Catalytic combustion of toluene over Fe–Mn mixed oxides supported on cordierite

The catalytic combustion of toluene over Fe–Mn mixed oxides supported on cordierite was investigated. The catalysts were synthesized by the impregnation method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and BET specific surface area measurement. The effects of the mole ratio of Fe to Mn, the loading of Fe–Mn mixed oxides on the catalyst support and the calcination temperature were all investigated. The results indicate that Fe–Mn/cordierite catalysts with a 4 mol ratio of Fe to Mn, used with 10 wt% loading, and calcined at 500 ^°C showed the highest catalytic activities as measured by the oxidation of toluene. Compared to unsupported powder catalysts of Fe–Mn mixed oxides, the Fe–Mn/cordierite catalyst showed higher activity for the catalytic combustion of toluene with less active component.     

Structured hierarchical Mn–Co mixed oxides supported on silicalite-1 foam catalyst for catalytic combustion

Silicalite-1 (S1) foam was functionalized by supporting manganese–cobalt (Mn–Co) mixed oxides to develop the structured hierarchical catalyst (Mn–Co@S1F) for catalytic combustion for the first time. The self-supporting S1 foam with hierarchical porosity was prepared via hydrothermal synthesis with polyurethane (PU) foam as the template. Subsequently, Mn–Co oxide nano sheets were uniformly grown on the surface of S1 foams under hydrothermal conditions to prepare the structured hierarchical catalyst with specific surface area of 354 m²·g⁻¹, micropore volume of 0.141 cm³·g⁻¹ and total pore volume of 0.217 cm³·g⁻¹, as well as a good capacity to adsorb toluene (1.7 mmol·g⁻¹ at p/p₀ = 0.99). Comparative catalytic combustion of toluene of over developed structured catalyst Mn–Co@S1F was performed against the control catalysts of bulk Mn–Co@S1 (i.e., the crushed Mn–Co@S1F) and unsupported Mn–Co oxides (i.e., Mn–Co). Mn–Co@S1F exhibited comparatively the best catalytic performance, that is, complete and stable toluene conversion at 248 °C over 65 h due to the synergy between Mn–Co oxides and S1 foam, which provided a large number of oxygen vacancies, high redox capacity. In addition, the hierarchical porous structure also improved the accessibility of active sites and facilitated the global mass transfer across the catalyst bed, being beneficial to the catalysis and catalyst longevity.     

Low-temperature catalytic oxidation of toluene over nanocrystal-like Mn–Co oxides prepared by two-step hydrothermal method

Nanocrystal-like Mn–Co samples with high porosity and large surface area were first prepared by a two-step hydrothermal process. The strong interaction between MnO_x and CoO_x and the formation of Mn–Co solid solution have been proved by various characterization techniques. The nanocrystal-like Mn–Co sample with appropriate Mn/Co molar ratio (1:2) showed an excellent catalytic activity for toluene oxidation with the complete conversion temperature of 250 °C. The unique structure with high porosity and large surface area and the high concentration of reducible oxygen species were mainly responsible for the significant enhancement of catalytic activity for toluene oxidation over Mn–Co oxide samples.     

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.     

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.     

Growth of carbon nanotubes on the surface of carbon fiber using Fe–Ni bimetallic catalyst at low temperature

This article provides a method for growing carbon nanotubes(CNTs) on carbon fibers(CFs) using iron and nickel as catalysts at low temperatures. This series of experiments was conducted in a vacuum chemical vapor deposition(CVD)furnace. It is found that Fe–Ni catalysts, which have a certain thickness and can be better combined with resins when manufacturing composite materials, are more ideal for the growth of CNTs than single metal catalysts. At the same time, it is proved that the CVD process worked best at 450 °C. The mechanical property test proved the reinforcing effect of CNTs on carbon fiber, the single-filament tensile strength of CFs obtained by using Fe–Ni catalyst at 450 °C was 11% higher than that of Desized CFs. The bonding strength of carbon fiber and resin has also been significantly improved. When synthesized at low temperature, CNTs exhibited a hollow multi-wall structure.     

Low temperature catalytic oxidation of nitric oxide over the Mn–CoOx catalyst modified by nonthermal plasma

Nonthermal plasma (NTP) treatment was investigated to modify the Mn–CoO_x catalyst for the low-temperature oxidation of nitric oxide. The catalysts were characterized by XRD, BET, TGA and XPS techniques. The results showed that the activity of NTP-treated catalysts improved significantly, and that NTP treatment has the advantage of changing the structural and morphological properties (higher surface areas and pore volume) and varying the relative surface concentration and oxidation states of surface species over catalysts. High surface areas and pore volume, high concentration of chemisorbed oxygen, Mn^4 + and Co^2 +, and the efficient synergetic catalytic effect between Co and Mn ions were thought to be the main reasons for the high activity of NTP-treated catalysts.     

Complete oxidation of formaldehyde at ambient temperature over γ-Al2O3 supported Au catalyst

Au supported on γ-Al₂O₃ prepared by deposition–precipitation (DP) using urea is found to be a highly active catalyst for the total oxidation of HCHO at room temperature under humid air, without the need for a reducible oxide as support. In-situ DRIFTS studies suggested that the surface hydroxyl groups played a key role in the partial oxidation of HCHO into the formate intermediates, which can be further oxidized into CO₂ and H₂O with participation of nano-Au. This study challenges the traditional idea of supporting noble metals on reducible oxides for HCHO oxidation at room temperature.     

Effect of preparation method on catalytic performance,structure and surface reaction rates of MgO supported Fe–Co–Mn catalyst for CO hydrogenation

The MgO supported Fe–Co–Mn catalyst was prepared using different preparation methods including co-precipitation, sol–gel, incipient wetness impregnation and dry impregnation. All of these catalysts were tested for Fischer–Tropsch synthesis under the same operational conditions of T = 300 °C, P = 1 bar, H₂/CO = 2/1 and GHSV = 4500 h^?1. It was found that the co-precipitated catalyst has shown the better catalytic performance for CO hydrogenation. The effect of the preparation method on different surface reaction rates was also investigated and it was found that the preparation methods can influenced the rates of different surface reaction rates. Catalyst characterization was carried out using XRD, SEM, BET, TPR, TGA and DSC.     

Mixed Cu–Ni–Co nano-metal oxides: A new class of catalysts for styrene oxidation

A series of mixed nano-metal oxides of Cu–Ni–Co on γ-alumina with different metal loadings have been synthesized through the ultrasonic cavitation-impregnation method. All the prepared catalysts were analyzed by BET, ICP, XRD, SEM–EDS and TEM. The heterogeneous catalytic oxidation of styrene was investigated using tert-butyl hydroperoxide (TBHP) as an oxidizing agent and acetonitrile as a solvent under mild conditions. The influence of the metal loadings, reaction temperatures, oxidizing agents and styrene/oxidant molar ratio was investigated on the styrene conversion and on the selectivity to benzaldehyde and styrene oxide.     

CO oxidation over Au supported on Mn–ZSM5 and Mn–MOR

Active gold catalysts for CO oxidation were obtained by the deposition–precipitation of gold on ZSM-5 and mordenite, both of them ion-exchanged with manganese. A strong promotion of Mn upon the activity of bimetallic Au/Mn catalysts was observed when compared with the monometallic Au–zeolites. In turn, when an in-situ reduction of the bimetallic catalysts was performed, a further increase in activity was observed. Characterizations suggested that smaller gold nanoparticles were stabilized in the bimetallic solids and that the reduction process caused a rearrangement of Au and Mn species on the catalyst surface.     

Supported copper–ceria catalysts for low temperature CO oxidation

In this investigation, CuO/CeO₂–M_xO_y (M_xO_y = Al₂O₃, ZrO₂ and SiO₂) nanocomposite oxide catalysts were prepared by deposition-precipitation and wet impregnation methods, and evaluated for CO oxidation. Catalysts were characterized by XRD, TEM, UV–vis DRS, BET surface area and H₂-TPR techniques. The synthesized catalysts exhibited high specific surface area, and uniform particle size distribution over the supports. The nanocrystalline texture of mixed metal oxides is clearly evidenced by TEM analysis. TPR and XRD results revealed synergetic interactions between copper oxide and ceria. Among various catalysts investigated, the CuO/CeO₂–Al₂O₃ combination exhibited excellent CO oxidation activity with T_1/2 = 374 K and 100% CO conversion at below 420 K.     

The catalytic performance of Ti-PILC supported CrOx–CeO2 catalysts for n-butylamine oxidation

Journal of Porous Materials - A series of titanium pillared clays (Ti-PILC) materials are synthesized by different preparation conditions and the influence of the texture/structure nature of...     

Preparation and characterization of CeOx@MnOx core–shell structure catalyst for catalytic oxidation of NO

The CeOx@MnOx catalyst with a core–shell structure was prepared and used for catalytic oxidation of NO. It was found that CeOx@MnOx catalyst showed higher intrinsic catalytic activity than CeMnOx catalyst prepared by citric acid method. Based on the characterization results of N₂ adsorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), temperature-programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS), we may conclude that the excellent catalytic performance of CeOx@MnOx catalyst is related to its low crystallinity, good reducibility, and high concentrations of Mn^4 + and active oxygen species.     

Preparation of a mesoporous ceria–zirconia supported Ni–Fe catalyst for the high temperature water–gas shift reaction

A Ni–Fe/ceria–zirconia catalyst with ordered mesostructure was prepared by the hard-template method employing mesoporous silica (KIT-6) as a template to impart its highly ordered structure to the ceria–zirconia mixed oxide support. Catalytic activities of the Ni–Fe/CeO₂–ZrO₂ catalyst for the water–gas shift reaction were superior to those of a commercial Fe–Cr-based catalyst. The ordered structure of Ni–Fe/CeO₂–ZrO₂ catalyst became more stable compared to one prepared without zirconia due to structural stabilization of the mixed oxide by added zirconia in the framework. Alloying of Ni and Fe and enhanced mobility of lattice oxygen in the oxide support may promote its catalytic activity and selectivity for the water–gas shift reaction.     

High catalytic activity in CO PROX reaction of low cobalt-oxide loading catalysts supported on nano-particulate CeO2–ZrO2 oxides

Co₃O₄/NP-ZrO₂, Co₃O₄/NP-CeO₂ and Co₃O₄/NP-Ce_0.8Zr_0.2O₂ catalysts were prepared via a reverse microemulsion/incipient wetness impregnation (RM–IWI) method. The catalytic properties for CO preferential oxidation (CO PROX) reaction in H₂-rich stream were investigated. The Co₃O₄/NP-Ce_0.8Zr_0.2O₂ catalyst with 1.8 wt.% Co₃O₄ loading has exhibited higher catalytic activity than that of the other two catalysts. The higher catalytic activity might be attributed to the combination effect of the highly dispersed cobalt oxide, the improvement in CeO₂ reducibility due to ZrO₂ incorporation in CeO₂ structures, and the strong cobalt oxide-support interaction.     

Effect of activation temperature on the surface copper particles and catalytic properties of Cu–Ni–Mg–Al oxides from hydrotalcite-like precursors

The Cu–Ni–Mg–Al oxides catalysts for furfural hydrogenation were prepared from the hydrotalcite-like precursors, and the effect of activation temperature on the Cu⁰ particles and catalytic properties of the catalyst was thoroughly investigated. The catalyst activated by H₂ at 300 °C was found to exhibit the best catalytic activity, due to the presence of the smallest Cu⁰ particles with a high dispersion. Moreover, the bigger Cu⁰ particles were active for furfuralcohol hydrogenolysis to 2-methylfuran in the liquid-phase (ethanolic solution), and the hydrogenation of the furan ring of furfuralcohol and 2-methylfuran on Cu⁰ particles was easily achieved in the vapour-phase.     

Mesoporous Pt–Ni catalyst and their electro catalytic activity towards methanol oxidation

Mesoporous Pt/Ni architecture has been prepared by template assisted electrochemical deposition of Pt–Ni over anodized aluminum oxide template followed by controlled de-alloying with nitric acid. Surface characteristics of the ordered bimetallic mesoporous Pt/Ni structure were systematically characterized through XRD, SEM, AFM and XPS analyses. It is designated by XPS analysis that presence of Ni significantly modifies surface characteristics and electronic states of Pt accompanied with a downshift in the d-band character of Pt. Mesoporous morphology is highly beneficial to offer readily accessible Pt catalytic sites for methanol oxidation reaction. The prepared bimetallic Pt/Ni was used as electro catalyst for DMFC. Comparison of electrocatalytic activity of bimetallic mesoporous Pt/Ni with bimetallic smooth Pt/Ni was interrogated using cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy analyses. Distinctly enhanced electrocatalytic activity with improved CO tolerance associated with bimetallic mesoporous Pt/Ni electrode towards methanol oxidation stems from a synergy existing between mesoporous structure with bi-metallic composition.     

Selective catalytic reduction of nitrogen oxides with hydrocarbons over Zn–Al–Ga complex oxides

Selective reduction of NO with hydrocarbons was studied using metal oxide catalysts having a spinel structure. A Zn–Al–Ga complex oxide was found to be very active and selective for the catalytic reduction of NO with both C₃H₆ and CH₄. It was revealed that the role of oxygen at the initial stage of the reaction strongly depends on the reductants; oxygen is mainly used for NO oxidation to NO₂ in the reduction with CH₄, whereas it is used both for NO oxidation to NO₂ and oxidation of C₃H₆ to an active intermediate in the reduction with C₃H₆. This revised version was published online in July 2006 with corrections to the Cover Date.     

Porous Mn–Co mixed oxide nanorod as a novel catalyst with enhanced catalytic activity for removal of VOCs

Mn–Co mixed oxide nanorod with porous structure and high surface area was fabricated by an oxalate route and further used for deep oxidation of VOCs. Compared to the single MnO_x or Co₃O₄, the Mn–Co mixed oxide showed an enhanced activity for ethyl acetate and n-hexane oxidation with T_90% was low to 194 and 210 °C at a high space velocity, respectively. The formation of solid solution with spinel structure inhibits the growth of nanoparticles which leads to its higher surface area, and the strong synergistic effect of Mn–Co species in the oxide makes a great contribution to its low temperature reducibility which plays a key role in VOCs' oxidation.