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Despite the potential advantages of using polar aprotic solvents for biomass upgrading reactions, fundamental understanding of these solvation effects is limited at present. Here, the authors show that further increases in catalyst performance in polar aprotic solvents can be achieved through the addition of inorganic salts.

Replica molding with elastomeric polymers has been used routinely to replicate features less than 10 nm in size. Because the theoretical limit of this technique is set by polymer-surface interactions, atomic radii, and accessible volumes, replication at subnanometer length scales should be possible. Using polydimethylsiloxane to create a mold and polyurethane to form the replica, we demonstrate replication of elementary steps 3−5 Å in height that define the minimum separation between molecular layers in the lattices of the ionic crystals potassium dihydrogen phosphate and calcite. This work establishes the operation of replica molding at the molecular scale. [ABSTRACT FROM AUTHOR]

The adsorption of carbon monoxide and ethylene, and their sequential adsorption, was studied over a series of Pt/SBA-15 catalysts with monodisperse particle sizes ranging from 1.7 to 7.1 nm by diffuse-reflectance infrared spectroscopy and chemisorption. Gas adsorption was dependent on the Pt particle size, temperature, and sequence of gas exposure. Adsorption of CO at room temperature on Pt/SBA-15 gives rise to a spectroscopic feature assigned to the C−O stretch:  (CO) 2075 cm-1(1.9 nm); 2079 cm-1(2.9 nm); 2082 cm-1(3.6 nm); and 2090 cm-1(7.1 nm). The intensity of the signal decreased in a sigmoidal fashion with increasing temperature, thereby providing semiquantitative surface coverage information. Adsorption of ethylene on Pt/SBA-15 gave rise to spectroscopic features at ∼1340, ∼1420, and ∼1500 cm-1assigned to ethylidyne, di--bonded ethylene, and -bonded ethylene, respectively. The ratio of these surface species is highly dependent on the Pt particle size. At room temperature, Pt particles stabilize ethylidyne as well as di-- and -bonded ethylene; however, ethylidyne predominated on the surfaces of larger particles. Ethylidyne was the only identifiable species at 403 K, with its formation being more facile on larger particles. Co-adsorption experiments reveal that the composition of the surface layer is dependent on the order of exposure to gases. Exposure of a C2H4-covered Pt surface to CO resulted in an ∼50% decrease in chemisorbed CO compared to a fresh Pt surface. The (CO) appeared at 2050 cm-1on Pt/SBA-15 pretreated with C2H4at room temperature. The di--bonded and -bonded species are the most susceptible to displacement from the surface by CO. The formation of ethylidyne appeared to be less sensitive to the presence of adsorbed carbon monoxide, especially on larger particles. Upon exposure of C2H4to a CO-covered Pt surface, little irreversible uptake occurred due to nearly 100% site blocking. These results demonstrate that carbon monoxide competes directly with ethylene for surface sites, which will have direct implications on the poisoning of the heterogeneously catalyzed conversion of hydrocarbons. [ABSTRACT FROM AUTHOR]