The solid-state reaction of the ZSM-5 zeolite with V 2 O 5 has been investigated by means of photoluminescence spectroscopy in combination with other spectroscopic techniques such as XAFS (XANES and FT-EXAFS), UV-vis, ESR, and FT-IR. It has been found that this reaction leads to the formation of the VO 2+ species as well as the vanadium oxide species, (Si-O) 3 VdO, which has a C 3V symmetrical geometry and is located at two different sites, i.e., at positions accessible to small molecules as well as at inaccessible positions. These vanadium oxide species formed in the zeolite exhibits unique and specific photocatalytic reactivity toward the isomerization of cis-2-butene at 273 K.
Ag+/ZSM-5 catalysts were prepared by an ion-exchange method and characterized by in-situ XPS, XAFS
(XANES and EXAFS), UV−Vis, photoluminescence, and FT-IR investigations. These Ag+/ZSM-5 catalysts
were found to exhibit an UV absorption band at around 190 nm due to the isolated Ag+ ions. The addition
of N2O molecules leads to a shift in this band to 220 nm due to the adsorption of N2O on the Ag+ ions. The
adsorption of N2O on the Ag+ ions could also be clarified by the appearance of characteristic FT-IR bands
at 2251 cm-1. UV irradiation of the Ag+/ZSM-5 catalysts in the presence of N2O led to the photocatalytic
decomposition of N2O into N2 and O2 at temperatures as low as 298 K. It was found that UV light at around
200−250 nm is effective for the reaction, suggesting that excitation of the isolated Ag+ ion plays a significant
role in the photocatalytic decomposition of N2O.
Cu(I) (Cu + ) ion catalysts anchored onto various oxides (SiO 2 ‚Al 2 O 3 , Al 2 O 3 , and SiO 2 ) were prepared by the combination of an ion-exchange method and a thermovacuum treatment. XAFS (X-ray absorption fine structure) investigations revealed that Cu + ions exist as linear two-coordinate Cu + on SiO 2 ‚Al 2 O 3 , while they exist as planar three-coordinate Cu + on Al 2 O 3 or SiO 2 . It was also found that the typical photoluminescence observed at 430 nm for the Cu + /(SiO 2 ‚Al 2 O 3 ) catalyst and that observed at 510 nm for the Cu + /Al 2 O 3 and Cu + /SiO 2 catalysts could be attributed to the radiative decay from the excited electronic state of the linear two-coordinate Cu + ions and planar three-coordinate Cu + ions, respectively. The addition of N 2 O onto the Cu + ion catalyst leads to the quenching of the photoluminescence of Cu + , indicating that N 2 O interacts with the photoexcited Cu + ion. UV irradiation of the catalysts in the presence of N 2 O led to the formation of N 2 and O 2 at 298 K, indicating that the photocatalytic decomposition of N 2 O proceeds on the Cu + ion catalysts. The reaction was found to proceed more efficiently on the Cu + /(SiO 2 ‚Al 2 O 3 ) catalyst than on the Cu + /Al 2 O 3 or Cu + /SiO 2 catalysts, suggesting that the two-coordinate Cu + species show higher activity for this reaction than the three-coordinate Cu + species.
The local structure of V oxide/ZSM-5 catalysts prepared by the solid-state reaction of the ZSM-5 zeolites having different Si/Al ratios have been investigated by means of in situ photoluminescence spectroscopy in combination with other spectroscopic techniques such as UV-Vis, solid-state NMR, and ESR. It was found that vanadyl ions are present as tetrahedrally coordinated V 5+ species bonded to terminal Si-OH groups and square pyramidally coordinated VO 2+ species at the zeolite cationic sites for zeolites having a low Si/Al ratio (Si/Al ) 20). On the other hand, for a high Si/Al ratio (Si/Al ) 950), only the tetrahedrally coordinated V 5+ species can be observed. UV irradiation of the V oxide/ZSM-5 catalyst in the presence of NO was found to lead to the photocatalytic decomposition of NO into N 2 , O 2 , and N 2 O. The increase of efficiency was found to be more remarkable on the V oxide/ZSM-5 catalyst with a high Si/Al ratio than with a low Si/Al ratio. The photoluminescence spectrum of the V oxide/ZSM-5 catalyst which can be attributed to the radiative decay process for the charge transfer excited triplet state of the tetrahedrally coordinated VO 4 unit species was quenched by the addition of NO or propane, its extent depending on the pressure of these molecules. These results suggest that the charge transfer excited triplet state of the isolated tetrahedrally coordinated V 5+ species plays a significant role not only in the photocatalytic decomposition of NO but also in its enhancement in the presence of propane.
The characteristics of the fluorescence spectra of 2,5-bis(4-diethylaminophenyl)-1,3,4-oxadiazole (BDD) doped in Si-Ti binary oxides by the sol-gel method were investigated as a function of time in its transitions from sol to gel to xerogel. The intensity of the fluorescence spectrum decreases with the increase in the Ti content. A characteristic BDD excimer fluorescence was observed during the transition from gel to xerogel only in a mixture of tetraethyl orthosilicate (TEOS) and tetraisopropoxy titanium (TPOT) but not in pure TEOS, indicating that the presence of a tetrahedrally coordinated titanium ion species plays a significant role in the formation of the excimer. A possible model has been proposed for the entrapment process of BDD during the sol to gel to xerogel transitions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.