Effects of cerium and vanadium on the activity and selectivity of MnO_x-TiO_2 catalyst for low-temperature NH_3-SCR

MnOx-TiO2, CeO2-MnOx-TiO2 and V2O5-MnOx-TiO2 catalysts for low-temperature NH3-SCR were prepared by sol-gel method. The results showed that both cerium and vanadium prevented the transformation ofanatase TiO2 to the mille phase. The addition of vanadium oxide induced the segregation of crystalline Mn2O3, which contributed little to low-temperature SCR and ammonia oxidation, from the MnOx-TiO2 solid solutions. However, the selectivity of the V-containing catalyst was almost 100% due to the decreased ammonia consumption and enhanced adsorption capacity of ammonia on Bronsted acid sites at relatively high temperatures. The electron-donating effect of cerium reduced the Mn^4＋/Mn^3- ratio to some extent, resulting in a decreased activity for ammonia oxidation. This, in combination with the enhanced ammonia adsorption capacity by Ce^n＋ as additional Lewis acid sites, endowed the Ce-doped catalyst a higher N2 selectivity than MnOx-TiO2 despite the slightly elevated light-offtemperamre for NO conversion.

Roles of Lewis and Brnsted acid sites in NO reduction with ammonia on CeO_2-ZrO_2-NiO-SO_4^(2-) catalyst

Nickel and sulfate co-modified CeO2-ZrO2 catalysts were prepared by sol-gel method. The catalysts were characterized by XRD, FTIR, XPS, NH3 chemisorption and NH3-SCR activity tests. The results showed that the enhanced acidity of CeO2-ZrO2 catalysts by nickel and sulfate co-modification was responsible for the broadened temperature window and improved the selectivity to N2 in NH3-SCR deNOx. The introduction of nickel to CeO2-ZrO2 solid solutions resulted in more Ce3+ on surface of catalyst, leading to an in...

Chemical deactivation of V2Os-WO3/Ti02 SCR catalyst by combined effect of potassium and chloride

V2O5-WO3/WiO2 catalyst was poisoned by impregnation with NHaC1, KOH and KC1 solution, respectively. The catalysts were characterized by X-ray diffraction （XRD）, inductively coupled plasma （ICP）, N2 physisorption, Raman, UV-vis, NH3 adsorption, temperature-programmed reduction of hydrogen （H2- TPR）, temperature-programmed oxidation of ammonia （NH3-TPO） and selective catalytic reduction of NOx with ammonia （NH3-SCR）. The deactivation effects of poison- ing agents follow the sequence of KC1 〉 KOH 〉〉 NH4CI. The addition of ammonia chloride enlarges the pore size of the titania support, and promotes the formation of highly dispersed V = O vanadyl which improves the oxidation of ammonia and the high-temperature SCR activity. K~ ions are suggested to interact with vanadium and tungsten species chemically, resulting in a poor redox property of catalyst. More importantly, potassium can reduce the Bronsted acidity of catalysts and decrease the stability of Bronsted acid sites significantly. The more severe deactivation of the KCl-treated catalyst can be mainly ascribed to the higher amount of potassium resided on catalyst.

Modification of CeO_2-ZrO_2 catalyst by potassium for NOx-assisted soot oxidation

Potassium-modified ceria-zirconia catalyst was synthesized by wetness impregnation method. The ageing treatment was performed in static air at 800℃ for 20 hr to evaluate the thermal stability of the catalyst. The catalysts were characterized by X-ray diffraction, BET surface area, oxygen storage capacity, NOx-temperature programmed desorption and soot-temperature programmed oxidation measurements. By introduction of potassium, the maximum soot oxidation rate temperature （Tin） of the ceria-zirconia based catalyst decreased from 525 to 428℃ in the presence of NO under a loose contact mode. The shift of Tm of the K-modified catalyst after ageing is only 15℃. The enhanced activity of the aged catalyst mainly lies in the promotional effect of potassium on the NOx/oxygen storage capacity as well as the soot-catalyst contact.

Influence of Layered Aluminoborophosphate on Flame Retardance, Crystallization Behaviors and Mechanical Properties of Polyamide 66 Systems

A layered aluminoborophosphate（LABP-DDA） was hydrothermally synthesized using dodecylamine as a structure-directing agent, and was added into polyamide 66（PA66） to obtain nanocomposites, PA66/LABP-DDA, via melt intercalation method. The characterization results of transmission electron microscopy（TEM） and small angle X-ray scattering （SAXS） indicate that LABP-DDA has been successfully exfoliated into nano-layers of PA66 matrix. The unstable γ phase of PA66 was found in the composites with the help of X-ray diffraction（XRD） and differential scanning calorimetry（DSC）. The heterogeneous nucleation effect of LABP-DDA resulted in an increasement of about 10 ℃ in melting temperature and an increasement of about 7% in crystallinity when compared with those of neat PA66. The introduction of LABP-DDA did not significantly affect the toughness and strength of PA66. The results of flammability test indicate that LABP-DDA possesses positive synergistic flame retarding effect in the presence of melamine polyphosphate（MPP） and the 77%PA66/（23-x）%MPP/x%LABP-DDA（x=1, 2） samples in thickness of 1.6 mm reached from Fail to V-1 rating based on UL94, compared with 77% PA66/23%MPE.

Oxidation Behaviors of C-ZrB_2-SiC Composite at 2100℃ in Air and O_2

The oxidation behaviors of graphite and ZrB2-SiC modified graphite composite were investigated at 2100℃ in1X105 Pa air and 0.2X105 Pa O2. The oxidation tests were conducted in an induction heating furnace. The oxidation of these two materials followed the linear rate law. The determined radius loss rates of graphite and C-ZrB2-Si C at 2100℃ were 2.18X10-2and 1.05X10-2%/s in 1X105 Pa air, and 3.23X10 2 and 2.21X10 2%/s in 0.2X105 Pa O2, respectively. The incorporation of ZrB2 and SiC decreased remarkably the oxidation rate of graphite because the oxide scale formed on the sample surface during oxidation helps in reducing the exposed surface area of the underneath substrate. In two different atmospheres with the same oxygen partial pressure, both graphite and ZrB2-SiC experienced more severe oxidation at 2100℃ in0.2X105 Pa O2than in 1X105 Pa air. The oxidation rate-controlling step for graphite and ZrB2-SiC was proposed to be the inward diffusion of oxygen through the boundary layer and through the pores in the oxide scale, respectively. A model based on diffusion theory was established to discuss the effect of the total gas pressure on their oxidation behaviors.

Fabrication of flexible α-MnO_2 nanowire membranes with superior mechanical strength

The Assembly of one-dimensional(1D)nanostructures such as nanowires/nanorods/nanotubes into twodimensional(2D)macrostructured films is attracting considerable research interest because of their unique properties and wide applications.In this study,flexible membranes were successfully fabricated using a-MnO2nanowires synthesized through a hydrothermal method.The effects of thickness and post-annealing temperature on the mechanical properties of the membranes were investigated in detail.Nano-indentation measurements showed that the modulus of the as-prepared 11.75 lm-thick membrane reached5.765 GPa,and the modulus increased with the increasing post-annealing temperature.Thus,the fabricated membranes with superior mechanical strength can have potential applications such as in photocatalysis,filtering,and supporting substrates.

Effect of cationic groups in organic sulfide electrolyte on the performance of CdS quantum dot sensitized solar cells

Two organic sulfide redox couples derived from2-mercapto-5-methyl-1,3,4-thiadiazole(McMT):tetrabutylammonium thiolate(McMT-TBA?)/disulfide dimer(BMT)and tetramethylammonium thiolate(McMTTMA?)/BMT were incorporated into quantum dots sensitized solar cells(QDSCs)as alternatives to the inorganic polysulfide electrolyte(Na2S/S).It was found in symmetrical cells test that the interfaces of the organic sulfide electrolytes/platinum counter-electrode have much lower charge transfer resistances as well as higher interface reaction rates compared with that for the inorganic one.Besides,QDSCs based on organic sulfide electrolytes exhibited obviouslyhigher fill factors,open circuit photovoltages,and therefore higher conversion efficiency,thanks to the prohibited recombination and lower redox potential.In addition,by comparing and analyzing the performance of devices based on organic sulfide electrolytes with different cationic groups,it is found that cationic group TMA?with smaller size was favorable for the mass transport in the electrolyte,which explains the better photovoltaic performance of McMT-TMA?/BMT based solar cell than that of McMT-TBA?/BMT based one.Eventually,a power conversion efficiency(PCE)of 0.63%was achieved for QDSCs using McMT-(TMA?)/BMT redox couple as electrolyte,which was till now the highest for CdS QDSC based on organic sulfide electrolyte.

Hydrothermal stability of MO_x-Ce_(0.75)Zr_(0.25)O_2 catalysts for NO_x reduction by ammonia

Various acidic components（MOx：phosphate,sulfate,tungstate and niobate） were loaded on Ce0.75 Zr0.25 O2 powders by an impregnation method.The as-prepared catalysts were hydrothermally treated at 760 oC for 48 h in air containing 10 vol.% H2 O to obtain the aged catalysts.The catalysts were characterized by X-ray diffraction,Fourier transform infrared spectroscopy,H2 programmed-reduction,NH3 adsorption and deNOx activity measurements.The results showed that,among the catalysts investigated,the phosphated Ce0.75 Zr0.25 O2 catalyst showed the highest hydrothermal stability.The remained high acidity of the phosphated catalyst with moderate redox property helped to maintain the excellent NH3-SCR activity of hydrothermally aged catalyst.Cerium tungstate led to the poor redox property of the tungstated catalyst although the acidity of catalyst was still high.The decomposition of sulfates at temperatures higher than 600 °C restrained the usage of sulfated catalysts in high temperature conditions.The overall dehydration of niobate to niobium oxides led to the low acidity of hydrothermally aged Nb2 O5-Ce0.75 Zr0.25 O2 catalyst.

NO_x-assisted soot oxidation over K/CuCe catalyst

CeO2 and CuOx-CeO2 supported potassium catalysts were synthesized by wetness impregnation method. The catalysts were characterized by BET, NO-TPO, NOx-TPD and soot-TPO measurements. By the decoration of potassium and copper, the maximum soot combustion temperature of the ceria-based catalyst decreased to 338 and 379 °C in the presence and absence of NO under a loose contact mode, re- spectively. The pronouncedly enhanced NO oxidation ability by copper introduction and NOx storage capacity by potassium modif...