Oxidation of benzyl alcohol by using gold nanoparticles supported on ceria foam

The efficacy of using cerium oxide foams as a support for Au nanoparticles and subsequent use as oxidation catalysts have been investigated. These were synthesized using L-asparagine to produce a cerium coordination polymer foam, which was calcined to give the oxide foam. Au nanoparticles were supported on the CeO(2) foams using a sol-immobilization method. The activity of the Au/foamCeO(2) for solvent-free benzyl alcohol oxidation was superior to standard Au/CeO(2) catalysts, and the activity was found to be dependent on the crystallization time of the precursor foam. A crystallization time of 4 h was found to produce the most active catalyst, which retained activity and a high selectivity to benzaldehyde (ca. 96 %) when re-used and this is related to the structure of the material. The high activity is attributed to the greater lability of surface oxygen in the support compared with commercial CeO(2) materials.

Photosynthetic pathway and ecological adaptation explain stomatal trait diversity amongst grasses

• The evolution of C(4) photosynthesis in plants has allowed the maintenance of high CO(2) assimilation rates despite lower stomatal conductances. This underpins the greater water-use efficiency in C(4) species and their tendency to occupy drier, more seasonal environments than their C(3) relatives. • The basis of interspecific variation in maximum stomatal conductance to water (g(max) ), as defined by stomatal density and size, was investigated in a common-environment screening experiment. Stomatal traits were measured in 28 species from seven grass lineages, and comparative methods were used to test for predicted effects of C(3) and C(4) photosynthesis, annual precipitation and habitat wetness on g(max) . • Novel results were as follows: significant phylogenetic patterns exist in g(max) and its determinants, stomatal size and stomatal density; C(4) species consistently have lower g(max) than their C(3) relatives, associated with a shift towards smaller stomata at a given density. A direct relationship between g(max) and precipitation was not supported. However, we confirmed associations between C(4) photosynthesis and lower precipitation, and showed steeper stomatal size-density relationships and higher g(max) in wetter habitats. • The observed relationships between stomatal patterning, photosynthetic pathway and habitat provide a clear example of the interplay between anatomical traits, physiological innovation and ecological adaptation in plants.

Deep oxidation of pollutants using gold deposited on a high surface area cobalt oxide prepared by a nanocasting route

Gold deposited on a cobalt oxide with high surface area (138 m(2)g(-1)), obtained through a nanocasting route using a siliceous KIT-6 mesoporous material as a hard template, has demonstrated high activity for the total oxidation of propane and toluene, and ambient temperature CO oxidation. The addition of gold promotes the activity when compared to a gold-free Co(3)O(4) catalyst prepared using the same nanocasting technique. The enhanced catalytic activity when gold is present has been explained for the deep oxidation of propane and toluene in terms of the improved reducibility of cobalt oxide when gold is added, rather than to the intrinsic activity of metallic gold particles. The improved behaviour for CO oxidation has been linked to the simultaneous presence of Au(δ+) and Au°.

The decomposition of H 2 O 2 over the components of Au/TiO 2 catalysts

Hydrogen peroxide is an important oxidant that is increasingly being employed in selective oxidation reactions over support metal catalysts. We present a density functional theory study of the adsorption of H 2 O 2 to the components of a model Au/TiO 2 system based on Au 10 nanoclusters and the rutile TiO 2 (110) surface. We find that H 2 O 2 decomposes easily to 2OH on the metal nanoparticles while the interaction with surface hydroxyls on TiO 2 (110) gives a low barrier to a surface OOH species. This work suggests that the production of H 2 O 2 takes place at the interface between the particle and oxide and we further show how this interface region is influenced by the hydroxylation of the surface.

Drought limitation of photosynthesis differs between C₃and C₄grass species in a comparative experiment

Phylogenetic analyses show that C₄ grasses typically occupy drier habitats than their C₃ relatives, but recent experiments comparing the physiology of closely related C₃ and C₄ species have shown that advantages of C₄ photosynthesis can be lost under drought. We tested the generality of these paradoxical findings in grass species representing the known evolutionary diversity of C₄ NADP-me and C₃ photosynthetic types. Our experiment investigated the effects of drought on leaf photosynthesis, water potential, nitrogen, chlorophyll content and mortality. C₄ grasses in control treatments were characterized by higher CO₂ assimilation rates and water potential, but lower stomatal conductance and nitrogen content. Under drought, stomatal conductance declined more dramatically in C₃ than C₄ species, and photosynthetic water-use and nitrogen-use efficiency advantages held by C₄ species under control conditions were each diminished by 40%. Leaf mortality was slightly higher in C₄ than C₃ grasses, but leaf condition under drought otherwise showed no dependence on photosynthetic-type. This phylogenetically controlled experiment suggested that a drought-induced reduction in the photosynthetic performance advantages of C₄ NADP-me relative to C₃ grasses is a general phenomenon.

CO bond cleavage on supported nano-gold during low temperature oxidation

The oxidation of CO by Au/Fe(2)O(3) and Au/ZnO catalysts is compared in the very early stages of the reaction using a temporal analysis of products (TAP) reactor. For Au/Fe(2)O(3) pre-dosing the catalyst with (18)O labelled water gives an unexpected evolution order for the labelled CO(2) product with the C(18)O(2) emerging first, whereas no temporal differentiation is found for Au/ZnO. High pressure XPS experiments are then used to show that CO bond cleavage does occur for model catalysts consisting of Au particles deposited on iron oxide films but not when deposited on ZnO films. DFT calculations, show that this observation requires carbon monoxide to dissociate in such a way that cleavage of the CO bond occurs along with dynamically co-adsorbed oxygen so that the overall process of Au oxidation and CO dissociation is energetically favourable. Our results show that for Au/Fe(2)O(3) there is a pathway for CO oxidation that involves atomic C and O surface species which operates along side the bicarbonate mechanism that is widely discussed in the literature. However, this minor pathway is absent for Au/ZnO.