使用来源广泛的甲醇为原料制取丙烯,是对石油路线生产丙烯的重要补充.尽管以ZSM-5分子筛为催化剂的固定床甲醇制丙烯(MTP)技术已经实现了工业应用,但进一步提高催化剂的寿命和丙烯的选择性一直是学术界和工业界的研究热点.MTP过程作为...使用来源广泛的甲醇为原料制取丙烯,是对石油路线生产丙烯的重要补充.尽管以ZSM-5分子筛为催化剂的固定床甲醇制丙烯(MTP)技术已经实现了工业应用,但进一步提高催化剂的寿命和丙烯的选择性一直是学术界和工业界的研究热点.MTP过程作为典型的酸催化反应,积碳是催化剂失活的主要原因,由于ZSM-5分子筛十元环孔道的空间限制作用,积碳主要分布在外表面.因此,消除外表面的酸性位点对延长催化剂的寿命至关重要,但修饰外表面酸性位点的同时往往会改变样品的其他性质,如孔径、整体酸量等.本文分别使用Na_2H_2EDTA和H_3PO_4处理高硅ZSM-5分子筛原粉(微孔内含有机模板剂)来选择性地减小或消除外表面的酸密度,而不影响分子筛内部的性质,并考察了处理后样品的MTP性能.使用N_2物理吸附、SEM和^(27)Al MAS NMR表征样品的织构性质、形貌和Al原子的化学环境,XPS和三异丙苯裂解实验表征外表面的硅铝比和酸密度.表征结果表明,Na_2H_2EDTA处理虽然可以选择性的脱除表面Al原子,但会在外表面产生新的酸点(可能是硅巢).H_3PO_4处理虽然不能脱除表面的Al原子,但外表面残留的P物种能够有效的减小酸密度.MTP评价结果表明,H_3PO_4处理能够有效的延长催化剂的寿命和维持丙烯的选择性,这是因为H_3PO_4处理既提高了外表面的容碳能力,也抑制了积碳沉积的速率.Na_2H_2EDTA处理仅能增加外表面的容碳能力,所以其只能延长催化寿命.通过进一步优化H_3PO_4后处理的条件,处理后的ZSM-5样品的催化寿命可以延长至前体的1.5倍,同时,丙烯的选择性也略有提高。展开更多
A series of ZSM-5 zeolites, with the morphologies of sphere, sphere with cubic particles on the surface, and cubic particles, were synthesized by hydrothermal method using n-butylamine as the template, assisted by the...A series of ZSM-5 zeolites, with the morphologies of sphere, sphere with cubic particles on the surface, and cubic particles, were synthesized by hydrothermal method using n-butylamine as the template, assisted by the addition of NaCl and crystal seed. X-ray diffraction(XRD),scanning electron microscope(SEM), X-ray fluorescence(XRF) and temperature-programmed desorption of ammonia(NH3-TPD) were used to characterize these samples. The samples were tested with toluene methylation reaction. The modified sample composed of spherical particles with 3 μm crystal particles on the surface had a para-xylene selectivity of 95% and maintained 79% of the initial conversion after running the reaction for 50 h. This modified sample showed the best stability among the tested three modified samples.展开更多
The SAPO-34 catalyst was fine-tuned with zinc cations through a straightforward template-assisted ion incorporation (TH) process, without the necessary template pre-removal and the preparation of NH4- SAPO-34 intermed...The SAPO-34 catalyst was fine-tuned with zinc cations through a straightforward template-assisted ion incorporation (TH) process, without the necessary template pre-removal and the preparation of NH4- SAPO-34 intermediate, which is more facile, efficient and cost-effective than the conventional ion exchange process. The template-assisted zinc cations incorporated SAPO-34 catalysts were characterized by XRD, XRF, N2 adsorption-desorption, XPS, SEM, EDX,NMR, respectively. Enhanced selectivity to ethylene and ratio of ethylene to propylene in MTO reaction are observed over the zinc cations modified SAPO-34 catalysts, due to the facilitated formation of lower methylbenzenes that favour the ethylene gen eration, as well as the increased diffusion hindrance originated from the zinc cations incorporation and the facil让ated generation of aromatics compound.展开更多
A series of ZnO-ZrO_(2) solid solutions with different Zn contents were synthesized by the urea coprecipitation method,which were coupled with H-ZSM-5 zeolite to form bifunctional catalysts.As a new benzene alkylation...A series of ZnO-ZrO_(2) solid solutions with different Zn contents were synthesized by the urea coprecipitation method,which were coupled with H-ZSM-5 zeolite to form bifunctional catalysts.As a new benzene alkylation reagent,syngas was used instead of methanol to realize the efficient conversion of syngas and benzene into toluene and xylene.A suitable ratio of ZnO-ZrO_(2) led to the significant improvement in the catalytic performance,and a suitable amount of acid helped to increase the selectivity of toluene/xylene and reduce the selectivity of the by-products ethylbenzene and C^(9+) aromatics.The highest benzene conversion of 89.2%and toluene/xylene selectivity of 88.7%were achieved over 10%ZnO-ZrO_(2)&H-ZSM-5(Si/Al=23)at a pressure of 3 MPa and a temperature of 450℃.In addition,the effect of the zeolite framework structure on product distribution was examined.Similar to the molecular dynamics of aromatic hydrocarbons,H-ZSM-5 zeolites comprise 10-membered-ring pores,which are beneficial to the activation of benzene;hence,the conversion of benzene is higher.H-ZSM-35 and HMOR zeolites exhibited small eight-membered-ring channels,which were not conducive to the passage of benzene;hence,the by-product ethylbenzene exhibits a higher selectivity.The distance between the active centers of the bifunctional catalysts was the main factor affecting the catalytic performance,and the powder mixing method was more conducive to the conversion of syngas and benzene.展开更多
Fluoride mediated nano-sized ZSM-5(ZSM-5-F) with a high Si/Al ratio of 181 was fabricated using a seed-induction method and evaluated the catalysis of the methanol to propylene(MTP) reaction. High propylene selectivit...Fluoride mediated nano-sized ZSM-5(ZSM-5-F) with a high Si/Al ratio of 181 was fabricated using a seed-induction method and evaluated the catalysis of the methanol to propylene(MTP) reaction. High propylene selectivity(45%) was similar to ZSM-5-OH synthesized via a hydroxide route. However, ZSM-5-F showed much longer lifetime(305 h) compared with ZSM-5-OH(157 h) in spite of similar crystal size and aluminum content. Characterization by NH_3-TPD, Py-IR, OH-IR, SEM, TG-DTA, XRD and ~1H MAS NMR techniques indicated that the enhanced catalytic performance of ZSM-5-F is attributed to the fewer structural defects in the form of internal silanol groups and silanol nests.展开更多
Nano structure including pore structure and amine assembly is critical for improving sorption and desorption kinetics for adsorptive CO_(2) separation.The present work delineates(1)the influence of the nano-scale pore...Nano structure including pore structure and amine assembly is critical for improving sorption and desorption kinetics for adsorptive CO_(2) separation.The present work delineates(1)the influence of the nano-scale pore structure of amine-functionalized solid sorbents,and(2)effect of changing the assembly of amine molecules on surface of nano-porous SiO_(2) on the rates of adsorption and desorption of CO_(2).50PEI-MSN sorbent with inverted cone-shaped pores was prepared by using mesoporous silica nanospheres(MSN)with inverted cone-shaped pores for the loading of polyethyleneimine(PEI).Co-structure-directing(CSD)method was used to synthesize the sorbent with arranged amine assembly at nano-scale(2N-CSD).By comparison with 50PE卜SBA15 as a benchmark sorbent,both sorbents have improved sorption and desorption kinetics.There are significant effects of nano pore structure and amine assembly on the sorption and desorption kinetics.The inverted cone-shaped pores in MSN allow loading polymeric amines in their narrower ends and leaving larger pore mouths open for the transport of CO_(2);50PEI-MSN shows a maximum sorption rate of 81.4 mg·g^(-1)·min^(-1) with average sorption rate of 25.4mg·g^(-1)·min^(-1) at 80℃ which are 34%and 59%higher than the corresponding values for 50PEI-SBA15;a maximum desorption rate of 38.4mg·g^(-1)·min^(-1) with average desorption rate of 11.8 mg·g^(-1)·min^(-1) ramping from 30 to 95℃ which are 37%and 156%higher than the corresponding values for 50PEI-SBA15.The arranged monolayer-like amine assembly on surface of nanoporous SiO_(2) likely provides high amine sorption sites through improved accessibility of amine,and 2N-CSD shows a maximum sorption rate of 60.5 mg·g^(-1)·min^(-1),with average sorption rate of 12.8mg·g^(-1)·min^(-1) at 300C which are 108%and 205%higher than the corresponding values for 50PEI-SBA15;a lower maximum desorption rate of 9.7 mg g'1min"1 and average desorption rate of 9.8mg·g^(-1)·min^(-1) ramping from 30 to 95℃ which is 250%higher than the corresponding value for 50PEI-SBA15.The present work demonstrates the importance of tailoring nano-scale pore structure and amine assembly for significantly improving sorption and desorption kinetics of adsorptive CO_(2) separation.展开更多
文摘使用来源广泛的甲醇为原料制取丙烯,是对石油路线生产丙烯的重要补充.尽管以ZSM-5分子筛为催化剂的固定床甲醇制丙烯(MTP)技术已经实现了工业应用,但进一步提高催化剂的寿命和丙烯的选择性一直是学术界和工业界的研究热点.MTP过程作为典型的酸催化反应,积碳是催化剂失活的主要原因,由于ZSM-5分子筛十元环孔道的空间限制作用,积碳主要分布在外表面.因此,消除外表面的酸性位点对延长催化剂的寿命至关重要,但修饰外表面酸性位点的同时往往会改变样品的其他性质,如孔径、整体酸量等.本文分别使用Na_2H_2EDTA和H_3PO_4处理高硅ZSM-5分子筛原粉(微孔内含有机模板剂)来选择性地减小或消除外表面的酸密度,而不影响分子筛内部的性质,并考察了处理后样品的MTP性能.使用N_2物理吸附、SEM和^(27)Al MAS NMR表征样品的织构性质、形貌和Al原子的化学环境,XPS和三异丙苯裂解实验表征外表面的硅铝比和酸密度.表征结果表明,Na_2H_2EDTA处理虽然可以选择性的脱除表面Al原子,但会在外表面产生新的酸点(可能是硅巢).H_3PO_4处理虽然不能脱除表面的Al原子,但外表面残留的P物种能够有效的减小酸密度.MTP评价结果表明,H_3PO_4处理能够有效的延长催化剂的寿命和维持丙烯的选择性,这是因为H_3PO_4处理既提高了外表面的容碳能力,也抑制了积碳沉积的速率.Na_2H_2EDTA处理仅能增加外表面的容碳能力,所以其只能延长催化寿命.通过进一步优化H_3PO_4后处理的条件,处理后的ZSM-5样品的催化寿命可以延长至前体的1.5倍,同时,丙烯的选择性也略有提高。
基金supported by the Key Research Program of Frontier Sciences,CAS(QYZDY-SSW-JSC024)the Youth Innovation Promotion Association of the CAS(2014165)the National Natural Science Foundation of China(21603223,21473182,91334205,91545104)~~
文摘A series of ZSM-5 zeolites, with the morphologies of sphere, sphere with cubic particles on the surface, and cubic particles, were synthesized by hydrothermal method using n-butylamine as the template, assisted by the addition of NaCl and crystal seed. X-ray diffraction(XRD),scanning electron microscope(SEM), X-ray fluorescence(XRF) and temperature-programmed desorption of ammonia(NH3-TPD) were used to characterize these samples. The samples were tested with toluene methylation reaction. The modified sample composed of spherical particles with 3 μm crystal particles on the surface had a para-xylene selectivity of 95% and maintained 79% of the initial conversion after running the reaction for 50 h. This modified sample showed the best stability among the tested three modified samples.
基金the National Natural Science Foundation of China(21603223,91745109,91545104,21473182,91334205)the Youth Innovation Promotion Association of the Chinese Academy of Sciences(2014165)for financial support
文摘The SAPO-34 catalyst was fine-tuned with zinc cations through a straightforward template-assisted ion incorporation (TH) process, without the necessary template pre-removal and the preparation of NH4- SAPO-34 intermediate, which is more facile, efficient and cost-effective than the conventional ion exchange process. The template-assisted zinc cations incorporated SAPO-34 catalysts were characterized by XRD, XRF, N2 adsorption-desorption, XPS, SEM, EDX,NMR, respectively. Enhanced selectivity to ethylene and ratio of ethylene to propylene in MTO reaction are observed over the zinc cations modified SAPO-34 catalysts, due to the facilitated formation of lower methylbenzenes that favour the ethylene gen eration, as well as the increased diffusion hindrance originated from the zinc cations incorporation and the facil让ated generation of aromatics compound.
基金financial support from the National Key Research&Development Program of China(2018YFB0604901)the National Natural Science Foundation of China(21706210)the Key Research&Development Program of Shaanxi Province(2020ZDLGY11-06)。
文摘A series of ZnO-ZrO_(2) solid solutions with different Zn contents were synthesized by the urea coprecipitation method,which were coupled with H-ZSM-5 zeolite to form bifunctional catalysts.As a new benzene alkylation reagent,syngas was used instead of methanol to realize the efficient conversion of syngas and benzene into toluene and xylene.A suitable ratio of ZnO-ZrO_(2) led to the significant improvement in the catalytic performance,and a suitable amount of acid helped to increase the selectivity of toluene/xylene and reduce the selectivity of the by-products ethylbenzene and C^(9+) aromatics.The highest benzene conversion of 89.2%and toluene/xylene selectivity of 88.7%were achieved over 10%ZnO-ZrO_(2)&H-ZSM-5(Si/Al=23)at a pressure of 3 MPa and a temperature of 450℃.In addition,the effect of the zeolite framework structure on product distribution was examined.Similar to the molecular dynamics of aromatic hydrocarbons,H-ZSM-5 zeolites comprise 10-membered-ring pores,which are beneficial to the activation of benzene;hence,the conversion of benzene is higher.H-ZSM-35 and HMOR zeolites exhibited small eight-membered-ring channels,which were not conducive to the passage of benzene;hence,the by-product ethylbenzene exhibits a higher selectivity.The distance between the active centers of the bifunctional catalysts was the main factor affecting the catalytic performance,and the powder mixing method was more conducive to the conversion of syngas and benzene.
文摘Fluoride mediated nano-sized ZSM-5(ZSM-5-F) with a high Si/Al ratio of 181 was fabricated using a seed-induction method and evaluated the catalysis of the methanol to propylene(MTP) reaction. High propylene selectivity(45%) was similar to ZSM-5-OH synthesized via a hydroxide route. However, ZSM-5-F showed much longer lifetime(305 h) compared with ZSM-5-OH(157 h) in spite of similar crystal size and aluminum content. Characterization by NH_3-TPD, Py-IR, OH-IR, SEM, TG-DTA, XRD and ~1H MAS NMR techniques indicated that the enhanced catalytic performance of ZSM-5-F is attributed to the fewer structural defects in the form of internal silanol groups and silanol nests.
基金Acknowledgements This work was partially supported by the National Basic Research Program （973 Program） of China （No. 2012CB215500）, the National High-tech R＆D Program（863 Program） of China （No. 2011AA11A273）, and the National Natural Science Foundation of China （NSFC, Nos. 21003114 and 21103163）. The authors thank Professor John A. Shelnutt at Georgia University, USA for fruitful discussions.
基金financially supported by the National Key Research and Development Program of China(No.2016YFB0600902-4)the Fundamental Research Funds for the Central Universities(No.DUT20RC(5)002)the CUHK Research Startup Fund(No.#4930981).
文摘Nano structure including pore structure and amine assembly is critical for improving sorption and desorption kinetics for adsorptive CO_(2) separation.The present work delineates(1)the influence of the nano-scale pore structure of amine-functionalized solid sorbents,and(2)effect of changing the assembly of amine molecules on surface of nano-porous SiO_(2) on the rates of adsorption and desorption of CO_(2).50PEI-MSN sorbent with inverted cone-shaped pores was prepared by using mesoporous silica nanospheres(MSN)with inverted cone-shaped pores for the loading of polyethyleneimine(PEI).Co-structure-directing(CSD)method was used to synthesize the sorbent with arranged amine assembly at nano-scale(2N-CSD).By comparison with 50PE卜SBA15 as a benchmark sorbent,both sorbents have improved sorption and desorption kinetics.There are significant effects of nano pore structure and amine assembly on the sorption and desorption kinetics.The inverted cone-shaped pores in MSN allow loading polymeric amines in their narrower ends and leaving larger pore mouths open for the transport of CO_(2);50PEI-MSN shows a maximum sorption rate of 81.4 mg·g^(-1)·min^(-1) with average sorption rate of 25.4mg·g^(-1)·min^(-1) at 80℃ which are 34%and 59%higher than the corresponding values for 50PEI-SBA15;a maximum desorption rate of 38.4mg·g^(-1)·min^(-1) with average desorption rate of 11.8 mg·g^(-1)·min^(-1) ramping from 30 to 95℃ which are 37%and 156%higher than the corresponding values for 50PEI-SBA15.The arranged monolayer-like amine assembly on surface of nanoporous SiO_(2) likely provides high amine sorption sites through improved accessibility of amine,and 2N-CSD shows a maximum sorption rate of 60.5 mg·g^(-1)·min^(-1),with average sorption rate of 12.8mg·g^(-1)·min^(-1) at 300C which are 108%and 205%higher than the corresponding values for 50PEI-SBA15;a lower maximum desorption rate of 9.7 mg g'1min"1 and average desorption rate of 9.8mg·g^(-1)·min^(-1) ramping from 30 to 95℃ which is 250%higher than the corresponding value for 50PEI-SBA15.The present work demonstrates the importance of tailoring nano-scale pore structure and amine assembly for significantly improving sorption and desorption kinetics of adsorptive CO_(2) separation.
