Francisco Tzompantzi

Effects of structural defects and acid-basic properties on the activity and selectivity of isopropanol decomposition on nanocrystallite sol-gel alumina catalyst

The surface acid-basic properties of sol-gel alumina catalysts were studied by Fourier transform infrared FTIR spectroscopy of pyridine adsorption and temperature-programmed desorption of CO and NH . The number of acid and 23 basic sites on the samples varied with the calcination temperatures of the samples. The populations of the three different aluminum ions—tetrahedral, pentacoordinated and octahedral, which were identified by the 27 Al MAS NMR, were strongly affected by the sample calcination temperature and the crystalline composition. In the reaction temperature range between 100 and 2508C, isopropanol decomposition on sol-gel alumina catalysts was carried out. It was found that isopropanol decomposition on alumina catalyst was a structural-defect sensitive reaction. The dehydrogenation selectivity to acetone depended on the surface basic sites and the concentration of aluminum vacancies in the crystalline structure of g-Al O. 23 Bimolecular reaction to isopropylether was largely governed by the pentacoordinated aluminum ions which were related to the coordinately unsaturated aluminum ions. A mechanism for the formation of isopropylether was proposed: oxygen . q vacancies were suggested to involve the adsorption step of isopropanol, an intermediate species, CH HC , reacted with 32

Photocatalytic Activity in the 2,4-Dinitroaniline Decomposition Over TiO2 Sol-Gel Derived Catalysts

Titania was prepared by the sol-gel method from titanium alkoxide. Depending on the pH of the gelling solution, specific surface areas between 88 and 10 m2/g were obtained. The band gap (Eg) of the samples was found between 3.05 and 3.32 eV. In samples gelled at pH5 and 9 and calcined at 400°C only anatase phase is observed, while for pH3 and pH7 brookite, anatase and rutile or anatase-rutile phases coexist. It was found that the photoactivity in the 2,4-dinitroanailine decomposition depends on the Eg and on the crystalline phases. The highest activity corresponds to the catalysts having the lowest Eg and more than one crystalline phases co-existing.

Effect of sulfation methods on TiO2–SiO2 sol–gel catalyst acidity

A series of x TiO2‐SiO2 (xD1.7, 4.0 and 6.7 wt.% TiO2) binary mixed oxides was prepared by a sol‐gel method in acidic and basic conditions. In order to upgrade the acidic properties of the obtained solids, their sulfation was carried out in three different ways: (1) by in situ (H2SO4 was admixed with the gel), (2) impregnating the dried solids with aqueous solutions of H2SO4, and (3) by impregnating as in (2) but with (NH4)2SO4. FTIR-pyridine adsorption and benzene deuteroexchange showed that the acid site strength depends on the sulfation method. The highest values of total acidity, determined by ammonia thermodesorption, correspond to the in situ sulfated samples. The obtained pore size distribution (4.0‐5.0 nm) was narrow and the specific BET areas (250‐350 m 2 /g) were large. X-Ray diffraction, RDF, XPS spectroscopy and catalytic activity in the 2-butanol dehydration show that one step sulfated in situ TiO2‐SiO2 sol‐gel preparations resulted in catalysts with homogeneous and strong acidity.

Photocatalytic degradation of 2,4-dichlorophenol with MgAlTi mixed oxides catalysts obtained from layered double hydroxides

MgAl and MgAlTi mixed oxides were obtained from the thermal treatment of LDH materials synthesized by the sol-gel method; these materials were characterized by N2 physisorption, XRD, UV-vis, XPS, EDS-SEM and TEM techniques. According to the results, Ti was incorporated in the LDH layer when content in the material was low. The MgAl and MgAlTi mixed oxides were evaluated in the photo-degradation of 2,4-dichlorophenol (2,4-DCP) in the presence of UV light. A superior efficiency in the photo-degradation of 2,4-DCP, in comparison with the Degussa P-25 TiO2 reference catalyst was observed, reaching a total decomposition of the 2,4-DCP molecule in less than 60 min. According to the results, Ti was incorporated in the LDH layer when the content in the material was low. The MgAl and MgAlTi mixed oxides were evaluated in the photo-degradation of 2,4-dichlorophenol (2,4-DCP) in the presence of UV light. A superior efficiency in the photo-degradation of 2,4-DCP with the MgAl and MgAlTi mixed oxides, in comparison with the Degussa P-25 TiO2 reference catalyst was observed, reaching a total decomposition of the 2,4-DCP molecule in less than 60 min.

Effect of Zirconia Precursor on the Properties of ZrO2-SiO2 Sol-Gel Oxides

Sol-gel zirconia-silica oxides were synthesized with two zirconium precursors, zirconium n-butoxide and zirconium acetylacetonate, and two different hydrolysis catalysts, HCl and H2SO4. The samples prepared with HCl were additionally sulfated with a 1 M solution of H2SO4. Characterization was performed with FTIR and 29Si-MAS-NMR spectroscopy, as well as with nitrogen adsorption. Because zirconium and silicon alkoxides have different hydrolysis rates, it was necessary to perform a pre-hydrolysis of the silicon alkoxide before mixing. The atom distribution in the ZrO2-SiO2 system depended on the zirconium precursor, which also determined the zirconium incorporation in the silica lattice, which was greater for zirconium acetylacetonate. The zirconium precursor also was responsible for the silanol concentration, which increases when samples were sulfated. Sulfating stabilizes the specific surface area. On sulfate samples calcined at 800°C BET areas larger than 500 m2/g were obtained.

ZrO2−SiO2 mixed oxides as supports for platinum catalysts

Mixed ZrO2−SiO2 oxides were prepared by the sol-gel method and used as supports for platinum catalysts. Activity tests show that Pt/ZrO2−SiO2 catalysts can be used in the aromatization of n-heptane.

EVALUATION OF SULFATED ALUMINAS SYNTHESIZED VIA THE SOL-GEL METHOD IN THE ESTERIFICATION OF OLEIC ACID WITH ETHANOL

Sulfated aluminas were synthesized via the sol-gel method by means of the addition of different ions during the gelling of titanium alkoxide. Both the Lewis and Brönsted acid sites were formed, depending on the sulfate precursor. The catalytic activity of sulfated aluminas was tested by performing the esterification reaction of free fatty acids with ethanol at 86°C by using a fatty acid-alcohol with a molar ratio of 1:10 and 3 wt.% of catalyst. The selectivity towards ethyl ester was 100% in all the catalysts. Through this study, we found that sulfated aluminas showed a higher activity in the esterification reaction than unsulfated γ-alumina. It has been found that the conversion of oleic acid varies according to the sulfate precursor (NH4)2SO4 > H2SO4 > NiSO4, which affects both the acidity strength and textural properties of the catalysts.

Effect of Sn addition on the catalytic properties of the metallic phase in Pt−Sn/Al2O3 catalysts

Platinum-tin/alumina supported catalysts have been studied. The TPR results show an assisted reduction of tin by platinum. The effect of alloying in cyclohexane dehydrogenation, o-xylene hydrogenation and cyclopentane hydrogenolysis is discussed.AbstractИсследовали платино-оловянные катализаторы, нанесенные на оксид алюминия. Результаты ТПВ свидетельствуют о восстановлении олова платиной. Овсуждают эффект сплавления в реакциях дегидрогенизации циклогексана, гидрировании о-ксилола и гидрогенолизе циклопентана.

Photocatalytic properties of Ba3Li2Ti8O20 sol–gel

Samples of Ba3Li2Ti8O20 were prepared by the sol–gel method at pH 3 and 9 using acetic acid and ammonia hydroxide respectively as hydrolysis catalysts. The band gap (Eg) of the solids prepared was calculated from the UV-Vis absorption spectra of samples thermally treated at different temperatures, the values obtained ranging from 3.37 to 3.09 eV. The Eg values of the powders synthesized at pH 9 were higher than those of samples prepared at pH 3. Surface characterization of the solids was carried out from adsorption isotherms and FTIR studies, and their photocatalytic activities on 2,4-dinitroaniline degradation were also measured. The decomposition rate followed Langmuir–Hinshelwood kinetics. According to the calculated kinetic parameters, better results were obtained once the crystalline structure of Ba3Li2Ti8O20 had formed.

IMPROVED SELECTIVITY TO C8-OLEFINS FOR ISOBUTENE OLIGOMERIZATION ON NIO-W2O3/Al2O3 CATALYSTS

Isobutene oligomerization on W2O3/Al2O3 and NiO-W2O3/Al2O3 catalysts (20 wt.% W2O3 and 5 wt.% NiO) was studied. The catalysts were prepared by impregnating ammonium tungstanate and nickel nitrate on a γ-alumina sol-gel support. The XRD patterns of the samples calcined at 500°C show the presence of large W2O3 conglomerates on the W2O3/Al2O3 sample and smaller ones on the NiO-W2O3/Al2O3 catalyst. Pyridine-FT-IR absorption spectra study shows a higher acidity on the nickel-containing sample. The isobutene oligomerization was carried out in a gas-phase flow reactor (50°–150°C), and selectivity as high as 100% to the formation of the olefins fraction was obtained. The role of NiO coordinating the π-allyl adsorption of the olefins as well as its role to the high selectivity were discussed.