Enhanced Catalytic Oxidation by Hierarchically Structured TS-1 Zeolite

Abstract

A TS-1 zeolite with a disordered network of mesopores penetrating the microporous crystalline zeolite framework was successfully synthesized by a one-pot carbon hard-templating synthesis approach. Besides conventional methods to characterize the mesoporosity, the use of variable-temperature 129Xe NMR spectroscopy was explored. At low temperature, a new resonance of 129Xe adsorbed in the mesopores could be distinguished from the signal of Xe in the micropores. The similarity of UV−vis and UV resonance Raman spectra of this mesoporous TS-1 zeolite with a conventional microporous TS-1 zeolite shows that the local coordination environment of Ti in these samples is identical. Further characterization (TEM, XRD) indicates that phase separation of titanium oxide is absent. The mesoporous TS-1 zeolite exhibits improved catalytic activity in the hydroxylation of phenol and ammoxidation of methyl ethyl ketone. The catalytic activity is substantially improved by introducing mesoporosity in TS-1, whereas the selectivity to the desired products is very similar. The improved catalytic activity of the TS-1 with the hierarchical structure is mainly attributed to the improved mass transfer of reactants and products into and out of the zeolite micropores. The generation of the hierarchical pore structure by the one-pot carbon-templating route becomes a general strategy for the synthesis of hierarchical zeolite with different compositions.

Direct Synthesis of Functional Zeolitic Materials

“…As reported, mesoporous TS-1 improved the catalytic activity of conventional TS-1 zeolite without changing the product selectivities. Similar synthetic pathway was followed by Xin et al in the synthesis of mesoporous TS-1 zeolite [131]. Improved catalytic yields were obtained using this hierarchical TS-1 on phenol hydroxylation and methyl ethyl ketone ammoxidation using H 2 O 2 as an oxidant.…”

Facile Synthesis of Yolk/Core-Shell Structured TS-1@Mesosilica Composites for Enhanced Hydroxylation of Phenol

“…Notably, our prepared composites CS-TS-1@mSiO2 (Entry 6) and YS-TS-1@mSiO2 (Entry 9) gave a higher phenol conversion of 25.2% and 27.6% than that of pristine TS-1 (23.7%), respectively. The turnover frequency (TOF) of YS-TS-1@mSiO2 (34.4) was even higher than some other hierarchical nanoporous TS-1 zeolite materials [18]. The enhanced activities should be attributed to the effect of external mesosilica layer that can effectively capture the large phenol molecules like a pump from the reaction solution due to the large specific surface area of mesopores.…”

“…Therefore, many studies were directed toward improving the accessibility of the active sites in TS-1 catalysts. To this end, introduction of a second mesopore into TS-1 zeolite crystals to form hierarchical structured TS-1 is an efficient strategy [15][16][17][18][19][20][21]. While significant achievements have been realized in this approach, the methods employed usually involved either cost-intensive mesostructured templates [15,[19][20][21] or complex synthetic procedures [17,18].…”

An acid-free route for the facile synthesis of iron-functionalized mesoporous silicas: Transformation between hollow nanospheres and cage-like mesostructures

“…Using UV excitation, low fluorescence interference and strong resonance Raman enhancement make it possible for the sensitive detection of highly-isolated Ti or Fe species in mesoporous silicas or microporous zeolites [58,59]. A 290 nm laser line was employed as the excitation line, which is close in energy to the charge transfer band as indicated in the UV-vis spectra of NS-n and NO 3 -NS-n samples.…”