Aerobic oxidation of alkyl chain in alkylphenols over combination of Pt and Pd catalysts

[Display omitted] •p-Cresol was oxidized with Pt/C + Pd(CH3COO)2 catalysts without base additive.•Pt° and Pd° nanoparticles were separately produced during reaction even under air.•Pd° is the key species for the formation of p-hydroxybenzaldehyde from p-cresol.•Oxidized products of p-cresol over Pt/...

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Bibliographic Details
Published in:Applied catalysis. A, General General, 2019-01, Vol.569, p.149-156
Main Authors: Nakagawa, Yoshinao, Tokuma, Kensuke, Nakaji, Yosuke, Miyagawa, Akari, Tamura, Masazumi, Tomishige, Keiichi
Format: Article
Language:English
Subjects:
Acetic acid
Acidic oxides
Aerobic oxidation
Catalysis
Catalysts
Chemical bonds
Chemistry
Cresol
Dimerization
Hydroxybenzaldehydes
Ionosphere
Metal particles
Noble metals
Oxidation
Oxygen
Palladium
Platinum
Polymerization
Pressure effects
Weight
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Summary:[Display omitted] •p-Cresol was oxidized with Pt/C + Pd(CH3COO)2 catalysts without base additive.•Pt° and Pd° nanoparticles were separately produced during reaction even under air.•Pd° is the key species for the formation of p-hydroxybenzaldehyde from p-cresol.•Oxidized products of p-cresol over Pt/C can reduce Pd(CH3COO)2 to Pd°. Oxidation of benzylic position in alkylphenols with molecular oxygen in acidic conditions, which is very difficult because of the intense dimerization or polymerization, was investigated with various combinations of noble metal catalysts. The combination of Pt/C and Pd(CH3COO)2 catalysts showed activity in the formation of p-hydroxybenzaldehyde formation from p-cresol. The best p-hydroxybenzaldehyde yield was 35%, which was obtained in 50 wt% aqueous acetic acid, Pt on carbon : Pd(CH3COO)2 weight ratio = 1 : 2, at 353 K. From XRD, TEM-EDX and XAFS characterizations, the Pt and Pd species were totally reduced to Pt and Pd metal particles, respectively, in spite of the oxidative reaction conditions. Polymerized products (“tar”) of p-cresol formed with Pt/C catalyst and air can be the reductants for Pd(CH3COO)2 into Pd metal. The catalysts or catalyst combinations without Pd metal showed no activity in the formation of p-hydroxybenzaldehyde, suggesting that Pd° is the active species. The effects of the air pressure and presence of radical scavenger were very small, suggesting that non-free-radical mechanism was involved.
ISSN:0926-860X
1873-3875
DOI:10.1016/j.apcata.2018.10.024