[show abstract][hide abstract] ABSTRACT: Gas-solid heterogeneous photocatalytic oxidation (PCO) of cyclohexane in humidified air over TiO2 and
Pt/TiO2 catalyst was studied.
Pt/TiO2 photocatalysts were synthesized by photodeposition method at different Pt loadings
(0.5–2 wt.%). The addition of 0.5 wt.% Pt does not significantly modify the TiO2 properties. The increase
in Pt loading induces to an aggregation of metallic particles on TiO2 surface.
The cyclohexane PCO was performed in a fluidized bed photoreactor at 60 and 100 ◦C. Pure TiO2 was
more active than 1 and 2 wt.% Pt/TiO2 samples at 60 ◦C. Nevertheless, the conversion level increases with
temperature on Pt/TiO2 photocatalysts. The cyclohexane was mineralized into CO2, water and low amount
of CO. A beneficial effect of Pt addition was found, since total CO2 selectivity was obtained. The Pt/TiO2
photocatalysts prepared by photodeposition provide the total cyclohexane PCO without CO production.
Photocatalysts deactivation was not observed in any performed test. Evidence of an opportune tuning of
temperature is highlighted.
[show abstract][hide abstract] ABSTRACT: The heterogeneous photocatalytic partial oxidation of cyclohexane in gas-phase as an alternative green process
for fine chemicals synthesis was successfully achieved on Au/TiO2 photocatalysts prepared by photodeposition
technique. Different gold loadings ranging between 0.5 and 2 wt.% of photodeposited Au on TiO2 synthesized
by sol-gel method were obtained by changing the concentration of gold precursor at fixed illumination intensity
and time. The cyclohexane partial photoxidation was conducted in a gas-solid photocatalytic fluidized bed reactor
at high illumination efficiency. Main observed reaction products were cyclohexanol, cyclohexanone and CO2.
The resulting selectivity was dramatically influenced by the gold content. The reaction temperature was a critical
parameter to reach the photocatalysts stability, avoiding deactivation phenomena while the tuning of Au content
of the photocatalysts, resulted in the promotion of the formation of cyclohexanol or cyclohexanone with high
selectivity. In particular, by increasing Au content, the process selectivity is completely reversed, passing from
high cyclohexanol selectivity (75%) to high selectivity to cyclohexanone (80%). These promising results
evidenced that Au/TiO2 catalysts in the selected operating conditions, are effective materials for the synthesis of
cyclohexanone and cyclohexanol in gas-phase by photocatalysis, at very low reaction temperatures and without
the additional step of catalyst recovering needed in the liquid partial oxidation of cyclohexane.
[show abstract][hide abstract] ABSTRACT: Ethanol oxidative dehydrogenation over Pt/TiO2 photocatalyst, in the presence and absence of blue phosphors, was performed. The catalyst was prepared by photodeposition of Pt on sulphated TiO2. This material was tested in a gas-solid photocatalytic fluidized bed reactor at high illumination efficiency. The effect of the addition of blue phosphors into the fluidized bed has been evaluated.
The synthesized catalysts were extensively characterized by different techniques. Pt/TiO2 with a loading of 0.5wt% of Pt appeared to be an active photocatalyst in the selective partial oxidation of ethanol to acetaldehyde improving its activity and selectivity compared to pure TiO2. In the same way, a notable enhancement of ethanol conversion in the presence of the blue phosphors has been obtained. The blue phosphors produced an increase in the level of ethanol conversion over the Pt/TiO2 catalyst, keeping at the same time the high selectivity to acetaldehyde.
International Journal of Photoenergy 08/2012; 2012. · 2.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: The influence of Pt features, such as particle size, dispersion, oxidation state and amount of metal, on the
improvement of the photoactivity of TiO2 for phenol and methyl orange degradation was studied.
The size of Pt deposits was precisely controlled by changing deposition time under medium light
intensity during the photodeposition, with sizes ranging from 3 to 6 nm. Pt oxidation state was also
strongly dependent on the photodeposition time.
Photocatalytic activity results showed that the fraction of metallic platinum (Pt0) was the crucial factor
for the improvement of the activity. When the fraction of Pt0 was similar, metal deposit size became the
dominant parameter influencing the activity.
The influence of the substrate to be degraded (phenol or methyl orange) was also studied.
Applied Catalysis B Environmental 07/2012; 126:76. · 5.83 Impact Factor
[show abstract][hide abstract] ABSTRACT: Au/TiO2 photocatalysts were used in ethanol oxidative dehydrogenation. Catalysts at gold loading ranging between
0.5-2 wt.% were synthesized by photodeposition (using different deposition times: 15 and 120 min) over an ownprepared
TiO2 by sol-gel method. For reference purposes, a commercial 1 wt.% Au/TiO2 catalyst (AUROliteTM,
Strem Chemicals) was also tested. Photocatalytic reactions were carried out in a gas-solid photocatalytic fluidized
bed reactor. Catalytic activity depends strongly both on Au loading and on the material properties, such as particle
size and distribution of metal on titania surface. Acetaldehyde was the main reaction product, with ethylene,
crotonaldehyde and CO2 as by-products. An important improvement of TiO2 photoactivity was achieved for the
catalyst with 0.5 wt.% gold prepared with 120 min deposition time. For an ethanol inlet concentration of 0.2
vol% at 60 °C, the maximum conversion and acetaldehyde selectivity were 82% and 95%, respectively. These
values are considerably higher than those obtained over pristine TiO2 and over the commercial catalyst.
[show abstract][hide abstract] ABSTRACT: Heterogeneous photocatalytic partial oxidation of ethanol was studied over different Pt/TiO2 as an alternative
green process for acetaldehyde production.
The catalysts were synthesized through the photodeposition of Pt over sol–gel TiO2 with platinum loads
of 0.5 and 1 wt.%. The effect of some experimental conditions during photodeposition, such as deposition
time and Pt loading, was investigated. A short deposition time at 0.5 wt.% Pt nominal loading led to small
average particle size of platinum (2–3 nm) homogeneously distributed all over the TiO2 surface.
Ethanol partial oxidation was tested in a gas–solid photocatalytic fluidized bed reactor at high illumination
efficiency, using different reaction temperatures. Activity results have been correlated with
characterization results of the different samples. Platinized samples prepared with short deposition times
showed high conversion levels and high selectivity to acetaldehyde. Materials prepared at longer times,
120 min, showed selectivities >98%, although with lower ethanol conversion.
Sample with 1 wt.% Pt loading prepared with 15 min deposition time combined a good compromise
between a relevant ethanol conversion and a very high selectivity to acetaldehyde at a selected reaction
temperature of 80 ◦C, with an acetaldehyde yield higher than 80%, which make of this catalyst a good
candidate for acetaldehyde production by photocatalysis.
[show abstract][hide abstract] ABSTRACT: A series of Bi3+-doped TiO2 catalysts with a doping concentration up to 2wt% were prepared by a sol–gel hydrothermal method. The prepared photocatalysts were characterized by different techniques to determine their structure, morphology and light absorption properties. The activities were evaluated in the photocatalytic oxidation of phenol in aqueous solution under UV–vis illumination. The experimental results indicate that the presence of Bi3+ in TiO2 catalysts enhances the photocatalytic reaction of phenol degradation, although the efficiency of the process markedly depends on the nominal content of the Bi3+ and on the calcination temperature. It was found that the optimal dosage of 0.5wt% Bi3+ in TiO2 and calcinations at 600°C 4h achieved the fastest reaction of phenol degradation under the experimental conditions. From the comparison of the initial rates of the photocatalytic degradation of phenol between home prepared undoped and Bi3+-doped TiO2 with commercial TiO2 Degussa P25, it can be inferred that home prepared TiO2 calcined at temperatures above 500°C clearly exceed the photocatalytic performance of P25. When bismuth is incorporated, the reaction rate values are even higher, especially at 600°C. Even when Bi3+-doped TiO2 (0.5wt% Bi3+) calcined at 600°C has almost the same BET surface than P25, its activity is better. In particular, the reaction rate for the sample with a 0.5% mass content of Bi3+ calcined at 600°C not only present higher value with respect to the other series but also a degree of mineralization close to 100%.
[show abstract][hide abstract] ABSTRACT: Highly efficient Bi2WO6–TiO2 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 TiO2 is incorporated on the Aurivillius structure. Interesting synergetic effect between TiO2 and Bi2WO6 leads to an improved charge carrier separation mechanism, causing the excellent photocatalytic performance under sunlike irradiation. The photocatalytic performance of Bi2WO6 and Bi2WO6–TiO2 was compared under different irradiation conditions and using increasing Rhodamine B concentration up to 25ppm. After the photocatalytic analysis of both systems, the mineralization efficiency of the heterostructure appears significantly higher with respect to Bi2WO6.
Journal of hazardous materials 01/2011; 185(2):1425-1434. · 4.14 Impact Factor
[show abstract][hide abstract] ABSTRACT: The influence of experimental conditions during the photodeposition in the preparation of supported Au on TiO2 has been studied. Besides preparation pH, light intensity and deposition time showed to have a high influence on the final properties of gold deposits.
Photodeposition using illumination with a high light intensity UV–vis lamp (140W/m2 UVA range) resulted to be an ineffectivemethodfor obtaining nanoparticles of goldonthe titania, producing very large and poorly distributed gold deposits. Thus obtained materials did not show any important improvement of their photocatalytic activity tested for phenol oxidation.
By contrast, photodeposition using a low light intensity of illumination (0.15W/m2 UVA range), produced materials with notably improved photocatalytic activity. The illumination with such a low light intensity allowed the control of the amount, aggregation and oxidation state of gold by changing deposition time, enabling a feasible method of tailoring Au–TiO2 with the appropriate properties for a high photocatalytic activity.
Best photocatalytic behaviour for phenol photodegradation was obtained for Au–TiO2 samples prepare by photodeposition at low light intensity with 120 min photodeposition time for catalysts with a 0.5% and 1% nominal content of gold and with 60 min photodeposition time for catalyst with a 2% nominal content of gold.
[show abstract][hide abstract] ABSTRACT: Highly efficient Bi(2)WO(6)-TiO(2) heterostructures are synthesized by means of a hydrothermal method; they have high photoactivity for the degradation of rhodamine B under sunlike irradiation. An interesting synergetic effect between TiO(2) and Bi(2)WO(6) leads to an improved charge carrier separation mechanism, causing the excellent photocatalytic performance.
Chemical Communications 07/2010; 46(26):4809-11. · 6.38 Impact Factor
[show abstract][hide abstract] ABSTRACT: TiO2–SiO2 mixed oxides have been synthesised and modified by Ag and Pt deposition. Due to the effect of the silica on the mixed oxide, the prepared materials presented high surface areas and stabilised anatase as the only crystalline phase after calcination at 700°C. Even using the same photodeposition experimental conditions, the yield for metal deposition depended highly on the metal considered, being much lower for Ag deposition. XPS studies permitted to estimate metal dispersion and oxidation state of the different samples, being both factors of high importance regarding photocatalytic improvement by metal deposition.
[show abstract][hide abstract] ABSTRACT: Platinum doped TiO2 materials were studied for the gas phase photocatalytic degradation of toluene. Platinum deposition was achieved by photodeposition method over TiO2 prepared by means of a sol–gel route. The effect of sulphuric acid pretreatment on the further platinisation process has been extensively studied. From the wide structural and surface analysis of the catalysts an interesting synergetic effect has been demonstrated. The previous sulphate treatment over TiO2 leads to improved dispersion of the Pt which presents a lower aggregation and homogeneous cluster size. This fact, together with the adequate control of anatase structural and surface parameter due to the sulphate treatment, renders a good photocatalytic performance for toluene oxidation reaction. The highest reaction rates and CO2 selectivities have been obtained for Pt–S–TiO2 samples.
[show abstract][hide abstract] ABSTRACT: A series of Au/TiO2 samples with gold loadings ranging from 0.11% to 1.26% have been prepared by deposition–precipitation, characterised by means
of XRD, SBET, XRF, TEM, XPS and DR UV–Vis techniques and tested in the gaseous CO oxidation and photocatalytic degradation of phenol in
aqueous media. The catalytic performances of the solids on both reactions depend on the gold content. Besides this, the gold
particle size plays a determinant role in the catalytic activity for the CO reaction, but apparently its influence on the
photocatalytic activity appears to be negligible and only very small gold particles seem to participate on the photocatalytic
process. On the other hand, the electronic properties of the solids, measured by its band gap energy, are a key factor in
the photochemical activity but do not have a clear influence in the CO oxidation reaction.
[show abstract][hide abstract] ABSTRACT: ZnO nanoparticles have been prepared by amine template assisted sol–gel precipitation and further hydrothermal treatment. We have investigated the effect of different pH values achieved by means of triethylamine (TEA) addition in the final surface and structural properties. Two sets of samples were obtained after thermal treatment, one with no hydrothermal pre-treatment and a second hydrothermally pre-treated. Surprisingly the precipitate obtained after the amine addition also exhibits good photocatalytic properties. It has been stated that calcination treatment leads in both sets of samples to a significant improvement in the photocatalytic properties of the studied systems. Therefore, interesting comparison has been performed between hydrothermal pre-treated and direct thermal treated samples. Surface and morphological features notably differ from ZnO prepared using different synthetic route. Wide surface and structural characterization of the samples have been carried out, and correlations with precipitation pH are pointed out from this characterization. In all cases, the amine templated ZnO obtained exhibit high conversion values for phenol photo-oxidation reaction. Further calcination treatment in all of the studied samples clearly leads to photocatalytic conversions higher than that exhibited by TiO2 Degussa P25. This fact is even more significant if we consider that hydrothermally and calcined ZnO exhibit almost null surface area values, leading to a startling intrinsic photoactivity. The structural excellence (crystallinity, lack of defects, crystallite size, etc.) of such systems is clearly responsible for their high photoactivity values.
[show abstract][hide abstract] ABSTRACT: An important improvement of the photocatalytic activity of sol–gel prepared TiO2 has been achieved by sulphate pre-treatment, calcination at high temperature and further platinisation of the samples.The presence of sulphuric acid clearly stabilised TiO2 surface area against sintering, maintaining at the same time anatase phase until higher calcination temperatures than in non-sulphated samples. Platinisation of the samples with different nominal amounts of platinum (from 0.5 to 2.5wt%) was performed and the influence of sulphate treatment on the dispersion and deposit size of platinum on the TiO2 surface was studied.Characterisation results and photocatalytic activity of these catalysts were compared with those of unmodified TiO2. Simultaneously sulphated and platinised TiO2 samples were highly active for phenol degradation, used as model reaction for the photocatalytic studies, having higher activities than only platinised or only sulphated samples. The activity of these samples were several orders of magnitude higher than that of the commercial TiO2 Degussa P25 (platinised or unmodified) as well, with independence of the nominal amount of platinum of the samples.A wide characterisation of the samples was performed and correlations between characterisation results and activity properties are reported.