14475-63-9Relevant academic research and scientific papers
Influence of the preparation method on the morphological and composition properties of Pd-Au/ZrO2 catalysts and their effect on the direct synthesis of hydrogen peroxide from hydrogen and oxygen
Menegazzo, Federica,Signoretto, Michela,Manzoli, Maela,Boccuzzi, Flora,Cruciani, Giuseppe,Pinna, Francesco,Strukul, Giorgio
, p. 122 - 130 (2009)
Bimetallic Pd-Au samples supported on zirconia were prepared by different methods and tested for the direct synthesis of hydrogen peroxide under very mild conditions (room temperature and atmospheric pressure), outside the explosion range and without halides addition. Further catalytic tests were performed at higher pressure using solvents expanded with CO2. Samples were characterized by N2 physisorption, metal content analysis, XRD, HRTEM combined with X-ray EDS, TPR, and FTIR. The effect of the addition of gold to Pd in enhancing the yield of H2O2 is sensitive to the preparation method: the best catalytic results were obtained by depositing gold by deposition-precipitation (DP) and by introducing in a second step Pd by incipient wetness impregnation. The origin of the differences between samples is discussed. The role of Au in the catalytic reaction seems to be a complex one, changing the chemical composition of the metallic particles, their morphology, and charge of the exposed Pd sites.
On the effect of the strength of acid sites in heterogeneous catalysts on the activity in the skeletal isomerization of n-butane
Shmachkova,Kotsarenko,Paukshtis
, p. 554 - 557 (2004)
The catalytic activity of three groups of acid catalysts different in the nature and strength of acid sites in the skeletal isomerization of n-butane was studied. It was found that the strength of the sites did not correlate with the rate of the reaction.
Synthesis of lead zirconate titanate from an amorphous precursor by mechanical activation
Junmin, Xue,Wang, John,Weiseng, Toh
, p. 139 - 146 (2000)
Many of the chemistry-based processing routes for functional ceramics inevitably involve calcining the chemical-derived precursors at an intermediate/high temperature, in order to form the designed ceramic phase. This is very undesirable, although widely used, as the calcination can result in an extensive degree of crystal growth and particle coarsening at the calcination temperature and therefore ruins almost all the advantages offered by the chemistry-based processing routes, such as an ultrafine particle size and high sintering-reactivity. Using a specifically designed PZT precursor prepared by co-precipitation, it is demonstrated that the precursor-to-ceramic conversion can alternatively be realized by mechanical activation. In this connection, a single phase, nanocrystalline perovskite PZT powder has been successfully derived from an amorphous hydroxide precursor by mechanical activation. The resulting PZT powder was well dispersed, and the particle size was in the range of 30-50 nm, as observed using the scanning electron microscopy and transmission electron microscopy. This is in contrast to the poor particle characteristics, represented by very coarse and irregular particle and agglomerate sizes, for the powder derived from calcination at 750 °C. The activation-triggered PZT powder was sintered to a density of 97.6% theoretical density at 1150 °C for 1 h. Sintered PZT ceramic exhibits a dielectric constant of 927 at room temperature and a peak dielectric constant of approximately 9100 at the Curie point of 380 °C when measured at the frequency of 1 kHz.
Thermoanalytical investigations on hydrous zirconia
Schuster, G.,Braun, G.,Henkel, K.,Querner, G.
, p. 471 - 478 (1988)
The variations in the thermoanalytical curves for three differently produced powders of hydrous zirconia are discussed in connection with X-ray measurements and powder-metallurgical characterization. They were shown to characterize ZrO2-H2O bonding and the thermal treatment for the calcination of hydrous zirconia. They allowed selection of the product with the most favorable microstructure for a high sinter activity, an explanation of the phase formation and phase transformations, and estimations of energy content of the amorphous material and the thermal stability of the tetragonal phase. It was shown that thermal analysis is an appropriate method for the optimizing of ZrO2-powder production.
FT-IR and laser Raman spectroscopic investigation of the formation and stability of low temperature t-ZrO2
Stefanic,Music,Popovic,Sekulic
, p. 391 - 394 (1997)
The influence of the preparation chemistry on the formation and the stability of metastable t-ZrO2 was studied. γ-Irradiation has very small (if any) influence on the t-ZrO2 → m-ZrO2 transition, while increased temperature and pressure caused gradual transition of pure t-ZrO2 to m-ZrO2. Metastable t-ZrO2 containing SO4/2- impurities proved to be more stable, and its transition was not uniform. The mentioned effects were monitored by FT-IR and laser Raman spectroscopy. X-ray diffraction was used as a complementary technique.
Thermodynamic complexity of sulfated zirconia catalysts
Liu, Naiwang,Guo, Xiaofeng,Navrotsky, Alexandra,Shi, Li,Wu, Di
, p. 158 - 163 (2016)
A series of sulfated zirconia (SZ) catalysts were synthesized by immersion of amorphous zirconium hydroxide in sulfuric acid of various concentrations (1–5?N). These samples were fully characterized by X-ray diffraction (XRD), thermogravimetric analysis and mass spectrometry (TGA-MS), and aqueous sulfuric acid immersion and high temperature oxide melt solution calorimetry. We investigated the enthalpies of the complex interactions between sulfur species and the zirconia surface (ΔHSZ) for the sulfated zirconia precursor (SZP), ranging from ?109.46?±?7.33 (1?N) to ?42.50?±?0.89 (4?N) kJ/mol S. ΔHSZ appears to be a roughly exponential function of sulfuric acid concentration. On the other hand, the enthalpy of SZ formation (ΔHf), becomes more exothermic linearly as sulfur surface coverage increases, from ?147.90?±?4.16 (2.14?nm?2) to ?317.03?±?4.20 (2.29?nm?2) kJ/mol S, indicating formation of energetically more stable polysulfate ?species.
Influence of precipitation chemistry and ball-milling on the thermal behavior of zirconium hydroxide
Stefanic,Music,Sekulic
, p. 119 - 133 (1996)
Zirconium hydroxide precipitates, obtained by rapid precipitation at pH 2.5, 7.5, and 10.5, were ball-milled for up to 60 h and then heated inside a differential scanning calorimeter (DSC) at temperatures of up to 600°C. Crystal phases produced after heating were analyzed by FTIR and laser Raman spectroscopy. It was found that without regard to the precipitation pH the first stage of ball-milling caused an increase of the crystallization temperature that resulted in the formation of pure t-ZrO2. The second stage of ball-milling caused a decrease of the crystallization temperature resulting in the formation of m-ZrO2. The ball-milling process also influenced the dependence of the crystallization enthalpy of zirconium hydroxide on the precipitation pH. In the case of zirconium hydroxide precipitated at pH 2.5, the ball-milling caused dehydration and an increase in its hygroscopy. The nature of these effects was discussed. The extension of FTIR spectra to the far infrared region made it possible to distinguish between t-ZrO2 and m-ZrO2 polymorphs by this technique. Also, the influence of laser power on the identification of ZrO2 polymorphs by Raman spectroscopy was elaborated.
CO oxidation by oxygen of the catalyst and by gas-phase oxygen(0.5–15)%CoO/ZrO2
Il’ichev,Fattakhova,Shashkin,Matyshak,Korchak
, p. 300 - 310 (2017)
CO adsorption on (0.5–15)%CoO/ZrО2 catalysts has been investigated by temperature-programmed desorption and IR spectroscopy. At 20°С, carbon monoxide forms carbonyl and monodentate carbonate complexes on Com2+On2- clusters located on the surface of crystallites of tetragonal ZrO2. With an increasing CoO content of the clusters, the amount of these complexes increases and the temperature of carbonate decomposition, accompanied by CO2 desorption, decreases from 400 to 304°С. On the 5%CoO/ZrО2 sample, the carbonyls formed on the Со2+ and Со+ cations and Со0 atoms decompose at 20, 90, and 200–220°С, respectively, releasing CO. At 20°С, they are oxidized by oxygen to monodentate carbonates, which decompose at 180°С. Adsorbed oxygen decreases the temperature of their decomposition on oxidation sites by ~40°C, and the sample remains in an oxidized state ensuring the possibility of subsequent CO adsorption and oxidation. The rate of the oxidation of 5%CoO/ZrО2 containing adsorbed CO by oxygen is higher than the rate of the oxidation of the same sample reduced by carbon monoxide, because the latter reaction is an activated one. In view of the properties of the complexes, it can be concluded that the carbonates decomposing at 180°С are involved in CO oxidation by oxygen from the gas phase in the presence of hydrogen, a process occurring at 50–200°С. The rate-limiting step of this process the decomposition of the carbonates, which is characterized by an activation energy of 77–94 kJ/mol.
Modified zirconia solid acid catalysts for organic synthesis and transformations
Reddy, Benjaram M.,Sreekanth, Pavani M.,Reddy, Vangala R.
, p. 71 - 78 (2005)
The sulfate, molybdate and tungstate promoted ZrO2 catalysts were investigated by X-ray diffraction, NH3-TPD, and Raman spectroscopy and were evaluated for various organic synthesis and transformation reactions. All catalysts exhibit good catalytic activity for synthesis of diphenylureas, coumarines and 1,5-benzodiazepines, acylation of alcohols, phenols and amines, and protection of carbonyl compounds. A series of sulfate, molybdate and tungstate promoted ZrO2 catalysts were prepared by wet impregnation method. To incorporate these promoters to Zr(OH)4, sulfuric acid, ammonium heptamolybdate, and ammonium metatungstate were used as precursors, respectively. Further, a Pt promoted Mo-ZrO2 catalyst was also prepared separately by impregnating with hexachloroplatinic acid. The surface and bulk properties of various promoted ZrO2 catalysts were investigated by means of X-ray powder diffraction, BET surface area, ammonia-TPD, and Raman spectroscopy techniques. The unpromoted ZrO2 when calcined at 873 K exists in the crystalline form with monoclinic phase dominating over the tetragonal phase. Incorporation of various promoters into Zr(OH)4 shows a strong influence on the bulk and the surface properties. Addition of promoters enhanced the tetragonal zirconia phase and the surface acidity. In the case of Pt/Mo-ZrO2 catalyst, a complete tetragonal ZrO2 phase is observed. The ammonia-TPD results indicate that the impregnated sulfate ions show a strong influence on the acidity of ZrO2, which is followed by molybdate. The prepared catalysts were evaluated for various organic synthesis and transformation reactions in the liquid phase. All catalysts exhibit good catalytic activity for synthesis of diphenylureas, coumarines and 1,5-benzodiazepines, acylation of alcohols, phenols and amines, and protection of carbonyl compounds. In particular, the sulfate and molybdate promoted catalysts exhibited excellent catalytic activity.
Evolution of the Catalytic Activity in Pt/Sulfated Zirconia Catalysts: Structure, Composition, and Catalytic Properties of the Catalyst Precursor and the Calcined Catalyst
Manoli, Jean-Marie,Potvin, Claude,Muhler, Martin,Wild, Ute,Resofszki, Gabor,Buchholz, Thomas,Paal, Zoltan
, p. 338 - 351 (1998)
A 3% Pt/sulfated zirconia catalyst was prepared and characterized before and after calcination at 900 K by XRD, XPS, EM, and in the catalytic hydroisomerization of n-hexane. The fresh sample exhibited small but definite catalytic properties. Calcination brought about a dramatic increase of the activity with practically constant high (90-100%) selectivity for hydroisomerization versus cracking. This increased activity was accompanied by the transformation of the predominantly amorphous support to predominantly tetragonal crystals and the wrapping up of most parts of surface Pt atoms into the bulk, as shown by the physical characterization methods. Hence metallic Pt particles exhibited mainly Pt-O rather than Pt-S interactions. S was present as sulfate. Pt-sulfated zirconia was different from traditional bifunctional metal catalysts on acidic supports. We attributed its higher catalytic activity and favorable isomerization selectivity to a few but very active centers, formed by interaction of Pt sites with sulfate groups on the high Miller-index surfaces of ZrO2. Calcination must be essential to create these active sites. H2 dissociating on Pt sites would provide the hydride species that are necessary for isomerization occurring on the acidic (sulfate-zirconia) part of that ensemble. We proposed the name compressed bifunctional sites for these centers of acid-metal cooperation. The assumption of such active sites, the maximum activity as a function of the hydrogen pressure, can also be explained in a consistent way.
