No abstract

On the basis of an insight in surface science that Pd surfaces partially covered with oxygen adatoms (O ad ) show higher reactivity for water dissociation than clean Pd surfaces, we studied the effect of O ad on the activity of carbon-supported palladium metal nanoparticle catalysts (Pd/C) for the selective hydration of nitriles to amides in water. A series of Pd/C with the same Pd loading (5 wt %) and a similar particle size (5.3−6.5 nm) but with different surface coverage of O ad were prepared and characterized by various spectroscopic methods. The freshly H 2 -reduced Pd/C shows no catalytic activity for hydration of acetonitrile, indicating that clean Pd metal surfaces are inactive. Air exposure of this catalyst under ambient conditions results in the formation of Pd metal NPs partially covered with O ad , which act as effective and recyclable heterogeneous catalysts for selective hydration of various nitriles to the corresponding amides. Theoretical studies based on density functional theory calculations clarified a cooperative mechanism between metallic Pd and O ad , in which O ad as a Brønsted base site plays an important role in the dissociation of water via hydrogen bonding, and the mechanism is verified by kinetic results (activation energy, H 2 O/D 2 O kinetic isotope effect, Hammett slope). The mechanistic finding demonstrates a new design strategy of metal nanoparticle catalysts based on a molecular-level understanding of catalysis on oxygen-adsorbed metal surfaces.

Just add O(2): Based on the fact that an oxygen-adsorbed Pd metal surface shows higher reactivity for water dissociation than a clean Pd surface, carbon-supported Pd nanoparticles (NPs) with surface oxygen atoms were developed as a highly effective and reusable heterogeneous catalyst for selective oxidation of silanes to silanols with water as a green oxidant (see figure).

A low transformation temperature (LTT) welding consumable has been developed to prevent cold cracking in high strength steel welded joints without preheating. In the LTT welded joint, the residual tensile stress is reduced by martensitic expansion of weld metal formed by the LTT consumable. In the weld cracking tests, cold cracking in the LTT weld metal is successfully prevented under high restraint conditions, but cold cracking occurs at very low joint restraint strength in case the weld metal is fully martensitic. Chemical compositions of the consumable are designed to retain austenite in martensite in the newly developed weld metal to absorb the diffusible hydrogen into the austenite to prevent cold cracking. In the newly developed LTT weld metal, cold cracking is almost fully suppressed without preheating under every joint restraint condition.