Silver/hydroxyapatite foam as a highly selective catalyst for acetaldehyde production via ethanol oxidation

In this study, highly dispersed sliver (Ag) nanoparticles supported on a hydroxyapatite showed a surprisingly high activity (1.38 s(-1) in turnover frequency (TOF)), selectivity (similar to 100%) and durability (similar to 100 h) for the oxidative dehydrogenation of ethanol to acetaldehyde. The structure of Ag nanoparticles is characterized using transmission electron microscopy (TEM), X-Ray Diffraction (XRD), in-situ and ex-situ X-ray photoelectron spectroscopy (XPS) and temperature-programmed surface reaction (TPSR). Density Functional Theory (DFT) calculations on Ag(1 1 1) were performed to understand the mechanism of catalytic reactions at a molecular level. The calculation results revealed that the barrier for the formation of acetaldehyde is 38.6 kJ/mol, and 126.4 kJ/mol for CO2 formation, thus leading to high selectivity to acetaldehyde. By combination of DFT calculation and experimental work, it can be concluded that ethanol oxidation predominantly took place on the terrace surface although step surface are more active. This study provides a methodology to develop completely selective practical catalysts especially for the utilization of biomass. (C) 2016 Elsevier B.V. All rights reserved.