Wet Impregnation Process Research Articles

Effect of chemically reduced palladium supported catalyst on sunflower oil hydrogenation conversion and selectivity

Catalytic hydrogenation of sunflower oil was studied in order to improve the conversion and to reduce the trans-isomerization selectivity. The hydrogenation was performed using Pd–B/γ-Al2O3 prepared catalyst and Pd/Al2O3 commercial catalyst under similar conditions. The Pd–B/γ-Al2O3 catalyst was prepared by wet impregnation and chemical reduction processes. It was characterized by Brunauer–Emmett–Teller surface area analysis (BET), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The result of sunflower oil hydrogenation on Pd–B/γ-Al2O3 catalyst showed a 17% higher conversion and a 23% lower trans-isomerization selectivity compared to the commercial Pd/Al2O3 catalyst. The chemical reduction of palladium supported catalyst using potassium borohydride (KBH4) has affected the Pd–B/γ-Al2O3 catalyst’s structure and particle size. These most likely influenced its catalytic performance toward higher conversion and lower trans-isomerization selectivity.

Noninvasive Spatiotemporal Profiling of the Processes of Impregnation and Drying within Mo/Al2O3Catalyst Bodies by a Combination of X-ray Absorption Tomography and Diagonal Offset Raman Spectroscopy

A combination of X-ray absorption microcomputed tomography (μ-CT) and diagonal offset raman spectroscopy (DORS) have been used to follow in real time the 2-D and 3-D evolution of Mo species within 3 mm γ-Al2O3 extrudates during catalyst impregnation and drying processes. In a first set of experiments, we have followed the real-time incipient wetness impregnation process using an aqueous solution of ammonium heptamolybdate (AHM). We observed that during the equilibration period, singly impregnated samples formed Al(OH)6Mo6O183– (Al–Mo) hot spots distributed over the entire sample volume and that these heterogeneities grow in number and size as a function of time. A second set of measurements focused on the coimpregnation of AHM with H3PO4 and the subsequent equilibration and drying stages. It was found that the presence of phosphorus in the impregnating solution prevented the formation of the hot spots via the formation of weakly bound HxP2Mo5O23(6–x)– species that were uniformly distributed over the sample after 70 min of equilibration. During drying, however, these species migrated to the periphery of the sample, resulting in an egg shell distribution of HxP2Mo5O23(6–x)–. We show that by performing these studies noninvasively with a sufficiently high time resolution, the behavior and evolution of the Mo species were reproduced more faithfully than by using more conventional and invasive cut-and-measure approaches.

Effect of Ceria on Gold–Titania Catalysts for the Water–Gas Shift Reaction: Fundamental Studies for Au/CeOx/TiO2(110) and Au/CeOx/TiO2 Powders

We have carried out a fundamental study of the WGS reaction on model Au/CeOx/TiO2(110) and powder Au/CeOx/TiO2 catalysts paying particular attention to the effect of ceria on the activity of the gold–titania systems. CeOx nanoparticles deposited on TiO2(110) act as anchoring sites for gold improving the dispersion of the admetal on the oxide support. When compared to a typical benchmark system like Cu(111), Au/CeOx/TiO2(110) catalysts exhibit TOFs, which are 10–30 times larger, and a substantial reduction in the apparent activation energy for the WGS, which decreases from 18 kcal/mol on Cu(111) to 7 kcal/mol on Au/CeOx/TiO2(110). Low concentrations of ceria (6 and 15 wt %) were deposited onto a titania powder support via a wetness impregnation process. 1 atom % gold was then deposited on the CeOx/TiO2 mixed-oxide supports via a deposition–precipitation (DP) method. The Au/CeOx/TiO2 powder catalysts were characterized with HRTEM and a combination of in situ time-resolved XRD and XAFS. The XRD measurements indicated that a main effect of ceria was to enhance the concentration of oxygen vacancies in the catalysts and, thus, help with the dissociation of water during the reaction. Results of in situ XAFS showed that the gold oxidation state in the Au/CeOx/TiO2 powder catalysts changed from ionic (Auδ+) to metallic (Au0) with the start of the WGS. The active phase for these powder catalysts contained gold particles with average sizes of ∼2 nm. This study shows that the phenomena observed in model Au/CeOx/TiO2(110) catalysts do provide useful concepts for the design and preparation of highly active and stable powder catalysts for the WGS reaction.

Preparation and Characterization of Cu-Ce-Sn-O Composite Catalysts and Their Application in Low-Temperature Carbon Monoxide Oxidation

Several series of Cu-Ce-Sn-O catalysts were prepared via the coprecipitation (CP), citrate-gel (CG), and hydrothermal (HT) method, respectively, combined with a wet impregnation process. The catalysts were characterized by means of XRD, XPS, and TPR. The catalytic behavior of the catalysts for low-temperature CO oxidation was investigated by using a microreactor-GC system. The results of catalytic activity measurements showed that the Cu-Ce-Sn-O catalysts were much more active than the CuO/CeO2 and CuO/SnO2 catalysts. The catalytic activity depended on the incorporated amounts of Sn, CuO loading, calcination temperature, preparation method, and content of highly dispersed active CuO species. The 7 wt% CuO/Ce0.2Sn0.8O2 catalysts prepared by the CP method and calcined at 650°C exhibited the highest catalytic activity, while the 7 wt%CuO/Ce0.2Sn0.8O2 catalysts prepared by the CG or HT method showed higher thermal resistance.

Copper and iodine co-modified TiO2 nanoparticles for improved activity of CO2 photoreduction with water vapor

Copper and iodine co-modified TiO2 nanoparticles (Cu–I–TiO2) were synthesized through a combined hydrothermal and wet-impregnation process. The structures and properties of the catalysts were characterized by XRD, BET, SEM/EDX, XPS, and UV–vis diffuse reflectance spectroscopy. Iodine ions were doped in the TiO2 lattice by replacing Ti4+ and, consequently, Ti3+ was generated to balance the charge. Iodine doping reduced the TiO2 crystal size and was responsible for visible light absorption. Cu species were found to deposit on the surface of TiO2 and resulted in a slightly increased particle size. The activity of the Cu–I–TiO2 catalyst was investigated by the photocatalytic reduction of CO2 with water vapor, and CO was found to be the major reduction product with trace amounts of CH4 generated. Under UV–vis irradiation, the activity of the co-modified catalyst (Cu–I–TiO2) was higher than that of the single ion-modified catalysts (Cu–TiO2 or I–TiO2). Under visible light irradiation, the addition of Cu to I–TiO2 did not lead to significant improvements in CO2 reduction. Methyl chloride (CH3Cl) was detected as a reaction product when CuCl2 was used as the precursor in the synthesis, thus suggesting that methyl radicals are reaction intermediates. When CuCl2 was used as the Cu precursor, a three-fold increase in CO2 photoreduction activity was observed, as compared to when Cu(NO3)2 was used as the Cu precursor. These differences in activities were probably due to enhanced Cu dispersion and the hole-scavenging effects of the Cl ions. However, the formation of by-products (e.g., CH3Cl) may be undesirable.

Application of Pt-Rh complex catalyst: Feasibility study on the removal of gaseous ammonia

The selective catalytic oxidation (SCO) of gas phase ammonia (NH3) to nitrogen and water has been proposed as an effective ammonia removal process. This study reports that the oxidation of NH3 with oxygen to form N2 was investigated by SCO using a Pt-Rh complex catalyst that was synthesized by the incipient wetness impregnation process. The catalysts were performed using fluorescent spectroscopy (FS) combined with UV-Vis absorption, cyclic voltammetry (CV), linear sweep voltammograms (LSV), zeta potentialmeasurements and dynamic light-scattering (DLS). The findings show that the ammonia removal by catalytic oxidation over the Pt-Rh complex catalyst was nearly 95% at a temperature of 623K and an oxygen content of 4%. N2 was the main end product of the NH3-SCO process. FS have been applied to evaluate the catalyst yields with fluorescent peaks of 270 and 390 nm at room temperature. These results suggest that FS was proven to be an appropriate and effective method to characterize the Rh clusters that enhance their intrinsic emission from Pt-Rh complex catalyst in catalytic treatment systems. The CV and LSV reversible redox ability may explain the significant activity of the catalysts. Key words: Selective catalytic oxidation (SCO), ammonia (NH3), Pt-Rh complex catalyst, fluorescent spectroscopy (FS), cyclic voltammetry (CV), linear sweep voltammograms (LSV).

High desulfurization characteristic of lanthanum loaded mesoporous MCM-41 sorbents for diesel fuel

Mesoporous La/MCM-41 and La/AlMCM-41(SiO2/Al2O3=30, 50) sorbents were prepared by an incipient wetness impregnation or ion-exchange (IE) process, and desulfurization performances were investigated for commercial diesel containing total sulfur of 560ppmw at ambient temperature and pressure. The high surface area, a big pore volume and diameter of sorbents played important role for sulfur removal efficiency. The sorbents were characterized by means of BET, XRD, HRTEM, ICP-MS, NH3-TPD and Py FT-IR techniques. The results of N2-adsoption isotherms, XRD, HRTEM and FT-IR for the sorbents revealed that no structure collapse occurred during the wet impregnation. The interaction between sulfur in thiophene and HO-La(OSiAl) was crucial for the removal of sulfur compounds.

Hydroxyapatite supported Ag3PO4 nanoparticles with higher visible light photocatalytic activity

Hydroxyapatite supported Ag3PO4 nanocomposites have been synthesized by a wet impregnation process. UV–vis absorption spectra show a red shift of the absorption edges for the composite systems compared to pure hydroxyapatite support. The surface structure and morphology of the nanocomposites were characterized by Brunauer–Emmett–Teller (BET) apparatus, X-ray diffraction (XRD), transmission electron microscopy (TEM). The results suggest that Ag3PO4 nanoparticles (6–17nm in diameter) are well dispersed on the hydroxyapatite support and Ag3PO4 nanoparticles density is larger for the higher Ag+ loading sample. The as-prepared nanocomposite photocatalysts showed a pronounced photocatalytic activity upon decomposition of methylene blue dye in aqueous solution under both visible light (wavelength>400nm) and UV–vis light irradiation. A synergic mechanism of inherent photocatalytic capability of Ag3PO4 and the accelerated electron/hole separation resulting from the photoinduced electrons captured by the slow-released Ag+ at the interface of Ag3PO4 and hydroxyapatite is proposed for the nanocomposites on the enhancement of photocatalytic performance in comparison to that of pure Ag3PO4 nanoparticles. The support of hydroxyapatite may also act as an absorbent which favors the mass transfer in heterogeneous photocatalysis reaction.

Sea urchin-like Ag–α-Fe2O3 nanocomposite microspheres: synthesis and gas sensing applications

Sea urchin-like Ag–α-Fe2O3 nanocomposite microspheres are developed for gas sensing applications. Such hierarchical nanostructures were synthesized by a two step approach including a hydrothermal reaction and a subsequent incipient wetness impregnation process. The large Brunauer–Emmett–Teller (BET) area and highly porous structure of the hierarchical architecture and the chemical and electronic sensitization effect of Ag nanoparticles endow the Ag–α-Fe2O3 nanocomposite microspheres with enhanced gas-sensing properties in comparison to pristine α-Fe2O3 sensors. The possible formation mechanism of the sea urchin-like nanostructures, and their sensing mechanism are discussed.

Removal of Gaseous Ammonia in Pt-Rh Binary Catalytic Oxidation

In this study, the oxidation of ammonia (NH3) to form nitrogen was investigated by selective catalytic oxidation (SCO) over a Pt-Rh binary catalyst fabricated by the incipient wetness impregnation process in a tubular fixed-bed flow quartz reactor (TFBR). The catalysts were analysed by three-dimensional excitation-emission fluorescent matrix (EEFM) spectroscopy, UV-Vis absorption, dynamic light-scattering (DLS), zeta potential measurements, and linear sweep voltammograms (LSV). At optimum conditions, namely, a temperature of 673 K and an oxygen content of 4%, nearly 100% of the NH3 was removed by catalytic oxidation over the Pt-Rh binary catalyst. The main product of the NH3-SCO process was N2. Additionally, for the freshly prepared Pt-Rh binary catalyst, three peaks (at 235/295 nm, 245/315 nm, and 240/365 nm) were observed via EEFM; however, the peak with the highest emission wavelength disappeared over time as Pt-Rh binary catalyst was exhausted by NH3. These results show that EEFM spectroscopy, which enhances intrinsic emission Pt clusters in the Pt-Rh binary catalyst, is an effective method for characterizing this catalyst in catalytic treatment systems. The UV-Vis absorption spectra revealed that the bands associated with such octahedral platinum (IV) species were observed at about 350 nm. Moreover, the LSV reversible redox ability may explain the significant activity of the catalysts.

Synthesis of mesoporous ZnO/SBA-15 composite via sonochemical route

Highly dispersed nano-sized ZnO was prepared inside a mesoporous SBA-15 via sonochemical method. Wet impregnation process accompanied by this method gave rise to roughly 43 wt.% zinc oxide which was loaded inside mesoporous silica as a host structure. The synthesised mesoporous SBA-15 and the impregnated ZnO were characterised, using X-ray diffraction (XRD), transmission electron microscopy, Fourier transform infrared spectroscopy and nitrogen physisorption. Low angle XRD peaks confirmed long-range order of two-dimensional hexagonal symmetry of SBA-15 and also shifting of the peaks to higher angle for ZnO loaded samples. The size of ZnO cluster inside the channels was smaller than the one which detected by XRD. With increasing ZnO content in SBA-15, the relative pressure (P/Po) position found by physisorption test was shifted towards higher pressure. Internal pore volume and surface area were reduced, but the pore diameter was increased.

Photocatalytic Activity of TiO<sub>2</sub> Nanotube Modified by Cobalt

Cobalt modified TiO2 nanotube was prepared by wet impregnation method from anodized nanotube. The microstructure and phase characteristic were studied by SEM, EDX and XRD analysis. The photocatalytic degradation of methylene blue under UV illumination was studied. Enhanced degradation efficiency could be obtained after sodium borohydride reducing. For the samples using low concentration of CoCl2 in wet impregnation process, the degradation efficiency increased with the increase of CoCl2 concentration and for high concentration, the degradation efficiency decreased. With increasing the post-treatment temperature, the degradation efficiency decreased.

Electrocatalysis Oxidation of Ammonia at PtPdRh Ternary Catalysts in an Acid Medium and Applied Fuel Cell Studies

This work describes the platinum-group metal electrocatalytic materials were synthesized by incipient wetness impregnation process combine with aqueous solutions of H2PtCl6, Pd(NO3)3 and Rh(NO3)3 that were coated on alumina substances employed as a model reaction test by ammonia (NH3) electrocatalysis oxidation (ECO) research for fuel cell applications. The electrocatalytic materials were characterized by dynamic light-scattering (DLS), with a particle size around nanoscale particle sizes with high dispersion phenomena. Further, ECO ability was determined by using cyclic voltammetry (CV) and linear sweep voltammograms (LSV) technique. The experimental results show that the significant reactivity of the PtPdRh ternary electrocatalysts in acid medium and the results also demonstrated that the potential and the current density of the main oxidation-reduction peak change for the PtPdRh ternary electrocatalyst.

The Influence of Calcination Temperature and Cytotoxicity Assessment of Honeycomb Platinum-Containing Cordierite Nanocomposite Catalysts via Incipient Wetness Impregnation Process

This work describes the platinum-containingcordieritenanocompositematerials were synthesized by incipient wetness impregnation process with aqueous solutions of H2PtCl6, Pd(NO3)3and Rh(NO3)3that were coated on cordierite ceramic honeycomb substances followed by calcinations temperature ranging from 973 to 1273 K. The nanocomposite materials were characterized by STEM, with a particle size around nanoscale particle sizes (~100 nm) with high dispersion phenomena. Further, cell cytotoxicity and the percentage cell survival was determined by using 3-(4,5-dimethylthiazol-2-yl)-5(3-carboxymethoxyphenol)-2-(4-sulfophenyl)-2H-tetrazoli um (MTS) assay on human fetal lung tissue cell (MRC-5). The experimental results show that the platrinum-containingcordieritenanocompositematerials only minor cause cytotoxicity effect in cultured human cells.

Synthesis of a TiO 2 ceramic membrane containing SrCo 0.8Fe 0.2O 3 by the sol–gel method with a wet impregnation process for O 2 and N 2 permeation

A SrCo 0.8Fe 0.2O 3 impregnated TiO 2 membrane (TiO 2–SrCo 0.8Fe 0.2O 3 membrane) was successfully prepared using a sol–gel method in combination with a wet impregnation process. The membrane was subjected to a single gas permeance test using oxygen (O 2) and nitrogen (N 2). The TiO 2 membrane was immersed in the SrCo 0.8Fe 0.2O 3 solution, dried and then calcined to affix SrCo 0.8Fe 0.2O 3 into the membrane. The effect of the acid/alkoxide (H +/Ti 4+) molar ratio of the TiO 2 sol on the TiO 2 phase transformation was investigated. The optimal molar ratio was found to be 0.5, which resulted in nanoparticles with a mean size of 5.30 nm after calcination at 400 °C. The effect of calcination temperature on the phase transformation of TiO 2 and SrCo 0.8Fe 0.2O 3 was investigated by varying the calcination temperature from 300 to 500 °C. X-ray diffraction spectroscopy (XRD) and Fourier transform infrared (FTIR) analysis confirmed that a calcination temperature of 400 °C was preferable for preparing a TiO 2–SrCo 0.8Fe 0.2O 3 membrane with fully crystallized anatase and SrCo 0.8Fe 0.2O 3 phases. The results also showed that polyvinyl alcohol (PVA) and hydroxypropyl cellulose (HPC) were completely removed. Field emission scanning electron microscopy (FESEM) analysis results showed that a crack-free and relatively dense TiO 2 membrane (∼0.75 μm thickness) was created with a multiple dip-coating process and calcination at 400 °C. The gas permeation results show that the TiO 2 and TiO 2–SrCo 0.8Fe 0.2O 3 membranes exhibited high permeances. The TiO 2–SrCo 0.8Fe 0.2O 3 membrane developed provided greater O 2/N 2 selectivity compared to the TiO 2 membrane alone.

Highly efficient CuO incorporated TiO 2 nanotube photocatalyst for hydrogen production from water

Highly dispersed CuO was introduced into TiO 2 nanotube (TNT) made by hydrothermal method via adsorption–calcination process or wet impregnation process, to fabricate CuO incorporated TNT photocatalysts (CuO-TNT) for hydrogen production. It was found that CuO-TNT possessed excellent hydrogen generation activity, which was constantly vigorous throughout 5 h reaction. Depending on the preparation method, hydrogen evolution rates over CuO-TNT were founded in the range of 64.2–71.6 mmol h −1 g −1 catalyst, which was much higher than the benchmark P25 based photocatalysts, and even superior to some Pt/Ni incorporated TNT. This high photocatalytic activity of CuO-TNT was mainly attributed to the unique 1-D tubular structure, large BET surface area and high dispersion of copper component. Compared to wet impregnation, adsorption–calcination process was superior to produce active photocatalyst, since it was prone to produce photocatalyst with more highly dispersed CuO.

Characterisation and hydrogen storage of Pt-doped carbons templated by Pt-exchanged zeolite Y

The successful insertion, via a simple ion exchange route, of Pt nanoparticles into the porosity of zeolite-templated carbon (ZTC) materials is demonstrated. Pt doping has been achieved via Pt ion exchange into zeolite Y prior to its use as a template. TEM images reveal that Pt nanoparticles are homogeneously dispersed in the ZTC matrix and that smaller (3–5 nm), more uniform particles with better distribution are obtained via the ion exchange route compared to when doping is performed using conventional methods such as post-synthesis incipient wetness impregnation of Pt onto already formed ZTCs. The Pt-exchanged ZTCs have high surface area (1400–2200 m 2/g), high micropore surface area (1200–1900 m 2/g), large pore volume (0.8–1.20 cm 3/g) and exhibit pore ordering replicated from the zeolite Y template. The Pt-exchanged ZTCs store between 3 and 5 wt.% hydrogen at −196 °C and 20 bar, and the amount of hydrogen adsorbed correlates well with the textural characteristics of the carbons. However, the Pt-exchanged ZTCs exhibit higher hydrogen storage capacity per unit surface area and higher isosteric heat of adsorption (9 kJ mol −1) than Pt impregnated ZTC prepared via incipient wetness (7.8 kJ mol −1). Our findings show that the ion exchange method is attractive as an alternative metal-doping route to the commonly used incipient wetness impregnation process.

Difference in the catalytic activity of transition metals and their cations loaded in zeolite Y for ethanol steam reforming

The catalytic activity for ethanol steam reforming of Na-Y zeolite supporting transition metals was compared with that of zeolite Y encapsulating transition metal cations. It was found that zeolite Y supporting Co or Ni, prepared by the incipient wetness impregnation process, produced mainly hydrogen at 300 °C. Acetaldehyde products indicated that hydrogen production was due to the dehydrogenation of ethanol molecules. On the other hand, for zeolite Y encapsulating cations such as Co 2+ or Ni 2+, prepared by an ion exchange process, the reforming reaction resulted in mainly ethylene production, which was considered to be due to the dehydration of ethanol molecules. The results indicate that the presence of cations in zeolite Y has a significant influence on the ethanol reforming reaction.

Deactivation of vanadia-based commercial SCR catalysts by polyphosphoric acids

Commercial vanadia-based SCR monoliths have been exposed to flue gases in a pilot-scale setup into which phosphoric acid has been added and the deactivation has been followed during the exposure time. Separate measurements by SMPS showed that the phosphoric acid formed polyphosphoric acid aerosols, which were characterized by particle number concentrations in the order of 1×1014#/m3 at 350°C and diameters <0.1μm. Three full-length monoliths have been exposed to flue gases doped with 10, 100 and 1000ppmv H3PO4 for 819, 38 and 24h, respectively. At the end of the exposure the relative activities were equal to 65, 42 and 0%, respectively. After exposure, samples of the spent monoliths have been characterized by ICP-OES, Hg-porosimetry, SEM–EDX and in situ EPR. The results showed that the polyphosphoric acids chemically deactivate the vanadia-based catalysts by decreasing the redox properties of the catalyst surface and by titrating the number of V(V) active species. When plate-shaped commercial catalysts have been wet impregnated with different aqueous solutions of H3PO4 obtaining P/V ratios in the range 1.5–5, the relative activity for the doped catalysts in the whole P/V range was 0.85–0.90 at 350°C. These results show that the presence of phosphor compounds in the flue gas may be much more harmful than indicated by simple wet chemical impregnation by phosphoric acid. The reason has been found in the nature of the polyphosphoric acid aerosol formed in the combustion process, which cannot be reproduced by the wet impregnation process.

Development of a simple method for the preparation of novel egg-shell type Pt catalysts using hollow silica nanostructures as supporting precursors

A simple method for the preparation of novel egg-shell type platinum catalysts was developed and achieved by utilizing unique hollow silica nanostructures, i.e., hollow silica nanospheres and nanotubes, as supports. The observation by transmission electron microscopy indicated that the well-dispersed hollow silica supported Pt catalysts with a Pt particle diameter of 8–14 nm can be successfully prepared by wet impregnation process and heat treatment. The Pt-loaded hollow silica nanostructures were also characterized by inductively coupled plasma, X-ray diffraction, specific surface area, Fourier transformation infrared spectroscopy, X-ray photoelectron spectroscopy and energy dispersive spectroscopy. It was thus demonstrated that a higher Pt loading amount (0.392%) could be obtained under the same conditions except the addition of ammonia, which was found to be more effective than that (0.061%) with the addition of HCl in the immobilization of Pt. In addition, the effect of soaking time, Pt precursor concentration and calcination temperature on the loading of Pt in hollow silica nanostructures were investigated as well.