The effect of hydrogen reduction of α-MnO2 on formaldehyde oxidation: The roles of oxygen vacancies

A series of α-MnO₂ catalysts with various Mn valence states were treated by hydrogen reduction for different periods of time. Their catalytic capacity for formaldehyde (HCHO) oxidation was evaluated. The results indicated that hydrogen reduction dramatically improves the catalytic performance of α-MnO₂ in HCHO oxidation. The α-MnO₂ sample reduced by hydrogen for 2 h possessed superior activity and could completely oxidize 150 ppm HCHO to CO₂ and H₂O at 70 °C. Multiple characterization results illustrated that hydrogen reduction contributed to the production of more oxygen vacancies. The oxygen vacancies on the catalyst surface enhanced the adsorption, activation and mobility of O₂ molecules, and thereby enhanced HCHO catalytic oxidation. This study provides novel insight into the design of outstanding MnO_x catalysts for HCHO oxidation at low temperature.     

Catalytic reduction of NO by CO over Pd — doped Perovskite-type catalysts

The perovskite type oxides (nominal formula LaTi_0.5Mg_0.5O₃) with addition of Pd were prepared by annealing the ethanol solution of precursors in nitrogen flow at 1200°C and characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption of NO (NO-TPD). Their activity was evaluated for NO reduction by CO under stoichiometric and oxidizing conditions and for direct decomposition of NO. Pd substituted samples exhibited high NO reduction activity and selectivity towards N₂. Nearly complete elimination of NO was achieved at 200°C. Two simultaneous reactions, NO reduction by CO and direct decomposition of NO as well as two forms of NO adsorption were observed on the surface of Pd substituted perovskite samples. The distribution of Pd in different catalytically active sites or complexes on at the catalyst surface may be responsible for the proceeding of two reactions: NO reduction with CO and direct NO decomposition.      

Catalytic oxidation of NO over Mn–Co–Ce–Ox catalysts: effect of reaction conditions

Manganese–cobalt–cerium oxide (Mn–Co–Ce–Ox) catalysts were synthesized by the co-precipitation method and tested for activity in low-temperature catalytic oxidation of NO in the presence of excess O₂. With the best Mn–Co–Ce mixed-oxide catalyst, approximately 80 % NO conversion was achieved at 150 °C and a space velocity of 35,000 h^?1. The effect of reaction conditions (reaction temperature, volume fractions of NO and O₂, gas hourly space velocity (GHSV), and catalyst stability) was investigated. The optimum reaction temperature was 150 °C. Increasing the O₂ content above 3 % results in almost no improvement of NO oxidation. This catalyst enables highly effective removal of NO within a wide range of GHSV. Furthermore, the stability of the Me–Co–Ce–Ox catalyst was excellent; no noticeable decrease of NO conversion was observed in 40 h.     

Catalytic behavior of nanoparticle α-PtO2 for ethanol oxidation

Fusion method is used to prepare α-PtO₂ and has a special needle-like microcrystalline morphology, with a diameter of ca. 6 nm and a length of ca. 50 nm. The two Pt–O bonds of α-PtO₂ are different in strength and α-PtO₂ decomposes thermally to Pt⁰ in two steps. α-PtO₂ is a p-type oxide semiconductor with a band-gap of 1.84 eV. α-PtO₂ is easily reduced by ethanol, its reduction product, Pt⁰, can directionally catalyze the oxidation of ethanol to acetic acid in the presence of air, while acetaldehyde, acetal and ethyl acetate are intermediates.     

Catalytic oxidation of 4-tert-butyltoluene over Ti-MCM-41

The surface-grafted titanium MCM-41 materials were prepared by anchoring titanocene onto the inner walls of MCM-41. The materials were characterized by powder X-ray diffraction (XRD), N2 adsorption-desorption isotherm and diffuse reflectance UV-visible (UV-vis) spectroscopies. The catalytic properties of Ti-MCM-41 were tested in oxidation of 4-tert-butyltoluene with tert-butylhydroperoxide (TBHP) in liquid phase. MCM-41 with loading 4.8 mol% Ti gave the maximal conversions of 23.6% of 4-tert-butyltoluene with a complete selectivity to 4-tert-butylbenzaldehyde.     

Catalytic combustion of methane over nano ZrO2-supported copper-based catalysts

The nano ZrO2-supported copper-based catalysts for methane combustion were investigated by means of N2 adsorption, TEM, XRD, H2-TPR techniques and the test of methane oxidation. Two kinds of ZrO2 were used as support, one （ZrO2-1） was obtained from the commercial ZrO2 and the other （ZrO2-2） was issued from the thermal decomposition of zirconium nitrate. It was found that the CuO/ZrO2-2 catalyst was more active than CuO/ZrO2-1. N2 adsorption, H2-TPR and XRD measurements showed that larger surface area, better reduction property, presence of tetragonal ZrO2 and higher dispersion of active component for CuO/ZrO2-2 than that of CuO/ZrO2-1. These factors could be the dominating reasons for its higher activity for methane combustion.     

Catalytic diastereoselective reduction of α,β-epoxy and α,β-aziridinyl ynones

The Noyori transfer hydrogenation of α,β-epoxy and α,β-aziridinyl ynones leads to the corresponding α,β-epoxy or α,β-aziridinyl propargylic alcohols with high reagent-controlled diastereoselectivity.     

Total oxidation of ethanol and toluene over ceria—zirconia supported platinum catalysts

The effect of platinum loading (0.09–1.00 mass %) on the performance of ceria-zirconia supported catalysts in the total oxidation of ethanol and toluene in air was investigated. The introduction of platinum promoted the reduction of surface cerium and decreased the acidity of the catalysts. In ethanol oxidation, the temperature of 50 % conversion decreased with increasing platinum content. This increase in catalytic performance was more pronounced for the catalysts with 0.59 mass % and 1.00 mass % Pt. On the other hand, higher amount of by-products (mainly acetaldehyde) was observed at increased platinum loadings. For all catalysts, a correlation between their H₂-TPR profiles and catalytic performance was revealed. In toluene oxidation, only the catalysts with 0.59 mass % and 1.00 mass % Pt exhibited a lower temperature of 50 % conversion than pristine ceria-zirconia. The effect of platinum loading was less pronounced than in ethanol oxidation and a correlation between reduction behaviour and catalytic performance was not observed. The superior catalytic performance of the catalysts with 0.59 mass % and 1.00 mass % of Pt in both ethanol and toluene oxidation was ascribed to the presence of large platinum nanoparticles, which were not observed at lower Pt loadings.     

Preparation,characterization and electrical transport properties of individual α-MnO2 and β-MnO2 nanorods

Electrical transport experiments are performed on individual α-MnO₂ and β-MnO₂ nanorods. Both of α-MnO₂ and β-MnO₂ nanorods are synthesized via hydrothermal routes. A three-region method is used to analyze their nonlinear current–voltage characteristics. Under low biases, the effective contact barrier height is roughly estimated to be 0.05 eV for α-MnO₂ and 0.15 eV for β-MnO₂, respectively. As the applied bias is high enough, the contact barriers are significantly tilted and the current is largely tunneling. The conductance of α-MnO₂ and β-MnO₂ nanorods at room temperature is roughly estimated to be 5.98 and 1.74 × 10^?3 cm^?1 Ω^?1, respectively. And the thermal-activation energy is roughly estimated to be 0.047 and 0.226 eV, respectively. Our results are probably the bases for their applications in nanosized electrical devices.     

Graphene-Ni-α-MnO2 and -Cu-α-MnO2 nanowire blends as highly active non-precious metal catalysts for the oxygen reduction reaction

Graphene-like carbon-Ni-α-MnO(2) and -Cu-α-MnO(2) blends can serve as effective catalysts for the oxygen reduction reaction with activities comparable to Pt/C.     

Low-temperature CO oxidation over CuO-CeO2/SiO2 catalysts：Effect of CeO2 content and carrier porosity

The effects of CeO2 contents and silica carder porosity with their pore diameters ranging from 5.2 nm to 12.5 nm of CuO-CeO2/SiO2 catalysts in CO oxidation were investigated. The catalysts were characterized by N2 adsorption/desorption at low temperature, X-ray diffraction (XRD), temperature-programmed reduction by H2 (H2-TPR), oxygen temperature programmed desorption (O2-TPD) and X-ray photoelectron spectroscopy (XPS). The results suggested that, the ceria content and the porosity of SiO2 carder possessed great impacts on the structures and catalytic performances of CuO-CeO2/SiO2 catalysts. When appropriate content of CeO2(Ce content ≤8 wt%) was added, the catalytic activity was greatly enhanced. In the catalyst supported on silica carrier with larger pore diameter, higher dispersion of CuO was observed, better agglomeration-resistant capacity was displayed and more lattice oxygen could be found, thus the CuO-CeO2 supported on Si-1 showed higher catalytic activity for low-temperature CO oxidation.     

Role of α-Sites in the selective catalytic reduction of NO x with ammonia over Fe-ZSM-5 catalysts

The catalytic properties of Fe-ZSM-5 zeolites with different iron contents have been investigated in the selective catalytic reduction (SCR) of NO _x with ammonia. The observed catalytic properties the zeolites are correlated with the concentration of the iron-containing sites that are stabilized in the zeolite and effect N₂O decomposition (??-sites). The catalysts activated at a high temperature to increase the ??-site concentration (by a factor of 5?C10) are more active in NO _x SCR with ammonia than the unactivated samples. However, the difference between the activities of the activated and unactivated catalysts is well below the difference between the ??-site concentrations in these catalysts. The nonlinear relationship between these parameters is evidence that the ??-sites in Fe-ZSM-5 is not the only factor determining the activity of Fe-ZSM-5 in NO _x SCR with ammonia. The activated catalysts show a low activity in nonselective ammonia oxidation and, accordingly, a high selectivity in the target process at high temperatures.     

Synthesis and stereoselective oxidation of α-thio-β-chloropropenyloxazolidin-2-ones

The investigation of the stereoselective reaction of α-thiopropanoyloxazolidin-2-ones with NCS to yield α-thio-β-chloropropenyloxazolidin-2-ones is described. Diastereoselective sulfur oxidation of the resulting α-thio-β-chloropropenyloxazolidin-2-ones shows modest diastereocontrol. However, via a combination of diastereoselective oxidation and subsequent kinetic resolution in the sulfoxide oxidation, diastereoselectivities of up to 94% de have been achieved.     

Catalytic combustion of benzene over CuO/CeO2 catalysts prepared using the precipitation–deposition method

Research on Chemical Intermediates - Catalytic combustion of benzene over CeO2-supported copper oxides has been investigated. The supported copper oxide catalysts were prepared by use of the...     

Catalytic synthesis of isoprenol from fatty acid ester over bimetallic Cu–Fe catalysts

Supported bimetallic Cu–Fe catalysts revealed high activity and selectivity in isoprenyl acetate hydrogenation to isoprenol under mild reaction conditions (2 MPa H₂ and 170 °C). The nature of the carrier has a significant impact on the catalytic properties of Cu–Fe catalysts. The best catalytic properties were found for the 5% Cu–5% Fe/Al₂O₃ bimetallic catalyst, which provides a 98% isoprenyl acetate conversion in 4 h with the isoprenol selectivity of 82%.     

Syngas production by combined carbon dioxide reforming and partial oxidation of methane over Ni/α-Al_2O_3 catalysts

Ni/α-Al2O3 catalysts were found to be active in the temperature range 600 ～ 900℃ for both CO2 reforming and partial oxidation of methane.The effects of Ni loading,reaction temperature and feed gas ratio for the combination of CO2 reforming and partial oxidation of CH4 over Ni/α-Al2O3 were investigated.Catalysts of xwt%Ni/α-Al2O3(x=2.5,5,8 and 12) were prepared by wet impregnating the calcined support with a solution of nickel nitrate.XRD patterns and activity tests have verified that the 5wt%Ni/α-Al2O3 was the most active catalyst,as compared with the other prepared catalyst samples.An increase of the Ni loading to more than 5wt% led to a reduction in the Ni dispersion.In addition,by combining the endothermic carbon dioxide reforming reaction with the exothermic partial oxidation reaction,the loss of catalyst activity with time on stream was reduced with the amount of oxygen added to the feed.