Solvent-Free Oxidation of Primary Alcohols to Aldehydes Using Au-Pd/TiO ₂ Catalysts

Abstract

The oxidation of alcohols to aldehydes with O2 in place of stoichiometric oxygen donors is a crucial process for the synthesis of fine chemicals. However, the catalysts that have been identified so far are relatively inactive with primary alkyl alcohols. We showed that Au/Pd-TiO2 catalysts give very high turnover frequencies (up to 270,000 turnovers per hour) for the oxidation of alcohols, including primary alkyl alcohols. The addition of Au to Pd nanocrystals improved the overall selectivity and, using scanning transmission electron microscopy combined with x-ray photoelectron spectroscopy, we showed that the Au-Pd nanocrystals were made up of a Au-rich core with a Pd-rich shell, indicating that the Au electronically influences the catalytic properties of Pd.

Solvent-free aerobic oxidation of hydrocarbons and alcohols with Pd@N-doped carbon from glucose

“…The TOF values became roughly constant in the range of 0.1-1 MPa O 2 , revealing that oxygen pressure does not affect the reaction rates, in some degree (Entries 2, 3, Table 3). Under the same conditions with previous reports 17,26,50 , the TOF of 1-phenylethanol oxidation (160°C, O 2 0.1 Mpa) reached B210,000 h À 1 , which could be comparable with the result (B269,000 h À 1 ) using the Au-Pd/TiO 2 catalyst reported by Hutchings et al 26 (Entry 4, Table 3). …”

“…The Pd catalyst afforded turnover frequencies (TOFs) that are a factor of B3-24 greater than those of previous active Pd heterogeneous catalysts (Pd@MgO, Pd@TiO 2 , Pd@CeO 2 , Pd@g-Al 2 O 3 , Pd@C) in the oxidation of ethylbenzene by air. For the benzyl alcohol oxidation, the Pd catalyst displayed very high activity at 120°C with 0.1 Mpa O 2 (TOF ¼ B150,000 h À 1 ), superior to those results previously reported 17,23,24,26,27 . The significantly enhanced activity, utilization of sustainable oxidant, mild reaction conditions and good recyclability made these oxidations highly appealing processes that can address key 'green chemistry' priorities in industry.…”

“…The Pd-catalysed oxidation of 1-phenylethanol proceeded very selectively to give acetophenone as product (Entry 5, Table 2). This novel catalyst is also suitable for the selective oxidation of 2-octanol to 2-octanone (TOF, 86 h À 1 ), which is inactive with the Au-Pd/TiO 2 catalyst (Entry 6, Table 2) 26 . Therefore, the present catalytic system has been successfully extended to the alcohol oxidations by air with good activity.…”

“…During the past decade, great progress has also been made in heterogeneous Pd catalysts for oxidation processes, for example, Pd/hydroxyapatite 17 , Pd/mesoporous silicas 18,19 polymer-supported Pd 20,21 , carbon nanotubesupported Pd 22,23 , Pd supported on metal oxide 24 , Pdcontaining metal-organic frameworks 25 etc. In the field of oxidation, the current Pd-based catalysis was focusing mainly on the oxidations associating with dehydrogenation processes (alcohol oxidation 26,27 , Wacker oxidation 28,29 , oxidative couplings 30 , etc.). The aerobic oxidation of hydrocarbons to more functional compounds (aldehydes, ketones, acids or esters), one of the most important processes in petrochemical transformation, has been seldom reported by Pd catalysts 31,32 .…”

Ligand-assisted preparation of highly active and stable nanometric Pd confined catalysts for deep catalytic oxidation of toluene

“…Remarkably, the CO 2 selectivity of GtPdS-D (98.1-100%) is higher than that of ImPdS (87.8-100%) at different temperature points. As is known, achieving precise control of the Pd particle size and overall particle size distribution of catalysts is one of the most important challenges to provide excellent catalysis properties [35]. Moreover, a high activity of a supported catalyst often calls for a large active surface area, i.e., high dispersion of the active phase [36].…”