Impregnation Of ZrO2 Research Articles

Influence of Boron, Tungsten and Molybdenum Modifiers on Zirconia Based Pt Catalyst for Glycerol Valorization.

The influence of boron, tungsten and molybdenum modifiers on zirconia-based Pt catalyst was studied for glycerol valorization. Zirconia modified supports were prepared by impregnation of ZrO2 with either boric, silicontungstic or phosphomolybdic acids to obtain supports with enhanced Brönsted acidic properties. The modified supports were subsequently impregnated with chloroplatinic acid to obtain Pt-based catalysts. Pt incorporation resulted in the increase in Lewis acidity of the solids, being more significant for the Pt//W/ZrO2 catalyst. Reduced Pt catalysts were tested for the liquid-phase glycerol hydrogenolysis, observing a synergistic effect between catalyst acid sites and metal function that proved to be crucial in glycerol hydrogenolysis. The Pt//W/ZrO2 catalyst was the most active catalyst in this reaction, being the only leading to 1,3-PDO (45% sel., 160 °C) while Pt//Mo/ZrO2 is the best option for 1,2-PDO (49% sel., 180 °C). Reusability studies carried out for Pt//W/ZrO2 showed that catalytic activity dropped after the first use, remaining constant for the second and subsequent ones. Selectivity to reaction products also changes during reuses. Therefore, the selectivity to 1,2 PDO increases in the first reuse in detriment to the selectivity to n-propanol whereas the selectivity to 1,3-PDO remains constant along the uses. This behavior could be associated to the lixiviation of W species and/or catalyst fouling during reaction runs.

Influence of ZrO2 Structure and Copper Electronic State on Activity of Cu/ZrO2 Catalysts in Methanol Synthesis from CO2

Cu/ZrO2 catalysts obtained by impregnation of ZrO2 and complexation with citric acid were studied for CO2 hydrogenation to methanol. The catalyst structure, texture, and active copper surface were determined using XRD, BET, and reactive adsorption of N2O, respectively. The XPS and Auger spectroscopies were used to determine the surface structure and copper electronic state. FT-IR pyridine adsorption was studied to determine acidity of the catalysts. The results of quantum-chemical calculations concerning the formation of oxygen vacancies in monoclinic and tetragonal ZrO2 have been also presented. It was found that selection of the appropriate conditions of the catalyst preparation influences the degree of copper dispersion, its electronic state, and contents of the zirconia polymorphic phases (tetragonal and monoclinic). The presence of oxygen vacancies stabilizes both the thermodynamically unstable t-ZrO2 phase and Cu1+ cations, which are present in the vicinity of oxygen vacancies. Complexes formed pref...

Environmental remediation from thiophene solution by photocatalytic oxidation using a Pd/ZrO2–chitosan nanocomposite

A modified sol–gel technique was used to prepare ZrO2 nanoparticles through impregnation of ZrO2 with Pd and/or chitosan (CS). The composite photocatalyst of Pd/ZrO2 was characterized by XRD, TEM, UV–vis, Pl, and BET and the photocatalytic activity was investigated under visible light irradiation by using a thiophene solution as a model pollutant. The results revealed the influence of the type and amount of the catalyst where CS can effectively prevent the agglomeration of ZrO2 nanoparticles. UV–vis spectroscopic investigation indicated also that the ability of the composite to absorb visible light is greatly improved. The catalyst was reproducible without significant loss in its activity during the first five cycles.

Synthesis and Characterization of a ZrO2/AC Composite as a Novel Adsorbent for Dibenzothiophene

Zirconium dioxide was impregnated into a commercial activated carbon (AC) by hydrothermal treatment employing an aqueous ZrOCl2•8H2O solution. The ZrO2/AC composites thus prepared were tested as adsorbents for dibenzothiophene (DBT) from a model diesel fuel. In comparison to the pure AC, impregnation of ZrO2 was found to lead to a ca. 17% increase in the adsorption capacity. The optimal ZrO2 loading and hydrothermal pH were determined as 0.1 mmol/g and 7, respectively. The spent adsorbents were regenerated by toluene washing, with the ZrO2/AC composite exhibiting a higher adsorptive capacity than pure AC even after three such recycles. The ZrO2/AC composite was also characterized by the physical adsorption of nitrogen and Boehm titrations. The results indicated that surface acidic sites on the impregnated ZrO2 may play an important role in the improved desulphurization performance of the composite.

Zirconia-Supported Cu-KNO3 Catalyst: Characterization and Catalytic Behavior in the Catalytic Combustion of Soot with a NO/O2 Mixture

The catalytic combustion of diesel soot was studied in the presence of catalysts: CuZrO2, KNO3ZrO2, and CuKNO3ZrO2. The catalysts were prepared by impregnation of ZrO2·nH2O into an aqueous solution of Cu(NO3)2, KNO3, or both salts simultaneously. The catalysts were characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and temperature-programmed reduction (TPR). Cu(n)KNO3ZrO2 catalysts present high activity, and the value of the combustion temperature decreases 200 °C with respect to the temperature of the process without catalyzing, with Tmax values between 370 and 380 °C. The activity is associated with KNO3 presence, and the role of KNO3 can be attributed to (i) an increase of contact between soot and the surface of the catalyst and (ii) a redox reaction in which the nitrate is reduced to nitrite by reaction with carbon and again reoxidized to nitrate. The copper contribution is associated with the reaction selectivity toward CO2 formation.

Additional effects of cobalt precursor and zirconia support modifications for the design of efficient VOC oxidation catalysts

The influence of the ZrO2 support modification by Y2O3 and the presence of ethylenediamine (“en”) during the preparation of Co/ZrO2 were studied and compared with a reference catalyst conventionally prepared by impregnation of ZrO2 with an aqueous solution of Co(NO3)2. The effect of the en/Co molar ratio (x=1–3) was studied. Activation of cobalt species was followed by differential thermal and thermogravimetric analyses (DTA/TG) analyses and by specific surface area measurements which evidence the complete cobalt precursor decomposition at 450°C, whatever the support composition and the en/Co molar ratio. The addition of an aqueous solution of ethylenediamine to a cobalt nitrate solution led to a strong increase in the catalytic activity of the activated solids for the toluene deep oxidation as compared to the reference catalyst. The best catalytic results were explained in terms of cobalt oxides dispersion (X-ray diffraction (XRD)) and also in terms of Co-support interaction (H2-temperature-programmed reduction (TPR)). The generated cobalt species were reducible at much lower temperatures and were more active in the toluene total oxidation. Finally, an efficient catalyst was produced combining the modifications of the support by yttrium oxide and of the precursor (use of ethylenediamine).

The catalytic activity of CoOx/sulphated-ZrO2 for the NO abatement with C3H6 in the presence of O2: the dependence of activity and selectivity on the sulphate content

Cobalt sulphated-ZrO2 catalysts were prepared by impregnation of ZrO2 with aqueous solutions of CoSO4, or impregnation of sulphated-ZrO2 with toluene solutions of Co(acetylacetonate)2. NO reduction with C3H6 in the presence of excess O2 was studied in a flow apparatus fed by a reactant mixture of NO:C3H6:O2=4000:2000:20,000 ppm in He. Diffuse reflectance spectroscopy (DRS) and X-ray photoelectron spectroscopy (XPS) results showed that the presence of sulphates prevented the formation of Co3O4. XPS indicated the presence of Co(II) alone. Irrespective of the preparation method, Fourier transformed infrared (FTIR) showed that catalysts with the same sulphate content had the same covalent sulphates. As the sulphate content in the sample increased, FTIR with CO or NO showed that the Lewis acid-strength of Co(II) increased, whereas the reducibility and heterogeneity of Co(II) decreased. Sulphated samples with a cobalt content higher than 2 atoms nm−2 were far more active and selective than the corresponding unsulphated CoOx/ZrO2. The presence of sulphates had a weaker effect on the catalytic behaviour of samples with lower Co content (<2 atoms nm−2). We conclude that cobalt and sulphate co-operate in determining the catalytic activity and selectivity of cobalt sulphated-ZrO2 catalysts.