Dispersion and support dictated properties and activities of Pt/metal oxide catalysts in heterogeneous CO oxidation

The source of activity of metal/metal oxides has always been an interesting,important but highly challenging research topic in heterogeneous catalysis.In CO oxidation reaction,this work clarifies dispersion and support dictated activities of Pt including single-atom(Pt1),2.8 nm(PtNP-S)and 36 nm(PtNP-L)Pt supported on both reducible TiO_(2) and“inert”Al_(2)O_(3) supports.The X-ray absorption fine structure(XAFS)shows that chemical state of Pt is affected by both dispersion and support:Pt1 presents fully oxidized state in both Pt1/TiO_(2) and Pt1/Al_(2)O_(3);PtNP-S in PtNP-S/TiO_(2) appear nearly oxidized state while about half of Pt is metallic state in PtNP-S/Al_(2)O_(3);PtNP-L in both PtNP-L/TiO_(2) and PtNP-L/Al_(2)O_(3) exhibit metallic state.All the Pt species supported on TiO_(2) present much lower apparent activation barriers(Eapp)than that on Al_(2)O_(3).Moreover,Pt1/TiO_(2) possesses dozen times of efficiency than PtNP-S/TiO_(2) although they have similar Eapp values.A truth is finally made clear that a reducible metal oxide with low oxygen vacancy formation energy is critical to endow Pt/metal oxide a high activity and the single-atom dispersion of Pt is the way to maximize the active sites of Pt/metal oxide.

Organophosphate esters in water,suspended particulate matter(SPM)and sediments of the Minjiang River,China

As organic pollutants of emerging concern,organophosphate esters(OPEs)have shown toxicity to organisms after entering the water environment.However,research on OPEs in freshwater in Southwest China is very limited.The levels,distribution and partitioning behavior of OPEs in the Minjiang River and their influencing factors is still unknown.In this study,six OPEs,tri-n-butyl phosphate(Tn BP),tri(2-chloroethyl)-phosphate(TCEP),trichloropropyl phosphate(TCPP),triphenyl phosphate(TPh P),tributoxyethyl phosphate(TBEP),and tris(2-ethylhexyl)-phosphate(TEHP),were determined in surface water,suspended particle matter(SPM)and sediments of the Minjiang River.The results showed that the average concentrations of∑_(6)OPEs in surface water,SPM and sediments of the Minjiang River were 199.32±124.95 ng/L,38463.79±45641.89 ng/g dry weight(dw)and 76.45±28.00 ng/g dw,respectively.High concentrations of OPEs were detected in SPM samples,indicating that more attention should be paid to pollution in SPM.It is worth noting that the variation trend of OPEs in SPM was almost opposite to that in water but basically similar to that in sediment.The proportions of alkyl OPEs in∑_(6)OPEs increased from surface water to SPM and sediments.Alkyl OPEs were the main pollutants in SPM(10.44%–80.88%of∑_(6)OPEs,mean of 54.52%)and sediments(59.08%–81.30%of∑_(6)OPEs,mean of 68.91%),whereas chlorinated OPEs were the most abundant components in surface water(43.16%–75.99%ofδ∑_(6)OPEs,mean of 55.50%).The water-sediment partition coefficient(logKOC)of OPEs was 4.97–7.58,while the water-SPM partition coefficient was 6.71–10.00.No significant correlations were found between log KOW and logKOC.KOW was not the main factor affecting the distribution of OPEs in the Minjiang River,China.