Rare earth oxide modified Cu-Mn compounds supported on TiO2 catalysts for low temperature selective catalytic oxidation of ammonia and in lean oxygen

Selective catalytic oxidation (SCO) of ammonia was carried out over Cu-Mn compounds catalysts modified with trivalent rare earth oxide Ce₂O₃ and La₂O₃ respectively. TiO₂ was used as support and different ratio of O₂ were tested in order to find an appropriate O₂ concentration (vol.%), and the results showed that 1%O₂ (vol.%) was propitious to SCO of ammonia. The effects of the two rare earth oxides modified catalysts Ce₂O₃-Cu-Mn/TiO₂ and La₂O₃-Cu-Mn/TiO₂ on the catalytic activity and selectivity of ammonia oxidation were investigated under the reaction condition of 500 ppm ammonia, 1%O₂ (vol.%), at the temperature from 125 to 250 °C. The results revealed the beneficial role of Ce₂O₃ and La₂O₃ in catalytic activity at low temperature and lean oxygen concentration, while the modification with Ce₂O₃ and La₂O₃ led to the negative influence on N₂ selectivity. For the catalysts modified with Ce showed lower NO and N₂O selectivity than the catalysts modified with La, then the effects of different Ce loadings on catalytic activity and selectivity were also considered, in combination with catalysts preparation methods, which include incipient wet impregnation, sol-gel method and co-precipitation. Results revealed that the catalysts prepared by sol-gel method obtained preferable catalytic activity compared with the others, reaching 99% ammonia at 200 °C, whereas 96% NO was detected. It also indicated that different catalyst preparation method significantly determined production distribution.     

Preparation and characterization of nano-rare earth composite materials:application in selectivity catalytic oxidation of ammonia and its cytotoxicity study

The manufacture,physical characterization,environmental applications and cytotoxicity properties of nanocomposites consisting of CuO/CeO2 nano-rare earth composite materials prepared using the coprecipitation method at molar ratio of 6:4 with aqueous solutions of copper nitrate and cerium nitrate were reported.The performance of the selective catalytic oxidation of ammonia to N2(NH3-SCO) over a CuO/CeO2 nano-rare earth composite materials in a tubular fixed-bed reactor(TFBR) at temperatures from 423 to 673 K in the presence of oxygen was elucidated.The catalytic redox behavior was determined by cyclic voltammetry(CV).The nanocomposite particles were characterized by TEM,with a tiny particle size around 10 nm with high dispersion phenomena.Further,cell cytotoxicity and the percentage cell survival were determined by using 3-(4,5-dimethylthiazol-2-yl)-5(3-carboxymethoxyphenol)-2-(4-sulfophenyl)-2H-tetra-zolium(MTS) assay on human lung MRC-5 cell line.Experimental results showed that no apparent cytotoxicity was observed when the MRC-5 was exposed to the CuO/CeO2 nanocomposite materials.     

Preparation and characterization of Ce_1-xNi_xO₂ as oxygen carrier for selective oxidation methane to syngas in absence of gaseous oxygen

A citric acid complex method was employed to prepare Ce/Ni mixed oxides with various Ce/Ni ratios useful for selective oxidation methane to syngas in the absence of gaseous oxygen,and the catalytic activity measurement was investigated in a fixed bed reactor at 800 oC.The prepared oxygen carriers were characterized by various characterization techniques such as TG-DSC,XRD and TPR.The results of TG-DSC indicated that the Ce1-xNixO2 precursor generated a stable phase after the heat-treatment at temperatures above 800 oC.The XRD characterization suggested that some Ce-Ni solid solution was formed when Ni2+ ions was incorporated into the lattice of CeO2,and it led to the generation of O-vacancy which could improve the oxygen mobility in the lattice of oxygen carriers.It was found that Ce0.8Ni0.2O2 gave the highest activity in the selective oxidation methane to syngas reaction,and the average methane conversion,CO and H2 selectivity reached to 82.31%,82.41% and 87.64%,respectively.The reason could be not only attributed to the fitting amount of NiO dispersed on the CeO2 surface and bulk but also to actual lattice oxygen amount increased in oxygen carrier.