The Promoting Effect of Ti on the Catalytic Performance of V-Ti-HMS Catalysts in the Selective Oxidation of Methanol

The effects of Ti modification on the structural properties and catalytic performance of vanadia on hexagonal mesoporous silica (V-HMS) catalysts are studied for selective methanol-to-dimethoxymethane oxidation. Characterizations including N2 adsorption–desorption (SBET), X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS UV-Vis), Micro-Raman spectroscopy, FTIR spectroscopy, and H2 temperature-programmed reduction (H2-TPR) were carried out to investigate the property and structure of the catalysts. The results show that Ti can be successfully incorporated into the HMS framework in a wide range of Si/Ti ratios from 50 to 10. Ti modification can effectively improve the distribution of vanadium species and thus enhance the overall redox properties and catalytic performance of the catalysts. The catalytic activity of the V-Ti-HMS catalysts with the Si/Ti ratio of 30 is approximately two times higher than that of V-HMS catalysts with comparable selectivity. The enhanced activity exhibited by the V-Ti-HMS catalyst is attributed to the improved dispersion and reducibility of vanadium oxides.

Mechanism on the Separation of Vanadium and Titanium from Vanadium Slag by Roasting with Ammonium Sulfate

The technology of simultaneously recovering V and Ti from vanadium slag via ammonium salt roasting has proven to be an efficient route. However, due to the phase stability and complex chemical composition of vanadium slag, intermediate materials containing Fe, V, Ti and Mn are difficult to be characterized critically. This work aims to investigate the decomposition and transformation of vanadium slag during ammonium salt roasting, using a combination of FT-IR, XRD, XPS and SEM techniques. It was found that the lattice structure of Fe-contained spinel would be transformed from FeV2O4 to Fe2+VnFe2−nO4 (0 < n < 2) during directly roasting in the air. However, there is no obvious change for Ti-contained and Mn-contained spinel. Using NH4HSO4 (ABS) as an additive and roasting the slag in the N2 atmosphere, those spinels would be decomposed into various sulfate salts. Meanwhile, when the slag was roasted with NH4HSO4 in the air, a part of Fe(II) in (NH4)2Fe(SO4)2 would be transferred into Fe(III), but V(III), Ti(IV) and Mn(II) from those salts would remain the same valance state. Ultimately, about 88% V and 81% Ti were recovered, when vanadium slag was roasted at 663.15 K with a 1:5 ratio of slag-to-NH4HSO4 and followed by 8 vol.% H2SO4 leaching.

Sealing effect of surface porosity of Ti-P composite films on tinplates

A novel chrome-free Ti–P composite film was prepared by casting a mixed solution containing titanium and phosphorus species, which is able to seal the pores on the tinplate surface. The obtained film was characterized using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). The surface porosity sealing effect on tinplates was verified by using a glow discharge spectrometer (GDS), porosity tests, and XPS. The results show that the film on the tinplates is composed of TiO₂, Ti₃(PO₄)₄·nH₂O, and FePO₄. Micropores on the tinplates are reduced apparently after film deposition, and the content of iron exposed in the pores is decreased significantly. An obvious concentration peak of phosphorus at a depth of around 0.75 μm infers that the film can penetrate into the micro-pores. The film lead to a 42.5% decrease in the surface porosity of the tinplates, exhibiting an outstanding surface porosity sealing effect in comparison with pure Ti or P films. Mechanistic analysis using XPS indicates that Ti₃(PO₄)₄·nH₂O and FePO₄ in the film play a role in sealing the surface porosity.

A novel chrome-free Ti–P composite film was coated on tinplates to seal the pores on the tinplate surface.

The Effect of Film Thickness on the Gas Sensing Properties of Ultra-Thin TiO₂ Films Deposited by Atomic Layer Deposition

Analyte sensitivity for gas sensors based on semiconducting metal oxides should be highly dependent on the film thickness, particularly when that thickness is on the order of the Debye length. This thickness dependence has previously been demonstrated for SnO₂ and inferred for TiO₂. In this paper, TiO₂ thin films have been prepared by Atomic Layer Deposition (ALD) using titanium isopropoxide and water as precursors. The deposition process was performed on standard alumina gas sensor platforms and microscope slides (for analysis purposes), at a temperature of 200 °C. The TiO₂ films were exposed to different concentrations of CO, CH₄, NO₂, NH₃ and SO₂ to evaluate their gas sensitivities. These experiments showed that the TiO₂ film thickness played a dominant role within the conduction mechanism and the pattern of response for the electrical resistance towards CH₄ and NH₃ exposure indicated typical n-type semiconducting behavior. The effect of relative humidity on the gas sensitivity has also been demonstrated.

Ordered micro/macro porous K-OMS-2/SiO2 nanocatalysts: Facile synthesis, low cost and high catalytic activity for diesel soot combustion

A series of novel oxide catalysts, which contain three-dimensionally ordered macroporous (3DOM) and microporous structure, were firstly designed and successfully synthesized by simple method. In the as-prepared catalysts, 3DOM SiO2 is used as support and microporous K-OMS-2 oxide nanoparticles are supported on the wall of SiO2. 3DOM K-OMS-2/SiO2 oxide catalysts were firstly used in soot particle oxidation reaction and they show very high catalytic activities. The high activities of K-OMS-2/SiO2 oxide catalysts can be assigned to three possible reasons: macroporous effect of 3DOM structure for improving contact between soot and catalyst, microporous effect of K-OMS-2 for adsorption of small gas molecules and interaction of K and Mn for activation of gas molecules. The catalytic activities of catalysts are comparable to or even higher than noble metal catalyst in the medium and high temperature range. For example, the T50 of K-OMS-2/SiO2-50, 328 °C, is much lower than those of Pt/Al2O3 and 3DOM Au/LaFeO3, 464 and 356 °C,respectively. Moreover, catalysts exhibited high catalytic stability. It is attributed to that the K+ ions are introduced into the microporous structure of OMS-2 and stabilized in the catalytic reaction. Meanwhile, the K+ ions play an important role in templating and stabilizing the tunneled framework of OMS-2.

Thickness Influence on In Vitro Biocompatibility of Titanium Nitride Thin Films Synthesized by Pulsed Laser Deposition

We report a study on the biocompatibility vs. thickness in the case of titanium nitride (TiN) films synthesized on 410 medical grade stainless steel substrates by pulsed laser deposition. The films were grown in a nitrogen atmosphere, and their in vitro cytotoxicity was assessed according to ISO 10993-5 [1]. Extensive physical-chemical analyses have been carried out on the deposited structures with various thicknesses in order to explain the differences in biological behavior: profilometry, scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction and surface energy measurements. XPS revealed the presence of titanium oxynitride beside TiN in amounts that vary with the film thickness. The cytocompatibility of films seems to be influenced by their TiN surface content. The thinner films seem to be more suitable for medical applications, due to the combined high values of bonding strength and superior cytocompatibility.

Si-doped mesoporous TiO2 continuous fibers: preparation by centrifugal spinning and photocatalytic properties

TiO(2) continuous fibers were prepared by a sol-gel method combined with centrifugal spinning without any template or binder polymer. The fibers were characterized using XRD, FT-IR, SEM, N(2) adsorption-desorption, and UV-vis DRS. The addition of silica was a crucial factor for obtaining long fibers because of the formation of Ti-O-Si networks. The effects of dopant contents and heat treatment temperatures were studied. It was found that the proper addition of silica into titania could improve the surface texture and enhance the thermal stability and crystal stability. When Si/Ti molar ratio was 0.15, mesoporous TiO(2) fibers with a BET surface area up to 127.7 m(2)g(-1) were obtained after heat treatment at 700 degrees C. It displayed the highest photoactivity of all, and the degradation rate of X-3B in aqueous solution reached 99.6% after 75 min under UV irradiation. Furthermore, the degradation rate and the mineralization rate of X-3B were 94.7% and 58.9% after 3h under solar irradiation, respectively. In addition, it was worthwhile to mention that the degradation efficiency was also more than 90% after 6 cycles.

Direct Vapor Phase Propylene Epoxidation over Deposition-Precipitation Gold-Titania Catalysts in the Presence of H2/O2: Effects of Support, Neutralizing Agent, and Pretreatment

The effects of titanium connectivity, deposition solution neutralizing agent, and catalyst pretreatment were examined for a series of Au-on-titanium-containing supports for the direct gas-phase epoxidation of propylene using hydrogen and oxygen. The degree of titanium isolation was examined using pure titania, monolayer-titania on silica, submonolayer-titania on silica, and titanium silicalite-1 (TS-1) supports. Activity and selectivity were shown to increase as the degree of titanium isolation increased, with TS-1 and submonolayer-titania supports providing the best stability and yield. Isolation of the titanium was found to significantly reduce the cracking of propylene to ethanal and carbon dioxide. Sodium carbonate was found to be the best neutralizing agent for catalysts prepared using deposition-precipitation (DP). DP with ammonium hydroxide gave catalysts with reduced selectivity and activity. Titania-modified silica was found to produce better catalysts when the support was not calcined prior to gold deposition. Similarly, calcination was detrimental to catalysts prepared via deposition of a 2 nm gold colloid onto titania-modified supports even though the gold did not sinter. The beneficial effects of Ti site isolation and support acid/base control are best seen at higher temperatures, where only a few catalysts can maintain selectivity.

Self-Assembled Monolayer and Multilayer of Trichlorogermane Hexyl Propylate and Formation of GeO(2)/SiO(2) Interface

Monolayer and multilayer films of trichlorogermane hexyl propylate (Ge6) were formed by the self-assembly method on hydroxylated silicon substrates. The results showed that this kind of trichlorogermane had virtually the same self-assembly behavior as trichlorosilanes. Ellipsometry proved that the self-assembled monolayers and multilayers (SAMs) of Ge6 exhibited a tilted orientation to the substrate surface. The multilayer film of Ge6 on silicon substrate was obtained by reducing the monolayer SAMs to alcohol hydroxylated surface with LiAlH(4) and repeating the self-assembly process. The self-assembled multilayer film was calcined in air at 500 degrees C to form a thin layer of GeO(2) on SiO(2)/Si substrate surface. The XPS measurement detected the formation of GeO(2) layer. Copyright 1999 Academic Press.