Sonogashira coupling reaction over supported gold nanoparticles: Influence of support and catalyst synthesis route
Summary, in English
This study investigates the impact of supports and synthesis routes on the performance of supported gold nanoparticles in the Sonogashira coupling reaction. The catalysts were synthesized by deposition-precipitation (DP) and incipient wetness impregnation (IMP), employing carriers of different nature (redox: CeO2, TiO2, and non-redox: Al2O3) and were characterized by various physical techniques such as X-ray fluorescence, powder X-ray diffraction, X-ray photoelectron spectroscopy, N-2 sorption, and high resolution. transmission electron microscopy. It is revealed that gold is present in the metallic state in all of the samples, independent of the nature of the support and the way of synthesis. The DP technique gave catalysts with smaller gold particles (4-14 nm), while the IMP route led to agglomeration due to presence of chlorine and resulted in distinctly larger gold particles (50-100 nm) on the supports. The evaluation of catalysts in the Sonogashira coupling of phenylacetylene and iodobenzene demonstrated that the catalysts' performance is negligibly dependent on the specific surface area of the catalysts. Synthesis paths, however, greatly affected the catalysts' activity and selectivity. All the catalysts prepared by DP gave significantly higher conversion of iodobenzene and selectivity to diphenylacetylene (desired hetero-coupled product) than their analogs prepared by IMP. This is shown to be related to the superior dispersion achieved by the DP route with the formation of smaller Au nanoparticle, which are highly active and selective. Thus, the present study explicitly establishes that the choice of proper synthesis method is vital to achieve sufficiently small nanoparticles leading to the best Sonogashira performance. Also, redox active oxide supports lead to a better performance than non-redox carriers. Despite significant leaching, the catalysis is shown to be heterogeneous. (C) 2015 Elsevier B.V. All rights reserved.