Solvent-free aerobic oxidation of alcohols over palladium supported on MCM-41

In present work, the [PdCl4]2− ions were successfully supported on as-synthesized [CTA+]MCM-41 materials through adsorption method. Subsequently, the composite materials were reduced by sodium borohydride, followed by being extracted of [CTA+] surfactants with acidified ethanol. The resulted solid (denoted as Pd-M41-AE) could be used as an efficient catalyst for the solvent-free aerobic oxidation of benzylic alcohol under atmospheric pressure. The structures of the samples were characterized by X-ray diffraction (XRD), N2 adsorption–desorption, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and thermogravimetry (TG) techniques. 0.4%Pd-M41-AE exhibited high activity (turnover frequency of 4344 h−1) for the oxidation of benzyl alcohol, remarkably superior than other kinds of Pd-M41 at 100 °C. Moreover, the superior turnover frequencies (69,162 h−1 for benzyl alcohol, 69,920 h−1 for 1-phenylethanol and 117,130 h−1 for cinnamyl alcohol, respectively) were achieved over 0.05%Pd-M41-AE at 160 °C. Recycling studies proved the recyclability of Pd-M41-AE as a heterogeneous catalyst, which did not lose the catalytic activity after four recycles appreciably.

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► Pd-M41-AE catalysts were prepared by adsorption–reduction and extraction procedures.
► Pd-M41-AE exhibited high activity and selectivity for oxidation of benzylic alcohol.
► 0.05%Pd-M41-AE gave a TOF as high as 69,920 h−1 for 1-phenylethanol at 160 °C.
► The activity of Pd-M41-AE did not lose after four reuses appreciably.