TY - JOUR
T1 - Control of Ti active-site microenvironment in titanosilicate catalysts and its effect on oxidation pathways
AU - Yu, Yunkai
AU - Wang, Rui
AU - Liu, Wei
AU - Chen, Zhen
AU - Liu, Haoxin
AU - Huang, Xin
AU - Tang, Zhimou
AU - Liu, Yueming
AU - He, Mingyuan
N1 - Publisher Copyright:
© 2020 Elsevier B.V.
PY - 2021/1/25
Y1 - 2021/1/25
N2 - The titanium (Ti) active-site microenvironment in titanosilicates is critical for oxidation performance, since it could influence oxidation pathways of the activation of H2O2, the stability of Ti−OOH species and the transfer ability of active “O” to reactant. Here, four kinds of Ti active sites in MWW-type titanosilicates were designed controllably by acid or alkali treatments, and their influences on oxidation pathways were explored. Through a series of characterizations, these microenvironments were identified, and they present different oxidation activities in this order: Ti(OSi)4(OTiO5)2 << Ti(OSi)4 < Ti(OSi)3OH < Ti(OSi)3OH(HO−Si)n. Ti(OSi)4(OTiO5)2 species cannot activate H2O2 because the framework tetrahedral Ti species in titanosilicates are shielded by extra-framework “OTiO5” (TiO6) species, leading to its inactivation in oxidation reactions. As the acid-treatment process washes off extra-framework TiO6 species, the obtained Ti(OSi)4 species are able to activate H2O2 and present an improved catalytic activity. With prolonging the acid treatment time, the Ti(OSi)3OH species is formed, and its stronger Lewis acidity contributes to the activation of H2O2 for Ti−OOH species formation. Further, upon treatment of Ti-MWW with alkali, the density of Si−OH groups near Ti active sites increases, which promotes the activation of H2O2 and stability of Ti−OOH species, simultaneously. These observations provide new ideas for designing Ti active-site microenvironment, which are expected to contribute significantly to the control of oxidation pathways.
AB - The titanium (Ti) active-site microenvironment in titanosilicates is critical for oxidation performance, since it could influence oxidation pathways of the activation of H2O2, the stability of Ti−OOH species and the transfer ability of active “O” to reactant. Here, four kinds of Ti active sites in MWW-type titanosilicates were designed controllably by acid or alkali treatments, and their influences on oxidation pathways were explored. Through a series of characterizations, these microenvironments were identified, and they present different oxidation activities in this order: Ti(OSi)4(OTiO5)2 << Ti(OSi)4 < Ti(OSi)3OH < Ti(OSi)3OH(HO−Si)n. Ti(OSi)4(OTiO5)2 species cannot activate H2O2 because the framework tetrahedral Ti species in titanosilicates are shielded by extra-framework “OTiO5” (TiO6) species, leading to its inactivation in oxidation reactions. As the acid-treatment process washes off extra-framework TiO6 species, the obtained Ti(OSi)4 species are able to activate H2O2 and present an improved catalytic activity. With prolonging the acid treatment time, the Ti(OSi)3OH species is formed, and its stronger Lewis acidity contributes to the activation of H2O2 for Ti−OOH species formation. Further, upon treatment of Ti-MWW with alkali, the density of Si−OH groups near Ti active sites increases, which promotes the activation of H2O2 and stability of Ti−OOH species, simultaneously. These observations provide new ideas for designing Ti active-site microenvironment, which are expected to contribute significantly to the control of oxidation pathways.
KW - Acid or alkali treatment
KW - Oxidation pathway
KW - Si−OH species
KW - Ti active-site microenvironment
KW - Titanosilicate
UR - https://www.scopus.com/pages/publications/85097753562
U2 - 10.1016/j.apcata.2020.117953
DO - 10.1016/j.apcata.2020.117953
M3 - 文章
AN - SCOPUS:85097753562
SN - 0926-860X
VL - 610
JO - Applied Catalysis A: General
JF - Applied Catalysis A: General
M1 - 117953
ER -