Synthesis, Characterization, and Catalytic Activity of Mesostructured Titanosilicates Assembled from Polymer Surfactants with Preformed Titanosilicate Precursors in Strongly Acidic Media

Abstract

Novel mesostructured titanosilicates designated as MTS-9 have been successfully synthesized from assembly of preformed nanosized titanosilicate precursors with polymer surfactants. Mesoporous MTS-9 shows highly hydrothermal stability in boiling water (over 120 h) as compared with that of Ti−MCM-41 and SBA-15. In phenol hydroxylation, Ti−MCM-41 shows very low catalytic activity (2.5%), but MTS-9 exhibits very high catalytic activity, with phenol conversion of 26%, which is comparable with TS-1. In styrene epoxidation, MTS-9 shows high activity and selectivity similar to those of TS-1, which are much different from those of Ti−MCM-41. In 2,3,6-trimethylphenol hydroxylation, Ti−MCM-41 is inactive because of the relatively low oxidation ability of Ti species in the amorphous wall of Ti−MCM-41, and TS-1 is also inactive because of the inaccessibility of the small micropores of TS-1 to the large diameter of a bulky molecule like 2,3,6-trimethylphenol. However, MTS-9 is very active for this reaction with conversion of 18.8% indicating that MTS-9 is an effective catalyst for the oxidation of bulky molecules. The MTS-9 samples were characterized with infrared, UV−visible, UV−Raman, and numerous other techniques. The results suggest that the titanium species in MTS-9 are TS-1-like, and that the pore walls of MTS-9 contains primary and secondary structural building units, similar to those of microporous zeolites. Such unique structural features might be responsible for the observed strong oxidation ability and high hydrothermal stability of the mesostructured titanosilicates. Heating MTS-9 at 500 °C leads to the transformation of titanium species, giving relatively low catalytic conversion in phenol hydroxylation, which suggests that increasing thermal stability of titanium sites like TS-1 species in the mesoporous wall is still a great task for preparation of mesostructured titanosilicates.

Desilication of TS-1 zeolite for the oxidation of bulky molecules

“…As previously reported [9][10][11][12][13][14][15][16][17][18][19], silicon is preferentially extracted into solution upon alkaline treatment while Al in ZSM-5 or Ti in the case of TS-1 remains in the solid. Along this manuscript, we address the effect of different alkaline treatments on the physical properties (porosity and crystallinity) and the catalytic behavior of desilicated TS-1 zeolites in the oxidation of small and bulky molecules.…”

“…A reported synthesis of TS-1 type zeolite [19] was judiciously adapted for the synthesis of a TS-1 titanosilicalite with 4 wt.% titania. In a typical run, 7.5 ml of TPAOH (tetrapropylammoniumhydroxide, 1.0M aqueous solution, Aldrich) were mixed with 10.5 ml of distilled water.…”

New Insights in the Formation of Combined Zeolitic/Mesoporous Materials by using a One‐Pot Templating Synthesis

“…[7] In the TS-1 zeolite synthesis, part of the zeolite structure directing agent (TPAOH) was replaced by a mesopore templating agent (CTMABr). The molar ratio of micro-and mesotemplate was 1:1 (50 % TPAOH / 50 % CTMABr) in all the syntheses, unless stated differently.…”

“…The TS-1 synthesis was applied [7] without addition of a mesotemplate, followed by a HT. These TS-1 zeolites are denoted as TS-1-xd-y°C-z%, whereby x represents the duration of the HT in days, y the temperature of the HT and z the amount of added TPAOH in molar percentage (100 % means 1 TBOT / 30 TEOS / 8 TPAOH / 1050 H 2 O, whereas 50% is 1 TBOT / 30 TEOS / 4 TPAOH / 1050 H 2 O).…”

“…Moreover, it is also unclear whether more exotic and expensive templates, such as silylated surfactants, are a necessity to achieve "true" hierarchical mesoporous zeolites. [6] In this report, we discuss the results of investigating the zeolitic growth and the formation of the mesoporous structure by applying a one-pot templating synthesis, based on a TS-1 zeolite recipe, [7] using a micro-and a mesotemplate (TPAOH and CTMABr, respectively). All materials were thoroughly characterised by a wide range of techniques, namely N 2 sorption, thermogravimetric analysis, FTIR and UV/Vis (DR) spectroscopy, XRD, elemental analysis and TEM.…”