Copper Manganese Oxides

Amorphous manganese oxide and binary copper manganese oxides were synthesized using the redox method, characterized, and tested in the catalytic oxidation of ethylene. The catalytic activity of the synthesized catalysts toward ethylene oxidation was high (100% conversion of 1.0% C 2 H 4 at 200 • C with space velocity of 35, 000 mL h −1 g −1 cat) and compared favorably with that of a commercial Hopcalite catalyst. The high catalytic activity was attributed a combination of factors including the poor crystallinity, the high surface areas (≥163 m 2 g −1), porosity, presence of Mn 4+ species, and compositional homogeneity of the synthesized copper manganese oxides. Incorporation of copper into the amorphous manganese oxide matrix significantly enhanced the catalytic activity of the resultant bimetallic oxides by increasing the reducibility and ease of removal of lattice oxygen species. The synthesized materials were characterized using FE-SEM, HR-TEM, BET, FAAS, XPS, and TPD methods.

Amorphous manganese oxide and binary copper manganese oxides were synthesized using the redox method, characterized, and tested in the catalytic oxidation of ethylene. The catalytic activity of the synthesized catalysts toward ethylene oxidation was high (100% conversion of 1.0% C 2 H 4 at 200 • C with space velocity of 35, 000 mL h −1 g −1 cat) and compared favorably with that of a commercial Hopcalite catalyst. The high catalytic activity was attributed a combination of factors including the poor crystallinity, the high surface areas (≥163 m 2 g −1), porosity, presence of Mn 4+ species, and compositional homogeneity of the synthesized copper manganese oxides. Incorporation of copper into the amorphous manganese oxide matrix significantly enhanced the catalytic activity of the resultant bimetallic oxides by increasing the reducibility and ease of removal of lattice oxygen species. The synthesized materials were characterized using FE-SEM, HR-TEM, BET, FAAS, XPS, and TPD methods.

In this study, mixed oxides of Mn-Cu and Fe-Cu on OMS-2 support having an octahedral structure were synthesized by the refluxing and impregnation methods. The characteristics of the materials were analyzed by XRD, FTIR, SEM, EDX, and H2-TPR. In the CO oxidation test, CuFeOx/OMS-2 had slightly higher catalytic activity but is significantly more stable than CuMnOx/OMS-2 and CuO/OMS-2. Due to its lower reduction temperature in H2-TPR analysis, the Mars-Van-Krevelen mechanism for CuFeOx/OMS-2 (Cu2+–O–Fe3+ ↔ Cu+–□–Fe2+) could take place more energetically than CuO/OMS-2 and CuMnOx/OMS-2 (Cu2+–O2−–Mn4+ ↔ Cu+–□–Mn3+). In addition, the interaction between Fe and Cu in the catalyst could improve the durability of the surface oxides structure in comparison with that between Mn and Cu. With the high specific rate and TOF of 28.6 mmol/h.g and 0.508, respectively, CuFeOx/OMS-2 has a great potential as an effective catalyst for low-temperature oxidation application in CO and possible VOCs removal.

The catalytic combustion of ethyl acetate over prepared metal oxide catalysts was investigated. CeO, Co2O3, Mn2O3, Cr2O3, and CeO-Co2O3 catalysts were prepared on monolith supports and they were tested. Before conducting the catalyst experiments, we searched for the homogeneous gas phase combustion reaction of ethyl acetate. According to the homogeneous phase experimental results, 45% of ethyl acetate was converted at the maximum reactor temperature tested (350 • C). All the prepared catalysts were tested in order to find the best catalyst for the complete combustion of ethyl acetate. According to the results, all these catalysts produced higher conversion rates than that of the homogeneous experiment; however, none of the prepared catalysts resulted in complete combustion. The maximum conversion obtained with the CeO catalyst at 350 • C was 72%.

Highly nanoporous manganese oxides, such as meso-MnO 2 and meso-Mn 2 O 3 , are synthesized using nanoporous silica KIT-6 as a hard template via nano-replication method. Manufactured ordered nanoporous materials exhibit significant properties, such as large and uniform pore sizes, high surface area and pore volume, and well-defined pore topologies. The catalytic performance of the synthesized materials during the repetitive decomposition of hydrogen peroxide is also examined in a specially-designed pulse-injection reactor. In comparison of catalytic decomposition of high-purity hydrogen peroxide, the decomposition activity of nanoporous MnO 2 was better than that of bulk MnO 2 , which can be attributed to larger surface area of nanoporous MnO 2 than that of bulk MnO 2. It was confirmed that nanoporous MnO 2 is a better catalyst in terms of its catalyst life in comparison with nanoporous Mn 2 O 3 .

The low-temperature oxidation of carbon monoxide remains a topic of intense research activity at the present time. It is of particular importance in breathing apparatus, but also has applications in carbon dioxide lasers and is of potential interest for space exploration. Most attention, ...

Mixed copper manganese oxide catalysts (Hopcalite) have been studied for the total oxidation of propane, as a model for hydrocarbon volatile organic compound emission control. Catalysts were prepared using coprecipitation with and without gold. Calcination temperature influenced the catalyst activity and those prepared at 300°C were the most active. Characterization showed that the catalysts had a nanowire-type morphology, and for

Binary copper manganese oxides were prepared by a novel redox method and their catalytic activity for CO oxidation at ambient temperature evaluated. The catalytic activity was found to be high, and compared favorably with a commercial Hopcalite catalyst. The most active catalyst was able to completely oxidize CO at ambient temperature. Catalytic activity decay, most likely due to carbon dioxide retention was observed. The catalysts were deactivated by moisture but expelling water at moderate temperatures easily restored their catalytic activity. The catalysts were characterized by means of BET, FE-SEM, TEM, EDAX, XPS, TPD and X-ray powder diffraction. The optimum copper loading was determined to be ∼9% of the manganese content.

Binary copper manganese oxides were prepared by a novel redox method and their catalytic activity for CO oxidation at ambient temperature evaluated. The catalytic activity was found to be high, and compared favorably with a commercial Hopcalite catalyst. The most active catalyst was able to completely oxidize CO at ambient temperature. Catalytic activity decay, most likely due to carbon dioxide retention was observed. The catalysts were deactivated by moisture but expelling water at moderate temperatures easily restored their catalytic activity. The catalysts were characterized by means of BET, FE-SEM, TEM, EDAX, XPS, TPD and X-ray powder diffraction. The optimum copper loading was determined to be ∼9% of the manganese content.

The authors have investigated the equilibrated adsorption of water vapors on GFG hopcalite, which was obtained using the extrusion shaping method, with bentonite clay as the binding compound. In the frames of the BET model, the values of the monolayer capacity and the size of medium area occupied by the water molecule in the filled
monolayer have been determined. The distribution of pores according to their sizes has been evaluated. It has been established that the modification of the bentonitic clay allows directed construction of the hopcalite porous structure, i.e. the formation of the mesoporous structure with a narrow distribution of the pores capacities by sizes, which was achieved varying the sizes of binding compound particles.

A Fe-Cu-Al-O water gas shift catalyst with a Fe : Cu atomic ratio of 4 : 1 upon pretreatment at 350 8C in H 2 exhibits a conversion higher than a physical mixture of Fe-Al-O and Cu-Al-O by B40% over a temperature range of 300 8C-450 8C. In situ ambient pressure X-ray photoelectron spectroscopy studies suggest that the surface region of Fe-Cu-Al-O was restructured into a double-layer structure consisting of a surface layer of Fe 3 O 4 and a metallic Cu layer below it upon pretreatment at 350 8C. The strong metal (Cu)-oxide (Fe 3 O 4 ) interface effect of this double layer structure enhances the catalytic activity of Fe 3 O 4 in WGS.

Three-dimensionally (3D) ordered and wormhole-like mesoporous iron oxides (denoted as Fe-KIT6 and Fe-CA) were respectively prepared by adopting the 3D ordered mesoporous silica KIT-6-templating and modified citric acid-complexing strategies, and characterized by a number of analytical techniques. It is shown that the Fe-KIT6-400 and Fe-CA-400 catalysts derived after 400°C-calcination possessed high surface areas (113-165 m(2)/g), high surface adsorbed oxygen concentrations, and good low-temperature reducibility, giving 90% conversion below 189 and 208°C for acetone and methanol oxidation at 20,000 mL/(g h), respectively. It is believed that the good catalytic performance of Fe-CA-400 and Fe-KIT6-400 was related to factors such as higher surface area and oxygen adspecies concentration, better low-temperature reducibility, and 3D mesoporous architecture.

A high surface area Co 3 O 4 ÀSiO 2 nanocomposite catalyst has been prepared by use of activated carbon as template. The Co 3 O 4 À SiO 2 composite, the surface of which is rich in silica and Co(II) species compared with normal Co 3 O 4 , exhibited very high activity for CO oxidation even at a temperature as low as À76°C. A rather unusual temperature-dependent activity curve, with the lowest conversion at about 80°C, was observed with a normal feed gas (H 2 O content ∼3 ppm). The U-shape of the activity curve indicates a negative apparent activation energy over a certain temperature range, which has rarely been observed for the heterogeneously catalyzed oxidation of CO. Careful investigation of the catalytic behavior of Co 3 O 4 ÀSiO 2 catalyst led to the conclusion that adsorption of H 2 O molecules on the surface of the catalyst caused the unusual behavior. This conclusion was supported by in situ diffuse reflectance Fourier transform infrared (DRIFT) spectroscopic experiments under both normal and dry conditions.

Methylation of phenol with methanol as an alkylating agent to produce 2,6-xylenol was investigated over copper manganese mixed oxide spinels, Cu x Mn 3−x O 4 (x = 0, 0.25, 0.5, 0.75, and 1) prepared through co-precipitation. The catalytic activity strongly depends on the composition, acid-base properties, and structural stability. Various parameters, including catalyst composition, reaction temperature, feed composition, and durability of the catalyst during methylation, were investigated. Mainly o-cresol and 2,6-xylenol, along with small amounts of mesitol, were found in the product. A high ortho-selectivity of 100%, with 2,6-xylenol selectivity of 74%, was observed over Cu 0.25 Mn 2.75 O 4 at 673 K. These catalysts were investigated using various techniques, including BET surface area, XRD, DRS UV-vis, TPD of NH 3 and CO 2 , TPR, and X-ray photoemission spectroscopy (XPS). Powder XRD of the catalysts revealed the formation of copper-manganese spinels with hausmannite (Mn 3 O 4 ) tetragonal structure, for x = 0-0.5, whereas an increase in copper content (x > 0.5) led to the formation of cubic Cu 1.5 Mn 1.5 O 4 phase. DRS UV-vis, and FTIR further supported the changes in structural phases observed by XRD. Temperature-programmed desorption of CO 2 and NH 3 showed that the catalysts have strong basicity along with weak acidity when x = 0 and 0.25. XPS and XAES analysis revealed the presence of only Cu 2+ ions in fresh sample with x = 0.25, whereas for x = 1.0, both Cu 1+ and Cu 2+ were observed. The deactivation of the catalysts is attributed to structural changes occurring during the reaction. Catalytic activity is correlated with structure, as well as with acid-base properties.

Amorphous manganese oxide and binary copper manganese oxides were synthesized using the redox method, characterized, and tested in the catalytic oxidation of ethylene. The catalytic activity of the synthesized catalysts toward ethylene oxidation was high (100% conversion of 1.0% C2H4 at 200 °C with space velocity of 35 000 mL-1 h-1 gcat-1 source and compared favorably with that of a commercial Hopcalite catalyst. The high catalytic activity was attributed a combination of factors including the poor crystallinity, the high surface areas (≥163 m2 g−1), porosity, presence of Mn4+ species, and compositional homogeneity of the synthesized copper manganese oxides. Incorporation of copper into the amorphous manganese oxide matrix significantly enhanced the catalytic activity of the resultant bimetallic oxides by increasing the reducibility and ease of removal of lattice oxygen species. The synthesized materials were characterized using FE-SEM, HR-TEM, BET, FAAS, XPS, and TPD methods.

Highlights:

Copper manganese oxides are highly active catalysts for ethylene oxidation. High activity attributed to amounts of Mn4+ species, and compositional homogeneity. Incorporation of copper enhances the activity of resultant bimetallic oxides.

Mesoporous copper manganese oxides with high surface areas (>268 m2/g) were prepared using the redox method and tested in the preferential oxidation of CO. These materials were highly active and selective under typical operating conditions of a proton-exchange membrane fuel cell. The synthesized catalysts preferentially oxidized CO with a stoichiometric amount of oxygen in the feed gas. The presence of CO2 and H2O in the feed gas retarded catalytic activity significantly at low (<90 °C) temperatures. The catalysts showed stable activity in long-term (12 h) experiments with realistic feeds. The high catalytic activity was attributed to a combination of factors, including high surface area, low crystallinity, low activation energy for CO oxidation, compositional homogeneity of the copper manganese oxides, and the presence of readily available lattice oxygen for CO oxidation. The high selectivity (100% with stoichiometric reactants) was ascribed to the lower activation energy for CO oxidation compared to the activation energy for H2 oxidation.

Binary copper manganese oxides were prepared by a novel redox method and their catalytic activity for CO oxidation at ambient temperature evaluated. The catalytic activity was found to be high, and compared favorably with a commercial Hopcalite catalyst. The most active catalyst was able to completely oxidize CO at ambient temperature. Catalytic activity decay, most likely due to carbon dioxide retention was observed. The catalysts were deactivated by moisture but expelling water at moderate temperatures easily restored their catalytic activity. The catalysts were characterized by means of BET, FE-SEM, TEM, EDAX, XPS, TPD and X-ray powder diffraction. The optimum copper loading was determined to be ∼9% of the manganese content.