NaA zeolite(Si/Al=1.00)has been commercially applied for capturing radioactive 90Sr^(2+)because of its high surface charge density,effectively stabilizing the multivalent cation.However,owing to its narrow micropore o...NaA zeolite(Si/Al=1.00)has been commercially applied for capturing radioactive 90Sr^(2+)because of its high surface charge density,effectively stabilizing the multivalent cation.However,owing to its narrow micropore opening(4.0Å),large micron-sized crystallites,and bulkiness of hydrated Sr^(2+),the Sr^(2+)exchange over NaA has been limited by very slow kinetics.In this study,we synthesized nanocrystalline low-silica X by minimizing a water content in a synthesis gel and utilizing a methyl cellulose hydrogel as a crystal growth inhibitor.The resulting zeolite exhibited high crystallinity and Al-rich framework(Si/Al of approximately 1.00)with the sole presence of tetrahedral Al sites,which are capable of high Sr^(2+)uptake and ion selectivity.Meanwhile,the zeolite with a FAU topology has a much larger micropore opening size(7.4Å)and a much smaller crystallite size(~340 nm)than NaA,which enable significantly enhanced ion-exchange kinetics.Compared to conventional NaA,the nanocrystalline low-silica X exhibited remarkably increased Sr^(2+)-exchange kinetics(>18-fold larger rate constant)in batch experiments.Although both the nanocrystalline low-silica X and NaA exhibited comparable Sr^(2+)capacities under equilibrated conditions,the former demonstrated a 5.5-fold larger breakthrough volume than NaA under dynamic conditions,attributed to its significantly faster Sr^(2+)-exchange kinetics.展开更多
Hydrogen(H)spillover in nonreducible oxides such as zeolites and Al2O3 has been a highly controversial phenomenon in heterogeneous catalysis.Since industrial catalysts are predominantly prepared using these materials ...Hydrogen(H)spillover in nonreducible oxides such as zeolites and Al2O3 has been a highly controversial phenomenon in heterogeneous catalysis.Since industrial catalysts are predominantly prepared using these materials as supports,it is important to understand the mechanism and catalytic functions of H spillover on their surfaces.In the past decade,fundamental studies on zeolite-encapsulated metal catalysts have revealed that H spillover and reverse spillover can be utilized in the design of hydrogenation and dehydrogenation catalysts with improved properties.Both experimental and theoretical studies have indicated that H spillover can occur in nonreducible oxides when they possess substantial acid sites that aid the surface migration of active H.In the present review,we will discuss the possible mechanisms of H spillover in nonreducible oxides and the unique opportunities of using this phenomenon for the design of advanced hydroprocessing catalysts.展开更多
基金supported by the institute of Civil Miltary Technology cooperation funded by the Defense Acquisition Program Administration and Ministry of Trade,Industry and Energy of Korea Government under grant No.22-CM-BR-14.
文摘NaA zeolite(Si/Al=1.00)has been commercially applied for capturing radioactive 90Sr^(2+)because of its high surface charge density,effectively stabilizing the multivalent cation.However,owing to its narrow micropore opening(4.0Å),large micron-sized crystallites,and bulkiness of hydrated Sr^(2+),the Sr^(2+)exchange over NaA has been limited by very slow kinetics.In this study,we synthesized nanocrystalline low-silica X by minimizing a water content in a synthesis gel and utilizing a methyl cellulose hydrogel as a crystal growth inhibitor.The resulting zeolite exhibited high crystallinity and Al-rich framework(Si/Al of approximately 1.00)with the sole presence of tetrahedral Al sites,which are capable of high Sr^(2+)uptake and ion selectivity.Meanwhile,the zeolite with a FAU topology has a much larger micropore opening size(7.4Å)and a much smaller crystallite size(~340 nm)than NaA,which enable significantly enhanced ion-exchange kinetics.Compared to conventional NaA,the nanocrystalline low-silica X exhibited remarkably increased Sr^(2+)-exchange kinetics(>18-fold larger rate constant)in batch experiments.Although both the nanocrystalline low-silica X and NaA exhibited comparable Sr^(2+)capacities under equilibrated conditions,the former demonstrated a 5.5-fold larger breakthrough volume than NaA under dynamic conditions,attributed to its significantly faster Sr^(2+)-exchange kinetics.
基金supported by the Basic Science Research Program of the National Research Foundation of Korea(No.NRF-2020R1A2C3003694)the KAIST Cross-Generation Collaborative Lab Project.
文摘Hydrogen(H)spillover in nonreducible oxides such as zeolites and Al2O3 has been a highly controversial phenomenon in heterogeneous catalysis.Since industrial catalysts are predominantly prepared using these materials as supports,it is important to understand the mechanism and catalytic functions of H spillover on their surfaces.In the past decade,fundamental studies on zeolite-encapsulated metal catalysts have revealed that H spillover and reverse spillover can be utilized in the design of hydrogenation and dehydrogenation catalysts with improved properties.Both experimental and theoretical studies have indicated that H spillover can occur in nonreducible oxides when they possess substantial acid sites that aid the surface migration of active H.In the present review,we will discuss the possible mechanisms of H spillover in nonreducible oxides and the unique opportunities of using this phenomenon for the design of advanced hydroprocessing catalysts.
