Nanosized hierarchical zeolites are desirable for the reduction of diffusion limitations in catalysis.Herein,we report a cost-effective strategy for the synthesis of nanosized germanosilicate ITQ-21 zeolites with abun...Nanosized hierarchical zeolites are desirable for the reduction of diffusion limitations in catalysis.Herein,we report a cost-effective strategy for the synthesis of nanosized germanosilicate ITQ-21 zeolites with abundant intracrystalline meso/macropores upon modulating zeolite crystallization.Using quaternary ammonium N-cyclohexyl-N,N-dimethylcyclohexanaminium hydroxide as the organic structure-directing agent,nanosized hierarchical ITQ-21 zeolites have been successfully prepared in a concentrated gel system free of any mesoporogen or seed crystals.A possible mechanism based on aggregation followed by a ripening process is proposed.The as-prepared nanosized hierarchical Al-ITQ-21 zeolites show good catalytic activity for the acetal reaction of converting bulky substrates.This work provides a facile route upon modulating crystallization to generate intracrystalline mesopores in zeolite catalysts.展开更多
Single-crystalline hierarchical zeolites possess fast mass transfer,good active site accessibility,and enhanced hydrothermal stability for improved catalytic performance,which are highly desired in petro-,coal-,and fi...Single-crystalline hierarchical zeolites possess fast mass transfer,good active site accessibility,and enhanced hydrothermal stability for improved catalytic performance,which are highly desired in petro-,coal-,and fine-chemical industries.Here,we for the first time report the mesoporogen-free synthesis of single-crystalline hierarchical Beta nanozeolites,which is achieved by L-lysine-assisted regulation of zeolite growth kinetics in a two-step crystallization process.In this strategy,at low crystallization temperatures,L-lysine molecules could efficiently chelate with both silica and aluminum species,which leads to the aggregation of amorphous aluminosilicate gel particles in a non-compact manner towards forming interstitial pores.At subsequently elevated temperatures,intraparticle ripening becomes the predominant crystal growth behavior,where adjacent nanoparticles coalesce into larger ones coupled with the transformation of the initial interstitial pores into the final intracrystalline mesopores.The as-prepared hierarchical Beta nanozeolite(sample meso-Beta-23)shows a large surface area(617 m^(2)g^(-1))and a large mesopore volume(0.79 cm^(3) g^(-1)),as well as a single-crystalline feature,thus exhibiting improved properties in both gas-and liquid-phase catalytic reactions,including cracking of 1,3,5-trimethylbenzene to produce benzene,toluene,and xylene(BTX)(26.1%BTX selectivity);ethylation of benzene to produce ethylbenzene(73%ethylbenzene selectivity);and conversion of highly concentrated lactic acid(105 wt%)to produce lactide(73% lactide yield)compared to their conventional counterparts.Such high-quality singlecrystalline hierarchical Beta nanozeolites may be promising for industrial applications in the conversion of various bulky feedstocks into value-added products.展开更多
基金the National Natural Science Foundation of China(Grant 21871104,21835002 and 21621001)the National Key Research and Development Program of China(Grant 2016YFB0701100)the 111 Project(B17020)for supporting this work.
文摘Nanosized hierarchical zeolites are desirable for the reduction of diffusion limitations in catalysis.Herein,we report a cost-effective strategy for the synthesis of nanosized germanosilicate ITQ-21 zeolites with abundant intracrystalline meso/macropores upon modulating zeolite crystallization.Using quaternary ammonium N-cyclohexyl-N,N-dimethylcyclohexanaminium hydroxide as the organic structure-directing agent,nanosized hierarchical ITQ-21 zeolites have been successfully prepared in a concentrated gel system free of any mesoporogen or seed crystals.A possible mechanism based on aggregation followed by a ripening process is proposed.The as-prepared nanosized hierarchical Al-ITQ-21 zeolites show good catalytic activity for the acetal reaction of converting bulky substrates.This work provides a facile route upon modulating crystallization to generate intracrystalline mesopores in zeolite catalysts.
基金the National Key Research and Development Program of China(Grant 2021YFA1501202)the National Natural Science Foundation of China(Grant 21920102005,21835002 and 21621001)+1 种基金the 111 Project(B17020)for supporting this workThe Centre for High-resolution Electron Microscopy(CħEM),supported by SPST of ShanghaiTech University under contract EM02161943,is acknowledged for its help in electron microscopy.
文摘Single-crystalline hierarchical zeolites possess fast mass transfer,good active site accessibility,and enhanced hydrothermal stability for improved catalytic performance,which are highly desired in petro-,coal-,and fine-chemical industries.Here,we for the first time report the mesoporogen-free synthesis of single-crystalline hierarchical Beta nanozeolites,which is achieved by L-lysine-assisted regulation of zeolite growth kinetics in a two-step crystallization process.In this strategy,at low crystallization temperatures,L-lysine molecules could efficiently chelate with both silica and aluminum species,which leads to the aggregation of amorphous aluminosilicate gel particles in a non-compact manner towards forming interstitial pores.At subsequently elevated temperatures,intraparticle ripening becomes the predominant crystal growth behavior,where adjacent nanoparticles coalesce into larger ones coupled with the transformation of the initial interstitial pores into the final intracrystalline mesopores.The as-prepared hierarchical Beta nanozeolite(sample meso-Beta-23)shows a large surface area(617 m^(2)g^(-1))and a large mesopore volume(0.79 cm^(3) g^(-1)),as well as a single-crystalline feature,thus exhibiting improved properties in both gas-and liquid-phase catalytic reactions,including cracking of 1,3,5-trimethylbenzene to produce benzene,toluene,and xylene(BTX)(26.1%BTX selectivity);ethylation of benzene to produce ethylbenzene(73%ethylbenzene selectivity);and conversion of highly concentrated lactic acid(105 wt%)to produce lactide(73% lactide yield)compared to their conventional counterparts.Such high-quality singlecrystalline hierarchical Beta nanozeolites may be promising for industrial applications in the conversion of various bulky feedstocks into value-added products.
