Urea Nitrate Combustion Method Research Articles

An improved preparation method for a CuO/CeO2-coated monolith for the CO–PrOx reaction

In this study, we present a method for directly coating monoliths with a CeO2/CuO catalyst using the urea-nitrate combustion method. The catalyst was characterized by means of XRD, SEM/EDX, and EPR measurements. Experimental results are described, when this catalyst was used for the preferential oxidation of CO. The catalytic activity for the CO–PrOx-reaction was measured by recording CO conversion as a function of the reaction temperature in a hydrogen-rich gas mixture in the presence and absence of water vapor. In a long-term test of over 310 h, the catalyst’s long-term stability was demonstrated. Direct coating is shown to be a promising approach by which a larger amount of catalyst can be deposited onto the monolith in a single step than would be possible with washcoats.

Enhancing conductivity of apatite-type lanthanum silicate by Li and Cu co-doping

Solid oxide fuel cells (SOFC) are all-solid power generation devices that directly convert chemical energy stored in fuel gases and oxidizers to electrical energy efficiently and without pollution at medium to high temperatures. Recognized as the green energy technology of the 21st century, it is of great significance to alleviating the energy crisis, meeting electricity demand, and reducing environmental pollution. Using the urea-nitrate combustion method, the solid electrolyte powder (LLSCO) of lanthanum silicate of apatite type La9.33LixSi5.5Cu0.5O25.5 + 0.5x (x = 0.1, 0.2, 0.3, 0.4) was successfully prepared by igniting 6-8 mins at 600 °C. According to XRD analysis, LLSCO has a typical P63/m apatite structure and high purity. The volume of LLSCO lattice increases further than that of LSO and LSCO and increases with the increase of Li+ doping. This is because when Li and Cu are doped simultaneously, Li+ enters the empty space in the LSO lattice that occupies the LaII position, which causes the lattice to expand. At the same time, Cu2+ enters the LSO lattice to replace the partial Si4+, which will also cause lattice expansion. The IR analysis shows that Cu2+ replaces Si4+ and enters the [SiO4] tetrahedron to form the [Si(Cu)O4] tetrahedron, while Li+ occupies the vacancy of the LaII position. The optimal sintering temperature of Li and Cu co-doped LLSCO was determined to be 1575 °C based on shrinkage rate, relative density with temperature, and microscopic morphology analysis. The conductivity of La9.33LixSi5.5Cu0.5O25.5+0.5x (x=0.1, 0.2, 0.3, 0.4) was significantly higher than that of LSO and LSCO. With the increase of Li doping, the impedance of the doping sample was lowest when x = 0.3, and the conductivity reached the highest of 9.27 × 10−4 S · cm ·−1 at 600°C.

Preparation of Al and Sm Co-doped Apatite-Type Lanthanum Silicate Electrolyte and analysis of the conductivity mechanism

The contradiction between the increasing demand for energy and the scarcity of traditional fossil energy sources is becoming increasingly acute, and it is urgent to accelerate the development and use of new, more efficient, and environmentally friendly energy sources. Apatite-type lanthanum silicate solid oxide electrolyte materials (La9.33Si6O26, LSO) are widely used in the field of fuel cell electrolytes due to their high ionic conductivity and high density. In this paper, Al and Sm co-doped LSO solid electrolytes were successfully prepared by the urea-nitrate combustion method. SEM images, relative density, and linear shrinkage of Al and Sm co-doped lanthanum silicate electrolytes sintered at different temperatures were compared. The results show that the best sintering temperature is 1500°C. The electrical conductivity of La9.33SmxSi5.5Al0.5O25.75+1.5x was analyzed by EIS. The conductivity of La9.33Sm0.2Si5.5Al0.5O26.05 is 2.56 × 10−4 S·cm−1 when measured at 600°C. The reason Al and Sm co-doping enhances the conductance is that Al doping generates oxygen vacancies and increases the interstitial oxygen (Oi) concentration. Doping of Sm not only increases the concentration of Oi but also reduces the concentration of cation vacancies, thus improving the conductivity of the electrolyte.

Comparison study of preferential oxidation of CO over nanocrystalline Cu/CeO2 catalysts synthesized by different preparation methods

Preferential oxidation of carbon monoxide in presence of excess hydrogen is a promising alternative to restrict the CO deposition in the Pt-anode in the practical polymer electrolyte membrane fuel cell application. In the present work, nanocrystalline copper-ceria catalysts have been synthesized by hydrothermal method, wet impregnation method and urea nitrate combustion method. Their characterizations have been carried out by using X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy . It has been found that Cu 2+ replaced Ce 4+ in cerium oxide, creating oxygen vacancy. The formation of more nano-sized CeO 2 leads to more oxygen vacancies in CeO 2 through the formation of interfacial Cu 1+ ions, which also enhances the CO oxidation activity. Among the synthesized Cu-CeO 2 catalysts, the catalyst prepared by hydrothermal method have shown both CO conversion and CO 2 selectivity as 100% towards CO oxidation at 373 K in the presence of excess H 2 making this catalyst viable for practical fuel cell application.

Analysis of the conduction mechanisms of the Ni doped apatite‐type lanthanum silicate electrolyte ceramics synthesized by the combustion method

AbstractIn this study, the nickel doped apatite‐type lanthanum silicate La9.33Si6‐xNixO26‐x (x = 0, .5, 1.0, 1.5, 2.0) (LSNO) electrolyte powders were successfully generated by using the urea nitrate combustion method at 600°C and 6–8 min. The optimal sintering temperature was determined to be 1500°C on the basis of the linear shrinkage, relative density as a function of temperature, and microcosmic analysis. It was observed that Ni2+ successfully replaced Si4+ in [SiO4] to form the [Si(Ni)O4] tetrahedra. LSNO had a typical p63/m apatite structure of high purity. A significant change in the cell volume of the doped samples was observed, and the cell volume increased with the doped nickel content. The conductivity reached the peak value at x = 1.0 (1.21 × 10−3 S·cm−1, 700°C). Nickel doping introduced the oxygen vacancies and expanded the channels for interstitial oxygen conduction. Further, it also directly reduced the amount of interstitial oxygen in the LSO structure. This led to an enhancement in the conductivity of La9.33Si6‐xNixO26‐x, followed by a decrease on increasing the doped nickel content. The conductivity enhancement in the Ni‐doped LSO resulted from the combination of two mechanisms, namely, the oxygen vacancy defect and lattice volume enhancement mechanism.

Preparation of praseodymium-doped La9.33(SiO4)6O2 apatite-type solid electrolytes and analysis of the conductivity mechanism

In order to improve the electrical conductivity of lanthanum silicate oxide electrolyte (LSO), La9.33Pr x Si6O26+1.5x (LPSO) solid electrolyte powder doped with praseodymium was synthesized at 600 °C by urea-nitrate combustion method with lanthanum oxide (La2O3) and Praseodymium nitrate hexahydrate (Pr(NO3)3·6H2O) as raw materials. It is shown that the Pr-doped LSO still have the typical apatite structure and occupy the LaII cation vacancy at the 6h position. Optimal sintering temperature is 1550 °C. La9.33Pr0.5Si6O26.75 reaches the highest conductivity (4.80×10−4 S·cm−1 at 600 ºC). The main factor that Pr-doped improves the performance of LSO is that Pr-doped that introduced more interstitial oxygen ions Oi* and increased lattice volume, so improved the transport efficiency of interstitial oxygen. The secondary factor is the decrease in the concentration of cation vacancy after Pr-doped, which reduced the negative defect stacking centers. Thereby, decreases space drag of interstitial oxygen transport which increases conductivity of LSO. The praseodymium doped to enhancement LSO conductivity mechanism that interstitial oxygen concentration-cation vacancies concentration-lattice volume composite enhancement mechanism was proposed.

One step closer to the low-temperature CO oxidation over non-noble CuO/CeO2 nanocatalyst: The effect of CuO loading

Concerning the catalytic field of CO oxidation for designing the cost-effective, stable, and highly active catalysts based on CuO/CeO2 nanocomposites, in this work, the urea-nitrate combustion method was used to synthesize a series of CuO/CeO2 catalysts with different CuO loadings (at%Cu) to test their catalytic activity in the CO oxidation, to find out the optimum at%Cu which allows the CuO/CeO2 composite to perform a higher activity in close to room-like temperature. The at%Cu of 0%, 2.5%, 5.0%, 7.5%, 10%, 20%, 30%, 40%, and 50% were set up to obtain a catalyst series. The resulting catalysts were characterized using EDX, PXRD, SEM, and other methods. It was shown that the CuO loading caused changes in the phase composition (crystalline CeO2, amorphous or crystalline CuO), the crystallite size (5–10 nm for CeO2; 20–33 nm for CuO), and the specific surface area (12.2–85.8 m2/g), as well as in the morphological and pore structure. These factors comprehensively influenced the catalytic performance of the samples. The initial temperature (ti) toward CO oxidation for the best catalyst obtained in this study belonged to the low-temperature region (ti < 50 °C). The temperature for 50% CO conversion (t50%) of the best catalysts was less than 100 °C that was much lower compared to pure CeO2 (t50% ≈ 312 °C). For CO oxidation, the active sites on the surface were correlated with the interactions between copper and cerium oxides; the improvement in catalytic activity is also related to the high concentration of oxygen vacancies or high oxygen storage capacity of the catalysts. Besides, the advantage in the specific surface area of the samples played as one of the decisive factors to the higher CO conversion. It was noted that the increase of CuO loading into the CuO/CeO2 catalysts exceeded 20% doesn’t lead to a further decrease in the temperature of CO oxidation. Thus, the optimum catalyst composition was determined to be the CuO/CeO2-20, and its properties were studied by the methods of Raman, XPS, TEM, H2-TPR, and EDS in detail. Results proved a strong synergistic effect – the coexistence of redox pairs Ce4+/Ce3+-Cu2+/Cu+, the formation of oxygen vacancies, as well as the presence of superficial lattice oxygen and adsorbed oxygen species leading to improve the catalytic activity of CuO/CeO2-20 catalyst. Moreover, the stability of the CuO/CeO2-20 catalyst was investigated and excellent results were obtained. We believe that the activity in CO oxidation of the CuO/CeO2-20 sample can even be enhanced by doping oxides of the other rare-earth and transition metals, which requires further study.

Influence of Oxygen Vacancy on Pseudocapacitance of La0.8Sr0.2CoO3-δ

Since the discovery of the charge storage mechanism involving a charge compensation by anion that can happen for some pseudocapacitive materials, oxides from the perovskite family have been intensively studied during the past five years, such as LaMO3-δ (M = Mn, Fe, Co, Ni). The oxygen vacancy present in some perovskites naturally becomes the center of this new mechanism. Indeed, the vacancies are suggested to host oxygen/hydroxyl ions to compensate the oxidation of the transition metal, and to release these ions during the reduction. Interestingly, there has not been any report dedicated to reveal the correlation between the oxygen vacancy with the pseudocapacitance of these materials.We propose here the study of the influence of the oxygen stoichiometry of the perovskite La0.8Sr0.2CoO3-δ, written as LSC82, used as pseudocapacitive electrode material. LSC82 has been prepared by a urea-nitrate combustion method, and then calcined at 850°C. Materials having different oxygen stoichiometries were obtained by different cooling rates. Electrochemical tests were performed on LSC82 based electrodes in 5M LiNO3 electrolyte to reveal the correlation between the oxygen stoichiometry and pseudocapacitve performance. The oxidation states of Co and the oxygen vacancies content in the various prepared LSC82 have been determined by various technics such iodometric titration, X-ray Absorption Spectroscopy and X-ray Photoelectron Spectroscopy. By associating electrochemical tests with spectroscopic technics, it is possible to connect oxygen vacancies content with electrochemical performances.Understanding the role of oxygen vacancies could give new lead to improving the performances of such materials.

Urea–nitrate combustion synthesis of CuO/CeO2 nanocatalysts toward low-temperature oxidation of CO: the effect of Red/Ox ratio

The low-temperature catalytic oxidation of carbon monoxide (CO) is the key process to overcome incomplete combustion of fossil fuels for both commercial (e.g., lowering automotive emissions) and domestic (e.g., indoor air quality improvement) applications. So the development of cost-effective and high-active catalysts made from non-noble metals is an actual material science challenge. Ce–Cu–O oxide system is one of the most prospective to investigate due to the feasibility of the Langmuir–Hinshelwood dual-site oxidation mechanism, and, in our previous work, it was shown that solution combustion synthesis using the urea as fuel in stoichiometric ratio with metal nitrates is a most reasonable fuel choice toward the synthesis of CuO/CeO2 nanocatalysts for effective CO oxidation. In this work, the effect of the Red/Ox (urea to nitrates or U/N) ratio on the catalytic oxidation activity of resulting CuO/CeO2 composites is in the spotlight. Series of CuO/CeO2 nanocatalysts were successfully synthesized via the urea–nitrate combustion method with U/N ratios from 0.2 to 1.4 and then were applied for CO oxidation. The samples before and after catalysis were characterized by EDX, SEM, PXRD, N2-ASA, H2-TPR, etc. It was shown that the U/N ratio strongly affects the qualitative and quantitative X-ray phase composition (c-CeO2, m-CuO, and am-CuO, in general), CeO2 and CuO crystallite sizes (4.9–63.0 nm and 14.7–28.3 nm, correspondently), specific surface area (4–46 m2/g) and porosity (0.009–0.033 cm3/g), as well as the morphology of nanocomposites and their catalytic characteristics (t50% = 113–199 °C and t100% = 137–348 °C). The sample synthesized at U/N = 0.2 shows the best oxidative performance (t50% = 113 °C and t100% = 137 °C) explained by the highest surface (46 m2/g), the lowest CeO2 crystallite size (4.9 nm), and the lowest degree of agglomeration of nanocrystals in the CuO/CeO2 composite. Besides, cyclic and water resistivity tests of this sample confirm the high stability of its catalytic activity in the CO oxidation process due to the close conjugation of the CeO2 and CuO components in the resulting nanocomposite, confirmed by the H2-TPR analysis results. Thus, it was shown that the optimization of Red/Ox ratio in the urea–nitrate combustion process contributes to obtaining the stable CuO/CeO2 nanocatalyst with gradual conversion of CO at quite low temperatures (ti ~ 50 °C). We believe that the subsequent reduction of CuO loading in the Ce–Cu–O system allows creating a cost-effective and stable composite nanocatalyst with high activity even at room temperature.

Improving the performance of nickel catalyst supported on mesostructured silica nanoparticles in methanation of CO2-rich gas by urea–nitrate combustion

In this work, NiO supported mesostructured silica nanoparticles (MSN) were synthesized via the urea–nitrate combustion method using urea as fuel and nitrate salts as oxidants with the different urea/nitrate ratios and calcination duration. The physicochemical properties of catalysts were investigated by several techniques, including N2 physisorption measurements, powder X-ray diffraction, N2-BET isothermal adsorption, hydrogen temperature-programmed reduction, carbon dioxide temperature-programmed desorption, scanning electron microscopy and transmission electron microscopy. The obtained catalysts were employed in the methanation of CO2-rich gas at a temperature range of 225–400 °C with the CO2/H2 ratio of 1/4 and CO2 concentration of 20 mol%. The results showed that using the urea–nitrate combustion method in synthesizing catalysts led to improved physicochemical properties that increased the activity of NiO/MSN catalysts. The catalyst prepared with the urea/nitrate molar ratio of 3 and calcined at 600 °C for 3 h showed the highest catalytic performance in methanation of CO2-rich gas, reaching CO2 conversion of 96% and CH4 selectivity of 100% at 375 °C. The best catalyst has excellent stability in CO2 solo-hydrogenation at a reaction temperature of 375 °C during 30 h of reaction thanks to the resistance to coke formation. Besides, adding 1 mol% CO in the feedstock should be simultaneously conducted to surge the effectivity of CO2 methanation.

Synthesize of magnetite Mg-Fe mixed metal oxide nanocatalyst by urea-nitrate combustion method with optimal fuel ratio for reduction of emissions in diesel engines

Abstract In the present study, Mg0.25Fe2.75O4 nanocatalyst for reduction of emissions in diesel engine was fabricated via urea-nitrate combustion method. The effect of urea concentrations as fuel on its structural characteristics and Oxygen Storage Capacity (OSC) was thoroughly investigated. The results of various characterization analyses showed that fuel ratio significantly affects crystallinity, textural, size and morphology of particles, and thermal stability of nanocatalyst. These are mainly due to increase in combustion temperature and duration. The Mg0.25Fe2.75O4 fabricated at fuel ratio of 2.5 times of stoichiometric ratio exhibited the lowest weight loss/high crystallinity (less than 1 wt %) and lowest lattice parameter (8.346 A) which are related to well diffusion of Mg cations into ferric oxide as host. The Raman and FTIR analyses showed the existence of strong peaks correspond to formation of tetrahedral and octahedral sublattices and also the formation of spinel structure of MgFe2O4. The reduction in crystalline size, obtained with higher amount of fuel, resulted in a higher surface area (23.6 m2/g), higher pore volume (0.0950 cc/g) and proper particle size distribution (25–35 nm). These cause a better catalytic activity. Moreover, the enhanced OSC (8661 μmol H2/g) along with shifting the reduction peaks to lower temperatures, as major attributes in relation to catalytic technologies, confirmed the strong effect of fuel ratio of 2.5 on fabrication process of Mg0.25Fe2.75O4. Finally, the highest reduction in HC (33%), CO (14-17%), PM1.0 (16%), and CO2 (12%) achieved, using the optimum sample-mixed diesel fuel at 90 ppm.

Improving conductivity of apatite-type lanthanum silicate by Nd and Zn co-doping

The electrical properties of apatite-type lanthanum silicate co-doped with Nd and Zn has been investigated. The Nd and Zn co-doped lanthanum silicate, La9.33NdxSi6-yZnyO26+(3x/2)-y (0 ≤ x ≤ 1, y = 0,1), are successfully synthesized by the urea nitrate combustion method. The phase, morphology and electrical properties are characterized by X-ray diffraction, scanning electron microscopy and electrochemical impedance spectra, respectively. La9.33NdxSi6-yZnyO26+(3x/2)-y ceramics has good apatite structure and high purity. The conductivity of La9.33NdxSi5ZnO25+(3x/2) first increases and then decreased accompanying with Nd content increasing, which higher than that of undoped La9.33Si6O26. The increase of the conductivity, which is attributed to Zn doped introduces oxygen vacancies and expands oxygen ions migration channel as well as Nd doped decreases the defect centers and increases the amount of interstitial oxygen ions. The decrease in conductivity is due to excess Nd blocking the oxygen ions migration channel. La9.33Nd0.8Si5ZnO26.2 exhibited the highest conductivity which values equal to 8.11 × 10−4 S cm−1 at 650 °C.

Preparation and Conductivity Research of Zinc Ions Doped La9.33(SiO4)6O2 Electrolyte

Solid electrolyte as a conductive medium has a good application prospect in the field of fuel cells. In order to improve the conductivity at low and medium temperature. The electrolyte of apatite type lanthanum silicateLa9. 33(SiO4)6O2 (ATLS) was doped with Zn at position of Si using urea nitrate combustion method. And XRD, SEM, IR were performed for ATLS electrolytes doped with Zn. The results showed that the combustion synthesis of zinc doped ATLS powders have apatite crystal structure after calcined 12 hours. Zn doping into the ATLS lattice has little impact on the crystal structure and morphology. Analysis of samples determine the best sintering temperature at 1250 for the La9. 33Si6-xZnxO26-x electrolyte. The electrolyte has good resistance stability by AC impedance test. When the amount of zinc ions doped x = 1. 0, the La9. 33Si6-xZnxO26-x has the highest ionic conductivity. Doping a moderate amount of ion at Si can enhance the conductivity of the ATLS electrolyte.

In-situ carbon-coated Na 2 FeP 2 O 7 anchored in three-dimensional reduced graphene oxide framework as a durable and high-rate sodium-ion battery cathode

Abstract Na 2 FeP 2 O 7 , which is considered as a promising cathode for sodium ion batteries (SIBs) on account of its economical efficiency and outstanding thermal stability, has been widely studied for the purpose of enhancing its electronic conductivity and interface ion transportation. In this paper, a double-carbon synergistically modified strategy was firstly introduced to facilitate the electrochemical performance of Na 2 FeP 2 O 7 . Na 2 FeP 2 O 7 particles are enwrapped in situ by a carbon layer and further anchored in reduced graphene oxide (RGO) framework through a facile urea-nitrate combustion method. Consequently, the excellent rate performance and durable cycle stability of this compound are identified, which exhibits a reversible sodium storage capacity of 65 mAh g −1 at a current density of 10 C and no obvious decay in capacity after circling for 300 cycles at 1 C. What's more, no drastic degradation in capacity is observed when the cycling current density is brought back to high rates after cycling for more than 360 cycles at various rates.

Preparation of Cu-MgO catalysts via urea-nitrate combustion method and their catalytic performance in vapor phase hydrogenation of furfural

A series of Cu-MgO catalysts was prepared via a urea-nitrate combustion method, and their catalytic performance was examined in the vapor phase hydrogenation of furfural. Characterization results showed that the amount of urea had important effects on the surface area, Cu dispersion and crystallite size of the catalysts. The Cu-MgO catalyst with a Cu loading of 12.1%(mass fraction) showed higher furfural conversion than the catalyst prepared by coprecipitation. The high activity was attributed to the higher dispersion of Cu on the catalyst surface. These results suggest that the combustion method is an efficient and simple route for the preparation of high activity Cu-MgO catalysts for furfural hydrogenation.

수성가스전이반응(Water Gas Shift Reaction)을 위한 Ce 첨가에 따른 Cu/Mn 촉매의 활성 연구

Cu/Mn/Ce catalysts for water gas shift (WGS) reaction were synthesized by urea-nitrate combustion method with the fixed molar ratio of Cu/Mn as 1:4 and 1:1 with the doping concentration of Ce from 0.3 to 0.8 mol%. The prepared catalysts were characterized with SEM, BET, XRD, XPS, <TEX>$H_2$</TEX>-TPR, <TEX>$CO_2$</TEX> TPD, <TEX>$N_2O$</TEX> chemisorption analysis. The catalytic activity tests were carried out at a GHSV of <TEX>$28,000h^{-1}$</TEX> and a temperature range of 200 to <TEX>$400^{\circ}C$</TEX>. The Cu/Mn(CM) catalysts formed Cu-Mn mixed oxide of spinel structure (<TEX>$Cu_{1.5}Mn_{1.5}O_4$</TEX>) and manganese oxides (<TEX>$MnO_x$</TEX>). However, when a small amount of Ce was doped, the growth of <TEX>$Cu_{1.5}Mn_{1.5}O_4$</TEX> was inhibited and the degree of Cu dispersion were increased. Also, the doping of Ce on the CM catalyst reduced the reduction temperature and the base site to induce the active site of the catalyst to be exposed on the catalyst surface. From the XPS analysis, it was confirmed that maintaining the oxidation state of Cu appropriately was a main factor in the WGS reaction. Consequently, Ce as support and dopant in the water gas shift reaction catalysts exhibited the enhanced catalytic activities on CM catalysts. We found that proper amount of Ce by preparing catalysts with different Cu/Mn ratios.

Synthesis and Conductivity Investigation of Cu Doped Apatite Type Lanthanum Silicate Electrolyte

In this paper, Cu-doped lanthanum silicate electrolyte (La9.33Si6-xCuxO26-x) precursor was synthesized by urea-nitrate combustion method using La2O3, CuO and TEOS as raw materials. The as-prepared precursor was lighted at 600 °C and sintered at 800 °C. The sintered powder samples were grinded and mixed absolutely by ball milled. Finally, we preformed and sintered powder samples to synthesis Cu-doped lanthanum silicate ceramics. Ac impedance method and analysis was used to test conductivity of as-prepared electrolyte, investigated the influence of balling time, sintering temperature and doping content on conductivity property of LSO sintered product. The final result shows that best balling time is 3 h, secondary sintering temperature is 1500 °C and the doping content is 0.3. Under this condition, the conductivity of Cu-doped lanthanum silicate electrolyte could reach 7.28×10-3 s/cm at 700 °C.

Effect of the loading content of CuO on the activity and structure of CuO/Ce-Mn-O catalysts for CO oxidation

A urea-nitrate combustion method was used to prepare Ce-Mn-O material, which was applied as the support for a series of CuO/Ce-Mn-O catalysts. The structure of the catalysts was characterized with N2 adsorption/desorption, X-ray diffraction (XRD), temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). The catalytic activity of the catalysts for the oxidation of CO was evaluated on a conventional fixed-bed quartz reactor. XRD results showed that the synergetic effect between manganese and cerium led to a little higher electron density of Ce3+ in the mixed oxides. When the CuO content was lower than 5 wt.%, Cu species were well dispersed onto the Ce-Mn-O support or/and they formed a solid solution with CeO2 (inside the fluorite lattice). At higher CuO content (CuO>5 wt.%), large CuO particles were observed. There was strong interaction among ceria, manganese and copper oxide because of the doping of Mn. This interplay changed the reducibility and the valence states of the components, leading to the improved activity of the CuO/Ce-Mn-O catalysts.

Preparation and NOx-assisted soot oxidation activity of a CuO–CeO2 mixed oxide catalyst

A CuO–CeO2 mixed oxide catalyst is synthesized via the urea-nitrate combustion method. The catalytic activity in the reaction of NOx-assisted soot oxidation is evaluated with a TG/DTG technique. The sample Cu1Ce9 possesses the lowest temperature (Tm=383°C) of the maximum soot oxidation rate and the largest specific surface area (65.1m2/g) among the samples examined. The XRD results show that the fluorite-type CeO2 exists in all the samples forming a solid solution with CuO. Crystalline copper oxide phases are not detectable if the Cu/(Cu+Ce) atomic ratio is lower than 0.25. The activity and NOx-TPD results prove that NO2 formed from NO and the nitrate species play crucial roles for soot oxidation in NOx atmosphere. Kinetic parameters, such as the activation energy and reaction order, corresponding to the oxidation of soot are calculated with a differential method.

Urea–nitrate combustion synthesis of ZrO2 and CeO2 doped CuO/Al2O3 nanocatalyst used in steam reforming of biomethanol for hydrogen production

The CuO/ZrO2/Al2O3 and CuO/CeO2/Al2O3 nanocatalysts for production of hydrogen via methanol steam reforming were prepared by the solution combustion method using urea as fuel. The effect of ceria and zirconia on physicochemical properties of nanocatalysts was investigated by XRD, FESEM, EDX, BET and FTIR techniques. XRD analysis showed that addition of zirconia to nanocatalysts made copper crystallites smaller. EDX results demonstrated high dispersion and uniform morphology of particles. The FESEM results proved that the powder prepared through the urea–nitrate combustion method had nanometric particles. Catalytic performance tests indicated the good practicability and high stability of synthesized catalysts via the solution combustion method for the steam reforming of methanol. Consequently, it was found out that the ceria containing catalyst was the best among other samples. The stability test represented that the CuO/CeO2/Al2O3 catalyst was quite stable for the methanol steam reforming.