Mesoporous CexZr1−xO2 solid solutions supported CuO nanocatalysts for toluene total oxidation

Mesoporous Ce_xZr_1−xO₂ solid solutions were prepared by the surfactant-assisted method and used as support of CuO nanocatalysts for catalytic total oxidation of toluene. The prepared CuO/Ce_xZr_1−xO₂ catalysts have a wormhole-like mesoporous structure with high surface area and uniform pore size distribution, and the CuO nanoparticles were highly dispersed on the surface of Ce_xZr_1−xO₂. The doping of ZrO₂ in CeO₂ promotes the dispersion of active copper species and enhances the reducibility of copper species. The effect of Ce/Zr ratio, calcination temperature and CuO loading amount on the catalytic performance of CuO/Ce_xZr_1−xO₂ was investigated in detail. The 400 °C-calcined 8%CuO/Ce_0.8Zr_0.2O₂ catalyst exhibits the highest activity with the complete toluene conversion temperature of 275 °C at the condition of GHSH = 33,000 h⁻¹ and the toluene concentration of 4400 ppm. The interfacial interaction between CuO and the Ce_xZr_1−xO₂ support, highly dispersed CuO nanoparticles and the nature of the support contribute to the high catalytic activity of mesoporous CuO/Ce_xZr_1−xO₂ nanocatalysts.     

Promotional effects of Ce on the activity of MnAl oxide catalysts derived from hydrotalcites for low temperature benzene oxidation

Ce/MnAl and MnAl mixed metal oxides catalysts have been obtained by calcination of layered double hydroxides precursors. The composite oxides catalysts were studied in total oxidation of benzene. Physicochemical properties of all the catalysts were characterized by using a series of specific analytical techniques. The results revealed that the 0.2Ce/MnAl catalyst exhibited the highest catalytic performance with T₉₀ about 210 °C at a high space velocity (SV = 60,000 mL g^− 1 h^− 1), ascribed to its lower-temperature reducibility, the abundant surface lattice oxygen (O_latt), and synergetic effect between Mn^4 + and Ce^3 +/Ce.     

Activity and stability of Pd/MMnOx (M = Co,Ni, Fe and Cu) supported on cordierite as CO oxidation catalysts

Several catalysts of the general formula, MMnO_x (M = Co, Ni, Fe and Cu), were synthesised through the impregnation method; their activities were shown to be enhanced by the addition of a small amount of Pd (0.01–0.1 wt%). These catalysts exhibit different activities for the catalytic oxidation of CO, due to the different valence states of various transition metal oxides. The introduction of Pd prominently enhanced both the reduction and oxidation capabilities of the catalysts. These catalysts were optimised for oxidation activities by designing orthogonal experiments. Based upon the catalysts’ properties, the stability of these samples and their ability to resist steam over Pd/CoMnO_x/cordierite were investigated.     

Effect of Pd deposition procedure on activity of Pd/Ce0.5Sn0.5O2 catalysts for low-temperature CO oxidation

Two methods for the preparation of Pd/Ce_0.5Sn_0.5O₂ catalysts have been used: solution combustion (SC) of Pd, Ce and Sn precursor mixtures, and incipient wetness impregnation by [Pd(NO₃)₂(H₂O)₂] solution of Ce_0.5Sn_0.5O_2 – δ support, obtained by the SC technique (SC + IWI). The formation of metallic palladium was observed in addition to ionic palladium in a Pd_x(Ce_0.5Sn_0.5)_1 – xO_{2 – x – δ} solid solution due to high-temperature Pd precursor decomposition during the SC process. IWI of Ce_0.5Sn_0.5O_2 – δ support has been demonstrated to lead to a uniform solid solution of Pd^2 + ions in the Ce_0.5Sn_0.5O_2 – δ matrix at 1% Pd content that resulted in high catalyst activity towards CO oxidation. The increase of Pd content to 5% showed no influence on catalytic activity. This observation is explained by the formation of low active PdO species when Pd content is more than 1%. The proposed SC + IWI method allows obtaining highly active Pd/Ce_0.5Sn_0.5O₂ catalysts with low palladium content.     

Preparation of Pd/(Ce1 − xYx)O2/γ-Al2O3/cordierite catalysts and its catalytic combustion activity for methane

A series of (Ce_1 − xY_x)O₂ (x = 0,0.15,0.35,0.5) coatings on γ-Al₂O₃ pre-coated cordierite honeycomb were prepared by sol–gel method, and then palladium was loaded by aqueous solution impregnation deposition with Pd(NO₃)₂ as precursor. The structure and morphology of samples were evaluated and the catalytic combustion activity for methane was also discussed. (Ce_1 − xY_x)O₂ synthesized by sol–gel has a single-phase cubic fluorite structure. Increasing the Y/Ce ratio can significantly improve the inner surface morphology of the honeycomb channels and also the coating mechanical stability, and leads to a considerable improvement in the catalytic activity of the prepared catalysts for methane.     

Characterization of CeO2–WO3 catalysts prepared by different methods for selective catalytic reduction of NOx with NH3

In this work, cerium–tungsten oxide catalysts were prepared by three methods: single step sol–gel (SG), impregnation (IM), and solid processing (SP). The catalysts were used for selective catalytic reduction (SCR) of NO_x with ammonia over a wide temperature range. The results indicated that the catalysts prepared by the SP and IM methods exhibited better SCR activity than that prepared via the SG method in 175–500 °C. The excellent activity can be attributed to larger surface area, higher surface concentrations of Ce and Ce^3 +, enhanced NO oxidization ability, and greater number of surface acid sites.     

Role of ceria in the improvement of SO2 resistance of LaxCe1 − xFeO3 catalysts for catalytic reduction of NO with CO

Perovskite-type catalysts with LaFeO₃ and substituted La_xCe_1 − xFeO₃ compositions were prepared by sol–gel method. These catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), CO temperature-programmed reduction (CO-TPR), and SO₂ temperature-programmed desorption (SO₂-TPD). Catalytic reaction for NO reduction with CO in the presence of SO₂ has been investigated in this study. LaFeO₃ exhibited an excellent catalytic activity without SO₂, but decreased sharply when SO₂ gas was added to the CO + NO reaction system. In order to inhibit the effect of SO₂, substitution of Ce in the structure of LaFeO₃ perovskite has been investigated. It was found that La_0.6Ce_0.4FeO₃ showed the maximum SO₂ resistance among a series of La_xCe_1 − xFeO3 composite oxides.     

Fractional-hydrolysis-driven formation of non-uniform dopant concentration catalyst nanoparticles of Ni/CexZr1 − xO2 and its catalysis in methanation of CO2

Ni/ceria–zirconia solid solution (Ni/Ce_xZr_1 − xO₂) with Ce and Ni enriched on the surface of the catalysts are prepared via a simple, low-cost method. The aqueous phase reactions simplify the preparation process, save the cost and lead the Ce to enriching on the surface of products. The impregnation method makes the Ni enriching on the surface of products which enhances the efficiency of active component. These catalysts exhibit significantly high catalytic performance. The formation mechanism is also investigated.     

Ru/CexZr1−xO2, a novel and effective catalyst for the catalytic wet air oxidation of 2-chlorophenol

We report for the first time the use of Ce_xZr_1−xO₂ solid solutions as supports for Ru catalysts to be implemented in the catalytic wet air oxidation of 2-chlorophenol. Such catalytic systems appeared to be very efficient, even at low temperature (393 K) and low pressure (3 MPa), and exhibited a great advantage over Ru/CeO₂ or Ru/ZrO₂.     

Enhanced catalytic activity of K-birnessite MnO2 confined in carbon nanotubes for selective oxidation of benzyl alcohol

K-birnessite MnO₂ encapsulated in carbon nanotubes (CNTs) was prepared by spontaneous redox between KMnO₄ and CNTs at room temperature and exhibited excellent catalytic activity for selective oxidation of benzyl alcohol. Research results showed that the enhanced catalytic activity can be attributed to the easier reducibility of MnO₂ confined in CNTs, the inhibition for Mn^4 + into Mn^3 + and the stability of catalysts due to the existence of K species.     

Influence of Ce addition on the structural,magnetic, and magnetocaloric properties in La0.7−xCexSr0.3MnO3 (0≤x≤0.3) ceramic compound

We report improvement in the magnetocaloric properties of Ce-doped lanthanum manganites. Polycrystalline La_0.7−xCe_xSr_0.30MnO₃ (0≤x≥0.3) samples were prepared using the conventional solid-state reaction method with phase purity and structure confirmed using X-ray diffraction. Temperature dependent magnetization measurements and Arrott analysis reveal second order ferromagnetic transition in parent sample and as well as in doped sample with Curie temperature decreasing progressively with increasing Ce-concentration from ~370 K for x=0.0 to 310 K for x=0.30. Magnetic entropy change (ΔS_M) was calculated by applying the thermodynamic Maxwell equation to a series of isothermal field dependent magnetization curves. A large ΔS_M associated with the ferromagnetic–paramagnetic transition in La_0.7−xCe_xSr_0.30MnO₃ samples has been observed. The value of ΔS_M was found to increase with Ce-doping up to x=0.15 and the highest value of 2.12 J kg⁻¹ K⁻¹ (at ΔH=2 T) was observed for La_0.55Ce_0.15Sr_0.30MnO₃ sample near the Curie temperature of 356 K. Also, improved relative cooling power of ~122 J kg⁻¹ was observed for the same sample. Due to the large magnetic entropy change and high Curie temperature, the La_0.55Ce_0.15Sr_0.30MnO₃ sample is suggested to be used as potential magnetic refrigerants for magnetic refrigeration technology above room temperature.     

Piezoelectric and dielectric properties of Ce substituted La2Ti2O7 ceramics

The ferroelectric and dielectric properties of cerium (Ce) substituted La₂Ti₂O₇ (LTO) have been investigated. Single phase, dense La_2?xCe_xTi₂O₇ (x = 0.15, 0.25, 0.35) ceramics were prepared by spark plasma sintering. The solubility limit of Ce in La_2?xCe_xTi₂O₇ was found to be between 0.35 and 0.5. The a-, b- and c-axes of the unit cell decrease with increasing Ce substitution. The Curie point (Tc) of La_2?xCe_xTi₂O₇ (x = 0, 0.15, 0.25, 0.35) decreases and dielectric constant and loss increase with increasing Ce substitution. Cerium can increase the d₃₃ of La₂Ti₂O₇. The highest d₃₃ was 3.9 ± 0.1 pC/N for La_1.85Ce_0.15Ti₂O₇ textured ceramic.     

Catalytic oxidation of toluene over copper and manganese based catalysts: Effect of water vapor

Copper and manganese based catalysts with different supports were prepared by impregnation method for toluene oxidation in the presence of water vapor. Their catalytic activity was tested in the absence and presence of water vapor. The results showed that the activity of catalysts CuMn(y)O_x/γ-Al₂O₃ was higher than that of catalysts CuO_x/γ-Al₂O₃ and MnO_x/γ-Al₂O₃. The presence of water vapor had a negative effect on catalytic activity due to the competition of water molecules with toluene molecules for adsorption on surface active sites. The durability to water vapor followed the order: CuMn(1)O_x/Cordierite > CuMn(1)O_x/TiO₂ > CuMn(1)O_x/γ-Al₂O₃.     

One-step synthesis of ternary MnO2–Fe2O3–CeO2–Ce2O3/CNT catalysts for use in low-temperature NO reduction with NH3

In this article, a facile one-step strategy for the synthesis of ternary MnO₂–Fe₂O₃–CeO₂–Ce₂O₃/carbon nanotubes (CNT) catalysts was discussed. The as-prepared catalysts exhibited 73.6–99.4% NO conversion at 120–180 °C at a weight hourly space velocity (WHSV) of 210 000 ml·g_cat^− 1·h^− 1, which benefited from the formation of amorphous MnO₂, Fe₂O₃, CeO₂, and Ce₂O₃, as well as high Ce^3 + and surface oxygen (O_ε) contents. The mechanism of formation of MnO₂–Fe₂O₃–CeO₂–Ce₂O₃/CNT catalysts was also proposed.     

Promoting effect of Fe in oxidative dehydrogenation of ethylbenzene to styrene with CO2 (I) preparation and performance of Ce1 − xFexO2 catalyst

To improve the lattice structure of CeO₂ and the transmission capacity of oxygen, Ce_1 − xFe_xO₂(x ≤ 0.2)solid solutions were prepared by a hydrothermal method and used in oxidative dehydrogenation of ethylbenzene to styrene with CO₂. Ce_1 − xFe_xO₂ solid solutions were characterized by powder X-ray diffraction, Raman spectroscopy, N₂-adsorption, H₂ temperature-programmed reduction and H₂–O₂ titration. Results showed that approximately 20% of Fe^3 + could dissolve into the CeO₂ lattice while portions of Fe₂O₃ were highly dispersed on the surface of the Ce_1 − xFe_xO₂ solid solution. The formation of Ce–Fe solid solutions could create more oxygen vacancies to promote the absorption and activation of CO₂, which improves the activity of the catalyst and increased ethylbenzene conversion by as much as 13%.     

A Ce–Sn–Ox catalyst for the selective catalytic reduction of NOx with NH3

A series of Ce–Sn–O_x catalysts prepared by the facile coprecipitation method exhibited good catalytic activity in a broad temperature range from 100 °C to 400 °C for the selective catalytic reduction of NO_x with NH₃ at the space velocity of 20,000 h^− 1. The Ce₄Sn₄O_x catalyst calcined at 400 °C showed high resistance to H₂O, SO₂, K₂O and PbO under our test conditions. The better catalytic performance was associated with the synergistic effect between CeO₂ and SnO₂, which strengthened the NH₃ and NO_x adsorption capacity on the surface of the catalyst.     

Ceramic monolith supported Mn–Ce–M ternary mixed-oxide (M=Cu,Ni or Co) catalyst for VOCs catalytic oxidation

The MO_x (M=Cu, Ni or Co) modified manganese-cerium mixed-oxide catalysts supported on ceramic monolith were prepared by sol-gel method and examined for the catalytic combustion of o-xylene. Results show that the addition of CuO_x could significantly enhance the catalytic properties of the monolithic catalysts, which may be correlated with the Mn-Cu synergistic interaction. The effects of the preparation parameters including the Cu content, the total amount of active phase and the calcination temperature and time, as well as the reaction conditions, i.e., the space velocity and concentration of o-xylene, on the catalytic performance for the combustion of o-xylene were also investigated. It is shown that the MnCeCu_0.4/monolith catalyst with the active phase loading of 11.4 wt% and calcined at 500 °C for 3 h displays the highest catalytic activity. When the concentration of o-xylene is 1000 ppm and the space velocity is 10,000 h⁻¹, the temperature at which 90% o-xylene conversion is reached is 277 °C. It is also seen that the optimum catalyst has a good catalytic stability and exhibits an excellent activity not only at a rather high space velocity but also within a wide range of o-xylene concentration. Furthermore, the optimum catalyst also show the high combustion performance for other hydrocarbons, e.g., n-butanol and styrene.     

Effects of WO3 doping on stability and N2O escape of MnOx–CeO2 mixed oxides as a low-temperature SCR catalyst

MnO_x–WO_x–CeO₂ catalysts synthesized using a sol–gel method were investigated for the low-temperature NH₃-SCR reaction. Among them, W_0.1Mn_0.4Ce_0.5 mixed oxides exhibited above 80% NO_x conversion from 140 to 300 °C. In addition, this catalyst exhibited high stability and CO₂ tolerance in a 50 h activity test at 150 °C. Substantially reduced N₂O production and enhanced N₂ selectivity were achieved by WO₃ doping, which was due to the weakened reducibility and increased number of acid sites. The decreased SO₂ oxidation activity as well as the reduced formation of ammonium and manganese sulfates resulted in a high SO₂ resistance of this catalyst.     

Experimental evidence and mechanism of the oxygen storage capacity in MnO2-Ce(1−x)ZrxO2/TiO2 catalyst for low-temperature SCR

The oxygen storage capacity of amorphous CeO₂ and its mechanism were investigated in a Zr-doped MnO_x-CeO₂/TiO₂ catalyst at low temperatures. The oxygen storage capacity of several catalysts was determined by the release of lattice oxygen upon reduction of Ce⁴⁺ to Ce³⁺. We designed a temperature programmed reduction analysis using ammonia gas to measure the amount of lattice oxygen release and identify a decrease in reaction-onset temperature from 136 °C to 75 °C upon doping the catalyst with Zr. Additional reduction was observed in Zr-doped MnO_x-CeO₂/TiO₂ and this was attributed to an increase in temperature sensitivity of thermal vibrations of the first Ce–O coordination shell. The temperature dependence of the thermal vibrations was identified by examining the behavior of the Debye–Waller factor as a function of temperature with fitting the extended X-ray absorption fine structure.     

Effect of Ce and Yb co-doping on conductivity of LaNbO4

La_1−x−yCe_xYb_yNbO₄ specimens with various Ce and Yb contents were prepared by solid reactions, and their crystal structure, element valence, sinterability and conductivity were investigated. LaNbO₄-type single phase was formed at 1200 °C in air, and the lattice of La_1−x−yCe_xYb_yNbO₄ was distorted from that of LaNbO₄ to various extents, depending on the added amount of Ce and Yb. Both La and Nb remained the same valence as they are in LaNbO₄; Ce⁴⁺, Ce³⁺ and Yb³⁺ were detected at room temperature. Highly densified La_1−x−yCe_xYb_yNbO₄ specimens were achieved by sintering at above 1215 °C in air with conductivity 1–2 orders higher than that of pure LaNbO₄ in dry air, wet air and wet 5% H₂–N₂ atmospheres. The conductivity changed with testing atmosphere owing to the competition of electron and proton conduction, and maximal value 4.7 × 10⁻⁴ S cm⁻¹ was obtained in wet air at 900 °C.