Supported Mono- and Bimetallic Gold Nanoparticle Catalysts for Different Organic Transformations

Abstract

Supported gold nanoparticles are emerging as an important class of catalysts for various organic transformations due to their tunable properties. This thesis embraces the fundamental studies of supported gold nanoparticles for different organic reactions from the viewpoint of understanding the role of synthesis methods, nature of carriers, and addition of second metal on the properties and functions of gold catalysts. The catalysts are synthesised by different routes, namely: deposition-precipitation, incipient wetness impregnation, and sol-immobilisation, and characterised ex situ by techniques such as X-ray fluorescence, N2 sorption, powder X-ray diffraction, X-ray photoelectron spectroscopy, and various types of electron microscopy. The reactions investigated include: (i) Sonogashira coupling, which is a unique method for the cross coupling between sp and sp2 or sp3 carbon atoms;
(ii) epoxidation of styrene to styrene oxide; (iii) oxidation of ethylbenzene to acetophenone; and (iv) oxidative cross coupling of non-activated arenes. All these transformations lead to important intermediates which have numerous applications in polymer, perfume and/or pharmaceutical industries. In Sonogashira coupling of phenylacetylene and iodobenzene over Au/CeO2, Au/TiO2, and Au/Al2O3 catalysts, impact of synthesis routes, nature of support and Au particle size was studied. It is found that the catalysts prepared by deposition-precipitation lead to higher activity than their analogues obtained by incipient impregnation method due to a better dispersion and smaller size (4-15 nm) of gold particles on the former than the latter. In addition, redox (CeO2, TiO2) supports are more active than non-redox (Al2O3) carrier. Evaluation of gold nanoparticles supported on mesoporous materials (MCM-41, SBA-15, KIT-6 and fumed SiO2) in styrene epoxidation demonstrates Au/MCM-41 as the best system, due to its smallest Au size (ca. 3 nm), leading to full styrene conversion in 10 h with 96% styrene oxide selectivity. This is the best performance reported for these types of catalysts to date. Still, the attainment of full selectivity was not possible by above systems and thus the bimetallic Au-Pd nanoalloy supported in TiO2 was investigated in styrene oxidation, which enables full conversion with 99% selectivity to styrene oxide in 12 h due to electronic interactions between Au and Pd. This study marks the first application of Au-Pd in styrene epoxidation. Besides, the Au-Pd/TiO2 catalyst also shows good activity in ethylbenzene oxidation. Oxidative cross coupling of bromoanisole with benzene is studied over Au/ZrO2, Au/TiO2, and Au/Al2O3, where the former leads to the best productivity of cross coupled product due to the combination of smaller gold nanoparticles and redox nature of support. Overall, these studies suggest that the attainment of superior performance on supported gold nanoparticle catalysts relies on the appropriate choice of support, catalyst preparation route, and/or addition of second metal that could interact with
gold.

Abstract (Swedish)

“Catalysis” is a field of science that relates to the increase of the rate of a chemical
reaction through the involvement of an additional substance, known as “catalyst”,
which acts without being consumed. Among all known types, heterogeneous catalysis, where the catalyst is in different phase than the reactants, plays a pivotal role in the sustainable development of the modern society with its dominance through catalysing more than 80% of industrial chemical processes.
Recently, “supported gold nanoparticles”, inorganic composite materials in which
nano-sized gold particles are carried on solid carriers such as metal oxides, have
emerged as an important class of catalysts enabling to attain superior selectivities
and yields of the desired products compared to previously known systems. One of
the key features of gold catalysts involve its adaptable properties, tuned through
the application of modern synthesis tools, carriers of different natures, and/or
combining gold with other metals, making them suitable to catalyse a number of
important organic reactions.
In this thesis, supported gold nanoparticle catalysts are investigated for organic
reactions, viz. Sonogashira cross coupling, styrene oxidation, ethylbenzene
oxidation, and oxidative cross coupling, which are useful in pharmaceutical,
perfume, polymer, and cosmetics industries. Through the precision synthesis,
advanced characterisation, and catalytic evaluations, synthesis-structure-activity
relationships are established, which helped to develop a fundamental understanding of gold catalysis in these reactions and enabled to design superior gold-based catalysts leading to better performance than those reported previously.

• author: Sisodiya, Sheetal
• supervisor: Ola Wendt; Joachim Schnadt
• opponent: Associate Professor Mossin, Susanne, DTU Technical University of Denmark, Kgs. Lyngby, Denmark
• organization: Centre for Analysis and Synthesis
• publishing date: 2017-05
• type: Thesis
• publication status: published
• subject: Natural Sciences
• keywords: Gold nanoparticles, coupling reaction, styrene epoxidation, bimetallic nanoparticle, supported gold nanoparticle
• pages: 156 pages
• defense location: Lecture hall F, Center for chemistry and chemical engineering, Naturvetarvägen 14, Lund
• defense date: 2017-06-15 09:15:00
• ISBN: 978-91-7422-533-4
• ISBN: 978-91-7422-534-1
• language: English
• LU publication?: yes
• id: c25319ec-d5a2-49a7-997b-b3b06a8ec9de
• date added to LUP: 2017-05-19 10:39:45
• date last changed: 2018-11-21 21:32:09