaken the intensity of each basic sites.Theprocess can be explained by the adsorb model of organic acid on NaX presented before.
文摘The stability of beta zeollie in acid solution and the effect of acid treatment on the polymorphs in beta zeolite were studied. This zeolite is easily dealuminated by HCI treatment but its framework highly resistent to acidity.In β zeolite, polymorph A is less stable than polymorph B.The chirality of β zeolite can be modified by the method of acid treatment.
基金the National Natural Science Foundation of China(Nos.U1462106 and 21673076)the National Key Research and Development Program of China(No.2016YFB0701100)
文摘Avery wide range of the C3^=/C2^= ratio from 0.72 to 7.56 with high C2^= + C3^= selectivity of around 66%in the methanol-to-hydrocarbons process can be realized over ZSM-5 catalyst in a fixed-bed reactor.We firstly conduct a single factor experiment of acidity,demonstrating that the acidity control of MTH catalyst is crucial to adjusting light olefins selectivity.Weak Bronsted acid sites favor to high C3^= selectivity(59.0%)due to the suppression of the conversion reactions from the alkene-based to arene-based cycle,while Lewis acid sites conduce to high C2^= selectivity(39.6%) due to the promotion of the conversion reactions for the aromatics formation and steric constraints of Lewis acid sites making the aromatics crack more efficiently to C2^=.
基金supported by National Key R&D Program of China(No.2018YFB1501601)National Natural Science Foundation of China(No.51676178)Transformational Technologies for Clean Energy and Demonstration,and Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDA 21060101).
文摘Liquid fuel intermediates could be produced via aldol condensation reaction between furfural or 5-hydroxymethylfurfural(HMF)and acetone.It was found that iron-modified MCM-41 zeolite can be an effective Lewis acid catalyst for C-C bond formation via aldol condensation of furfural or HMF with acetone.The 4-(2-furyl)-3-buten-2-one and 1,5-di-2-furanyl-1,4-pentadien-3-one(FAc and F_(2)Ac),or 1,5-di-2-furanyl-1,4-pentadien-3-one and 1,5-bis[(5-hydroxlmethyl)-2-furanyl]-1,4-pentadien-3-one(HAc and H_(2)Ac),as two main condensation products of furfural with acetone or HMF with acetone,were observed.After 24 h at 160℃,86.9%conversion of furfural with 60.0%yield of the FAc as well as 7.5%yield of the F_(2)Ac and 88.9%conversion of the HMF with 41.1%yield of the HAc as well as 3.5%yield of the H_(2)Ac were achieved.Although furfural or HMF conversion was almost same after 24 h at 160℃,iron-modified MCM-41 zeolite catalyst displayed an enhanced selectivity to condensation products of furfural with acetone.In addition,catalysts showed an improved selectivity to the F_(2)Ac and H_(2)Ac at higher reaction temperature.The reusability and regeneration studies showed that iron-modified MCM-41 zeolite catalyst could not be reused directly,but could be regenerated by calcination in air,and the catalytic perfor-mance of regenerated catalyst was acceptable.
基金support provided by the Shandong Energy Institute(SEI S202107)Nature Science Foundation of Shandong Province(ZR2022MB053 and ZR2022QB216).
文摘Zeolites are typically synthesized in alkaline or fluoride-containing near-neutral media.Sophisticated organic structure-directing agents have been investigated for such systems with the aim of discovering materials with unprecedented structures and properties for novel technical applications.In contrast,zeolite crystallization in strongly acidic media has yet to be explored.This study demonstrates that a zeolitic silicate phase crystallizes from acidic gels using trimethylamine as an organic additive with the composition 1 SiO_(2):0.3 TMA:0.3 HCl:0.15 HF:55 H_(2)O:(0.1-0.4)GeO_(2).This phase has an interrupted four-connected framework analog to the octahedron/tetrahedron-mixed framework of the mineral family pharmacosiderite.In comparison to the pharmacosiderite-type HK_(3)(Ge_(7)O_(16))(H_(2)O)_(4),the four GeO_(6)-octahedra forming the central[HGe_(4)O_(4)O_(12)]-cluster are replaced by four SiO_(4)-tetrahedra in a[Si_(4)O_(6)(OH)2.89]-unit in the new phase.However,the structure is distorted and may contain connectivity and point defects;thus,healing by the occasional incorporation of GeO_(6)-units is necessary.The refined unit cell has a cubic symmetry,space group P-43m(#215),with a=7.7005(1)Å.Acidic-medium synthesis is a useful way to find new zeolites that move in a fundamentally different direction from sophisticated organic structure-directing agents.