Catalytic Activity of Y Zeolite Supported CeO2 Catalysts for Deep Oxidation of 1, 2-Dichloroethane (DCE)

Three Y zeolites supported CeO₂ catalysts (CeO₂/USY, CeO₂/HY, CeO₂/SSY) were prepared and used for deep oxidation of 1,2-dichloroethane (DCE) in low concentration (about 1,000 ppm). The catalysts were characterized by XRD, N₂ adsorption/desorption and H₂-TPR. The results showed that the catalytic activity of the supported CeO₂ catalysts was much higher than that of Y zeolites, in particular, CeO₂/USY exhibited the highest activity, T_98% values of DCE was about 270 °C. And the catalytic activity was strongly related to the interaction between CeO₂ and Y zeolites.     

Arsenate and arsenite adsorbents composed of nano-sized cerium oxide deposited on activated alumina

Cerium oxide composited activated alumina was prepared and used as arsenate and arsenite adsorbents by oxidation of cerium chloride in H₂O₂ solution. The preparation conditions affected arsenic adsorption capabilities in the Al₂O₃–CeO₂. Efficient adsorption of arsenic was achieved when CeO₂ was deposited on 6.0 g of powdered activated alumina at 0.01 M Ce³⁺ concentration and H₂O₂/Ce = 0.5. The arsenic adsorption was particularly enhanced in the presence of the nano-size CeO₂ on the Al₂O₃ support, obeying the Langmuir adsorption isotherm model with maximum adsorption capacities of 13.6 and 10.5 mg/g, respectively, for arsenate and arsenite.     

Mesoporous CeO2 Catalyst Synthesized by Using Cellulose as Template for the Ozonation of Phenol

Mesoporous CeO₂ was synthesized by a sol-gel method using the biological renewable microcrystalline cellulose (MCC) as the template and Ce(NO₃)₃?6H₂O as the precursor of CeO₂. XRD, TEM, N₂ adsorption–desorption, and XPS were used for mesoporous CeO₂ characterization. The results show that CeO₂ nano-particles possess an average size of 7 ~ 10 nm, and specific area of CeO₂ synthesized with MCC template is approximately 5.5 times higher than CeO₂ synthesized without MCC. The ozonation catalyzed by CeO₂-T (with MCC) could remove 91.7% of phenol compared to 51.6% for single ozonation and 68.3% for CeO₂-W (without MCC) catalyzed ozonation. The COD removal efficiency is significantly higher for ozonation with CeO₂-T (69.2%) than that of CeO₂-W (49.5%) or ozonation alone (21.0%). The good performance of CeO₂-T is attributed to the high specific area and Ce(III)/Ce(IV) redox couple. During catalytic ozonation, the activation energy of catalytic ozonation (20.7 kJ mol^?1) is much lower than that of single ozonation (54.7 kJ mol^?1).     

Hydrogen Production from Ethanol over Rh–Pd/CeO2 Catalysts

The work presents a study by temperature programmed desorption, in situ infra red spectroscopy and catalytic steam reforming of ethanol (SRE) over CeO₂ and the bimetallic Pd-Rh/CeO₂; comparison with the monometallic catalysts (Rh/CeO₂ and Pd/CeO₂) was also made for the steam reforming study. Comparing TPD of ethanol over CeO₂ and the bimetallic catalysts indicated two main differences: the direct oxidation route to acetate over CeO₂ is suppressed by the presence of the metal and the lowering of the dehydrogenation reaction temperature by about 100 K. In situ IR study indicated that the bimetallic catalyst breaks the carbon–carbon bond of ethanol at low temperature <400 K, as evidenced by the presence of adsorbed CO species. SRE over ½ wt.% Rh–½ wt.% Pd/CeO₂, at 770 K at realistic conditions showed that maximum conversion and selectivity could be achieved. This high activity considering the very small amounts of transition metals on CeO₂ is discussed in light of their electronic and geometric effects.     

Influence of Ethanol Washing in Precursor on CuO–CeO2 Catalysts in Preferential Oxidation of CO in Excess Hydrogen

In this study, influence of ethanol washing in precursor on CuO–CeO₂ catalysts in preferential oxidation of CO in excess hydrogen (PROX) was investigated. BET, FTIR and TPR techniques were used. The results showed that ethanol washing was beneficial to improve the catalytic performance of CuO–CeO₂ catalysts in the PROX. The CO conversion over CuO–CeO₂ catalysts without ethanol washing was only 85% at 190 °C, while the highest CO conversion over CuO–CeO₂ catalysts with 200 mL ethanol washing was beyond 99% at 120 °C. XRD and TPR results showed that ethanol washing depressed the growth of CuO–CeO₂ catalysts and improved the reducibility of CuO–CeO₂ catalysts. The FTIR measurement proved that the absorption water was decreased by the way of ethanol washing, indicating that the amount of the H–O–H bridge between adsorption water and precursor of CuO–CeO₂ catalysts was decreased and depressed the growth of CuO–CeO₂ catalysts.     

Fabrication of electronspun porous CeO2 nanofibers with large surface area for pollutants removal

The porous CeO₂ nanofibers with diameter of 100–140 nm were successfully synthesized by single-capillary electrospinning of a Ce(NO₃)₃·6H₂O/PVP precursor solution, followed by calcination. The preparation parameters, including solution parameters and process parameters, affecting the spinnability and the morphology of nanofibers were investigated and discussed systematically. And the effects of different calcination temperatures on the microstructure CeO₂ nanofibers were also studied. A plausible mechanism was proposed to explain the formation process of the CeO₂ nanofibers. The N₂ adsorption-desorption isotherm analysis showed that the specific surface area and average pore size of the nanofibers were 195.75 g/m² and 2.4 nm, respectively. Moreover, as absorbent, the porous CeO₂ nanofibers adsorbed the MO effectively. The adsorption experiment indicated that the adsorption process can be divided into two stages, including quick adsorption and gradual adsorption. And the adsorption capacities were not only determined by the specific surface area, but closely related to the pore size. Finally, the adsorption data were modeled by the pseudo-first-order and pseudo-second-order kinetics equations. The results showed that the pseudo-second order kinetics could best describe the adsorption of MO onto the porous CeO₂ nanofibers.     

Important properties associated with catalytic performance over three-dimensionally ordered macroporous CeO2–CuO catalysts

Three-dimensionally ordered macroporous CeO₂–CuO catalysts were prepared by the template and sol–gel method. The catalysts were characterized via SEM, TEM, XRD, H₂-TPR, XPS, CO₂-TPD and N₂ adsorption–desorption techniques. It is found that the CeO₂–CuO catalysts present the well-defined interconnected macroporous structure in three dimensions, and the skeleton of macroporous structure is composed of the CuO and CeO₂ particles. Catalytic performance for preferential CO oxidation is determined by various properties including composition, structural and textural properties as well as reduction and desorption behavior. The 3DOM CeO₂–CuO structure improves the interaction between CuO and CeO₂, the structural and textural properties, the reduction of oxides and desorption of the adsorbed molecules on the active sites.     

Mesoporous copper–cerium–oxygen hybrid nanostructures for low temperature catalytic oxidation of carbon monoxide

Mesoporous copper–cerium–oxygen hybrid nanostructures were prepared by one-pot cetyltrimethylammonium bromide surfactant-assisted method, and were characterized by thermogravimetry, X-ray diffraction, transmission electron microscopy, nitrogen adsorption–desorption, X-ray photoelectron spectroscopy and temperature-programmed reduction techniques. Low temperature carbon monoxide oxidation was used as probe reaction to investigate the application of the prepared mesoporous copper–cerium–oxygen hybrid nanostructures in catalysis. The product calcined at 400 °C, with disordered wormlike mesoporous structure, high specific surface area (SSA) of 117.4 m²/g and small catalyst particle size of 8.3 nm, shows high catalytic activity with the 100 % CO conversion at 110 °C, indicating its potential application in catalysis. Catalytic activity results from the samples calcinied at different temperature suggested that high SSA, small catalyst particle size, finely dispersed CuO species and synergistic effect between CuO and CeO₂ were responsible for the high catalytic activity of the catalysts.     

Preparation of amine-modified SiO<Subscript>2</Subscript> aerogel from rice husk ash for CO<Subscript>2</Subscript> adsorption

Amine-modified SiO₂ aerogel was prepared using 3-(aminopropyl)triethoxysilane (APTES) as the modification agent and rice husk ash as silicon source, its CO₂ adsorption performance was investigated. The amine-modified SiO₂ aerogel remains porous, the specific surface area is 654.24 m²/g, the pore volume is 2.72 cm³/g and the pore diameter is 12.38 nm. The amine-modified aerogel, whose N content is up to 3.02 mmol/g, can stay stable below the temperature of 300 °C. In the static adsorption experiment, amine-modified SiO₂ aerogel (AMSA) showed the highest CO₂ adsorption capacity of 52.40 cm³/g. A simulation was promoted to distinguish the adsorption between the physical process and chemical process. It is observed that the chemical adsorption mainly occurs at the beginning, while the physical adsorption affects the entire adsorption process. Meanwhile, AMSA also exhibits excellent CO₂ adsorption–desorption performance. The CO₂ adsorption capacity dropped less than 10 % after ten times of adsorption–desorption cycles. As a result, AMSA with rice husk ash as raw material is a promising CO₂ sorbent with high adsorption capacity and stable recycle performance and will have a broad application prospect for exhaust emission in higher temperature.     

Vanadium oxide supported γ-alumina with bimodal porous structure for intra-particle diffusion enhancement in styrene oxidation reaction

Porous γ-alumina with well arranged secondary mesopores has been contrived using nanosized templating units. The pore size of templated mesopores is precisely controlled as the pore shrinkage is insignificant. The primary pore diameter is ca. 4 nm and the secondary pore diameter is ca. 50 nm. The porous material was characterized using N₂ adsorption/desorption, TEM, XRD and FT-IR. γ-alumina with bimodal pore size distribution shows improved intra-particle diffusion compared to γ-alumina with unimodal pore size distribution in a simple dye adsorption test. γ-alumina with different porous structures were then impregnated with vanadium oxide for catalytic effect comparison. It was perceived that secondary pores improve the styrene oxidation rate after the conversion of styrene reaches 30%.     

Processing of biomorphic porous TiO2 ceramics by chemical vapor infiltration and reaction (CVI-R) technique

Porous biomorphic TiO₂ ceramics were manufactured from paper preforms by chemical vapor infiltration and reaction (CVI-R) in a three-steps process. First, the cellulose fibers of the paper were converted into carbon (C_b) by pyrolysis in an inert atmosphere. Then, C_b-template was infiltrated with a precursor system consisting of TiCl₄, CH₄ and H₂ to produce porous TiC ceramics, which were oxidized in a final step with air at temperatures in the range of 400–1200 °C. Depending on the conversion degree, TiC/TiO₂ or TiO₂ ceramics were obtained. The kinetics of the oxidation process was studied by thermal gravimetric analysis (TGA) and activation energies of 63 and 174 kJ mol⁻¹ were estimated for the lower (400–800 °C) and higher (950–1200 °C) temperature regions, respectively. The TiO₂ ceramics were characterized by Raman spectroscopy (anatase/rutile ratio), SEM/EDX (morphology, composition) and nitrogen gas adsorption (pore structure). It was shown, that the anatase/rutile ratio as well as the pore structure of the resulting TiO₂ ceramics could be controlled varying the oxidation temperature. The TiO₂ samples obtained by oxidation of TiC biomorphic porous ceramics are lightweight but nevertheless have very good mechanical performances. Their bending strength varies between 30 and 40 MPa at a porosity of 65–70%. These structures have many potential applications, e.g. light structured materials, implants because of their bio-compatibility, catalyst support or catalyst for photo catalytic applications.     

Catalytic Performance of Aged Rh/CeO2–ZrO2 for NO–C3H6–O2 Reaction Under a Stoichiometric Condition

The activity of Rh/CeO₂ for NO reduction by C₃H₆ was gradually deceased by mixing with ZrO₂ until 68 mol%. Rh supported on CeO₂–ZrO₂ with higher OSC was found to show lower catalytic activity. High OSC of CeO₂–ZrO₂ would probably stabilize the surface of Rh in oxidized state, resulting in low activity and low efficiency of C₃H₆ utilization for NO reduction. In situ FT-IR spectroscopy suggested that mononitrosyl species such as Rh(NO)^δ? and Rh(NO)^δ+ are reaction intermediates in the NO–C₃H₆–O₂ reaction over Rh/CeO₂–ZrO₂ catalysts.     

Catalytic Removal of Toluene over Co3O4–CeO2 Mixed Oxide Catalysts: Comparison with Pt/Al2O3

The catalytic oxidation of toluene, chosen as VOC probe molecule, was investigated over Co₃O₄, CeO₂ and over Co₃O₄–CeO₂ mixed oxides and compared with the catalytic behavior of a conventional Pt(1 wt%)/Al₂O₃ catalyst. Complete toluene oxidation to carbon dioxide and water was achieved over all the investigated systems at temperatures below 500 °C. The most efficient catalyst, Co₃O₄(30 wt%)–CeO₂(70 wt%), showed full toluene conversion at 275 °C, comparing favorably with Pt/Al₂O₃ (100% toluene conversion at 225 °C).     

Effects of Ga doping on Pt/CeO2‐Al2O3 catalysts for propane dehydrogenation

This paper describes catalytic consequencesThis paper describes catalytic consequences of Pt/CeO₂‐Al₂O₃ catalysts promoted with Ga species for propane dehydrogenation. A series of PtGa/CeO₂‐Al₂O₃ catalysts were prepared by a sequential impregnation method. The as‐prepared catalysts were characterized employing N₂ adsorption‐desorption, X‐ray diffrtaction, temperature programmed reduction, O₂ volumetric chemisorption, H₂‐O₂ titration, and transmission electron microscopy. We have shown that Ga³⁺ cations are incorporated into the cubic fluorite structure of CeO₂, enhancing both lattice oxygen storage capacity and surface oxygen mobility. The enhanced reducibility of CeO₂ is indicative of higher capability to eliminate the coke deposition and thus is beneficial to the improvement of catalytic stability. Density functional theory calculations confirm that the addition of Ga is prone to improve propylene desorption and greatly suppress deep dehydrogenation and the following coke formation. The catalytic performance shows a strong dependence on the content of Ga addition. The optimal loading content of Ga is 3 wt %, which results in the maximal propylene selectivity together with the best catalytic stability against coke accumulation. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4365–4376, 2016     

Water–Gas Shift Reaction over CuO/CeO2 Catalysts: Effect of the Thermal Stability and Oxygen Vacancies of CeO2 Supports Previously Prepared by Different Methods

A series of CuO/CeO₂ catalysts were prepared through a two-step process: (1) CeO₂ supports were firstly prepared by precipitation (P), hydrothermal (HT) and sol-gel (SG) methods, respectively; and (2) CuO was deposited on the above CeO₂ supports by deposition-precipitation method. The as-synthesized CeO₂ supports and CuO/CeO₂ catalysts were characterized by N₂-physisorption, XRD, XPS, Raman, and H₂-TPR. The CuO/CeO₂ catalysts were examined with respect to their catalytic activity for the water–gas shift reaction, and their catalytic activities are ranked as: CuO/CeO₂-P > CuO/CeO₂-HT > CuO/CeO₂-SG. The results suggest that the CeO₂ prepared by precipitation (i.e., CeO₂-P-300) has the best thermal stability and the most amounts of surface oxygen vacancies, which make the corresponding CuO/CeO₂-P catalyst present the largest pore volume, the smallest crystal size of CuO, the highest microstrain (i.e., the highest surface energy) and the most amounts of active sites (i.e., the moderate copper oxide (crystalline) interacted with surface oxygen vacancies of ceria). Therefore, the catalytic activity of CuO/CeO₂ catalysts, in nature, depends on the thermal stability and the number of surface oxygen vacancies of the CeO₂ supports previously prepared by different methods.     

Macroporous Monolithic Pt/γ-Al2O3 and K–Pt/γ-Al2O3 Catalysts Used for Preferential Oxidation of CO

Macro-porous monolithic γ-Al₂O₃ was prepared by using macro-porous polystyrene monolith foam as the template and alumina sol as the precursor. Platinum and potassium were loaded on the support by impregnation method. TG, XRD, N₂ adsorption–desorption, SEM, TEM, and TPR techniques were used for catalysts characterization, and the catalytic performance of macro-porous monolithic Pt/γ-Al₂O₃ and K–Pt/γ-Al₂O₃ catalysts were tested in hydrogen-rich stream for CO preferential oxidation (CO-PROX). SEM images show that the macropores in the macro-porous monolithic γ-Al₂O₃ are interconnected with the pore size in the range of 10 to 50 μm, and the monoliths possess hierarchical macro-meso(micro)-porous structure. The macro-porous monolithic catalysts, although they are less active intrinsically than the particle ones, exhibit higher CO conversion and higher O₂ to CO oxidation selectivity than particle catalysts at high reaction temperatures, which is proposed to be owing to its hierarchical macro-meso(micro) -porous structure. Adding potassium lead to marked improvement of the catalytic performance, owing to intrinsic activity and platinum dispersion increase resulted from K-doping. CO in hydrogen-rich gases can be removed to 10 ppm over monolithic K–Pt/γ-Al₂O₃ by CO-PROX.     

Positive Effect of Water Vapor on CO Oxidation at Low Temperature over Pd/CeO2–TiO2 Catalyst

CO oxidation at low temperature over Pd/CeO₂–TiO₂ catalyst was carried out in the feed containing different contents of water vapor (H₂O). A positive effect of H₂O was observed on the catalytic performance of Pd/CeO₂–TiO₂ in CO oxidation at low temperature. The extent of this effect depends on the content of H₂O in the feed; with a H₂O content being 2.5 vol%, the catalyst Pd/CeO₂–TiO₂ exhibits the highest stability (longest life time for CO oxidation at 80 °C). The results of in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and temperature-programmed reaction (TPReaction) reaction illustrated that H₂O in the feed supplies sufficient OH groups in the presence of O₂, which can react with adsorbed CO on Pd species to produce CO₂. Moreover, H₂O may also enhance the adsorption of CO and suppress the formation of some carbonate species.     

Biotemplated hierarchical TiO2–SiO2 composites derived from Zea mays Linn. for efficient dye photodegradation

Five typical silicon-accumulating tissues (including leaves, roots, stalks, silks, and husks) of corn plant (Zea mays Linn.), for the first time, were applied as both structure-directors and silicon-precursors to synthesize biomorphic hierarchical porous TiO₂–SiO₂ composites. By combination of an effective microwave-assisted HCl pretreatment and a simple in situ growth, the hierarchical porous architectures of corn tissues and silicon bodies were inherited into the obtained TiO₂ frameworks, which led to both of the structure- and SiO₂-introduced enhancements of photocatalytic performances. UV–visible absorption spectra indicate that all TiO₂–SiO₂ prepared as above exhibit enhanced visible-light harvesting efficiencies, especially in the range from 400 to 750 nm. Moreover, N₂ sorption measurements show that biotemplated composite derived from corn leaves has 2.5 times higher specific surface area than that of the commercial P25. Using methylene blue as the target pollutant, all biomorphic TiO₂–SiO₂ were proved to possess strong adsorption abilities and enhanced photocatalytic activities. The present work may provide a new route for the fabrication of hierarchical porous silicon-based materials based on silica-rich plants and develop a new method to protect the natural environment by utilizing waste biomass.     

Chemical Removal of CeO2 Segregated on the Surface of CeO2–ZrO2 Binary Oxides for Improvement of OSC

A chemical treatment to remove residual CeO₂ phase on CeO₂–ZrO₂ (CZ) solid solution was carried out. A CZ was treated by H₂O₂ for the reduction of Ce⁴⁺ to Ce³⁺ and then HNO₃ for the dissolution of Ce³⁺ compounds (H–CZ). H₂-TPR, TEM-EDX and XPS analyses revealed the removal of CeO₂ phase and the homogeneous distribution of Ce species. About 20% improvement in oxygen storage capacity (OSC) of H–CZ was confirmed at 773 K by the weight measurements under H₂/N₂ and air atmospheres, indicating that the HNO₃/H₂O₂ treatment was effective to avoid the deterioration of the OSC by segregated CeO₂ on the CZ binary oxides.     

Synthesis of highly dispersed MnOx–CeO2 nanospheres by surfactant-assisted supercritical anti-solvent (SAS) technique: The important role of the surfactant

In this work, highly dispersed mesoporous MnO_x–CeO₂ hollow nanospheres have been prepared using a surfactant-assisted supercritical anti-solvent (SAS) technique. The phase equilibria of methanol–CO₂, precursor-methanol–CO₂ and surfactant, precursor-methanol–CO₂ systems were measured to preliminarily screen suitable surfactants. The MnO_x–CeO₂ particles were characterized using N₂ adsorption/desorption, transmission electron microscopy (TEM) and X-ray diffraction (XRD). Polyvinylpyrrolidone (PVP) and poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (P123) both efficiently reduced the interconnectivity and agglomeration of MnO_x–CeO₂ particles and led to the formation of highly dispersed particles with higher specific surface areas, more uniform pores and larger pore volumes. The effects of the SAS process parameters including the surfactant to precursor mass ratio, the temperature and the pressure, on the morphology, particle size, particle size distribution, specific surface area and pore volume of the particles were also investigated. In addition, the catalytic activities of the synthesized hollow nanospheres for the low temperature denitrification (deNO_x) in the presence of NH₃ were evaluated. Over the entire experimental temperature range (100–220 °C), NO conversions of the MnO_x–CeO₂ particles prepared by introducing PVP or P123 during SAS were much higher than those for MnO_x–CeO₂ particles prepared without surfactants.