Double Impregnation Method Research Articles

Model Catalyst Performance and Efficiency during the Hydro-treatment of Heavy Oil Residuum

Fixed bed tubular plug flow reactor is used to investigate model catalysts performance during the hydrodesulphurization of Heavy Arabian Oil atmospheric residuum. The effects of temperature (300-380℃), pressure (30-80 atm) and particle size with characteristic lengths (Lpo = 0.0059cm), Lp1 = 0.0327cm) on the rate of the Hydrodesulphurization reaction are investigated. Supported Co-Mo/ γ-AL2O3 catalysts, CAT-1 with Co= 3wt.% and Mo= 10.6wt.% and 0.5wt.% MS 13X and CAT-2 with the same composition but without the addition of MS 13X loadings were prepared using the double impregnation method. All prepared catalysts were characterized for their porous structure and composition. A Kinetic equation was developed for pulverized CAT-1 particles, RHDS= 9.9696*1010 exp (-17058/T) * PH2 *CS2.2 / (1+0.00802 * PH2). Effectiveness factors and effective diffusivity coefficients were estimated for both catalyst particle sizes. CAT-1 catalyst sample showing slightly higher activity lost approximately 20% of its initial activity after 450 hours of operation compared to 11% lost for CAT-2 sample. The presence of MS 13X in CAT-1 is accompanied with lighter HC products (C1-C4 up to 210℃) giving rise to more hydrocracking orientations especially at high temperatures with higher API degrees of the treated products.

CO oxidation over gold supported on Cs, Li and Ti-doped cryptomelane materials

Cryptomelane-type manganese oxides were synthesized by redox reaction under acid and reflux conditions. Different metals (cesium, lithium and titanium) were incorporated into the tunnel structure by the ion-exchange technique. Gold was loaded onto these materials (1wt%) by a double impregnation method. The obtained catalysts were characterized by high-resolution transmission electron microscopy, energy-dispersive X-ray spectrometry, scanning electron microscopy, X-ray diffraction and temperature-programmed reduction. The catalytic activity of these materials was evaluated in the oxidation of carbon monoxide. The incorporation of Cs, Li or Ti into cryptomelane was detrimental in terms of catalytic activity. Further addition of gold to cryptomelane doped materials significantly improved the catalytic performance, especially for Cs-K-OMS-2 and Li–K-OMS-2 (to a smaller extent). Addition of gold to the Ti containing material did not show a significant improvement. The observed trends are related to the effect of gold on samples reducibility and to the gold particle size. The lattice oxygen can also be considered accountable for the activity of the materials, since the most active cryptomelane catalysts are those with higher lattice oxygen donating ability for the oxidation of the CO molecule.

Application of Au/TiO2 catalysts in the low-temperature water–gas shift reaction

Au/TiO2 catalysts were synthesized by three different methods, with different gold loadings, and tested for the low temperature water–gas shift (WGS) reaction. Gold was loaded by a Double Impregnation Method (DIM), Deposition–Precipitation (DP) and Liquid Phase Reductive Deposition (LPRD). For each procedure, catalysts were synthesized with three different loadings of gold, up to ca. 2.5 wt.%, identified as 1, 2 or 3 for low, intermediate or high amounts of nanosized gold, respectively. The prepared materials were characterized by High-Resolution Transmission Electron Microscopy (HR-TEM), X-Ray Diffraction (XRD), X-Ray Photoelectron Spectroscopy (XPS), Temperature Programmed Reduction (TPR) and Absorption Atomic Spectroscopy (AAS).The performance of the catalysts was compared based on the CO conversions (XCO) and turnover frequencies (TOFs) obtained in the WGS reaction. The two best catalysts obtained were Au/TiO2-DP-3 and Au/TiO2-LPRD-3. Both showed XCO and TOF values higher than that of the commercial Au/TiO2-WGC (supplied by the World Gold Council). Although TOF was higher for Au/TiO2-LPRD-3 (at 250–300 °C), this sample suffers deactivation. The Au/TiO2 DP-3 material was thus selected as the best synthesized catalyst, with a XCO ≈ 85% at 300 °C (XCO of the WGC sample was ≈52% at 300 °C). The Au/TiO2 DP-3 material has small gold nanoparticles before and after use, which can account for the improved catalytic activity, well known to be related with gold nanoparticle size. However, stability was found to be better for the WGC sample.

Gold supported on metal oxides for volatile organic compounds total oxidation

Au was loaded (1wt.%) on different commercial oxide supports (CuO, Fe2O3, La2O3, MgO, NiO, Y2O3) by a double impregnation method (DIM). Samples were characterised by N2 adsorption at −196°C, scanning electron microscopy, high-resolution transmission electron microscopy, selected area electron diffraction, energy dispersive X-ray spectrometry, high-angle annular dark-field imaging (Z-contrast), X-ray diffraction and temperature programmed reduction. The materials were tested for the total oxidation of two volatile organic compounds: ethyl acetate and toluene. Toluene was more difficult to oxidise than ethyl acetate. Gold loaded on CuO and NiO yielded the best catalysts, although there was a larger increase in catalytic activity upon gold loading for less active oxides like MgO and Y2O3. The oxidation state of gold does not seem to play a significant role in the catalytic activity, with the exception of Au/Y2O3 where Au3+ was detected, leading to a decrease in the activity. The catalytic activity seems to be related with the reducibility of the support and the gold nanoparticle size, following a Mars-van Krevelen type of mechanism. The role of gold is to enhance the reducibility and reactivity of the surface of the oxide support and to increase the exchange rate between lattice and surface oxygen.

Developing highly active photocatalysts: Gold-loaded ZnO for solar phenol oxidation

Gold nanoparticles were loaded on ZnO materials by a double impregnation method. Materials were characterized by spectroscopic, microscopic and N2 adsorption techniques, and tested on the photocatalytic oxidation of phenol in aqueous solutions, under simulated solar light. Compared with bare ZnO, the Au-loaded catalysts presented increased activity, which has been evaluated in terms of the pseudo-first-order kinetic constant (kapp) and phenol mineralization. The best activities were obtained with the Au-loaded ZnO samples produced by chemical vapor deposition, and by thermal decomposition of zinc acetate (kapp=5.6min−1mgAu−1 for both materials), achieving mineralizations of 92% and 82%, respectively. Depending on the ZnO material, on the gold nanoparticle dimensions and on the irradiation wavelength used, gold particles may act as electron sinks or light harvesters. Selective trapping of photogenerated holes and radicals by selective scavengers showed that holes are crucial, but free radicals do also participate on phenol’s photodegradation pathway.

Effect of the preparation method on the catalytic activity and stability of Au/Fe2O3 catalysts in the low-temperature water–gas shift reaction

The low temperature water–gas-shift reaction has been studied over a series of nanosized Au/Fe2O3 catalysts. The effect of the synthesis method on the catalytic activity has been analysed. A series of catalysts with different Au loadings has been prepared by different methods: deposition–precipitation (DP), liquid phase reductive deposition (LPRD) and double impregnation method (DIM). The Au/Fe2O3 catalysts prepared by DP showed the highest CO conversion. The catalysts were characterised by hydrogen temperature programmed reduction (TPR-H2), high-resolution transmission electron microscopy (HRTEM), X-ray powder diffraction and X-ray photoelectron spectroscopy. TPR-H2 analysis revealed that gold promotes the reducibility of the Fe2O3 support, which is crucial in this redox reaction. HRTEM evidences a very good dispersion of gold over the iron support, with nanoparticles in the range 2.2–3.1nm for the DP and LPRD series, and a negligible increase in the average particle size of the used samples. For the DIM series, much larger Au particles (∼6.6nm) were obtained.

The application of biodegradable chelates in the preparation of Ni–TiO2/Al2O3 photocatalysts by the Double Impregnation Method

Abstract Ni–TiO 2 /Al 2 O 3 photocatalysts prepared by Double Impregnation Method using a new biodegradable chelates e.g. S,S-ethylenediaminedisuccinic acid (EDDS), tetrasodium salt of N-(1,2-dicarboxyethyl)- d , l -aspartic acid (available as product Baypure CX 100) and poly(aspartic acid) (available as product Baypure DS), instead of typically used EDTA, were tested in the photo removal of typed pollutants. The physicochemical properties of the studied photocatalysts were determined by BET, XRD, SEM/EDX, XPS, UV–vis/DRS and Raman spectroscopy. EDDS–Ni photocatalyst obtained the highest activity and enabled the 99% removal of phenol (Ph), Triton X-100 (TX) and wash-up liquid (WL). Although, beside EDDS–Ni, the best results of Ph and TX photo oxidation were obtained using TiO 2 /Al 2 O 3 , the new photocatalysts were appropriate for the decomposition of more complicated compositions of wastewater. The surface modification by Ni is connected with the affordability of TiO 2 and the excess of Ni in comparison to Ti (above 1:1) may inhibit the photo oxidation of TX. The adverse effect was observed in case of Ph and WL removal. 2 h treatment has resulted in the significant decomposition of pollutants and was economically justified.

Promotion of Alumina Supported Cobalt Catalysts by Iron

Several alumina supported cobalt (Co), iron (Fe) mono metallic, and Co–Fe bimetallic catalysts were synthesized, characterized, and studied for the carbon dioxide (CO2) hydrogenation reaction. The catalysts were synthesized by coimpregnation and double-impregnation methods, and characterized by X-ray diffraction (XRD), ultraviolet–visible-near infrared (UV–vis-NIR), and diffuse reflectance infrared fourier transform (DRIFT) spectroscopy. The surface areas of the catalysts were also determined. Appropriate amounts of Fe promote the catalytic reactivity of alumina supported cobalt catalysts for the CO2 hydrogenation reaction. Furthermore, it was beneficial that this catalyst was synthesized by the double-impregnation method, where Fe was initially deposited, and then, Co was deposited on the alumina support. The hydrogenation of CO2 revealed the presence of formate species on the catalyst during reaction. It appears that iron promotes the supported cobalt catalyst by (i) protecting cobalt from strongly interacting with the alumina support and (ii) forming a Co–Fe alloy.

Exotemplated ceria catalysts with gold for CO oxidation

Cerium oxides were synthesized by an exotemplating procedure using both activated carbon and carbon xerogel as templates. The template effect and the preparation method were investigated. The surface area of the materials varied from 73 to 114 m 2 g −1, being similar to samples prepared by standard precipitation and calcination techniques (150 and 98 m 2 g −1, respectively), but much larger than a commercial ceria sample (20 m 2 g −1), used for comparison purposes. Samples prepared using xerogel as template have, approximately, twice as much porosity than those prepared with activated carbon, and the mesopores of the first are roughly 4 times larger than those of the latter. Cerianite CeO 2 was the only phase detected by XRD for all materials. Gold was loaded onto these materials by a double impregnation method. The catalytic performance of these ceria oxide materials alone and loaded with gold was tested in the oxidation of carbon monoxide. Xerogel prepared samples showed to be the most active in CO oxidation. Addition of Au increased the activity up to two orders of magnitude, at room temperature. With the unloaded samples, complete conversion was only achieved above 400 °C, but when Au was loaded, full CO conversion occurred already at 75 °C. Analysis of selected samples by HAADF and HRTEM showed that the gold particle size was 5–10 nm for the most active sample, and 8–13 nm for the least active. H 2-TPR experiments proved that addition of gold significantly helped to improve the reducibility of the surface oxygen on CeO 2. Both for ceria and Au/ceria materials, it was observed that the temperature at which the CO conversion started is related to the temperature of the first peak of the TPR spectrum, showing that the activity depends on the availability of surface oxygen. Experiments without oxygen in the feed, in the presence of ceria catalysts, suggest that the lattice oxygen can react with CO. It is shown that there is a significant correlation between the catalytic activity and the lattice oxygen donating ability. The TPR results suggest that gold is in its reduced state in the “fresh” Au/ceria samples.

Removal of recalcitrant pollutants from wastewater

Triton X-100 was oxidized in aqueous solutions with the presence of O 2 using photocatalysis and H 2O 2 addition alone or coupled. New supported TiO 2/Al 2O 3 catalysts modified with vanadium and cobalt were used. Catalysts were prepared using the classical impregnation method (CIM) and the double impregnation method (DIM). The effect of the physico-chemical properties of the catalysts on its activity were studied. The research on the interactions between the metal precursor and the titania–alumina surface by means of FT-IR/PAS (Fourier transform infrared photoacoustic spectroscopy) were also conducted.

FT-IR/PAS of the EDTA adsorbed on alumina with the various surface areas

Fourier transform infrared photoacoustic spectroscopy (FT-IR/PAS) was applied to investigate samples with the adsorbed species formed during preparation metal supported catalysts. In the studies conducted gamma alumina with the various surface areas was used. Samples prepared by the double impregnation method (DIM) have similar spectral characteristic. This allowed to conclude that surface areas of γ-Al 2 O 3 used had no influence on the nature of the examined species.

A Plate-Type Anodic Alumina Supported Nickel Catalyst for Methane Steam Reforming

An anodic alumina supported nickel catalyst (Ni/Al2O3/Alloy) was synthesized using a double impregnation method with a high temperature calcination in between, to investigate reactivity performance thereof during steam reforming of methane (SRM) reactions in continuous and daily start-up and shut-down (DSS)-like operations. The catalyst was structurally characterized using X-ray diffraction (XRD), BET and temperature programmed reduction (TPR) technologies. The TPR results showed that almost all nickel content from the first impregnation was transformed into nickel aluminate, whereas nickel from the second impregnation predominantly existed in the more reducible forms of NiO and xNiO·Al2O3 (x < 1). The existence of these NiO and NiAl2O4 phases was identified by XRD.The catalyst provided high and stable SRM reactivity near the equilibrium value, while no deactivation was observed in continuous durability testing for 200 h at 800°C and 130 h at 700°C, and in DSS-like mode operation at 700°C. The investigation of the influence of methane and/or steam treatments on the reactivity of Ni/Al2O3/Alloy showed the catalyst is not disturbed by the methane treatment, whereas it is remarkably deactivated by the steam treatment. In addition, no differences in the reduction effect were found when using hydrogen or methane to regenerate a steamed catalyst.

High activity supported gold catalysts by incipient wetness impregnation

It is generally thought that catalysts produced by incipient wetness impregnation (IW) are very poor for low temperature CO oxidation, and that it is necessary to use methods such as deposition–precipitation (DP) to make high activity materials. The former is true, indeed such IW catalysts are poor, and we present reactor data, XPS and TEM analysis which show that this is due to the very negative effect of the chloride anion involved in the preparation, which results in poisoning and excessive sintering of the Au particles. With the DP method, the chloride is largely removed during the preparation and so poisoning and sintering are avoided. However, we show here that, contrary to previous considerations, high activity catalysts can indeed be prepared by the incipient wetness method, if care is taken to remove the chloride ion during the process. This is achieved by using the double impregnation method (DIM). In this a double impregnation of chloroauric acid and a base are made to precipitate out gold hydroxide within the pores of the catalyst, followed by limited washing. This results in a much more active catalyst, which is active for CO oxidation at ambient temperature. The results for DIM and DP are compared, and it is proposed that the DIM method may represent an environmentally and economically more favorable route to high activity gold catalyst production.

Photoacoustic infrared analysis of nickel catalysts precursors

Photoacoustic spectroscopy (FT-IR/PAS) has been used for identification of different forms of nickel precursors formed during CIM (classical impregnation method) and DIM (double impregnation method) process and different pH of the solution containing nickel ions.

Hydrogenolysis of n-Butane over Ru/Al2O3 Catalysts

Preliminary studies were undertaken of the preparation parameters of DIM (double impregnation method) influencing metal loading, ruthenium catalyst dispersion and n-butane hydrogenolysis. Ruthenium red was used as the metal precursor of Ru/Al2O3 catalysts. The infrared spectra of ruthenium red and EDTA adsorbed on alumina indicated that interaction occurs between adsorbates and the support surface. An extension of the impregnation time by ruthenium red caused a slight shift of the asymmetric –COO− band that may be explained by interaction between ruthenium and adsorbed EDTA. The small change in the –COO− band position was due to the nature of the metal–EDTA bond formed. An increase in metal loading led to an increase in ruthenium dispersion. Measurements of the rate of hydrogenolysis of n-butane were carried out in a gradientless reactor. All kinetic experiments were conducted under conditions where the hydrogen/n-butane molar ratio was 9:1, and involved isothermal determination of the relationship between the n-butane reaction rate and the corresponding degree of conversion (iso-X). The absence of propane and the presence of isobutane (at lower temperature) among the products were discussed.

The Influence of the Physicochemical Properties of Supported Nickel Catalysts Obtained by the Double-Impregnation Method on the Hydrogenolysis of n-Butane

All catalysts examined were obtained by the double-impregnation method. The influence of nickel dispersity on the catalytic activity and selectivity of alumina-supported catalyst was observed. The reaction rate attained a maximum value at mean nickel crystallite sizes between 1.5 nm and 1.6 nm. The selectivity towards methane was highest in the same crystallite size range. At crystallite sizes below 1.5 nm, the selectivity towards i-butane increased while that towards ethylene reached a value of 60% in the same size range.

Effects of oxidation on neurofibrillar argyrophilia.

The effect of oxidation on neurofibrillar argyrophilia was studied by subjecting nervous tissues containing both normal and degenerating fibers to the action of potassium permanganate, periodic acid, chromic acid, lead tetraacetate, and sodium bismuthate prior to silver impregnation. The argyrophilic response of normal fibers to such treatment was studied with the Nonidez silver nitrate block technic, the double impregnation method of Bielschowsky on both blocks and sections, and a silver proteinate procedure. The response of degenerating fibers was studied by the Cajal formula 6 block technic and the modified Bielschowsky procedure of Nauta and Ryan for sections. The experimental data indicated that such oxidation did not produce any differential staining effects between normal or degenerating fibers.

Histological Technic for Cerebellar Climbing and Mossy Fibers

In order to, avoid disadvantages attendant upon the use of fresh frozen sections, or of block impregnation with silver, in staining climbing or mossy fibers of the cerebellum, Rio Hortega's double impregnation method for nerve fibers is useful. This consists of prolonged formalin fixation prior to cutting frozen sections (which thereafter are easier to cut) and preliminary treatment with ammoniacal aqueous and alcoholic washes, mordanting in pyridine silver, and treatment with pyridine-silver-carbonate. Following this, sections are handled individually through one of several reduction methods after which they may be directly mounted or gold toned.