Pd on carbon nanotubes for liquid phase alcohol oxidation

Abstract

Pd nanoparticles supported on carbon nanotubes (CNTs) showed a higher selectivity than Pd nanoparticles supported on activated carbon (AC) in the liquid phase oxidation of benzylic alcohol to benzaldehyde. Under solventless conditions a significant improvement in selectivity was observed for Pd/CNTs, whereas using Pd/AC a considerable over-oxidation of benzaldehyde was observed. Differently from other solvents cyclohexane improved significantly the selectivity to benzaldehyde for both catalysts. Characterisation by means of transmission electron microscopy revealed differences in metal dispersion between Pd/AC and Pd/CNTs that can be ascribed to textural, chemical and physical differences between Active Carbon and Carbon Nanotubes. The higher activity in the case of Pd on AC than on CNTs can be attributed to the improved Pd dispersion in the first case. On recycling Pd/CNTs resulted more stable (activity loss 50% in 7 runs) than Pd/AC (activity loss 70% in 7 runs) even a structural change of catalysts after reaction is observed. The Pd leaching and particle coalescence are the main reasons for the loss of activity. An extraordinary improving of catalyst life has been observed by alloying the Pd nanoparticles with Au, When CNTs are used as support the strong Pd leaching can be greatly limited and the activity/selectivity maintained at least for 8 runs.

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

“…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.…”

“…Compared with homogeneous catalysts, the heterogeneous catalysts, which are convenient for recycling from the reaction environment and readily used in flow reactors, are more popular, in particular in large-scale production 16 . 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.).…”

Catalytic Performance of Co3O4 on Different Activated Carbon Supports in the Benzyl Alcohol Oxidation

“…Sheldon [5] describes the capability of molecular oxygen (O 2 ) or hydrogen peroxide (H 2 O 2 ) as oxidant agents, which are environmental friendly. On this way many works have using these oxidants with supported metals such as Pd [6], Pt [7], Rh [8] and Ru [9] as catalysts during the oxidation reactions. Although these catalysts have showed important catalytic results, their high cost is the main problem.…”

Modulation of the textures and chemical nature of C–SiC as the support of Pd for liquid phase hydrogenation

“…For example, activated carbon (AC), carbon nanofibers and carbon nanotubes (CNTs) have been widely studied in a series of catalytic reactions e.g., FischerTropsch synthesis [2,3], fine chemical synthesis via hydrogenation [4], dehydrogenation [5] and oxidation [6]. Recently, SiC attracts attention as an alternative catalyst support because of its properties such as high mechanical strength, high heat conductivity and easy shaping in addition to chemical inertness.…”