Supported Gold Nanoparticles for Alcohols Oxidation in Continuous-Flow Heterogeneous Systems

Abstract

Gold nanoparticles (AuNPs) were anchored on alkynyl carbamate-functionalized support materials having the suitable features for application as catalysts in continuous-flow packed bed reactors. The functionalization step was carried out by grafting with the di-functional organosilane [3-(2-propynylcarbamate)propyl]triethoxysilane (PPTEOS) three commercial micrometer-sized oxide supports, i.e. silica, alumina, and titania. The alkynyl-carbamate moieties were capable to straightforwardly reduce the gold precursor HAuCl4 yielding the supported AuNPs systems Au/SiO2@Yne, Au/Al2O3@Yne, and Au/TiO2@Yne. A comparison among the three materials revealed that silica allowed the highest organic functionalization (12 wt%) as well as the highest gold loading (3.7 wt%). Moreover, TEM investigation showed only for Au/SiO2@Yne the presence of homogeneously distributed, spherically shaped AuNPs (av. diameter 15 nm). Au/SiO2@Yne is an efficient catalyst, both in batch and flow conditions, in the oxidation of a large variety of alcohols, using H2O2 as oxidizing agent, at a temperature of 90 °C. Furthermore, under flow conditions, the catalyst worked for over 50 h without any significant decrease in the catalytic activity. The catalytic activity of the three catalysts was evaluated and compared in the oxidation of 1-phenylethanol as a model substrate. We found that the flow approach plays a strategic role in preserving the physical and chemical integrity of the solid catalysts during its use, with remarkable consequences for the reaction conversion (from 2% in batch to 80 % in flow) in the case of Au/TiO2@Yne

Fe@Hierarchical BEA Zeolite Catalyst for MW-Assisted Alcohol Oxidation Reaction: A Greener Approach

“…Moreover, this simple catalytic system using only 0.1% mol of catalyst when compared to the substrate, could provide high TON values (up to ca. 600) comparing favorably to other systems reported in the literature [21][22][23][24][25].…”

“…Moreover, this simple catalytic system using only 0.1% mol of catalyst when compared to the substrate, could provide high TON values (up to ca. 600) comparing favorably to other systems reported in the literature [21][22][23][24][25]. The enhanced catalytic activity of Fe immobilized hierarchical zeolites over their parent zeolites could be related to their textural characteristics that can impose more or less important diffusional constrains to 1-phenylethanol to access the active sites.…”

Recent Progress in Catalytic Oxidative Transformations of Alcohols by Supported Gold Nanoparticles

“…At the same time, the Nanni group reported the synthesis of Au NP systems based on alkynyl carbamate‐modified commercial micrometer‐sized oxide supports (abbreviated OS), i.e., silica, alumina and titania . Among them, Au/SiO 2 @Yne was selected as catalyst for the aerobic oxidation of various alcohols under both batch and flow conditions, which showed a great potential value for industrial applications.…”

Iron(III) Amine Bis(phenolate) Complex Immobilized on Silica‐Coated Magnetic Nanoparticles: A Highly Efficient Catalyst for the Oxidation of Alcohols and Sulfides

“…In the past decade, the oxidation of alcohols by metal complexes and metal nanoparticles as homogeneous or heterogeneous catalysts in the presence of green oxidants such as O 2 , tert ‐butyl hydroperoxide (TBHP), and H 2 O 2 have been investigated widely. Notably, precious metals such as Pt, Au, Pd, and Ru are the most frequently used metals in catalytic systems for the oxidation of alcohols to acids, and reports related to earth‐abundant metal complexes for this purpose are rare . Accordingly, heterogeneous catalysts that contain Fe complexes can be very economical and environmentally friendly.…”

“…[6] The oxidationo fa lcohols to carboxylic acids and ketones is af undamental class of organict ransformation that has great potentialf or biological systems as well as industrial processes. In the past decade, the oxidation of alcohols by metal complexesa nd metal nanoparticlesa sh omogeneous or heterogeneous catalysts in the presence of green oxidants such as O 2 , [7] tert-butyl hydroperoxide (TBHP), [8] and H 2 O 2 [9] have been investigated widely.N otably,p recious metals such as Pt, [10] Au, [11] We aimed to immobilize ac omplexo fi ron(III) amine bis(phenolate)o ns ilica-coated magneticn anoparticles as an ew magnetically recoverable catalyst (Fe 3 O 4 @SiO 2 -APTES-FeL GDC ). Both the chemical nature and the structure of catalystw erec onfirmed by using field-emission transmission electron microscopy,f ield-emission scanning electron microscopy,F TIR spectroscopy,t hermogravimetric analysis, vibrating sample magnetometry,X -ray photoelectrons pectroscopy,X RD, atomic absorption spectroscopy,a nd elemental analysis.…”