Preparation of Silver-Palladium Alloyed Nanoparticles for Plasmonic Catalysis under Visible-Light Illumination.

Localized surface plasmon resonance (LSPR) in plasmonic nanoparticles (NPs) can accelerate and control the selectivity of a variety of molecular transformations. This opens possibilities for the use of visible or near-IR light as a sustainable input to drive and control reactions when plasmonic nanoparticles supporting LSPR excitation in these ranges are employed as catalysts. Unfortunately, this is not the case for several catalytic metals such as palladium (Pd). One strategy to overcome this limitation is to employ bimetallic NPs containing plasmonic and catalytic metals. In this case, the LSPR excitation in the plasmonic metal can contribute to accelerate and control transformations driven by the catalytic component. The method reported herein focuses on the synthesis of bimetallic silver-palladium (Ag-Pd) NPs supported on ZrO2 (Ag-Pd/ZrO2) that acts as a plasmonic-catalytic system. The NPs were prepared by co-impregnation of corresponding metal precursors on the ZrO2 support followed by simultaneous reduction leading to the formation of bimetallic NPs directly on the ZrO2 support. The Ag-Pd/ZrO2 NPs were then used as plasmonic catalysts for the reduction of nitrobenzene under 425 nm illumination by LED lamps. Using gas chromatography (GC), the conversion and selectivity of the reduction reaction under the dark and light irradiation conditions can be monitored, demonstrating the enhanced catalytic performance and control over selectivity under LSPR excitation after alloying non-plasmonic Pd with plasmonic metal Ag. This technique can be adapted to a wide range of molecular transformations and NPs compositions, making it useful for the characterization of the plasmonic catalytic activity of different types of catalysis in terms of conversion and selectivity.

Reaction mechanism studies on atomic layer deposition of Nb2O5 from Nb(OEt)5 and water.

The reaction mechanism in the atomic layer deposition of Nb(2)O(5) from Nb(OEt)(5) and deuterated water was studied in situ with a quadrupole mass spectrometer (QMS) and a quartz crystal microbalance (QCM). The responses of these in situ measurement techniques to the characteristics of the ALD processes were thoroughly clarified and the process parameters carefully optimized. Also the effect of the reaction temperature on the extent of decomposition reactions of Nb(OEt)(5) interfering with the ALD process was investigated. Decomposition did occur at 400 degrees C but not at temperatures of 350 degrees C and below. Also the reaction mechanism was studied as a function of reaction temperature and found to be about the same until decomposition of the precursor started. Deuterated ethanol was found to be the most important gaseous byproduct of the ALD process but also some diethyl ether apparently formed. About one of the five ethoxide ligands of Nb(OEt)(5) was released during the Nb(OEt)(5) pulse and the rest during the D(2)O pulse. Finally separate experiments were performed to study the adsorption of ethanol as well as 2-propanol on the surface of Nb(2)O(5). Ethanol was found to adsorb. It could also be stated that water can replace the adsorbed ethanol. On the other hand 2-propanol apparently did not adsorb on the surface of Nb(2)O(5).