Do titanyl groups exist in titanium silicates? An experimental study

Mark Crocker; Ruud H.M. Herold; Bert G. Roosenbrand; Kees A. Emeis; Antonio E. Wilson

doi:10.1016/S0927-7757(98)00371-9

Do titanyl groups exist in titanium silicates? An experimental study

Mark Crocker, Ruud H.M. Herold, Bert G. Roosenbrand, Kees A. Emeis, Antonio E. Wilson

Research output: Contribution to journal › Article › peer-review

8 Scopus citations

Abstract

Two synthetic routes have been investigated, aimed at the preparation of silica-supported titanyl (>Ti=O) and titanol (>Ti(OH)₂) groups, the latter corresponding to the hydrated form of the titanyl group. In the first synthetic route, the titanyl complex TiOCl₂(NMe₃)₂ was reacted with an aerosil, and the resulting material thermally treated to remove residual Cl and NMe₃ ligands. In an alternative route, silica (aerosil and silica-gel) was reacted with Ti(CH₂Ph)₄ to afford mainly anchored >Ti(CH₂Ph)₂ moieties, which were subsequently hydrolysed. Characterization of the resulting materials using a combination of surface analytical techniques revealed that in all cases at least two titania phases were obtained, corresponding to isolated tetrahedral Ti sites, and an amorphous form of TiO₂ containing six-coordinate titanium. For the syntheses based on Ti(CH₂Ph)₄, UV-vis and XPS data indicated that the relative proportion of the two phases formed was dependent on the support employed, aerosil affording predominantly (≡SiO)₂Ti(OH)₂ sites. No evidence was found for the presence of three-coordinate titanyl species, >Ti=O, even when the aerosil-supported ₂Ti(OH)₂ sites were calcined at 500°C. It is, therefore, concluded that titanyl groups are unlikely to be present in significant concentrations in titanium silicates. When tested in the epoxidation of 1-octene with terl-butyl hydroperoxide, the model systems were found to display epoxidation activity comparable with that of a wide-pore Ti-zeolite, Ti-MCM-41. The observed turnover frequency was found to increase with increasing dispersion of the titania, consistent with the notion that isolated, Lewis acidic Ti(IV) centres are the most active sites for epoxidation catalysis.

Original language	English
Pages (from-to)	351-368
Number of pages	18
Journal	Colloids and Surfaces A: Physicochemical and Engineering Aspects
Volume	139
Issue number	3
DOIs	https://doi.org/10.1016/S0927-7757(98)00371-9
State	Published - Sep 1 1998

Keywords

Catalyst
Epoxidation
Titania
Titanium silicates
Titanyl

ASJC Scopus subject areas

Surfaces and Interfaces
Physical and Theoretical Chemistry
Colloid and Surface Chemistry

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10.1016/S0927-7757(98)00371-9

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@article{99112b89584f47779f1a5a95633532d0,

title = "Do titanyl groups exist in titanium silicates? An experimental study",

abstract = "Two synthetic routes have been investigated, aimed at the preparation of silica-supported titanyl (>Ti=O) and titanol (>Ti(OH)2) groups, the latter corresponding to the hydrated form of the titanyl group. In the first synthetic route, the titanyl complex TiOCl2(NMe3)2 was reacted with an aerosil, and the resulting material thermally treated to remove residual Cl and NMe3 ligands. In an alternative route, silica (aerosil and silica-gel) was reacted with Ti(CH2Ph)4 to afford mainly anchored >Ti(CH2Ph)2 moieties, which were subsequently hydrolysed. Characterization of the resulting materials using a combination of surface analytical techniques revealed that in all cases at least two titania phases were obtained, corresponding to isolated tetrahedral Ti sites, and an amorphous form of TiO2 containing six-coordinate titanium. For the syntheses based on Ti(CH2Ph)4, UV-vis and XPS data indicated that the relative proportion of the two phases formed was dependent on the support employed, aerosil affording predominantly (≡SiO)2Ti(OH)2 sites. No evidence was found for the presence of three-coordinate titanyl species, >Ti=O, even when the aerosil-supported 2Ti(OH)2 sites were calcined at 500°C. It is, therefore, concluded that titanyl groups are unlikely to be present in significant concentrations in titanium silicates. When tested in the epoxidation of 1-octene with terl-butyl hydroperoxide, the model systems were found to display epoxidation activity comparable with that of a wide-pore Ti-zeolite, Ti-MCM-41. The observed turnover frequency was found to increase with increasing dispersion of the titania, consistent with the notion that isolated, Lewis acidic Ti(IV) centres are the most active sites for epoxidation catalysis.",

keywords = "Catalyst, Epoxidation, Titania, Titanium silicates, Titanyl",

author = "Mark Crocker and Herold, {Ruud H.M.} and Roosenbrand, {Bert G.} and Emeis, {Kees A.} and Wilson, {Antonio E.}",

year = "1998",

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doi = "10.1016/S0927-7757(98)00371-9",

language = "English",

volume = "139",

pages = "351--368",

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TY - JOUR

T1 - Do titanyl groups exist in titanium silicates? An experimental study

AU - Crocker, Mark

AU - Herold, Ruud H.M.

AU - Roosenbrand, Bert G.

AU - Emeis, Kees A.

AU - Wilson, Antonio E.

PY - 1998/9/1

Y1 - 1998/9/1

N2 - Two synthetic routes have been investigated, aimed at the preparation of silica-supported titanyl (>Ti=O) and titanol (>Ti(OH)2) groups, the latter corresponding to the hydrated form of the titanyl group. In the first synthetic route, the titanyl complex TiOCl2(NMe3)2 was reacted with an aerosil, and the resulting material thermally treated to remove residual Cl and NMe3 ligands. In an alternative route, silica (aerosil and silica-gel) was reacted with Ti(CH2Ph)4 to afford mainly anchored >Ti(CH2Ph)2 moieties, which were subsequently hydrolysed. Characterization of the resulting materials using a combination of surface analytical techniques revealed that in all cases at least two titania phases were obtained, corresponding to isolated tetrahedral Ti sites, and an amorphous form of TiO2 containing six-coordinate titanium. For the syntheses based on Ti(CH2Ph)4, UV-vis and XPS data indicated that the relative proportion of the two phases formed was dependent on the support employed, aerosil affording predominantly (≡SiO)2Ti(OH)2 sites. No evidence was found for the presence of three-coordinate titanyl species, >Ti=O, even when the aerosil-supported 2Ti(OH)2 sites were calcined at 500°C. It is, therefore, concluded that titanyl groups are unlikely to be present in significant concentrations in titanium silicates. When tested in the epoxidation of 1-octene with terl-butyl hydroperoxide, the model systems were found to display epoxidation activity comparable with that of a wide-pore Ti-zeolite, Ti-MCM-41. The observed turnover frequency was found to increase with increasing dispersion of the titania, consistent with the notion that isolated, Lewis acidic Ti(IV) centres are the most active sites for epoxidation catalysis.

AB - Two synthetic routes have been investigated, aimed at the preparation of silica-supported titanyl (>Ti=O) and titanol (>Ti(OH)2) groups, the latter corresponding to the hydrated form of the titanyl group. In the first synthetic route, the titanyl complex TiOCl2(NMe3)2 was reacted with an aerosil, and the resulting material thermally treated to remove residual Cl and NMe3 ligands. In an alternative route, silica (aerosil and silica-gel) was reacted with Ti(CH2Ph)4 to afford mainly anchored >Ti(CH2Ph)2 moieties, which were subsequently hydrolysed. Characterization of the resulting materials using a combination of surface analytical techniques revealed that in all cases at least two titania phases were obtained, corresponding to isolated tetrahedral Ti sites, and an amorphous form of TiO2 containing six-coordinate titanium. For the syntheses based on Ti(CH2Ph)4, UV-vis and XPS data indicated that the relative proportion of the two phases formed was dependent on the support employed, aerosil affording predominantly (≡SiO)2Ti(OH)2 sites. No evidence was found for the presence of three-coordinate titanyl species, >Ti=O, even when the aerosil-supported 2Ti(OH)2 sites were calcined at 500°C. It is, therefore, concluded that titanyl groups are unlikely to be present in significant concentrations in titanium silicates. When tested in the epoxidation of 1-octene with terl-butyl hydroperoxide, the model systems were found to display epoxidation activity comparable with that of a wide-pore Ti-zeolite, Ti-MCM-41. The observed turnover frequency was found to increase with increasing dispersion of the titania, consistent with the notion that isolated, Lewis acidic Ti(IV) centres are the most active sites for epoxidation catalysis.

KW - Catalyst

KW - Epoxidation

KW - Titania

KW - Titanium silicates

KW - Titanyl

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U2 - 10.1016/S0927-7757(98)00371-9

DO - 10.1016/S0927-7757(98)00371-9

M3 - Article

AN - SCOPUS:0032171163

SN - 0927-7757

VL - 139

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EP - 368

JO - Colloids and Surfaces A: Physicochemical and Engineering Aspects

JF - Colloids and Surfaces A: Physicochemical and Engineering Aspects

IS - 3

ER -

Do titanyl groups exist in titanium silicates? An experimental study

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