Tuning interaction strength between CeO_(2) and iridium to promote CO oxidation over Ir/TiO_(2)

The interaction between support and noble metal plays a crucial role in heterogeneous catalysis design.However,how to tune metal support interactions to optimize the activity still needs further exploration.CeO_(2) was introduced to promote CO oxidation ove r Ir/TiO_(2) by adjusting the interaction strength between iridium(Ir)and CeO_(2).The strong interaction between Ir and CeO_(2) blocks CO adsorption and causes low CO oxidation activity.However,introducing CeO_(2) on Ir/TiO_(2) produces localized interaction between Ir and CeO_(2),which can tune the surface electronic state of Ir,so a"volcano curve"relationship between CO oxidation activity and electronic state is built.Limited amount of CeO_(2) on Ir/TiO_(2)(Ir/Ce_(0.2)Ti)leads to CO complete oxidization at 22℃,and a new pathway for CO oxidation was explored.The study demonstrates that the utilization of tuning interaction strength between active metal and support is a potential method to increase the catalytic activity.

Plant-pollinator interactions in a biodiverse meadow are rather stable and tight for 3 consecutive years

Plant-pollinator interactions can be highly variable across years in natural communities.Although variation in the species composition and its basic structure has been investigated to understand the dynamic nature of polli­nation networks,little is known about the temporal dynamic of interaction strength between the same plant and pollinator species in any natural community.Pollinator-mediated selection on the evolution of floral traits could be diminished if plant-pollinator interactions vary temporally.To quantify the temporal variation in plant-pol­linator interactions and the interaction strength(observed visits),we compared weighted networks between plants and pollinators in a biodiverse alpine meadow in Shangri-La,southwest China for 3 consecutive years.Although plant-pollinator interactions were highly dynamic such that identical interactions only accounted for 10.7%of the total between pair years,the diversity of interactions was stable.These identical interactions con­tributed 41.2%of total visits and were similar in strength and weighted nestedness.For plant species,72.6%of species were visited by identical pollinator species between pair years,accounting for over half of the total vis­its and three-quarters at the functional group level.More generalized pollinators contributed more connective­ness and were more central in networks across years.However,there was no similar or even opposite trend for plant species,which suggested that specialized plant species may also be central in pollinator networks.The variation in pollinator composition decreased as pollinator species numbers increased,suggesting that general­ized plants experienced stable pollinator partition.The stable,tight interactions between generalized pollinators and specialized plants represent cornerstones of the studied community.

Litter mixing significantly affects decomposition in the Hulun Buir meadow steppe of Inner Mongolia, China

Aims We explored the decomposition rates of single-and mixed-species litter,the litter-mixing effect and the effect of component litters in a mixture on decomposition.Methods In a litter bag experiment,shoot litters from two dominant grasses(Leymus chinensis and Stipa baicalensis)and one legume(Melissitus ruthenica)were decomposed separately and as a mixture from May 2010 to September 2011 in the Hulun Buir meadow steppe of Inner Mongolia,China.We separated the litter mixture into its individual component litters(i.e.the different single-species litters)and analyzed the changes in litter mass remaining and litter nitrogen(N)remaining during single-and mixed-species litter decomposition.Important Findings(i)Litter mixing had significant positive effects on litter decomposition.The litter-mixing effect was strongest for the mixture of S.baicalensis and L.chinensis litters,followed by the mixture of S.baicalensis and M.ruthenica litters.(ii)Single-species component litters decomposed faster in the mixtures than separately(positive effect),but these effects were not significant for legume species M.ruthenica litter.Relative to single-species litter decomposition,the decomposition rates of the two grass(S.baicalensis and L.chinensis)litters significantly increased when they were mixed with each other or with M.ruthenica litter.(iii)For each species litter type,the percentage of litter N remaining during decomposition(NR)differed between the single-species litter and mixed litter treatments.The NR of S.baicalensis litter was higher when it was decomposed in the mixture than in isolation.However,the NR of L.chinensis litter was lowest in its mixture with M.ruthenica among the treatments.Regardless of its decomposition in the mixture or in isolation,the NR of M.ruthenica litter varied little among treatments.There was a significant positive relationship between the NR and percentage of initial litter mass remaining in both the single litter and mixed litter treatments.These results suggest that N transfer may happen among component litters in mixture and further affect the decomposition.