Lehigh University

About: Lehigh University is a education organization based out in Bethlehem, Pennsylvania, United States. It is known for research contribution in the topics: Catalysis & Fracture mechanics. The organization has 12684 authors who have published 26550 publications receiving 770061 citations.

Strategies for designing supported gold-palladium bimetallic catalysts for the direct synthesis of hydrogen peroxide.

Abstract: Hydrogen peroxide is a widely used chemical but is not very efficient to make in smaller than industrial scale. It is an important commodity chemical used for bleaching, disinfection, and chemical manufacture. At present, manufacturers use an indirect process in which anthraquinones are sequentially hydrogenated and oxidized in a manner that hydrogen and oxygen are never mixed. However, this process is only economic at a very large scale producing a concentrated product. For many years, the identification of a direct process has been a research goal because it could operate at the point of need, producing hydrogen peroxide at the required concentration for its applications. Research on this topic has been ongoing for about 100 years.

Beneficial and detrimental effects of uv on aquatic organisms: implications of spectral variation

Abstract: Solar ultraviolet radiation (UVR) may have beneficial as well as detrimental effects on living systems. For example, UV-B radiation (280-320 nm) is generally dam- aging, while UV-A radiation (320-400 nm) may cause damage or stimulate beneficial photorepair of UV-B damage. The nature of both direct and indirect effects of UVR in nature depends on both the photon flux density and the spectral composition of the radiation incident on aquatic organisms across environmental UVR gradients in space (depth, trans- parency, elevation) and time (diel, seasonal, interannual). Here we use the common and widespread freshwater cladoceran Daphnia pulicaria as a model organism to demonstrate the potential importance of these wavelength-specific effects of UVR to the ecology of aquatic organisms. UVR-exposure experiments are used to manipulate both natural solar and artificial UVR sources to examine the beneficial as well as detrimental effects of different wavelengths of UVR. Changes in the spectral composition of solar radiation are also examined along several natural environmental gradients including diel gradients, depth gradients, and dissolved organic carbon (DOC) gradients. The implications of variation in the spectral composition of UVR for aquatic organisms are discussed. The first biological weighting function (BWF) for a freshwater cladoceran is presented here. It demonstrates that the shortest UV-B wavelengths in sunlight are potentially the most damaging per photon. However, due to the greater photon flux density of longer wavelength UVR in sunlight, the net potential damage to Daphnia in nature is greatest for the longer wavelength UV-B and shorter wavelength UV-A radiation in the 305-322 nm range. Overall the contribution of UV-B to the total mortality response of Daphnia exposed to full-spectrum solar radiation for 7 h on a sunny summer day is 64% while UV-A con- tributes 36%. The BWF for Daphnia is used with the transmission spectrum for Mylar D to demonstrate that Mylar D cuts out only about half of the damaging UVR in sunlight. Following exposure to damaging UV-B, Daphnia exhibits a dramatic increase in survival in the presence of longer wavelength UV-A and visible radiation due to the stimulation of photoenzymatic repair. We present data that demonstrate the importance of both atmospheric ozone and DOC in creating strong environmental gradients in the intensity (irradiance) and spectral composition of solar UVR in nature. The light-absorbing component of DOC, chromophoric dissolved organic matter (CDOM), is particularly important in creating depth refugia from damaging UV-B in freshwater ecosystems. CDOM may also cause intense variations in the ratio of potentially beneficial UV-A to detrimental UV-B radiation to which aquatic organisms are exposed. In addition to changes in atmospheric ozone, future changes in CDOM related to climate change or other environmental disturbances may substantially alter the underwater exposure of a variety of aquatic organisms to different wavelengths of solar UVR.

In Situ Raman Spectroscopy of SiO2-Supported Transition Metal Oxide Catalysts: An Isotopic 18O−16O Exchange Study

Abstract: The molecular structures of dehydrated group 5−7 transition metal oxides (V2O5, Nb2O5, CrO3, MoO3, WO3, Re2O7) supported on SiO2 were investigated with time-resolved 18O−16O exchange in situ Raman spectroscopy measurements. The supported group 5−7 dehydrated surface transition metal oxides were exclusively present as isolated species on SiO2 because of the absence of bridging M−O−M vibrations. The SiO2-supported group 5 (VOx and NbOx) surface metal oxides exhibit band splitting into two Raman vibrations (M16O and M18O), which is consistent with monoxo surface OM(−O−Si)3 species. The SiO2-supported group 6 (CrOx, MoOx, and WOx) surface metal oxides consist of both monoxo OM(−O−Si)4 and dioxo (O)2M(−O−Si)2 structures. The dioxo surface species give rise to triplet band splitting corresponding to M(16O)2, M(18O)2, and 18OM16O. Identification of the intermediate surface 18OM16O struc-ture was guided by recent DFT calculations. The SiO2-supported group 7 (ReOx) metal oxide system exclusively contains trioxo su...