Influence of cobalt on performance of Cu-CeO2 catalysts for preferential oxidation of CO

Copper and cobalt oxides supported on CeO2 were investigated for preferential oxidation of carbon monoxide(CO-PROX)in the presence of excess hydrogen and CO2.(Cuo)1-x(Co3 O4)x/3-(CeO2)2.5(x=0,0.25,0.50,0.75,0.85 and 1)catalysts were prepared by coprecipitation method.These mixed oxide catalysts were characterized by several physicochemical techniques,such as BET surface area(SBET),X-ray diffraction(XRD),high resolution transmission electron microscopy(HRTEM),temperature programmed reduction(TPR)and X-ray photoelectron spectroscopy(XPS).XRD studies show the peaks related to CuO and Co3 O4 phases in copper and cobalt containing CeO2 catalysts.The average particle size of the CeO2 crystallites is in the range of 8-10 nm as evaluated from HRTEM studies.XPS studies demonstrate that Cu,Co and Ce in(cuO)1-x(Co3O4)x/3-(CeO2)2.5 catalysts are presented in+2 and+1,+3 and+2 and+4 and+3 oxidation states,respectively.The catalyst with x=0.75 shows better activity and selectivity towards CO-PROX.Though the catalyst with only copper(CuO-CeO2,x=0)shows good activity but reverse water gas shift(RWGS)reaction is noticed at high temperature.On the other hand,RWGS reaction is suppressed on the cobalt containing CuO-ceO2 catalyst.Cobalt on CeO2 with x=1 shows hardly any activity for PRoX reaction at low temperatures.No methanation activity is observed on CuO-CeO2 or Co3O4-CeO2 catalysts.In contrast,combination of copper and cobalt on CeO2 shows methanation of CO where enhanced activity is observed with increasing in cobalt content.

LaNiO_(3)/g-C_(3)N_(4) nanocomposite:An efficient Z-scheme photocatalyst for wastewater treatment using direct sunlight

The major findings in this report are(ⅰ)development of nanocomposite photocatalyst working through Z-scheme charge transfer pathway across the heterojunction,(ⅱ)utilization of direct sunlight as the photo-source,and(ⅲ)prospect of ligand-hole in photocatalysis through enhanced sub-band gap absorption,The photocatalysts,namely LaNiO_(3),g-C_(3)N_(4) and LaNiO_(3)/g-C_(3)N_(4) nanocomposites were synthesized via facile route and were characterized for their structure,morphology,microstructure,texture,elemental mapping and surface oxidation states by using several physicochemical techniques.The photocatalytic performance of the nanocomposite was tested through the degradation of hazardous azo dye pollutants,namely reactive black 5 and methylene blue as well as the colorless antibiotic-pollutant tetracycline hydrochloride in aqueous solution in presence of natural sunlight with excellent recycling activity.The 10%LaNiO_(3)/g-C_(3)N_(4) nanocomposite sample shows the best catalytic activity,degrading respectively 94%,98.6%and 88.1%of reactive black 5,methylene blue and tetracycline hydrochloride in60,180 and 120 min.The photocatalytic activity of the nanocomposite phase is several times superior to that of the pure phases.The improvements of photocatalytic activity of g-C_(3)N_(4) in the nanocomposite have been rationalized through the construction of direct Z-scheme heterojunction and suppression of electron-hole pair recombination efficiency.The enhanced photo-absorption of the nanocomposite can possibly be related to sub-bandgap absorption,which is associated to the midgap state originating from ligand-hole formation or defects in the structure.The photodegradation process is mediated through the formation of super oxide radical(O_(2))and hole(h^(+))as the main responsible species.