Effect of the grafting agent on the structure and catalytic performance of Ti-MCM-22

Abstract

Ti-MCM-22 prepared by grafting with Ti(OEt)4 has more Ti(iv) at Td sites than those prepared with Ti(OPr)4 and Ti(OBu)4, and gives higher catalytic activities in cyclohexene and cyclooctene epoxidation using t-butylhydrogen peroxide as the oxidant.

Nanosponge TS‐1: A Fully Crystalline Hierarchical Epoxidation Catalyst

“…The band centered at 205 nm is typical of a 4‐coordinated Ti(OSi) 4 framework species (sometimes denoted as “closed sites”), while the band at 330 nm indicates the presence of anatase‐like TiO 2 domains, with bands of “open sites”(Ti(OSi) 3 (OH), 230 nm) and 5‐ and 6‐coordinated isolated framework‐attached titanium species (e.g., Ti(OH)(H 2 O)(OSi) 3 or Ti(OH) 2 (H 2 O) 2 (OSi) 2 ; [ 4c,34 ] bands at 260–290 nm) between those two border bands. [ 4c ] Excluding anatase‐like species, all others can contribute to the catalytic activity in epoxidation [ 13a,34,35 ] and other selective oxidation reactions, [ 21b ] although their mechanism remains controversial. [ 36 ] In addition, neighboring silanol groups may, in specific cases, such as phenol hydroxylation, contribute to transition state stabilization and thus further promote selective oxidation.…”

“…[ 36 ] In addition, neighboring silanol groups may, in specific cases, such as phenol hydroxylation, contribute to transition state stabilization and thus further promote selective oxidation. [ 21b ] The benchmark catalyst conventional 3D TS‐1 contains exclusively framework 4‐coordinated Ti‐species (band maximum observed at 204 nm), while the TS‐1‐PITi 30 contains a considerable share of single titanium atom extra‐framework species ( Figure ) because additional titanium is introduced into the structure during silica–titania pillaring (broad adsorption at 230–300 nm). [ 13a,18 ] When decreasing the Ti content of both the parent nanosheet TS‐1 and the pillaring mixture (TS‐1‐PITi 53), absorption above 230 nm also decreased.…”

“…[ 17 ] TS‐1 nanosheets can be prepared using a diquarternary ammonium surfactant template with OH − counter‐anions (C 16 H 33 N + (CH 3 ) 2 C 6 H 12 N + (CH 3 ) 2 C 6 H 13 ; C 16‐6‐6 ). Moreover, their catalytic properties can be improved by treatment with a diluted NH 4 F solution, [ 16 ] by silica–titania pillaring [ 18 ] or by grafting with titanium butoxide, [ 19 ] Ti‐cyclopentadienyl complexes, [ 20 ] or TiCl 4 [ 21 ] to create additional titanium sites on the external surface. In particular, silica–titania pillared MFI nanosheets catalyze not only the epoxidation of CC double bonds [ 18 ] and the oxidation of sulfides to sulfoxides [ 22 ] but also the photocatalytic degradation of organic compounds in water.…”

Improving Ti Incorporation into the BEA Framework by Employing Ethoxylated Chlorotitanate as Ti Precursor: Postsynthesis, Characterization, and Incorporation Mechanism

“…This indicates the Ti species concentration on the zeolite surface, and it might be ascribed to the steric hindrance of TEOT. 13,37,38 As we reperformed the synthesis of the Ti-β-TEOT sample under N 2 atmosphere at a pressure of 0.5 MPa, the surface Si/Ti ratio rose up to 63.9. Ti-β-D exhibits the surface Si/Ti ratio of 54 (Table 1, entry 4), indicating an improved diffusibility of Cp 2 TiCl 2 through the zeolite pore system.…”

“…Further, in order to maintain the original structure of Ti precursor and avoid reactions between Ti precursor and solvent, usually TiCl 4 is dissolved in aprotic solvent such as DCM or toluene, 12,22,23 and TEOT is dissolved in ethanol. 13,14,24 However, little research has been done to explain the structure and influence of Ti precursor on Ticontaining zeolite for the postsynthesis method, and a more effective Ti-β zeolite postsynthesis strategy is desired to be developed.…”