G. Colón

Advanced Nanoarchitectures for Solar Photocatalytic Applications

UV-Visible ار راد ن .د TiO2 ( تیفرظ راون مان هب نورتکلا یاراد یژرنا زارت لماش VB و ) رگید زارت ی یژرنا اب ( ییاناسر راون مان هب نورتکلا زا یلاخ و رتلااب VB یم ) .دشاب ت ود نیا نیب یژرنا توافت یژرنا فاکش زار ، پگ دناب هدیمان یم .دوش هک ینامز زا نورتکلا لاقتنا VB هب VB یم ماجنا دریگ ، TiO2 اب ودح یژرنا بذج د ev 2 / 3 ، نورتکلا تفج کی دیلوت یم هرفح .دیامن و نورتکلا هرفح ی نا اب هدش دیلوت یم کرتشم حطس هب لاقت ثعاب دناوت شنکاو ماجنا اه یی ددرگ . TiO2 دربراک ،دراد یدایز یاه هلمج زا یم ناوت اوه یگدولآ هیفصت یارب (CO2) و بآ و ... نآ زا هدافتسا درک .

Modification of the oxygen storage capacity of CeO2–ZrO2 mixed oxides after redox cycling aging

Abstract High surface area CeO2–ZrO2 mixed oxides were treated at 900–950°C either under wet air or under successive reducing and oxidizing atmospheres in order to study the evolution of the oxygen storage capacity (OSC) of these solids after different aging treatments. Several complementary methods were used to characterize the redox behavior: temperature programmed reduction (TPR) by H2, TPO, magnetic susceptibility measurements to obtain the Ce3+ content, FT-IR spectroscopy of adsorbed methanol and a method to compare the oxygen buffering capacity (OBC) of the oxides. All the results confirm that the mixed oxides exhibit better redox properties than pure ceria, particularly after aging. The enhancement in the OSC at moderate temperature has to be related to a deeper penetration of the reduction process from the surface into the under-layers. Redox cycling aging promotes the reduction at low temperature of all the mixed oxides, the improvement being much more important for low surface area aged samples. The magnitude of this effect does not depend on the BET surface areas which have similar values after cycling. This underlines the critical influence that the preparation and activation procedure have on the final OSC behaviors of the ceria–zirconia mixed oxides.

Surface and structural characterization of CexZr1-xO2 CEZIRENCAT mixed oxides as potential three-way catalyst promoters

The textural and structural properties of high specific surface area (HS) CexZr1-xO2 mixed oxides (CeZrMO) and their modification upon thermal aging have been investigated. Results from BET area determination and complete porosity analysis, as well as high-resolution electron microscopy, XRD, Raman and FTIR spectroscopies are presented. Some relationships between the molar composition of the binary systems and their textural and structural properties are presented. In addition, it has been possible to propose an explanation for structural features of the mixed oxides (solid-solution structures and possible phase segregation) as a function of Ce content, a point of great interest for the knowledge of phase composition and stability of CeZrMO.

TiO2 activation by using activated carbon as a support: Part I. Surface characterisation and decantability study

In the present work, the effect of mixing TiO2 with different portions of activated carbon (AC) has been studied. Transmission electron microscopy (TEM), scanning electron micrograph (SEM), laser scattering, FTIR and UV spectrophotometric analysis have shown changes of some of the TiO2 physico-chemical characteristics in catalysts containing an AC concentration lower than 15% in weight. Changes in the catalyst colour, the vibration bands of the hydroxylic groups from FTIR studies and the UV absorption spectrum have been observed. It seems that these changes correspond with TiO2 acid–base changes. SEM and TEM studies show a perfect TiO2 particles distribution on the AC surface in catalysts with lower AC contents, that also yields a homogeneous particle size distribution. One of the most interesting features of the resulting catalysts is their fast decantability in comparison with that of TiO2. This way one of the most important drawbacks of photocatalysis, the catalyst separation from the solution, may be overcome. The present study shows that the AC not only exerts a synergistic effect when is combined with TiO2 as some authors suggest, but it also modifies the catalyst characteristics.

Photocatalytic deactivation of commercial TiO2 samples during simultaneous photoreduction of Cr(VI) and photooxidation of salicylic acid

Abstract TiO 2 Degussa P25 and Hombikat UV-100 photocatalysts have been widely characterized. Certain structural and morphological differences have been found. Photocatalytic behaviour has been studied for Cr(VI) reduction and for salicylic acid oxidation, in photoreactions with single and mixed substrates. In the photoreaction with mixed substrates, higher conversion values have been found in comparison to those observed for single substrates. However, clear deactivation process can be noticed. This photocatalytic deactivation is higher for Degussa P25 photocatalyst than for Hombikat UV-100 and can be explained in terms of the surface features exhibited for both TiO 2 during the photoprocesses.

Synthesis, characterization and photocatalytic properties of iron-doped titania semiconductors prepared from TiO2 and iron(III) acetylacetonate

Specimens of iron-doped titania containing different amounts of Fe (0.5–5%) were prepared from TiO2 (Degussa P-25) and Fe(III) acetylacetonate by the wet impregnation method. Samples were characterized by X-ray diffraction analysis, specific surface area (BET) measurements, SEM-EDX, atomic absorption and IR and diffuse reflectance spectra. From the structural point of view, the samples were similar to those obtained with Fe(NO3)3 · 9H2O as the precursor, but with a more homogeneous distribution of iron for each mixed oxide sample on the particle surfaces but not between particles. The photocatalytic activity of these samples under near-UV irradiation was better for oxalic acid degradation than for EDTA, and similar for both types of mixed oxide samples. Mixed oxides showed however lower activity than TiO2. Some photodegradation under visible irradiation, not occurring with TiO2, could be observed for oxalic acid when using 5% Fe-containing samples.

TiO2 activation by using activated carbon as a support: Part II. Photoreactivity and FTIR study

Abstract It has been demonstrated that the modification of the TiO2 acid–base properties by the presence of activated carbon (AC) considerably modify the interaction of some molecules with the catalyst surface and hence its photocatalytic characteristics. FTIR studies have shown that while phenol interacts with TiO2 yielding a phenoxide, in the catalyst low AC containing catalysts mixtures the surfacial hydroxylic groups are inserted in the aromatic ring in the symmetric position to the –OH group. Additionally, the 4-aminophenol study shows that the molecule interacts with the TiO2 surface by means of the amino group, while in the catalyst containing AC the interaction takes place through the hydroxylic group. These results have confirmed the catalyst acid–base properties changes determined by the characterisation studies already performed. Also, it has been observed that catalysts with the lowest AC content show better catalytic behaviour than the untreated TiO2 and those with higher AC load. Another interesting result is the efficiency of these catalysts under solar irradiation.

A novel preparation of high surface area TiO2 nanoparticles from alkoxide precursor and using active carbon as additive

Abstract TiO 2 nanoparticles have been prepared by a novel alkoxide sol–gel precipitation. The presence of active carbon in different percentages could act as an interesting template. Upon calcination, carbon is eliminated leaving surface features significantly different from TiO 2 prepared in the absence of carbon. Wide surface and structural characterisation of samples have been carried out. Correlations with carbon percentage is pointed out from this characterisation. Interesting spherical aggregates of nanosized TiO 2 are observed from TEM images probably stabilised by the presence of carbon. Physicochemical correlations made will be very useful in further application of these TiO 2 to be used as potential high surface area photocatalyst.

Novel Bi2WO6–TiO2 heterostructures for Rhodamine B degradation under sunlike irradiation

Highly efficient Bi(2)WO(6)-TiO(2) heterostructure is synthesized by means of a hydrothermal method having highly photoactivity for the degradation of Rhodamine B under sunlike irradiation. From the structural characterization it has been demonstrated that TiO(2) is incorporated on the Aurivillius structure. Interesting synergetic effect between TiO(2) and Bi(2)WO(6) leads to an improved charge carrier separation mechanism, causing the excellent photocatalytic performance under sunlike irradiation. The photocatalytic performance of Bi(2)WO(6) and Bi(2)WO(6)-TiO(2) was compared under different irradiation conditions and using increasing Rhodamine B concentration up to 25 ppm. After the photocatalytic analysis of both systems, the mineralization efficiency of the heterostructure appears significantly higher with respect to Bi(2)WO(6).

Liquid-phase alkylation of naphthalene by isopropanol over zeolites. Part II : Beta zeolites

The title reaction has been studied on various HY-based catalysts. Surface acidity has been evaluated by adsorption microcalorimetry and FTIR analysis, using pyridine as probe molecule. Catalytic tests were carried out at 623 K and 40 bar in liquid phase, with decalin as solvent, in flow reactor. Isopropylation is accompanied by oligomerisation/cracking of the reactant alcohol, cracking of the solvent, isomerization of the products of the main reaction. Pore filling by coke is fast for non-dealuminated HY, where naphthalene conversion remains high due to the occurrence of transalkylation between polyisopropylnaphthalenes trapped in the pores and naphthalene; this does not occur on dealuminated HY, owing to the low density of the acid sites and the presence of a secondary mesoporous system which allows easy diffusion of the reaction products in the zeolite pores.