Shu Guo Zhang

Photocatalytic decomposition of NO at 275 K on titanium oxide catalysts anchored within zeolite cavities and framework

Abstract Titanium oxide species prepared in the Y-zeolite cavities via an ion-exchange method and those of the Ti-silicalite catalyst prepared hydrothermally exhibit high photocatalytic reactivity for the direct decomposition of NO into N2, O2 and N2O at 275 K with a high selectivity for the formation of N2. The in situ photoluminescence and XAFS investigations indicate that these titanium oxide species are highly dispersed and exist in a tetrahedral coordination in the zeolite cavities and its framework. The charge transfer excited state of these titanium oxide species plays a significant role in the direct decomposition of NO with a high selectivity for the formation of N2, while the catalysts involving the aggregated octahedrally coordinated titanium oxide species and the bulk powdered TiO2 catalyst mainly produce N2O.

Design of photocatalysts encapsulated within the zeolite framework and cavities for the decomposition of NO into N2 and O2 at normal temperature

Abstract The design of photocatalysts encapsulated within the zeolite frameworks and cavities is the most promising approach in developing photocatalysts which will operate efficiently and effectively towards the purification of toxic agents such as NO x and SO x in the atmosphere. In the present study, the vanadium silicalite (VS-2) and Ag + /ZSM-5 catalysts were prepared by hydrothermal synthesis and ion-exchange, respectively, and the in situ characterization of these catalysts and their photocatalytic reactivities for the decomposition of NO have been investigated using dynamic photoluminescence, XAFS (XANES, EXAFS), ESR, FT—IR, LTV—VIS, solid-state NMR and XRD techniques along with an analysis of the reaction products. Results obtained with the VS-2 catalyst showed that vanadium oxide moieties are present within the zeolite framework as a 4-fold tetrahedrally coordinated vanadium oxide species having a terminal oxovanadium group (VO). UV irradiation of the VS-2 catalyst in the presence of NO led to the photocatalytic decomposition of NO to form N 2 , N 2 O and O 2 . On the other hand, it was found that the zeolite cavities can stabilize the Ag + ions in an isolated state through their connection with two lattice oxygen anions of the zeolite (2-coordination geometry). These isolated Ag + ions exhibit high photocatalytic reactivities for NO decomposition to form N 2 , N 2 O and NO 2 . Dynamic studies of the excited state of these catalysts showed that the charge transfer from the excited state of the vanadium oxide species or Ag + ions to NO plays a vital role in the initiation of the decomposition of NO into N and O. These findings have demonstrated that metal oxide species and metal ions included within the zeolite frameworks and cavities are strong candidates for new types of environmentally applicable photocatalysts.

Photoluminescence property and photocatalytic reactivity of V-HMS mesoporous zeolites Effect of pore size of zeolites on photocatalytic reactivity

Abstract The photoluminescence properties and photocatalytic reactivities of the V-HMS mesoporous zeolite have been investigated by means of in situ photoluminescence, UV-vis, EXAFS, XRD and ESR measurements. It was found that the V-HMS zeolite involves a vanadium species which is highly dispersed and incorporated in the framework of the mesoporous zeolites having a V=O bond and a C3v symmetry. This species plays an important role as the emitting site of this zeolite. It was also found that the zeolite exhibits photocatalytic reactivity under UV irradiation in the presence of cis-2-butene, resulting in the formation of trans-2-butene and 1-butene. The photocatalytic reactivity of the V-HMS mesoporous zeolite was found to be much higher than that of the V-silicalite microporous zeolite (VS-1). The efficiency of the dynamic quenching of the photoluminescence of the V-oxide species in the excited state in the V-HMS mesoporous zeolite by smaller molecules such as O2 was found to be the same as that of the VS-1 microporous zeolite. By comparing these results with results obtained on the VS-1 microporous zeolite photocatalyst, we can conclude that the pore size effect plays a significant role as one of the major factors which determine the photocatalytic reactivities of porous zeolite photocatalysts.

Characterization and photocatalytic reactivities of Cr-HMS mesoporous molecular sieves.

Investigations of the local structures and photocatalytic reactivity of Cr-containing mesoporous molecular sieves (CrHMS) have been carried out. Cr-HMS involves tetrahedrally coordinated Cr-oxide species which are highly dispersed and incorporated with terminal Cr=O groups in the framework of molecular sieves. On the other hand, the imp-Cr/HMS prepared by an impregnation method consists of both tetrahedrally and octahedrally coordinated Cr-oxide species. The Cr-HMS exhibits much higher photocatalytic reactivity under UV irradiation for the isomerization of cis-2-butene than the imp-Cr/HMS and Cr-silicalite microporous catalysts. The charge transfer excited state of the tetrahedrally coordinated Cr-oxide species plays a significant role in the photocatalytic reaction. 453

Photoinduced surface chemistry

Abstract A comprehensive understanding of the basic mechanisms and dynamics behind photoinduced surface chemistry is indispensable for the advancement of photo or photon-based sciences and technologies. Recent investigations into the mechanisms and dynamics of molecules adsorbed on photostimulated metal surfaces and the characterization of electronically excited molecules included within restricted molecular environments such as zeolite cavities have provided many useful applications for the control of photochemical surface reactions. Significantly and in practical terms, environmental applications of photocatalysis to design systems which will reduce toxic agents in the atmosphere and in water as well as operate effectively and efficiently under visible light will have profound implications for the future of this planet.

Characterization of the VS-1 catalyst using various spectroscopic techniques and its unique photocatalytic reactivity for the decomposition of NO in the absence and presence of C3H8

Abstract A Vanadium silicalite (VS-1) catalyst was prepared by hydrothermal synthesis. In situ characterizations were carried out and the photocatalytic reactivity of VS-1 were investigated using dynamic photoluminescence, XAFS (XANES, EXAFS), UV–Vis and FT-IR techniques, along with an analysis of the reaction products. It was found that VS-1 involves a highly dispersed tetrahedrally coordinated V-oxide species having a VO bond within the zeolite framework. VS-1 exhibits photocatalytic reactivity for the decomposition of NO under UV irradiation, leading to the formation of N 2 , O 2 , N 2 O and NO 2 . The photocatalytic reaction of NO was dramatically enhanced in the presence of propane, leading to the formation of N 2 , propylene, and oxygen-containing compounds such as CH 3 COCH 3 and CO 2 , etc. with a good stoichiometry. The photocatalytic reactivity of VS-1 was found to be much higher than that of V/SiO 2 . The efficiency of the dynamic quenching of the photoluminescence of the V-oxide species in the excited state of VS-1 by small molecules such as NO or propane was found to be larger than that of V/SiO 2 . These results indicate that the high reactivity of the charge transfer excited triplet state of the V–O moieties, (V 4+ –O − ) * , of the VS-1 catalyst plays a significant role in the higher photocatalytic performance as compared with the V/SiO 2 catalyst.

In situ characterization of the vanadium silicalite catalyst (VS-2) and its photocatalytic reactivity

The in situ characterization of the vanadium silicalite catalyst (VS-2) and its photocatalytic reactivity have been investigated using dynamic photoluminescence, XAFS (XANES, EXAFS), ESR, FT-IR, UV-VIS, solid state wide-line 51V NMR and XRD techniques along with an analysis of the reaction products. Results obtained with the VS-2 catalyst showed that vanadium oxide moieties are present within the zeolite framework as a 4fold tetrahedrally coordinated V oxide species having a terminal monoxovanadyl group (V=O). This VS-2 catalyst exhibited an absorption band at around 270-340 nm and an intense phosphorescence at around 450-550 nm with a vibrational fine structure and both are attributed to the chargetransfer processes. UV irradiation of the VS-2 catalyst in the presence of NO and cis-2-butene at 295 K led to the photocatalytic decomposition of NO to form N2, O2 and N2O while the photocatalytic isomerization of cis-2butene produced 1-butene and trans-2-butene, respectively. Dynamic studies of the excited state of the catalyst and its photocatalytic reactions showed that the charge transfer excited state of the vanadium oxide species incorporated into the zeolite framework plays a vital role in these reactions.