Green Oxidation of n‐Octanol on Supported Nanogold Catalysts: Formation of Gold Active Sites under Combined Effect of Gold Content, Additive Nature and Redox Pretreatment

Abstract

What prompted you to investigate this topic?The selective oxidation of alcohols to yield valuable chemical products is very important in fine organic synthesisa nd has great industrial importance.T he traditional oxidation processes use strong oxidants, which increaset he cost of the reaction and produce al arge amount of toxic waste. Thus, there is the need for more beneficiala nd sustainable technologies, using renewable feedstocks, like biomass, replacing fossil resources. Supported gold catalysts show remarkable activity for the oxidation of alcohols from biomass conversionp roducts in the liquid phase, with high activity,h igh selectivity and betterr esistancet od eactivation, compared to traditional platinum group metals.T he activity of gold catalysts is strongly dependent on many factors, and still requires further study. What inspired you for the cover image?The reaction of 1-octanol, representative of the class of less reactive aliphatic alcohols,f ound in large quantities in the products of biomass transformation,i sp resented. According to our research, the aerobic oxidation of this alcohol into valuable chemical, pharmaceutical and agrochemical products using gold supported catalysts occurs predominantly on cationic gold.

Supported Gold Nanoparticles as Catalysts in Peroxidative and Aerobic Oxidation of 1-Phenylethanol under Mild Conditions

“…Thus, the catalytic activity in the aerobic oxidation of 1-phenylethanol of the remaining catalysts was studied with R = 100. As it can be seen in Table 5, catalysts with a low gold content with an oxidative pretreatment were the most active, as in the case of 1-octanol ( Figure 1b,e,f) [39].…”

“…Catalysts were previously characterized by adsorption of N 2 at −196 • C on a Micromeritics Tristar 3000 Apparatus, Micromeritics Instrument Corporation (Norcross, GA, USA), X-ray diffraction (XRD) on a Philips XPert PRO diffractometer (Amsterdam, Netherlands), X-ray photoelectron spectroscopy (XPS), on a ESCALAB 200A, VG Scientific (Waltham, MA, USA), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), as well as scanning transmission electron microscopy-high angle annular dark field (STEM-HAADF) using one single microscope (JEOL JEM-2100F, JEOL Ltd., Tokyo, Japan), temperature programmed reduction (H 2 -TPR) on a ChemiSorb 2750, (Micromeritics Instrument Corporation, Norcross, GA, USA) [38,39,42], and diffuse reflectance Fourier transform infrared (DRIFT) spectra of adsorbed CO [43] on a Bruker EQUINOX 55/S FTIR spectrometer (Billerica, MA, USA).…”

“…The most active catalysts were those with low Au loading, after an oxidative pretreatment. Regarding selectivity, it is important to note that when using molecular oxygen as an oxidizing agent, a different behaviour is observed in the distribution of oxidation products, depending on the pretreatment, the nature of the support and the gold content [39]. However, when TBHP was used as oxidizing agent, in the absence of a solvent, the main product, in all cases, was acid with a small amount of ester (up to 20%).…”

“…Taking into account the high alcohol/gold ratio, the catalysts, even in the as-prepared state, reached more than 50% of acetophenone yield after 6 h of reaction, despite the low activity in the first hours (Scheme 1). As in the oxidation of 1-octanol [38,39], the sample modified with lanthanum oxide demonstrated the best catalytic performance (Table 2): 98% yield of acetophenone was achieved already in 1 h when 4% Au/La 2 O 3 /TiO 2 pretreated in H 2 was used. It should also be noted that the activity of the studied catalysts increased with increasing gold content.…”

“…Previously, in a series of our works [36][37][38][39], it was shown that 1-octanol, a representative of the less reactive alcohols, whose physical properties impose constraints to implementation of green chemistry approaches, could be effectively oxidized under mild conditions and using Au/(Me x O y )/TiO 2 catalysts. It was found that the formation of an active surface responsible for the catalytic properties is strictly dependent on the modifying additives used for improving metal-support interaction, a way to transform and stabilize positively charged gold active sites.…”