CeO2 Nanocatalysts Research Articles

Facile synthesis of NiPt–CeO2 nanocomposite as an efficient catalyst for hydrogen generation from hydrazine borane

NiPt–CeO2 nanocomposites (NCs) have been easily prepared via a surfactant aided co-reduction route and characterized by ICP-AES, XRD, TEM, HRTEM, SAED, EDX and XPS techniques. The characterized results show that the NiPt–CeO2 NCs with an average particle size of 3 nm are in amorphous state and well-dispersed. The as-synthesized NiPt–CeO2 NCs are successfully applied as a highly efficient catalyst for rapid and high-extent dehydrogenation of hydrazine borane (Hy-B). The amorphous NiPt–CeO2 NCs obtained due to the addition of CeO2 display much better activity than that of Ni-, Pt–CeO2, and crystalline NiPt NCs. Especially, Ni0.9Pt0.1–CeO2 NCs with a low noble-metal content exhibit markedly high catalytic activity to release 5.74 equiv. (H2 + N2) per Hy-B in only 12.3 min with a high turnover frequency (TOF) value of 234 h−1 (molH2·molmetal−1·h−1). In the presence of this special amorphous state Ni0.9Pt0.1–CeO2 nanocatalyst, the hydrolysis of the group BH3 and the decomposition of the moiety N2H4 occur simultaneously and thus accelerate the rate of releasing hydrogen from Hy-B. This excellent catalytic performance is due to the synergistic effect between NiPt and CeO2 and the promotion effect of NaOH.

Beneficial use of CeO2 nanocatalyst for black liquor conversion under sub and supercritical conditions

Black liquor is an alkaline liquid residue from paper industry, containing ∼80wt% of water and ∼20wt% of organics and minerals. Hydrothermal conversion of black liquor in a batch reactor is particularly interesting towards hydrogen production, as the carbon dioxide is highly solubilized in the basic aqueous media. Thus hydrogen with higher purity than other processes is obtained. Cerium oxide nanocatalyst (cubic CeO2) is used to improve the amount of hydrogen produced and to decrease the coke formation, based on the water splitting into active species. Experiments have been carried out at sub and supercritical conditions 350°C or 450°C, 25MPa) in a batch reactor for 15min or 60min. CeO2 nanocatalyst improved the conversion of black liquor at sub and supercritical conditions as expected. The amount of carbonaceous solid recovered was decreased due to the catalytic effect. Recovered hydrogen was not significantly affected by the catalyst as it was involved in secondary reactions such as hydrogenation. Oxidations reactions, as well as O2 production, were also improved using catalyst and supercritical media. Supercritical water media combined with catalyst clearly affects the fragmentation of dissolved lignin compared to subcritical conditions. Then it was assumed that water splitting occurs and produces active hydrogen and oxygen species. Thus these actives species produced using catalyst are able to improve hydrogenation and oxidation reactions, as well as recombination into H2 and O2.

Abatement of toluene from polluted air over Mn/Clinoptilolite–CeO2 nanopowder: Impregnation vs. ultrasound assisted synthesis with various Mn-loading

Total oxidation of toluene over Mn(5%, 10%, 15%)/Clinoptilolite–CeO2 nanocatalysts was performed. Mn was doped via two different methods of impregnation and sonochemistry. The catalysts were characterized by XRD, FESEM, EDX, BET and FTIR analyses. The physicochemical characterizations showed superior properties of sonochemically synthesised nanocatalysts like homogenous morphology, small and dispersed particles, and strong interaction. Addition of CeO2 as a promoter to acid-treated clinoptilolite remarkably increased catalytic activity. XRD analysis demonstrated acid treatment of clinoptilolite induces noticeable decrease in crystals size and their crystallinity, while the specific surface area increased. Furthermore, no obvious peaks related to MnOx were found in XRD patterns even at high loadings of Mn which might be attributed to the high dispersion of particles in sonochemistry method. Due to the effect of sonication power, even at high loadings of Mn(15%), the morphology of the catalyst was agglomeration free and surface area was high. Comparison of catalytic activity of sonochemically and impregnated Mn(5%)/Clinoptilolite–CeO2 nanocatalyst showed that sonochemically synthesized catalyst can oxidize toluene 5–10% more than impregnated one at all temperature ranges. Increasing metal content enhanced the catalytic activity.

The beneficial use of HCl‐activated natural zeolite in ultrasound assisted synthesis of Cu/clinoptilolite–CeO2 nanocatalyst used for catalytic oxidation of diluted toluene in air at low temperature

AbstractBACKGROUNDTo remove toluene (a representative volatile organic compound (VOC)) from a waste gas stream, catalytic oxidation was utilized over Cu/Clinoptilolite–CeO2 nanocatalyst. The nanocatalyst with different loadings of Cu (5, 10, 15 wt%) was sonochemically synthesized and its performance in catalytic oxidation of toluene was studied. Characterization by XRD, FESEM, BET, EDX and FTIR were applied.RESULTSXRD results indicated well‐dispersed small copper particles even at high loadings of copper. Non‐sonicated Cu/Clinoptilolite–CeO2 catalyst showed agglomerated, non‐uniform morphology, while small particles with uniform shape and size with different degrees of agglomeration were observed in sonicated Cu/Clinoptilolite–CeO2 catalyst. A narrow particle size distribution with average size 21 nm was observed in the sonicated sample. BET analysis demonstrated considerable effects of HCl treatment in increasing the specific surface area of clinoptilolite. It also showed the strong influence of CeO2 addition as a promoter that sharply enhanced the surface area to 71.7 m2 g−1.CONCLUSIONCatalytic performance tests revealed that Cu(15%)/Clinoptilolite–CeO2 synthesized with ultrasound had the best performance of about 98% toluene abatement even at high concentrations of toluene (3000 ppm). A stability test of the synthesized nanocatalyst confirmed its constant activity for 1440 min, making it a promising catalyst for removal of VOCs. © 2014 Society of Chemical Industry

Single-chamber solid oxide fuel cells with nanocatalyst-modified anodes capable of in situ activation

Practical applications of single-chamber solid oxide fuel cells (SC-SOFCs) are partially limited by the difficulties and complications associated with the initialization process, which mainly involves the reduction of NiO to Ni in the anode. Here we propose a facile approach to the in situ activation (initialization) of SC-SOFCs with a state-of-the-art sintered nickel-based anode using a methane–oxygen gas mixture, combined with the introduction of nanocatalysts into the anode. RuO2, CeO2 or Co3O4 with the high activity for methane oxidation are investigated for above purpose. XRD results demonstrate that the nanocatalysts are successfully introduced into the anode via a simple solution impregnation technique. Using FESEM, different nanoparticle morphologies are observed for the three catalysts. The time dependence of the cell voltage operating on the methane–oxygen gas mixture demonstrates successful activation following nanocatalyst introduction. Single cells with different nanocatalyst-modified anodes, initialized by in situ reduction, deliver high open circuit voltages of approximately 1.0 V and significant peak power outputs of approximately 1000 mW cm−2 at a furnace temperature of 650 °C. XRD and FESEM analysis indicates that only the CeO2 retains a same structure and morphology after the test. It suggests that the CeO2 nanocatalyst is the most promising for practical applications.

Synthesis and characterization of Pt/Al2O3–CeO2 nanocatalyst used for toluene abatement from waste gas streams at low temperature: Conventional vs. plasma–ultrasound hybrid synthesis methods

To assess the synergism effect of plasma and ultrasound treatment on the physicochemical properties and catalytic performance of supported-Pt nanocatalysts, a series of nanostructured Pt(1wt.%)/Al2O3–CeO2(30wt.%) catalysts were prepared by plasma and/or ultrasound-assisted impregnation methods and tested for the total oxidation of toluene. The nanocatalysts were characterized by XRD, FESEM, FTIR, EDX and N2 adsorption–desorption measurements. XRD data confirmed the formation of CeO2 as the crystalline phase with an average crystallite size of about 8.7nm for all samples. EDX dot mapping indicated homogenous dispersion of elements. The results indicated that the remarkable synergetic effect of ultrasound irradiation on the surface morphology and elemental dispersion, especially when it is coupled with plasma treatment. All treated nanocatalysts showed lower temperature activity and better catalytic performance in toluene oxidation with high stability, in particular, ultrasound–plasma assisted synthesized nanocatalyst exhibited the approximately complete oxidation of toluene at 180°C. It is observed that even at higher concentrations of toluene (3000ppm) or GHSV, plasma–ultrasound assisted synthesized nanocatalyst had still enough destruction ability to reduce the pollutant. Therefore, the plasma–ultrasound hybrid synthesis method can lead to an excellent preparation of supported nanocatalysts, esp., those for VOCs oxidation.

ZrO2/CeO2 nanocomposite: Two step synthesis, microstructure, and visible-light photocatalytic activity

ZrO2/CeO2 nanocomposite with photocatalytic activity in visible-light region was synthesized by calcination of the precursor prepared via a one-step hydrothermal method. The as-prepared composite includes ZrO2 nanoparticles assembled on the rough surface of CeO2 nanorods. CeO2 nanorods which have an average diameter of 500nm and lengths of 5–10μm were characterized to be the cubic structure, and ZrO2 nanoparticles with an average size of 300nm can be indexed as tetragonal and monoclinic structures. ZrO2/CeO2 composite photocatalyst exhibited photocatalytic activity under visible-light irradiation in the decomposition of rhodamine B (RhB) dye. Moreover, ZrO2/CeO2 nanocomposite showed an enhanced photocatalytic activity compared to the monocomponent ZrO2 and CeO2 nanocatalysts.

A Multi‐Yolk–Shell Structured Nanocatalyst Containing Sub‐10 nm Pd Nanoparticles in Porous CeO2

AbstractThe fabrication of catalytically stable nanocatalysts containing fine noble metal nanoparticles is an important research theme. We report a method for the synthesis of a hierarchically structured Pd@hm‐CeO2 multi‐yolk–shell nanocatalyst (h=hollow; m=mesoporous) containing sub‐10 nm Pd nanoparticles from pre‐made hydrophobic Pd nanoparticles. In the developed method, monodisperse hydrophobic Pd nanoparticles are first reacted with an iron oxide precursor iron(III) acetylacetonate to allow the deposition of iron oxide on their surface. In a Brij 56–water–cyclohexane reverse micelle system, the surface growth of iron oxide is found to mediate and, thus, facilitate the encapsulation of hydrophobic Pd nanoparticles in SiO2 to yield Pd‐Fe2O3@SiO2 nanoparticles in a high concentration. After removal of Fe2O3 by acid, the obtained Pd@SiO2 core–shell particles are reacted solvothermally with Ce(NO3)3 in an ethylene glycol–water–acetic acid mixture to produce multi‐core–shell Pd@SiO2@m‐CeO2 nanospheres. In each multi‐core–shell Pd@SiO2@m‐CeO2 nanosphere, several Pd@SiO2 particles are separately embedded in mesoporous CeO2. After selective removal of silica by NaOH, Pd@SiO2@m‐CeO2 nanospheres are transformed into the multi‐yolk–shell Pd@hm‐CeO2 nanocatalyst. Even with a low Pd loading at 0.4 wt %, the as‐prepared multi‐yolk–shell Pd@hm‐CeO2 nanocatalyst displays high catalytic activity in CO oxidation with 100 % CO conversion at 110 °C. In comparison, under the same catalytic conditions, the same amount of the same‐sized Pd nanoparticles supported on SiO2 achieves 100 % CO conversion at 180 °C. More importantly, the multi‐yolk–shell structure of the Pd@hm‐CeO2 nanocatalyst significantly enhances the stability of the catalyst. No loss in catalytic activity was observed on the Pd@hm‐CeO2 nanocatalyst treated at 550 °C for six hours. The Pd@hm‐CeO2 nanocatalyst also exhibited excellent catalytic performance and stability in the aerobic selective oxidation of cinnamyl alcohol to cinnamaldehyde.

Synthesis and physicochemical characterizations of nanostructured Pt/Al2O3–CeO2 catalysts for total oxidation of VOCs

Pt/Al2O3–CeO2 nanocatalysts with Pt loading of 1% and ceria loading of 10, 20 and 30% were successfully prepared via wet impregnation method to be utilized in catalytic oxidation of BTX. The nanocatalysts were characterized using XRD, FESEM, TEM, N2 adsorption, FTIR and TPR-H2 techniques. The XRD patterns confirmed the formation of cerium oxide as the crystalline phase on alumina with the average crystallite size of 8.1–8.7nm, derived by Scherrer equation. FESEM images confirmed that these nanocatalysts had ceria particles in nano-ranges. TEM analysis showed that platinum particles were fairly well dispersed on Al2O3–CeO2 with an average size of 5–20nm. BET surface area presented large surface area for nanocatalysts. TPR patterns showed that by adding 1% platinum to support, the reducibility is highly increased. These patterns also revealed the promoting effect of ceria on reducibility of Pt and Al2O3. The results of toluene oxidation indicated that the synthesized nanocatalysts were highly active and able to remove nearly 100% of toluene and xylene and about 85% of benzene as representative VOCs. The presence of nanoparticles along with good characteristics of the synthesized nanocatalysts presented them as highly efficient materials for catalytic oxidation of VOCs.