Ceria Alumina Research Articles

Investigation of after treatment technique to mitigate emission in IC Engine

Environmental pollution is a wide-reaching problem and it is likely to influence the health of the living population to a great extent. We need to mitigate the effects of harmful emissions before it is ungovernable. This project will concentrate on the reduction of NOx using ceria alumina catalyst, on a diesel engine as 5.2 kW water-cooled single-cylinder diesel engine. Solution and catalyst will play an important role in this process. Usually, the material is of high cost, here we have to choose low-cost material and solution. This leads to reduced nitrogen oxide (NOx) after treatment. Selective catalytic reduction (SCR) based on a solution like aqueous urea. This paper discusses the development of a static mixer and SCR reactor compatible with CI engine.

Highly Active and Stable Palladium Catalysts on Novel Ceria-Alumina Supports for Efficient Oxidation of Carbon Monoxide and Hydrocarbons.

Precious metal catalysts with superior low-temperature activity and excellent thermal stability are highly needed in environmental catalysis field. In this work, a novel two-step incipient wetness impregnation (T-IWI) method was developed for the fabrication of a unique and highly stable CeO2/Al2O3 support (CA-T). Pd anchored on CA-T exhibited a much higher low-temperature catalytic activity and superior thermal stability in carbon monoxide (CO) and hydrocarbon (HC) oxidations, compared to Pd anchored on conventional CeO2/Al2O3 (CA), which was prepared by a one-step IWI method. After aging treatment at 800 °C, the CO oxidation rate on Pd/CA-T (1.69 mmol/(gPd s)) at 120 °C was 4.1 and 84.5 times of those on Pd/CA (0.41 mmol/(gPd s)) and Pd/Al2O3 (0.02 mmol/(gPd s)), respectively. It was revealed that the CA-T support with well-controlled small CeO2 particles (ca. 12 nm) possessed abundant defects for Pd anchoring, which created rich Pd-CeO2 interfaces with strengthened interaction between Pd and CeO2 where oxygen could be efficiently activated. This resulted in the significantly improved oxidation activity and thermal stability of Pd/CA-T catalysts. The T-IWI method developed herein can be applied as a universal approach to prepare highly stable metal oxide-alumina-based supports, which have broad application in environmental catalyst design, especially for automobile exhaust aftertreatment.

CO2 conversion to synthetic natural gas: Reactor design over Ni–Ce/Al2O3 catalyst

Within the Power-to-Gas concept, the catalytic conversion of renewable hydrogen and carbon dioxide to methane for injection to the gas grid has recently attracted much attention. In the present work, the implementation of a nickel–ceria–alumina catalyst on a multitubular reactor for CO2 methanation was studied. The reaction kinetics were experimentally obtained and considered for a CFD model by means of Ansys® Fluent software, to evaluate the behaviour of a multitubular heat-exchange reactor. The simulations showed that most reaction occurs at the beginning of the reactor tube and the temperature raises rapidly. At the kinetic regime zone, a proper control of the temperature is required to avoid excessive hot-spots. In contrast, the final reactor volume is mainly controlled by the reaction thermodynamics. In this zone, the reaction is shifted toward products by using a cooling medium at low temperature. The effect of several design variables on the final methane yield and on the temperature profile was carried out, and finally, a reactor able to convert the CO2 present in the biogas to synthetic natural gas is proposed. The modelling showed that the proposed reactor tube (di=9mm and L=250mm) should be able to obtain a high methane content (>95%), at high GHSV (14,400h−1), and keeping the hot-spots at minimum (Δ100K). Within this reactor design approach, almost 1000 of tubes are necessary for the methanation of a medium-size biogas plant.

Effect of ethylene glycol on structure, thermal stability, oxygen storage capacity, and catalytic CO and CH4 oxidation activities of binary CeO2–Al2O3 and ternary CeO2–ZrO2–Al2O3 cryogels

Porous and homogeneous cryogels of binary ceria-alumina (CA) and ternary ceria-zirconia-alumina (CZA) were prepared from cerium nitrate, zirconium (IV) dinitrate oxide hydrate, and aluminium sec-butoxide by a one-pot sol–gel technique in an aqueous system and subsequent freeze drying, and effect of ethylene glycol (EG) used for chelation of cerium ions on structure, thermal stability, reducibility, oxygen storage capacity, and catalytic carbon monoxide and methane oxidation activities of the catalysts was investigated. EG did not significantly affect surface area, pore volume, mean pore size, and surface morphology of the catalysts after calcination and subsequent oxidative/reductive atmosphere heating at 900 °C. Whereas use of EG resulted in much finer particles of cerium oxides and ceria-zirconia solid solution for CA and CZA, respectively, distributed throughout alumina with high dispersion. X-ray diffraction (XRD) and Raman spectra suggested that while a cubic CeO2 phase was observed for CA after the oxidative heating regardless of whether or not EG was employed, finely-divided cerium oxides or crystalline CeAlO3 were respectively obtained after the reductive heating depending on whether EG was respectively used or not used. As for CZA, while a pseudo-cubic t″ phase was seen after the reductive heating regardless of whether EG was used or not, mixed phases of pseudo-cubic t″ and cubic or a cubic one were respectively observed after the oxidative heating depending on whether EG was respectively employed or not employed. The solid solubility of zirconia in ceria was improved by EG for CZA. The oxygen storage capacity and catalytic CH4 and CO oxidation activities were also enhanced by employing EG for both catalysts, which was ascribed fundamentally to the finer particles of cerium oxides and ceria-zirconia solid solution for CA and CZA, respectively, although CO oxidation on CA was unimproved by EG after the reductive heating.

Spectroscopic characterization and catalytic activity of Rh supported on CeO2-modified Al2O3 for low-temperature steam reforming of propane

The present work aims at clarifying the effects of CeO2 addition to Al2O3 support on the surface chemical characteristics and catalytic activity of supported Rh catalysts for low-temperature steam reforming of propane. Steam reforming of propane was carried out at 500°C over Rh catalysts supported on alumina modified with different CeO2 loading (0, 5, 10, 20, 50, 75, and 100wt%). The Rh catalyst supported on 20wt% CeO2-modified alumina (2Rh/20CeAl) showed the highest propane and steam conversions, followed in decreasing order by those with 10, 5, 50, 75, 0, and 100wt% CeO2. TPR results show that the interaction between ceria and rhodium improves the reducibility of both rhodium oxide and ceria. XPS analysis indicates strong ceria–alumina interaction and strong Rh-support interaction for Rh catalysts with CeO2 loading less than 20wt%. Field-Emission SEM and AES results revealed that at 20wt% CeO2 loading, ceria was dispersed as separate nano-particles with sizes of 100–200nm on the alumina surface. At high CeO2 loading (≥50wt%) ceria particles formed conglomerates covering alumina surface. The 2Rh/20CeAl catalyst showed the highest activity for propane steam reforming possibly because the high CeO2 dispersion created a large area of ceria–alumina interface which helped increase Rh dispersion, and the strong interaction between Rh and support helped enhance the reducibility of ceria and rhodium oxide. Rh loaded onto the interfacial region of ceria and alumina is considered to be most active for the 2Rh/20CeAl catalyst.

Hydrogen production and coke minimization through reforming of kerosene over bi-metallic ceria–alumina supported Ru–Ni catalysts

Steam reforming of kerosene was investigated to produce syngas as a fuel for solid-oxide fuel cells. Catalytic performances of synthesized bi-metallic Ru–Ni containing ceria–alumina supported catalysts were compared with mono-metallic catalysts containing only Ni or Ru, in the reforming reaction of kerosene. These catalysts had mesoporous structures with narrow pore size distributions. Performance of the catalyst containing 1% Ru and 15% Ni was the most stable with minimum coke and CH4 formation, as compared to the mono-metallic catalysts and bi-metallic catalysts containing less Ni. Incorporation of 1% Ru into Ni based catalysts significantly improved catalyst stability. All of the catalysts were very active, giving complete conversion of kerosene at 800°C. Increase of H2O/C ratio in the feed stream also caused more stable operation with less CH4 and CO formation. Results also proved that high hydrogen yields could be obtained by steam reforming of kerosene, producing a synthesis gas which might be used as a fuel in solid oxide fuel cells.

Aerobic Oxidative Esterification of Benzyl Alcohol and Acetaldehyde over Gold Supported on Nanostructured Ceria–Alumina Mixed Oxides

AbstractAu nanoparticles supported on nanostructured ceria‐alumina mixed oxides (10 and 30 wt % ceria) were prepared by a deposition–precipitation method. Their properties were studied by N2 adsorption, XRD, TEM, X‐ray photoelectron spectroscopy, and UV/Vis spectroscopy under temperature‐programmed reduction or oxidation. The materials catalyzed the liquid‐phase aerobic oxidative esterification of benzyl alcohol and benzaldehyde effectively and showed a much better performance than Au supported on the individual oxides. The reactions occurred with high turnover numbers (up to 19 000) in methanol solutions in the absence of any auxiliary base and gave mainly methyl benzoate. The strong synergetic effect of ceria and alumina can be explained by the enhanced oxygen storage capacity of the materials prepared from mixed oxides compared to that of pure alumina and ceria. The order of the catalytic activity (Au/Al2O3<Au/CeO2<Au/Ce(10)‐Al<Au/Ce(30)‐Al) correlated well with the oxygen activation capacity of the materials.

Understanding of the oxygen activation on ceria- and ceria/alumina-supported gold catalysts: a study combining 18O/16O isotopic exchange and EPR spectroscopy

Gold supported on ceria or ceria–alumina mixed oxides are very active catalysts for total oxidation of a variety of molecules. The key step of the oxygen activation on such catalysts is still a matter of debate. Gold–ceria (Au/CeO2) and gold–ceria–alumina (Au/CeO2/Al2O3) catalysts were prepared by deposition–precipitation of gold precursor with urea as in former works where their efficiency to catalyze the oxidation of propene and propan-2-ol was demonstrated. To understand the phenomenon of oxygen activation over this class of catalysts, efficient techniques generally used to characterize the interaction between oxygen and cerium-based oxides were applied; the oxygen storage capacity (OSC) measurement, the 18O2/16O2 isotopic exchange study (OIE), as well as characterizations by in situ Raman and electron paramagnetic resonance (EPR) spectroscopies. Each of the techniques allowed showing the impact of the gold nanoparticles on the activation of dioxygen, on the kinetic governing the gas-phase/solid oxygen atom exchange, and on the nature and the location of the adsorbed oxygen species. Gold nanoparticles were shown to increase drastically the OSC values and the rate of oxygen exchange. OIE study demonstrated the absence of pure equilibration reaction (16O2(g) + 18O2(g) ↔ 2 16O18O(g)), indicating that gold did not promote the dissociation of dioxygen. Peroxo adspecies were observed by Raman spectroscopy only in the presence of gold. On the contrary, EPR spectroscopy indicated that the concentration of superoxo adspecies was lower for oxide-supported gold samples than for bare oxides. The combination of techniques allowed reinforcing the hypothesis that the gold nanoparticules promote the activation of dioxygen by generating extremely mobile diatomic-oxygenated species at the gold/ceria interfacial perimeter. This specific gold–ceria interaction, which leads to the increase in oxygen mobility, is probably also responsible for the higher catalytic performance of Au/CeO2 and Au/CeO2/Al2O3 in oxidation reaction compared to bare supports.

Methane Oxidation Over Pd Supported on Ceria–Alumina Under Rich/Lean Cycling Conditions

Catalysts with highly dispersed palladium on alumina, alumina doped with 20 wt% ceria and ceria have been prepared, characterized and examined for net-lean methane oxidation. In particular, the activity and selectivity were investigated during rich/lean cycling of the feed. The ceria content is found to influence both the general and the instantaneous activity responses. The results indicate that the active phase of palladium changes between reduced and oxidised Pd during the rich/lean cycling, and that the process is influenced by the presence of ceria.

In situ characterization of iron-promoted ceria–alumina gold catalysts during the water-gas shift reaction

In this work an in situ XRD and XANES study of two gold catalysts supported on iron-promoted ceria–alumina carriers was carried out during the water-gas shift reaction (WGS). The first catalyst, Au/CeO2–FeOx/Al2O3, was prepared using a commercial alumina support in order to obtain a Ce–Fe oxide solid solution and in the second one, Au/FeOx/CeO2–Al2O3, an iron oxide monolayer was deposited onto a ceria–alumina commercial support to promote its redox properties. Catalytic activities in the WGS were remarkably different for both systems. The catalytic activity of the Au/CeO2–FeOx/Al2O3 catalyst was higher than the one shown by the Au/FeOx/CeO2–Al2O3 catalyst that resulted active at much higher temperatures. In situ XRD demonstrates the formation of magnetite (Fe3O4) during the WGS reaction and the presence of big gold particles, ca. 21nm in diameter, in the low-activity system. This in contrast to the high-activity system that shows undetectable gold nanoparticles and the absence of diffraction peaks corresponding to magnetite during the WGS. The data obtained using in situ XANES states that Ce4+ species undergo reduction to Ce3+during the WGS for both catalysts, and also confirms that in the high-activity catalyst iron is just present as Fe3+ species while in the low-activity catalyst Fe3+ and Fe2+ coexist, resulting in iron spinel observed by XRD. These results allow us conclude that the Au/CeO2–Fe2O3/Al2O3 catalyst is a suitable catalyst for WGS when avoiding the formation of magnetite, in such a case Fe3+ species favors reduction and water splitting increasing the catalytic activity in the WGS reaction.

Biogas reforming for syngas production over nickel supported on ceria–alumina catalysts

A series of 8wt% nickel catalysts supported on alumina and alumina-modified with different amounts of ceria were prepared. The effect of the supporting ceria loading at the catalytic performance for the biogas reforming reaction was investigated. The physicochemical properties of the final catalysts were determined by using different techniques: N2 adsorption–desorption isotherms, X-ray diffraction (XRD), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and transmission electron microscopy (TEM). Catalytic performance was evaluated for the biogas reforming reaction using a feed gas mixture of CH4/CO2=1.5, simulating a clean model of biogas. It was shown that nickel catalysts supported on ceria–alumina exhibit slightly higher conversion values, compared to the one supported on alumina above 800°C, which can be mainly attributed to the redox properties of ceria. In particular, the 8wt% nickel catalyst supported on 20wt% ceria–alumina was proven to have the best catalytic performance with a highest H2/CO ratio of about 1.3. The biogas reforming reaction catalyzed by nickel–alumina doped with ceria catalysts seems to be an appropriate process in order to produce syngas suitable for methanol or Fischer–Tropsch synthesis reactions, which require H2/CO ratio values between one and two (1 to 2).

Effect of the ceria–alumina composite support on the Mo-based catalyst’s sulfur-resistant activity for the synthetic natural gas process

Ceria–alumina composite supports were prepared by the co-precipitation (cop), impregnation (imp) or deposition–precipitation (dp) methods. Co–Mo catalysts supported on these composite supports were prepared by the imp method and their catalytic activities for sulfur-resistant methanation of synthesis gas were investigated. The catalysts were characterized by nitrogen adsorption, X-ray diffraction (XRD), and hydrogen temperature-programmed reduction (TPR). It was found that the preparation method of ceria–alumina composite support had a marked influence on the surface area, the interaction between ceria and alumina, and the catalytic performance for sulfur-resistant methanation. Among them, the ceria–alumina composite support prepared by dp method achieves the best methanation activity due to its smaller ceria particle size, better ceria dispersion, weak interaction between ceria–alumina as suggested by XRD and TPR results.

Preferential CO oxidation over nanosized gold catalysts supported on ceria and amorphous ceria–alumina

1wt.% Au supported on CeO2–Al2O3 (Ce/Ce+Al: 0, 2, 5, 10, 15, and 20mol%) was prepared by impregnation in organic medium of high-surface area supports prepared by Evaporation Induced Self Assembly (EISA) route. For comparison, a 1wt.% Au/CeO2 was also prepared using a commercial support. All the prepared catalysts present a BET surface area roughly between 200 and 340m2g−1. The reducibility, the oxygen storage capacity (OSC) and the oxygen mobility determined by oxygen isotopic exchange (OIE) of the 1wt.% Au/CeO2–Al2O3 are enhanced by the presence of gold and increases with the cerium content in the support. The values of the OSC and the oxygen mobility in the Au/CeO2–Al2O3 catalysts with high cerium loading are higher than those determined on their Au/CeO2 counterpart. The activity in CO oxidation of the Au/CeO2–Al2O3 catalysts increases with the cerium content in the support, which could be linked to the better oxygen mobility of these systems, whereas in CO-PrOx the Au/CeO2–Al2O3 catalysts with medium cerium loading (Ce/Ce+Al=5 and 10mol%) present the highest CO conversion at 50–60°C. The catalysts are stable at 100°C in CO+O2+H2 mixtures. The addition of CO2 in the stream strongly deactivates Au/CeO2, whereas Au/CeO2–Al2O3 is less affected. Whatever the catalyst, the presence of steam has no significant effect on the catalytic performances.

Gold catalysts supported on nanostructured Ce–Al–O mixed oxides prepared by organic sol–gel

Nanostructured ceria–alumina mixed oxides containing different concentrations of ceria (10 and 30wt.%) were prepared by the sol–gel method using organo-metallic precursors of alumina and ceria. The size of alumina and ceria particles in the prepared Ce–Al–O mixed oxides was smaller than that of pure alumina or ceria. The gold catalysts (3wt.% Au) supported on ceria–alumina mixed oxides by deposition–precipitation (DP) using HAuCl4 and urea were characterized by several techniques: TEM, XPS and UV–vis spectroscopy, and temperature programmed reduction/oxidation (TPR/TPO). The catalytic activity of prepared Au/CeO2–Al2O3 catalysts in CO oxidation was higher than that of Au/Al2O3 and Au/CeO2 catalysts. Nanostructured ceria incorporated into an alumina matrix has been found quite effective for gold species activation in CO oxidation. In fact, transient analysis of CO oxidation provided an estimate of the relative content of (Au–ceria vacancy) active sites in catalysts. Obtained values are in good agreement with the order of activity for tested samples and gold dispersion according to EXAFS data.

Textural, structural, and morphological characterizations and catalytic activity of nanosized CeO 2–MO x (M = Mg 2+, Al 3+, Si 4+) mixed oxides for CO oxidation

The present work focuses on the combination of ceria with another oxide of different ionic valences from period 3 (Mg 2+, Al 3+, and Si 4+) using coprecipitation method, followed by calcination at 450 and 750 °C, respectively. The textural, structural, morphological and redox properties of nanosized ceria–magnesia, ceria–alumina and ceria–silica mixed oxides have been investigated by means of N 2 physisorption, XRD, Raman, HRTEM, DRS, FT-IR, and H 2-TPR technologies. XRD results of these mixed oxides reveal that only nanocrystalline ceria ( ca. 3–6 nm for the 450 °C calcined samples) could be observed. The grain size of ceria increases with the increasing calcination temperature from 450 to 750 °C due to sintering effect. The highest specific surface area is obtained at CeO 2–Al 2O 3 mixed oxides when calcination temperature reaches 750 °C. Raman spectra display the cubic fluorite structure of ceria and the existence of oxygen vacancies, and displacement of oxygen ions from their normal lattice positions in the ceria-based mixed oxides. DRS measurements confirm that the smaller the grain size of the ceria, the higher indirect band gap energy. H 2-TPR results suggest that the reductions of surface and bulk oxygen of ceria were predominant at low and high calcination temperature, respectively. Finally, CO oxidation were performed over these ceria-based mixed oxides, and the combination of CeO 2–Al 2O 3 exhibited highest activity irrespective of calcination temperature, which may due to excellent textural/structural properties, good homogeneity, and redox abilities.

Structure and morphology of Pd/Al 2O 3 and Pd/CeO 2/Al 2O 3 combustion catalysts in Pd–PdO transformation hysteresis

Catalytic combustion of methane has been studied for many years due to its applications in power generation and emissions clean-up. Among different catalysts, Pd-based materials are the most active for the catalytic combustion of methane. In this work we have investigated the Pd–PdO transformation process on Pd–alumina and Pd–ceria–alumina combustion catalysts by combining different analytical techniques. Both decomposition of PdO and reoxidation of Pd take place via the formation of an intermediate, which has been identified as a surface or interfacial PdO x on the basis of X-ray Photoelectron Spectroscopy analysis. The results obtained by coupling temperature programmed oxidation with high resolution transmission electron microscopy and X-ray photoelectron spectroscopy indicate that PdO decomposition is a thermodynamically driven process, in which the support affects only the amount of PdO species involved in each decomposition step. On the contrary, Pd reoxidation is a kinetically limited process, which is strongly affected by the environment. In particular, the presence of promoters such as CeO 2 or residual PdO significantly speeds up Pd oxidation, thus reducing the characteristic Pd–PdO hysteresis.

The electrical properties of microwave sintered gadolinia doped ceria–alumina nano-composite electrolyte

Gadolinia doped ceria–alumina (GDC–Al 2O 3) nano composites have been prepared by chemical synthesis route and sintered using 2.45 GHz microwave energy as well as conventional technique. The electrical properties of the sintered samples are investigated by ac impedance spectroscopy. It has been observed that the conductivity of microwave sintered GDC–Al 2O 3 composite is higher than that of conventional sintered GDC–Al 2O 3 composite and pure GDC sample. Higher concentration of vacancies at the interfaces of GDC and Al 2O 3 phases may be responsible for the better conductivity of GDC–Al 2O 3 composite compared to pure GDC. The fine grain microstructure of microwave sintered samples creates more interfaces compared to conventional sintered sample which in turn responsible for the better performance of microwave sintered composite sample. The micro-structural results of microwave sintered samples also reveal the presence of elongated, needle like Al 2O 3 grains. The X-ray diffraction results have shown the formation of additional GdAlO 3 phase.

Phase transition in ceria alumina

Al-doped CeO2 samples were prepared by conventional solid state reaction. The electrical conductivity of CeO2 doped with Al2O3 has been studied at different temperatures for various molar ratios. The isothermal conductivity increases with dopant concentration due to the vacancy migration phenomenon induced by doping. It has been found that the conductivity increases and shows a jump from 450 to 520°C due to the phase transition of ceria from cubic to orthorhombic type. A slight deflection is seen for 0.5 and 0.6 moles of alumina at about 250°C due to its phase transition from γ to α type. AC impedance measurements proved that the oxide ion conductivity predominantly arises from the grain and grain boundary contribution as two well defined semi-circles are clearly seen. The sample characterization and the study of phase transition changes were done by using X-ray diffraction analysis, Fourier transform infrared spectral and differential scanning calorimetry (DSC) measurements. On increasing the concentration of dopant, the transition temperature shifts towards lower side which is confirmed by DSC as well as conductivity measurements.

Reactivity of Ru-based catalysts in the oxidation of propene and carbon black

The relationship between the state of Ru on different supports and catalytic activity in the oxidation of propene and carbon black was investigated for catalysts prepared by different impregnation methods. It is demonstrated that the addition of ruthenium to ceria (CeO 2), alumina (Al 2O 3) and ceria–alumina significantly improves the reactivity: the temperature of carbon black oxidation decreases by 100–140 °C. It is also shown that the addition of Ru to the different supports is very beneficial for the total oxidation of propene. Temperature programmed reduction (TPR) experiments of the catalysts showed that the oxygen species of ruthenium oxides are reduced at low temperatures which is the main reason of its high reactivity in oxidation reactions.

Gold supported on ceria and ceria–alumina promoted by molybdena for complete benzene oxidation

New gold–molybdena catalysts supported on ceria and ceria–alumina in reaction of complete benzene oxidation were studied. The catalysts were characterized by means of XRD, TPR, XPS and Raman spectroscopy. High and stable catalytic activity was established in the temperature region 200–240°C. The presence of gold causes a modification in ceria structure leading to an increase of Ce3+ and oxygen vacancies formation. The loading of Al3+ increases additionally the oxygen vacancies, while a tendency of decrease of Ce3+ amount was observed. The presence of alumina results also in a larger share of active oxygen species proved by analysis of O 1s XPS spectra. The differences in the activities within the starting temperature range (150–180°C) and in the region of 100% conversion (200–240°C) could be explained by supposing that in the LT region the electron transfer between nanosized gold and ceria particles via oxygen vacancies has a crucial role. In the HT region the oxygen mobility, provoked by the defective structure of ceria due to the presence of Al3+, becomes of prevailing importance. It was also concluded that alumina prevents the gold and ceria agglomeration, which is the main factor to avoid deactivation under extreme reaction conditions.