Silica Titania Catalysts Research Articles

Adsorption and degradation of the cationic dyes over Co doped amorphous mesoporous titania–silica catalyst under UV and visible light irradiation

Cobalt doped amorphous mesoporous titania–silica with Ti/Si mass ratio of 0.8 (Co–TiO 2–SiO 2) was synthesized and used for the photodegradation of six cationic dyes (gentian violet, methyl violet, methylene blue, fuchsin basic, safranine T, and Rhdamine B) under UV and visible light illumination. The catalyst was characterized by a combination of various physicochemical techniques, such as N 2 physisorption, diffuse reflectance UV–vis, X-ray diffraction, and FT-IR. Co–TiO 2–SiO 2 exhibited activity under UV light and had better activity under visible light when compared with that of Degussa P25 TiO 2. The activity of Co–TiO 2–SiO 2 was also compared with that of Co-MCM-41, Co doped mesoporous titania with a crystalline framework (Co–MTiO 2) and titania-loaded Co doped MCM-41 (TiO 2/Co-MCM-41) for the degradation of gentian violet under visible light irradiation. It was also found that the degradation rates of Co–TiO 2–SiO 2 for gentian violet, methyl violet, methylene blue, fuchsin basic and safranine T were greater in alkaline media than in acid and neutral media, while it did not exhibit any significant activity for the photodegradation of Rhdamine B in alkaline media or in acid media under visible light irradiation.

Non-hydrolytic synthesis of mesoporous silica–titania catalysts for the mild oxidation of sulfur compounds with hydrogen peroxide

A SiO(2)-TiO(2) mesoporous xerogel prepared in one-step by a non-hydrolytic route shows excellent performance in the mild oxidation of sulfides, sulfoxides and thiophenes with aqueous solutions of H(2)O(2).

Photo-degradation of yperite over V, Fe and Mn-doped titania–silica photocatalysts

The photocatalytic decomposition of yperite (bis(2-chloroethyl)sulfide), a chemical warfare agent, was achieved by using titania-silica catalysts doped with several transition metal ions. The preparation of these catalysts was achieved by impregnation of a titania-silica mixed oxide previously synthesized using a sol-gel route with salts of the doping elements (vanadium, iron, manganese). The above catalysts were characterized using several spectroscopic techniques: FTIR, Raman, DR-UV-Vis, and XPS. The band gap energy was measured for each photocatalytic system. The reaction was carried out in two different types of reactors, i.e. naturally aerated and a closed quartz tube aerated under a constant flow, and using two types of irradiation, UV-Vis and Vis. The investigated systems proved to be extremely active, leading to an almost complete degradation of yperite in 2 h of irradiation. An excellent correlation between the photocatalytic performances and the band gap has been found. Based on the characterization data and on the temporal evolution of the reaction products, a reaction mechanism has been suggested. This mechanism considers two distinct pathways for the decomposition of yperite, namely the C-S bond cleavage and the S oxidation.

Selective Oxidation of Diphenylmethane Over Cobalt Doped Mesoporous Titania–Silica Catalyst with High Ti Content

Cobalt doped mesoporous titania–silica with Ti/Si molar ratio of 0.5 (Co–TiO2–SiO2) was synthesized for the oxidation of diphenylmethane in acetic acid using aqueous hydrogen peroxide as oxidant for the first time. Fast hot catalyst filtration experiment proved that the catalyst acted as a heterogeneous one. Recycling of the catalyst indicates that the catalyst can be used a number of times without losing its activity to a greater extent. The effects of reaction time and reaction temperature on the performance of the catalyst were investigated. Moreover, cobalt doped mesoporous titania with a crystalline structure and cobalt doped mesoporous titania–silica with different molar ratio were also studied. It was found that Co–TiO2–SiO2 with Ti/Si molar ratio of 0.5 showed the highest activity.

Modeling the adsorption of aromatic compounds on the TiO2/SiO2 catalyst

The Grand Canonical Monte Carlo method was used to analyse the phenomenon of adsorption of aromatic compounds (i.e. phenol, toluene, benzoic acid and salicylic acid) on the surface of the titania-silica (TiO2/SiO2) catalyst. We found that different types of interactions play important roles in the adsorption of molecules having polar and non-polar groups. Moreover, we found that the interactions between sorbate molecules are strong, and are the cause of multilayer adsorption occurring in the investigated temperature and pressure range.

Synthesis of dimethyl ether from methanol over aluminium phosphate and silica–titania catalysts

A series of solid–acid catalysts with different content of components were prepared by co-precipitation (sol–gel) method. These samples comprised silica–titania and modified γ-Al 2O 3 with phosphorus. To determination of optimum ones, the effects of various contents of phosphorus have been investigated. Dehydration of methanol to dimethyl ether (DME) on solid–acid catalysts was studied in a fixed-bed reactor at a temperature of 300 °C under atmospheric pressure and a GHSV of 15,600 h −1. The catalysts have been characterized using BET, XRD, FT-IR, NH 3–TPD and elemental analysis techniques and also the results were reported. According to the experimental results, silica–titania catalysts have exhibited low activity for DME synthesis. Phosphorus-modified catalysts have shown better performance compared to the untreated γ-Al 2O 3. It was found that surface areas increase with increasing in the molar ratio of aluminium-to-phosphorus at aluminium phosphate catalysts. Also, by modifying alumina with phosphorus, it was observed that the surface acidity of aluminium phosphate catalysts decrease with increasing in the molar ratio of Al/P at aluminium phosphate catalysts. The sample of non-stoichiometric aluminium phosphate (molar ratio of Al/P = 2) have exhibited the best conversion without any by-product.

Selective catalytic reduction of NO with NH 3 over mesoporous V 2O 5–TiO 2–SiO 2 catalysts

Mixed vanadia–titania–silica catalysts (3 or 6 wt% V 2O 5, and 16–34 wt% TiO 2) were one-pot prepared by sol–gel and hydrothermal methods in the presence of surfactants. Sodium silicate (25.5–28.5% silica) or tetraethylorthosilicate was used as a precursor for silica; tetraisopropylorthotitanate or titanyl acetylacetonate, for titania; and vanadyl sulfate or vanadium acetylacetonate, for vanadia. Cetyltrimethylammonium bromide, octadecyltrimethylammonium bromide, or dodecylamine was used as a surfactant. The catalysts were characterized by adsorption and desorption curves of N 2 at 77 K, NH 3-DRIFTS, H 2-TPR, XRD, in situ Raman spectroscopy, XPS, and TEM. The catalysts were tested in NO reduction with ammonia using a total flow rate of 100 ml/min and a feed composition of nitric oxide 0.1 vol%, ammonia 0.1 vol%, oxygen 3 vol%, in helium. Vanadia was found to be entrapped in these catalysts as V(V) species in which the population of VO monomeric bonds strongly depended on the dispersion. Titanium also existed in a very oxidated state, and for high dispersions it adopted a tetrahedral coordination. These structures led to surfaces on which mainly Lewis acid sites are effective under reaction conditions. Under such conditions, the dominant route followed an Eley–Rideal mechanism, yielding in such a way very high activity and selectivity. A comparison with a conventional V 2O 5–TiO 2 catalyst led to the conclusion that the intrinsic activity of one-pot prepared polymeric sol–gel catalysts is higher.

Chemoselective oxidation of 2-thiomethyl-4,6-dimethyl-pyrimidine and 2-thiobenzyl-4,6-dimethyl-pyrimidine over titania-silica catalysts

Mixed oxides titania-silica catalysts (3 wt.% TiO 2) were prepared using the sol–gel technique. The catalysts were characterized using adsorption–desorption isotherms of N 2 at 77 K, XRD, SAXS, UV-Vis, FTIR and XPS. They were tested in sulfoxidation of 2-thiomethyl-4,6-dimethyl-pyrimidine and 2-thiobenzyl-4,6-dimethyl-pyrimidine in presence of H 2O 2. The catalysts were used as such or after modification with l(+)-tartaric or R (−)-α-metoxyphenylacetic acid at 373 K. The chemoselectivity was found to be influenced by the solvent, properties of catalyst and nature of the substrate. The enantiomeric excess (e.e.) obtained using modified catalysts was lower than 30%.

Synthesis, characterization and catalytic properties of titania–silica catalysts

The preparation of titania doped (0.63–3.2 mmol g−1) silica (TiO2/SiO2) was described together with a mixed oxide sample (TiO2–SiO2) at a nominal molar ratio near to 1. These materials were thoroughly characterized by XRD, N2 adsorption at 76 K and ammonia adsorption measurements as well as FTIR spectroscopy. The activity of the materials towards 1-butene isomerization was also tested. FTIR results showed a band at 612 cm−1 attributed to bulk TiO2 phase, in the doped 3.2 mmol g−1 TiO2/SiO2 sample, that was paralleled to an exhibited perturbation for the SiO2 bands in the low frequency region, specifically those at 470 and 808 cm−1. The former band was similarly obtained in the TiO2–SiO2 sample, with a lower decrease in intensity, together with the appearance of a new band at 948 cm−1 attributed to Ti–O–Si linkages. This deed indicated the decrease in population of Ti–O–Ti bridges in the mixed oxide sample. FTIR spectra of adsorbed D2O established the presence of different types of titania hydroxyl groups (3615 and 3520 cm−1) that were composed during desorption of water from the titania surface. The activity towards 1-butene isomeriztion was found to increase gradually, in the doped samples, to achieve its maximum at the titania loading 3.2 mmol g−1, however, a tremendous decrease was obtained for the mixed oxide sample. This behavior was correlated with the acidity of the samples. The dependence of the reaction on either Ti–O–Ti or Ti–O–Si sites was evaluated and discussed.

Titania–silica as catalysts: molecular structural characteristics and physico-chemical properties

Recent results on characterization and applications of titania–silica materials as photocatalysts, acid catalysts and oxidation catalysts are reviewed. The similarities and differences in structural characteristics and physico-chemical properties between titania–silica mixed and supported oxides are emphasized. The generation of new catalytic active sites either on the silica surface or in the silica matrix is discussed with respect to the formation of Ti–O–Si bonds and the local structure. The insights obtained from these studies allow a fundamental understanding of the relationships between the structural characteristics and the physico-chemical/reactivity properties of titania–silica catalysts.

New technology for selective catalytic oxidation of ammonia to nitrogen

The selective catalytic oxidation (SCO) of ammonia to N 2 was studied by using a series of noble metal-V 2 O 5 -WO 3 catalysts supported on titania-silica (TS) prepared by coprecipitation method. In the V 2 O 5 - WO 3 catalyst system, the use of TS as a support was very effective to enhance catalytic activity compared with TiO 2 or SiO 2 alone. The addition of a slight amount of Pd and Ir to V 2 O 5 -WO 3 /TS catalyst caused also remarkable enhancement of the catalytic activity without decreasing the selectivity to N 2 . The present catalysts provide remarkably high catalytic performance for SCO of ammonia to N 2 under the practical reaction conditions for an industrial application.

Surface Acidity and Properties of Titania-Silica Catalysts

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSurface Acidity and Properties of Titania-Silica CatalystsMercedes Galan-Fereres, Luis J. Alemany, Rafael Mariscal, Miguel A. Banares, James A. Anderson, and Jose L. G. FierroCite this: Chem. Mater. 1995, 7, 7, 1342–1348Publication Date (Print):July 1, 1995Publication History Published online1 May 2002Published inissue 1 July 1995https://doi.org/10.1021/cm00055a011RIGHTS & PERMISSIONSArticle Views660Altmetric-Citations45LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (802 KB) Get e-Alerts Get e-Alerts

Titania Silica Mixed Oxides: II. Catalytic Behavior in Olefin Epoxidation

Various titania-silica aerogels prepared by an alkoxide-sol-gel route have been tested in the epoxidation of bulky olefins using cumene hydroperoxide as oxidant. The drying method, the titanium content between 2 and 20 wt%, and the calcination temperature between 473 and 1073 K were the most important preparation parameters, influencing the catalytic behaviour of the aerogels. The aerogels dried by semicontinuous extraction with supercritical CO 2 at low temperature (LT aerogel) were found to be much more efficient epoxidation catalysts than aerogels prepared by high-temperature supercritical drying and conventionally dried xerogels. The reaction rate of cyclohexene epoxidation over LT aerogels increased monotonically with increasing Ti content. In the range of 333-363 K the catalysts containing 20 wt% Ti0 2(20LT) showed high activity and selectivity (79-93% to peroxide and 87-100% to epoxide) in the oxidation of various cyclic olefins, including cyclododecene, norbornene, cyclohexene, and limonene. Catalytic experiments, FTIR, and UV-vis spectroscopy indicated that the LT aerogels consist of two different types of active species: titanium well-dispersed in the silica matrix and titania nanodomains. The key factors determining the activity and selectivity of sol-gel titania-silica catalysts are the morphology (surface area and pore size) and the relative proportions of Ti-O-Si and Ti-O-Ti structural parts. A comparative study of the epoxidation of cyclohexene, cyclododecene, and norbornene over structurally different titania-silica catalysts, indicates that 20LT shows better catalytic behaviour in these reactions than Ti zeolites and silica-supported titania.

Surface and acidic properties of some mixed oxide catalysts in relation to their catalytic activities

A series of silica-alumina catalysts were prepared to contain different proportions of alumina. The catalysts were calcined at 773–973 K. Another series of silica-titania catalysts of different chemical compositions were prepared and calcined between 773 and 973 K. The textural properties (surface area and pore structure) of the catalysts were determined by low-temperature nitrogen adsorption at 77 K. The surface acidity (acid amount and acid strength) was determined for each catalyst by thermal programmed desorption (TPD) of pyridine. The catalytic cracking of cumene at 673–773 K and the catalytic conversion of isopropanol at 473–593 K were investigated using microcatalytic technique. Cracking of cumene is a first-order catalytic reaction which takes place on relatively strong acid sites and the reaction is structurally sensitive. Dehydration of isopropanol on mixed oxide catalysts is a zero-order reaction and proceeds on most of the acid sites. Dehydration of isopropanol is related to the surface acid density and is structurally insensitive.

Ammonia adsorption on vanadia supported on titania—silica catalyst: An infrared spectroscopic investigation

The adsorption of ammonia on catalysts containing 7% (w/w) of vanadia supported on titania on silica containing between 8 and 34% (w/w) of titania was studied by IR spectroscopy. For comparison purposes, adsorption of ammonia on silica, vanadia on silica, titania, vanadia on titania and titania on silica was also investigated. Typically, hydrogen-bonded and coordinatively adsorbed ammonia and NH 4 + species were observed. V OH groups could be detected on vanadia on silica, their acidities being higher than those of Si OH groups. The relative concentrations of hydrogen-bonded and NH 4 + species were significantly reduced in comparison with the coordinatively adsorbed ammonia when the vanadia on titania on silica catalysts were pretreated at 773 K in vacuo. This trend was much less pronounced when the titania content was increased from 8 to 34% (w/w). It is speculated that the observed high activity for the NO + NH 3 reaction for catalysts containing 34% (w/w) of titania is related to their ability to retain high concentrations of acidic surface hydroxyl groups under the reaction conditions.