Titania-pillared Clay Research Articles

Use of V2O5/Ti-PILC Catalyst for the Reduction of NO by NH3.

Titania-pillared interlayer clays (Ti-PILCs) exhibited peculiar physicochemical characteristics as catalyst supports compared to that of titania for the reduction of NO by NH3. Korean natural bentonite (KNB) was employed as a basic component of PILC due to its high pillaring capacity. For the freeze-dried Ti-PILC, the development of needle-like crystallites revealing the formation of a “house-of-cards” structure by delamination of long-ranged layered structure of Ti-PILC has been observed. Freeze-drying creates a unique pore structure of Ti-PILC catalyst such as multi-modal pore size distribution simultaneously containing micropores and meso- or macropores in the pore network. In particular, V2O5/Ti-PILC catalyst exhibits high performance of NO removal by NH3 mainly due to the strong catalyst surface acidity and redox properties examined by NH3 TPD and TPR-TPO studies, respectively. Without the addition of the catalyst promoter, WO3 and MoO3 to the catalyst, V2O5/Ti-PILC catalyst shows competitive NO removal activity to a commercial one.

Synthesis and Photocatalytic Activity of Titania Pillared Clays

TiO2-pillared clays such as montmorillonite, saponite and mica were prepared with an intercalation of polynuclear titanium complex formed by the reaction of Ti(i-C3H7O)4 and acetic acid. Characterization of the products was performed by XRD, XPS, IR, UV-V spectra, the measurement of surface area and pore size distribution. The photocatalytic decomposition of carboxylic acids has been studied on TiO2-pillared montmorillonite, saponite and mica. TiO2-pillared mica showed higher catalytic activity than TiO2 for the photocatalytic decomposition of acetic acid and adipic acid. On the contrarily, TiO2 was the most active catalyst and TiO2-pillared mica showed low activity for the photocatalytic decomposition of capric acid. The results show that the molecular size of carboxylic acid contributes to the catalytic activity of TiO2-pillared clays.

Catalytic Performance and Characterization of VO2+-Exchanged Titania-Pillared Clays for Selective Catalytic Reduction of Nitric Oxide with Ammonia

VO2+ ion-exchanged TiO2-pillared clays (VO–TiO2-PILC) were investigated for selective catalytic reduction of nitric oxide by ammonia in the presence of oxygen. They were also characterized for surface area and pore size distribution and by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR), and Fourier transform infrared (FTIR) spectroscopy. It was found that VO–TiO2-PILC catalysts were highly active for the selective catalytic reduction (SCR) reaction. The maximum activity was obtained with 2.1–3.5 wt% vanadium, which was close to or slightly higher than the activity of the commercial V2O5+WO3/TiO2 catalyst. The VO–TiO2-PILC catalysts were also resistant to water vapor and sulfur dioxide at high temperatures (>350°C). XRD patterns of VO–TiO2-PILC were similar to that of TiO2-PILC, showing no peaks due to vanadium oxides, even when the vanadium content reached 13.2 wt%. XPS and ESR spectra indicated that vanadium was present mainly as the +5 valence form (probably as V2O5) on the fresh catalysts, but was partially reduced to the +4 form (VO2+) after being heated at 300°C in He. The FTIR spectra of the adsorbed NO+O2 suggested that vanadium oxides were anchored directly on the titania pillars of the catalysts. NH3 molecules adsorbed on the Brønsted acid and Lewis acid sites to form, respectively, NH+4 ions and coordinated NH3 species. These NH3 adspecies were active in reaction with NO and NO+O2. The Brønsted acidity increased with increasing vanadium content, which was consistent with an increase in the SCR activity for low temperatures (e.g., 200°C). By comparison, the adsorption of NOx (x=1, 2) on the catalysts was very weak, especially under reaction conditions. The present results indicate that the reaction path for NO reduction by NH3 on VO–TiO2-PILC is similar to that on V2O5/TiO2; i.e., N2 originates mainly from the reaction between gaseous or weakly adsorbed NO and NH3 adspecies.

Characterization of the microporosity of chromia- and titania-pillared montmorillonites differing in pillar density.: I. Adsorption of nitrogen

The microporosity of chromia- and titania-pillared clays differing in pillar density has been explored. Nitrogen adsorption data determined at very low relative pressures were used. These data were analyzed by means of the α s method and the BET, Langmuir, Dubinin–Radushkevich and Dubinin–Stoeckli approaches. The applicability of these methods for determination of the PILCs' microporosity was studied. The surface area calculated by the α s method can be considered as a total surface area of the materials studied. The BET method underestimates, whereas the Langmuir approach overestimates, the total surface area of these solids. The Dubinin–Radushkevich method can be applied only to characterize textural features of PILCs exhibiting homogeneously distributed narrow micropores (<0.7–1.0 nm width). The same holds for the Dubinin–Stoeckli relation. The method developed by Zhu et al. is useful for the determination of the porous structure of PILCs having a significant contribution of supermicropores (0.7–2.0 nm width). A good agreement between the total micropore volume of the materials studied and that obtained from the α s method was found. All the methods applied demonstrated that these solids possess micropores over a broad pore-size range. Chromia-pillared montmorillonites contain a significant amount of ultramicropores (<0.7 nm width), whereas titania-pillared clays show an important contribution of supermicropores. An alteration of the pillar density can provide a family of pillared clays that differ in the surface area, micropore volume, and micropore size distribution.

Effect of Hydrothermal Treatment of Titania-pillared Montmorillonite for Photocatalytic Degradation of Dibutyl Phthalate in Water

Abstract Titania-pillared clay could adsorb dibutyl phthalate (DBP), one of endocrine disruptors, and degrade it photocatalytically. Hydrothermal treatment of this material, which increased the crystallinity of titania pillars, enhanced the photocatalytic activity without losing the adsorption ability and reduced the elution of titania pillars.

Photocatalytic Properties of Titania Pillared Clays by Different Drying Methods

Photocatalysts based on titania pillared clays (TiO2PILCs) have been prepared through a sol-gel method. Different drying methods, air drying (AD), air drying after ethanol extraction (EAD), and supercritical drying (SCD) have been employed and found to have significant effects on the photocatalytic efficiency of the resultant catalysts for the oxidation of phenol in water. Titania pillared clay (TiO2PILC) obtained by SCD has the highest external and micropore surface area, largest amount and smallest crystallite size of anatase, and exhibited the highest photocatalytic activity. Furthermore, silica titania pillared clay (SiO2-TiO2PILC) after SCD, titania coated TiO2PILC (SCD) and SiO2-TiO2PILC (SCD) were synthesized to study the key factors controlling the photocatalytic activity. It is concluded that the dispersion of nanometer-sized anatase on the surface of the PILC particles and the suspensibility of the particles are the most important factors for high photocatalytic efficiency.

Vanadium-doped titania-pillared montmorillonite clay as a catalyst for selective catalytic reduction of NO by ammonia

AbstractA series of V-doped titania-pillared clay catalysts, characterized by ICP-AES chemical analysis, X-ray diffraction, BET surface area measurement, and ESR spectroscopy, have been tested in the selective catalytic reduction of NO by NH3. An ESR analysis shows that V dopant is anchored to the titania pillars. Vanadyl species with differing degrees of in-plane V-O π-covalent bonding are produced depending on the method of sample preparation. Polymeric V species appear as the V content is increased. Catalytic performance of these systems depends on the method of preparation and on the V content. The best catalyst, converting 90-100% NO in the temperature range 523-623 K, is obtained by exchange of pillared montmorillonite with vanadyl ions, at an extent of exchange below the level where significant amounts of polymeric V species appear. The co-pillared catalyst, containing vanadyl centres characterized by a higher degree of in-plane ncovalent bonding (according to ESR), is less selective than the exchanged samples.

Iron Oxide and Chromia Supported on Titania-Pillared Clay for Selective Catalytic Reduction of Nitric Oxide with Ammonia

TiO2-pillared clay (PILC) with high surface area, large pore volume, and large interlayer spacing was used as the support for mixed Fe2O3and Cr2O3as the catalyst for selective catalytic reduction (SCR) of NO with NH3. The Fe/Cr ratio was varied at a fixed total amount of oxide dopant of 10% (wt). The Fe–Cr/TiO2-PILC with Fe/Cr=3 showed the highest activity. Compared with commercial V2O5/TiO2catalysts, the activity (on a per gram basis) of the doped pillared clay was approximately twice as high under H2O- and SO2-free conditions and was approximately 40% higher under conditions with H2O and SO2. In addition, its activity for SO2oxidation was only 20%–25% of that of the V2O5-based catalysts. TPD of NH3on the Fe–Cr/TiO2-PILC catalyst showed that both M=O and M–OH (M=Fe or Cr) were necessary for the SCR reaction.In situIR spectra of NH3showed that there was a higher Brønsted acidity than the Lewis acidity on the surface under reaction conditions and that there existed a direct correlation between the SCR activity and the Brønsted acidity among pillared clays with different Fe/Cr ratios. These results, along with the transient response to O2, indicated that a similar mechanism to that on the V2O5catalyst was operative. The TiO2-pillared clay used as the support also contributed to the high activity of the Fe–Cr catalyst. The TiO2pillars combined with the tetrahedral SiO2surfaces of the clay apparently gave rise to a high dispersion of Fe2O3.

Selective dehydration of 1-phenylethanol to 3-oxa-2,4-diphenylpentane on titanium pillared montmorillonite

Activity and selectivity of titanium pillared clay (Ti-PILC) are higher than those obtained with a zeolite (Y-82) in dehydration of 1-phenylethanol. Under hydrogen, 48% conversion and 98.4% selectivity are obtained on Ti-PILC as compared with 30% conversion and 81.4% selectivity on Y-82 zeolite in the same conditions. Physico-chemical characterizations (adsorption of nitrogen and TPD of ammonia) suggests that these results may be explained by a better accessibility of the strong acid sites of the Ti-PILC.

ESR characterization of catalytically active V centres supported on alumina-, titania-, and zirconia-pillared montmorillonite clays

Vanadium-doped alumina-, titania-, and zirconia-pillared montmorillonites obtained by various preparative procedures have been investigated with the aid of ESR. Analysis of the spectra shows that localization of vanadium dopant in the pillared clay structure depends on the type of pillared matrix and on the mode of preparation. In V-doped alumina- and titania-pillared clays the vanadyl ions are bound to the pillars. In zirconia-pillared samples, beside the vanadyl centres bound to the pillars, also species associated with the interlayer surface of clay play an important role. In all cases copillaring produces species of relatively stronger in-plane π covalency than that observed for other members of the respective series, the effect being most pronounced for (V-Ti)-PILC and (V-Zr)-PILC samples. Catalytic experiments with oxidative dehydrogenation of propane demonstrate superior catalytic properties of these centres. This effect is interpreted in terms of the in-plane π covalency facilitating electron transfer between the electron donor and electron acceptor sites at the catalyst surface.

Photocatalytic activities of microcrystalline titania incorporated in sheet silicates of clay

Photochemical and photocatalytic properties of microcrystalline TiO{sub 2} incorporated in the interlayer space of montmorillonite were investigated in reference to those of TiO{sub 2} powder particles which were prepared by agglomeration of a titania sol that was used in the preparation of the titania-pillared clay. The pillared TiO{sub 2} microcrystallites having ca. 15-{angstrom} pillar height showed a ca. 0.58-eV blue shift in its absorption and fluorescence spectra compared with those of the TiO{sub 2} particles, exhibiting the quantum size effect. The excited electronic states of the pillared TiO{sub 2} were determined to be 0.36 V more negative than that of the TiO{sub 2} powder particles. Photocatalytic activities of the pillared TiO{sub 2} were greater than those of the TiO{sub 2} powder particles for decomposition of 2-propanol to give acetone and hydrogen and of n-carboxylic acids with up to eight carbons (from acetic acid to caprylic acid) to give the corresponding alkanes and carbon dioxide, though the pillared TiO{sub 2} exhibited lower activities for decomposition of capric acid, having 10 carbons in a molecule.