Direct synthesis of hydrogen peroxide(DSHP)was studied over Pd loaded on HZSM-5 nanosheets(Pd/ZN).Pd nanoparticles with average size of ca.4.3 nm were introduced into the adjacent nanosheet layers(thickness of ca.2.9 ...Direct synthesis of hydrogen peroxide(DSHP)was studied over Pd loaded on HZSM-5 nanosheets(Pd/ZN).Pd nanoparticles with average size of ca.4.3 nm were introduced into the adjacent nanosheet layers(thickness of ca.2.9 nm)by impregnation method.Pd/ZN with theoretical Si/Al molar ratio of 25 showed the highest selectivity for H2O2 among the prepared catalysts,together with highest formation rate of H2O2(38.0 mmol·(g cat)^-1·h^-1),1.9 times than that of Pd supported on conventional HZSM-5 zeolite(Pd/CZ-50).Better catalytic performance of nanosheet catalysts was attributed to the promoted Pd dispersion which promoted H2 dissociation,more BrΦnsted acid sites and stronger metal-support interaction which inhibited the dissociation of O-O bond in H2O2.The embedded structure sufficiently protected the Pd nanoparticles by space confinement which restrained the Pd leaching,leading to a better catalytic stability with 90%activity retained after 3 cycles,which was almost 3 times than that of Pd/CZ-50(30.4%activity retained).展开更多
A series of triphenylethoxysilane(TPEOS)-modified nanosheet HZSM-5 catalysts(ZN-x,x=4%,8%and16%,mass)were synthesized by chemical liquid deposition to selectively change external acidity distributions.TPEOS modificati...A series of triphenylethoxysilane(TPEOS)-modified nanosheet HZSM-5 catalysts(ZN-x,x=4%,8%and16%,mass)were synthesized by chemical liquid deposition to selectively change external acidity distributions.TPEOS modification was found to passivate some external Br?nsted and Lewis acid sites by37.8%,in which Br?nsted acid sites(BAS)were found more easily sacrificed by breaking the surface Al AO bond of bridging hydroxyl groups and forming Si AOASi bonds.The selectivity of ZN-8 catalyst for light olefins(ethylene,propylene and butene)in n-decane catalytic cracking is up to 26%(450℃,WHSV=10.95 h^(-1)),which is ca.78%higher than that of parent one.The better performance was attributed to the appropriate external acid density in ZN-8,which inhibits bimolecular hydrogen transfer reaction of light olefins on the adjacent acid sites,resulting in more olefins,few coke precursors and thus an excellent catalytic stability.展开更多
Direct synthesis of hydrogen peroxide from hydrogen and oxide(DSHP)is considered as a green pathway for H2O2 production because of the simple reaction route and 100%theoretical atom efficiency.Here,1.5 wt%Pd and 0.5 w...Direct synthesis of hydrogen peroxide from hydrogen and oxide(DSHP)is considered as a green pathway for H2O2 production because of the simple reaction route and 100%theoretical atom efficiency.Here,1.5 wt%Pd and 0.5 wt%Au were loaded on HZSM-5 nanosheets through sequential isovolumetric impregnation.TEM images and CO-TPD curves showed that Pd nanosheets were successfully synthesized between HZSM-5 nanosheets under zeolite confinement effect,and Au particles were loaded on the edge of Pd nanosheets and formed a structure that Pd nanosheets with edge decorated by Au nanoparticles(Au–Pd/ZN).The results showed that the selectivity for H2O2 could be reached around 60%in a 30 min reaction and the initial H2O2 productivity could reach 338.5 mmol gcat1 h1 on the Au–Pd/ZN catalyst.The enhanced selectivity and productivity could be related with high content of terrace sites and Au particles on the step sites of bimetallic nanosheets,in which both the terrace sites and the step sites replaced by Au particles showed higher dissociation activation energy for breaking the O–O bond than traditional step sites on Pd particles,inhibited the by-product reactions(2H2O2→2H2OþO2,2H2þO2→2H2O).展开更多
基金Financial supports by the National Natural Science Foundation of China(21776210)Science and Technology Research Project of Henan Province(No.202102210048)。
文摘Direct synthesis of hydrogen peroxide(DSHP)was studied over Pd loaded on HZSM-5 nanosheets(Pd/ZN).Pd nanoparticles with average size of ca.4.3 nm were introduced into the adjacent nanosheet layers(thickness of ca.2.9 nm)by impregnation method.Pd/ZN with theoretical Si/Al molar ratio of 25 showed the highest selectivity for H2O2 among the prepared catalysts,together with highest formation rate of H2O2(38.0 mmol·(g cat)^-1·h^-1),1.9 times than that of Pd supported on conventional HZSM-5 zeolite(Pd/CZ-50).Better catalytic performance of nanosheet catalysts was attributed to the promoted Pd dispersion which promoted H2 dissociation,more BrΦnsted acid sites and stronger metal-support interaction which inhibited the dissociation of O-O bond in H2O2.The embedded structure sufficiently protected the Pd nanoparticles by space confinement which restrained the Pd leaching,leading to a better catalytic stability with 90%activity retained after 3 cycles,which was almost 3 times than that of Pd/CZ-50(30.4%activity retained).
基金Financial supports by the National Natural Science Foundation of China(21776210 and 22008055)。
文摘A series of triphenylethoxysilane(TPEOS)-modified nanosheet HZSM-5 catalysts(ZN-x,x=4%,8%and16%,mass)were synthesized by chemical liquid deposition to selectively change external acidity distributions.TPEOS modification was found to passivate some external Br?nsted and Lewis acid sites by37.8%,in which Br?nsted acid sites(BAS)were found more easily sacrificed by breaking the surface Al AO bond of bridging hydroxyl groups and forming Si AOASi bonds.The selectivity of ZN-8 catalyst for light olefins(ethylene,propylene and butene)in n-decane catalytic cracking is up to 26%(450℃,WHSV=10.95 h^(-1)),which is ca.78%higher than that of parent one.The better performance was attributed to the appropriate external acid density in ZN-8,which inhibits bimolecular hydrogen transfer reaction of light olefins on the adjacent acid sites,resulting in more olefins,few coke precursors and thus an excellent catalytic stability.
基金supports by the National Natural Science Foundation of China(21776210)are gratefully acknowledged.
文摘Direct synthesis of hydrogen peroxide from hydrogen and oxide(DSHP)is considered as a green pathway for H2O2 production because of the simple reaction route and 100%theoretical atom efficiency.Here,1.5 wt%Pd and 0.5 wt%Au were loaded on HZSM-5 nanosheets through sequential isovolumetric impregnation.TEM images and CO-TPD curves showed that Pd nanosheets were successfully synthesized between HZSM-5 nanosheets under zeolite confinement effect,and Au particles were loaded on the edge of Pd nanosheets and formed a structure that Pd nanosheets with edge decorated by Au nanoparticles(Au–Pd/ZN).The results showed that the selectivity for H2O2 could be reached around 60%in a 30 min reaction and the initial H2O2 productivity could reach 338.5 mmol gcat1 h1 on the Au–Pd/ZN catalyst.The enhanced selectivity and productivity could be related with high content of terrace sites and Au particles on the step sites of bimetallic nanosheets,in which both the terrace sites and the step sites replaced by Au particles showed higher dissociation activation energy for breaking the O–O bond than traditional step sites on Pd particles,inhibited the by-product reactions(2H2O2→2H2OþO2,2H2þO2→2H2O).
