Ce Catalyst Research Articles

Enhancement of biphenyl hydrogenation over gold catalysts supported on Fe-, Ce- and Ti-modified mesoporous silica (HMS)

Mesoporous metallosilicates (HMS–M; M = Ce, Fe, Ti) were used as supports for the preparation of Au catalysts, and were tested in the liquid-phase hydrogenation of biphenyl at 5 MPa and 488 K. Irrespective of the support, uniformly dispersed Au nanoparticles in range 3.2–6.5 nm were obtained. The highest turn over frequency (TOF), expressed per surface Au atom, was achieved on the Au/HMS–Fe, furthermore this catalyst gave the highest selectivity to the most saturated compound (bicyclohexyl with the highest cetane number) by means of enhancing the second aromatic-ring hydrogenation. From the catalyst activity-structure correlation, the highest activity of the Au/HMS–Fe catalyst is linked with: (i) the higher ratio of positively charged metallic gold Au δ+ /Si (XPS), and (ii) the higher stability of Au nanoparticles (HRTEM). A linear correlation between the activity (per gram of metal) of the catalysts and their ratio Au δ+ /Si is observed; however, Au/HMS–Ce catalyst displays a different behaviour in terms of activity per gram of metal exposed caused by the fact that ceria is not incorporated in the framework.

CATALYTIC OXIDATION OF TOLUENE IN CONTAMINANT EMISSION CONTROL SYSTEMS USING MN‐CE/γ‐AL2O3

Toluene, the alkyl benzene, is a common constituent of contaminant streams emitted by hydrocarbon fuel combustion systems. The oxidation of toluene to less toxic compounds can be enhanced through catalysis. The capacity of Mn‐Ce/γ‐Al2O3 to catalyze toluene oxidation was investigated using a fixed bed flow reactor, operating within a temperature range of 160–400°C. Mono‐metallic catalysts were prepared with the manganese and cerium contents of 1–21 wt% on γ‐Al2O3 support and bi‐metallic catalysts were prepared with cerium (0.5–21 wt%) on 18.2 wt% manganese. The results indicate that the 18.2 wt% Mn–10.0 wt% Ce catalyst combination had the best catalytic efficiency for toluene oxidation. Increase in cerium loading reduces the surface area of catalytic materials measured by BET, but increases catalytic activity. Data obtained through TGA (Thermogravimetric analysis), XRD (X‐ray diffraction) and toluene‐TPR (Temperature Programmed Reduction) measurements show that the reduction of the catalysts in the process of toluene oxidation is directly proportional to observed weight loss under hydrogen flow. From these results, it is concluded that cerium improves the catalytic role of manganese in toluene oxidation. Oxygen mobility is also promoted in a redox mechanism in which MnO2 serves as the active sites. These results are useful in the development of toluene emission control systems for hydrocarbon fuel combustion systems.

Oxidation state of Ce and ethanol–oxygen reaction of mesoporous titania-supported cerium oxide

Cerium-incorporated mesoporous titania, Ce-meso TiO 2, was prepared by the co-condensation method using Ce(NH 4) 2(NO 3) 6 and Ti(O i C 3H 7) 4 as precursors and n-dodecylamine as a structural directing agent. The catalysts obtained had high surface area and narrow pore size distribution similar to mesoporous titania. The population of Ce(III) in these catalysts was investigated by XANES spectroscopy. Although the precursor was tetravalent, the concentration of Ce(III) was nearly 100% and 80% in Ce-meso TiO 2 catalysts prepared with the precursor mixing ratios of Ti/Ce = 20 and 50, respectively. In Ce-meso TiO 2 prepared with Ti/Ce = 100, the concentration increased from 39% to 69% after the calcination from 473 K to 673 K. In the catalyst prepared without n-dodecylamine, the concentration was only 30%, which is almost the same as the value obtained for P-25 supported Ce catalyst. These results imply that the lower valence becomes stable by the presence of mesoporous titania framework. In the ethanol–oxygen reaction, ethylene and carbon dioxide were formed on the Ce/P-25 catalyst. The activity and selectivity depended little on the calcination temperature of the catalyst, which concurs with the constant concentration of Ce(III). On the other hand, the main products on the Ce-meso TiO 2 catalyst were acetaldehyde and acetic acid. The selectivity for acetic acid increased with the calcination temperature of the catalyst. The concentration of trivalent Ce was correlated with the formation of acetic acid. Additionally, the local structure of Ti in the Ce-meso TiO 2 catalyst was investigated by Raman spectroscopy. The structure of the support framework had little influence on the ethanol–oxygen reaction.

Thermoelectric carbon monoxide sensor using Co-Ce catalyst

A thermoelectric (TE) carbon monoxide sensor has been examined, which is composed of a Co-Ce oxide catalyst layer and a TE layer. The catalyst plays an important role in this sensor. The Co-Ce oxide catalysts were prepared by a co-precipitation and tablet compression method. Several factors including the atomic ratio of Co/Ce, pH value, tablet compression pressure, calcination temperature, and operating temperature were investigated. EDS analysis was utilized to determine the final composition between Co and Ce. Methods of BET, XRD, SEM and H 2 -TPR were used to characterize the catalysts. When the Co 10.0 Ce catalyst showed a high temperature difference output (44 °C) at an operating temperature of 92 °C, the TE sensor possessed good sensing property to 3 vol% CO with a high output voltage signal (42 mV). The response and recovery time of the TE sensor was 72 s and 68 s, respectively. Furthermore, high selectivity of the sensor was also obtained in the operating temperature from 90 °C to 125 °C.

Gas Phase Hydrogenation of Maleic Anhydride to γ-Butyrolactone by Cu–Zn–Ce Catalyst in the Presence of n-Butanol

A series of Cu–Zn–Ce catalysts were prepared by coprecipitation method and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, temperature programmed reduction, and N2 adsorption. The catalytic activities of the Cu–Zn–Ce catalysts in gas phase hydrogenation of maleic anhydride in the presence of n-butanol were studied at 220–280 °C and 1 MPa. The conversion of maleic anhydride was more than 97%. After reduction, CuO species present in the calcined Cu–Zn–Ce catalysts were converted to metallic copper (Cu°). The presence of ZnO in the Cu–Zn–Ce catalysts was beneficial to stabilizing the catalytic activity in maleic anhydride hydrogenation to γ-butyrolactone. At the same time, n-butanol was dehydrogenated to butyl aldehyde, then to butyl butyrate via reactions, such as disproportionation and esterification. Cu–Zn–Ce catalysts are beneficial to the H2 compensation in the coupling process of hydrogenation and dehydrogenation.

Macrodynamic study and catalytic reduction of NO by ammonia under mild conditions over Pt–La–Ce–O/Al2O3 catalysts

Catalytic reduction of NO using ammonia upon series prepared catalysts under 423–573 K in a fixed bed reactor was investigated. Results showed that the performance of supported platinum catalyst could be improved by addition of La and Ce to it. Experimental studies indicated that the suitable molar ratio of Pt:La:Ce would be 1.0:3.78:3.56, Pt–La–Ce (c). Results also found Pt–La–Ce (c) catalyst had good stability and tolerance to certain amounts of sulfur compounds under the used experimental conditions. Characterization for the fresh and used catalysts showed the Pt–La–Ce (c) catalyst had a stable structure. In addition, based on experimental data and using a nonlinear regression algorithm method, an empirical macrodynamic equation was obtained in this study.

Studies on cerium oxidation in catalytic ozonation process: A novel approach for organic mineralization

Abstract A novel regenerative catalytic system has been developed using cerium and ozone in nitric acid medium. It was found that cerium(III) was oxidized to cerium(IV) by ozone in nitric acid medium with good conversion yields. The conversion rate of Ce(III) was measured under various parameters viz. ozone–air flow rate, initial concentration of Ce(III), and concentration of nitric acid at 25 °C. It was found that the conversion of Ce(III) increased with increasing ozone flow rate and concentration of nitric acid while decreased with increasing Ce(III) concentration. The pseudo first order kinetic constants were evaluated for Ce(III) oxidation. The efficiency of this hybrid system comprising of ozone and cerium redox pair towards organic mineralization was evaluated taking phenol as the model organic pollutant and compared with Ce(III) catalyzed and uncatalyzed ozonation processes. The presence of Ce(III) catalyst increased the destruction efficiency of phenol compared to uncatalyzed ozonation whereas a synergetic effect was observed between the cerium redox pair (Ce(III) and Ce(IV)) and ozone towards phenol mineralization and a maximum TOC removal was obtained in the latter case. Kinetic interpretations have been made with some simplifying assumptions owing to the much complex nature of ozone and metal ion interactions. This hybrid catalytic ozonation process may find its suitability for continuous organic destruction at room temperature.

Hydrogen Clean-up by Preferential CO Oxidation over Pt–Co–Ce/MgO

1.4 wt% Pt–1.25 wt% Co–1.25 wt% Ce catalyst on MgO support was prepared using incipient to wetness impregnation technique and tested in a micro-reactor flow system for the low temperature preferential oxidation of CO in hydrogen rich streams. 100% CO conversion was achieved at 130 °C with a feed composition of 1.0% CO, 1.0% O2, 60% H2 and He as balance at a space velocity of 24,000 cm3/g-h. The addition of 25% CO2 did not affect the performance of the catalyst significantly, while 10% H2O in the feed decreased the activity. 100% CO conversion was obtained at 150 °C in the presence of 25% CO2 and 10% H2O in the feed.

Hydrogen production on Ni–Pd–Ce/γ-Al 2O 3 catalyst by partial oxidation and steam reforming of hydrocarbons for potential application in fuel cells

A series of catalysts of nickel–palladium–cerium supported upon alumina have been investigated in order to obtain a suitable catalyst that could be used in the process of producing hydrogen for the potential application in fuel cell by partial oxidation and steam reforming (POSR) of mixtures of hydrocarbons. Investigated results showed that little addition of cerium into Ni–Pd catalyst could definitely improve its stability of hydrogen production from mixtures of hydrocarbons by POSR method. The experimental results also showed that the optimum compositions of Ni–Pd–Ce catalyst were the molar ratio of Ni to Pd as 1:0.09 and containing of Ce 0.5 wt%, shortened as Ni–Pd–Ce-0.5 catalyst. XRD results for the typical catalysts showed that it mainly displayed the γ-Al 2O 3 and Ni peaks. SEM and TG results for the fresh and used Ni–Pd–Ce-0.5 catalysts, lasted for 540 h, did not show much difference on their surface patterns and TG curves, respectively. This indicated this catalyst would be a practical catalyst to produce hydrogen from liquid fuel by POSR method for potential application in fuel cells.

Steam reforming and water–gas shift of ethanol on Rh and Rh–Ce catalysts in a catalytic wall reactor

Ethanol is a renewable, portable, and non-toxic liquid that is a possible source of hydrogen for PEM fuel cells. This work describes an auto-thermal flat plate catalytic wall reactor for steam reforming of ethanol into H 2 and CO 2. Catalytic methane combustion on Pt is coupled to ethanol steam reforming on Rh and Rh–Ce across an auto-thermal wall. At a steam/carbon ratio of 3/1 the reactor gave >99% conversion of ethanol. An H 2/CO ratio of 3/1 was obtained at a residence time of ∼100 ms and an upstream temperature of ∼800 °C. Methane selectivities of less than 1% were obtained with Rh–Ce. Water–gas shift was also considered in order to increase the H 2/CO ratio. The reactor was lengthened to include a cooler water–gas shift section using a Pt–Ce catalyst. The extended reactor produced >99% conversion of ethanol and an H 2/CO ratio of 30/1 at a steam/carbon ratio of 4/1. The residence time was ∼400 ms, and the upstream temperature was ∼900 °C in the extended reactor. The reactor was stable for at least 100 h with no detectable degradation in performance.

Selective oxidation of CO in hydrogen-rich stream over Cu–Ce catalyst promoted with transition metals

Cu–Ce/ γ-Al 2O 3 catalysts promoted with Co were tested for the low temperature selective oxidation of CO in excess hydrogen. The effects of Cu–Ce composition, Co as a dopant, stoichiometric ratio ( λ=2O 2/CO), water vapor and CO 2 on the selective oxidation of CO to CO 2, O 2 consumption and selectivity of O 2 to CO oxidation as a function of temperature are presented. Also, the catalytic properties of the catalysts were investigated by using X-ray diffraction, CO-/H 2-temperature programmed reduction, temperature programmed oxidation, CO-/CO 2-/H 2O-temperature programmed desorption (TPD). Small addition (0.2 wt) of Co onto the Cu–Ce/ γ-Al 2O 3 brought large increase in selective CO oxidation activity. In the presence of either CO 2 (13 vol%) or H 2O (10 vol%) in the reformed gas feed, both Cu–Ce/ γ-Al 2O 3 and Cu–Ce-Co/ γ-Al 2O 3 showed decreased activity in CO oxidation at low temperatures, especially, under 200°C. Compared with the Cu–Ce/ γ-Al 2O 3, however, the Cu–Ce-Co/ γ-Al 2O 3 gives higher resistivity for the CO 2 and H 2O. From the CO 2/H 2O-TPD results, it could be explained that the main cause for the decrease in catalytic activity with CO 2 and H 2O in the feed may be attributed to the competitive adsorption of CO and CO 2 as well as the blockage of the active sites by water vapor at low reaction temperatures.

Interaction of poly(vinyl alcohol) with the Belousov–Zhabotinsky reaction mixture

The Ce catalyst of the BZ reaction was fixed in a poly(vinyl alcohol–co–vinyl sulfate) copolymer network. The prepared gel system is able to support spatial pattern formation. The preparation of the Ce salt of the copolymer and the gelation procedure are described. Spectrophotometric measurements prove that fixing of Ce in the gel matrix occurs due to a complex formation process. The poly(vinyl alcohol) (PVA) matrix interacts with the oscillating BZ mixture and causes partial inhibition of oscillations in batch BZ solutions and a decrease of wave velocities in thin gel layers. The inhibiting effect of PVA was compared to that of the analogous small molecule secondary alcohol, isopropanol. As a probable reason for the inhibition, two possible side reactions of the PVA with single components of the BZ reaction mixture were examined.

Studies on the surface behavior of non-chromium type high temperature co shift catalysts

The activity of an iron-base catalyst modified by molybdenum and cerium for CO shift reaction was investigated in a flow microcatalytic reactor. The results show that the activity of the modified catalyst is obviously improved. The surface behavior of Fe−Mo−Ce catalyst and the role of molybdenum and cerium in the catalyst are discussed.

Kinetics of wet oxidation of black liquor over a Pt–Pd–Ce/alumina catalyst

The catalytic oxidation of industrial wastewater from paper and pulp mills has been investigated in a slurry reactor at a temperature range 433–463 K and at pressures from 1.5 to 2.2 MPa. Adding Ce on alumina support promotes the catalytic activity for oxidation of black liquor. Pt–Pd–Ce/alumina catalyst shows a promising activity for wet catalytic oxidation of black liquor. The oxidation reaction over a Pt–Pd–Ce catalyst is characterized by an initial fast reaction step followed by a slow reaction step. The rate of total organic carbon (TOC) reduction was described by first-order kinetics with respect to TOC concentration in black liquor for both initial and later reaction steps. The activation energies were determined to be 54.53 and 50.13 kJ/mol for the initial and later oxidation steps, respectively. Comparison of the data with the generalized kinetic model was also presented.

Graft Polymerization of 2-Hydroxyethyl Methacrylate onto Plasma Pretreated Cotton, Silk, and Polyester Fibers

Abstract Graft polymerization of 2-hydroxyethyl methacrylate was made onto plasma pretreated fabrics of cotton, silk, and polyester. Homopolymerization also took place during the graft polymerization, but the percent of the homopolymer formation was comparatively small. Therefore, kinetic analyses of graft polymerization were undertaken based on the first-order reaction of the monomer. Through a comparison of the rate constants which were obtained from the rate equation of the graft polymerization of 2-hydroxyethyl methacrylate, the dependence of plasma pretreatment on various factors and the resulting polymerization were clarified. Polymerizability was compared to that obtained with the Ce(IV) catalyst and without catalysts.

Oscillating heterogeneous reaction with oxalic acid

Catalysed oxidation of oxalic acid with bromate ions at constant flow of nitrogen was investigated. Oscillations of the catalyst and bromine and the stepwise decrease of the concentration of bromate ions were followed by the polarographic method. Optimum conditions for the oscillations are at the stoichiometric ratio of the reactants. Oscillations of the concentration of bromine are enabled by the Ce(III) or Mn(II) catalyst. The oscillating behaviour of oxalic and malonic acids at heterogeneous conditions is compared.

Effects of Catalyst son the Lower Fatty Acids Formation Reactions by the Liquid Phase Air Oxidation of Petroleum Hydrocarbons

In order to investigate the effect of catalyst on liquid phase air oxidation of petroleum hydrocarbons in the preparation of lower fatty acids, the authors studied the oxidation of petroleum naphtha at 160°C, 40atm, in the presence of Na, Mg, Al, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cd, Sn, Ba, Ce, Pb, or Bi Catalyst (used as salt of naphthenic acid or octylic acid), and observed the following results.1. Compared with non-catalytic reaction, the induction periods were shortened by the salts of metals which belonged subgroup a in periodic table, and prolonged by the salts of metals which belonged subgroup b.2. Manganese salt was the only catalyst which increased the ratio of (secondary oxidation of intermediate products)/(primary oxidation of hydrocarbons). The addition of V or Cd salt was apt to suspend reaction.3. The yield of formic acid was in the order of Mn>none>Co. The yield of acetic acid was in the order of Mn, Cu>none>Na, Co, Ni, Zn, Sn, Bi, Pb. The ratio of acetic acid to formic acid was in the order of Co>none>Mn.These phenomena were observed regardless of the types of raw hydrocarbons-paraffinic or naphthenic-, and the types of anion component of catalyst-naphthenic acid or octylic acid-.