Unraveling the surface reactions during liquid-phase oxidation of benzyl alcohol on Pd/Al2O3:: an in situ ATR-IR study

被引：175

作者：

Keresszegi, C ^{[1
]}

Ferri, D ^{[1
]}

Mallat, T ^{[1
]}

Baiker, A ^{[1
]}

机构：

[1] ETH Honggerberg, Dept Chem & Appl Sci, Swiss Fed Inst Technol, CH-8093 Zurich, Switzerland

来源：

JOURNAL OF PHYSICAL CHEMISTRY B | 2005年 / 109卷 / 02期

关键词：

D O I：

10.1021/jp0459864

中图分类号：

O64 [物理化学（理论化学）、化学物理学];

学科分类号：

070304 ; 081704 ;

摘要：

The palladium-catalyzed liquid-phase reaction of benzyl alcohol to benzaldehyde was investigated in the presence and absence of oxygen by attenuated total reflection infrared (ATR-IR) spectroscopy. The 5 wt % Pd/Al2O3 catalyst was fixed in a flow-through ATR-IR cell serving as a continuous-flow reactor. The reaction conditions (cyclohexane solvent, 323 K, 1 bar) were set in the range commonly applied in the heterogeneous catalytic aerobic oxidation of alcohols. The in situ ATR-IR study of the solid-liquid interface revealed a complex reaction network, including dehydrogenation of benzyl alcohol to benzaldehyde, decarbonylation of benzaldehyde, oxidation of hydrogen and CO on Pd, and formation of benzoic acid catalyzed by both Pd and Al2O3. Continuous formation of CO and its oxidative removal by air resulted in significant steady-state CO coverage of Pd during oxidation of benzyl alcohol. Unexpectedly, benzoic acid formed already in the early stage of the reaction and adsorbed strongly (irreversibly) on the basic sites of Al2O3 and thus remained undetectable in the effluent. This observation questions the reliability of product distributions conventionally determined from the liquid phase. The occurrence of the hydrogenolysis of the C-O bond of benzyl alcohol and formation of toluene indicates that Pd was present in a reduced state (Pd) even in the presence of oxygen, in agreement with the dehydrogenation mechanism of alcohol oxidation.

引用

页码：958 / 967

页数：10

共 71 条

[1] Quantitative modulated excitation Fourier transform infrared spectroscopy [J].

Baurecht, D ;

Fringeli, UP .

REVIEW OF SCIENTIFIC INSTRUMENTS, 2001, 72 (10) :3782-3792

[2]

Bellamy L. J., 1954, The Infrared Spectra of Complex Molecules

[3] Selective oxidation of alcohols and aldehydes on metal catalysts [J].

Besson, M ;

Gallezot, P .

CATALYSIS TODAY, 2000, 57 (1-2) :127-141

[4] Relation between crystallite size and dispersion on supported metal catalysts [J].

Borodzinski, A ;

Bonarowska, M .

LANGMUIR, 1997, 13 (21) :5613-5620

[5] Looking on heterogeneous catalytic systems from different perspectives:: Multitechnique approaches as a new challenge for in situ studies [J].

Brückner, A .

CATALYSIS REVIEWS-SCIENCE AND ENGINEERING, 2003, 45 (01) :97-150

[6] Time-resolved in situ ATR Spectroscopy of 2-propanol oxidation over Pd/Al2O3:: Evidence for 2-propoxide intermediate [J].

Bürgi, T ;

Bieri, M .

JOURNAL OF PHYSICAL CHEMISTRY B, 2004, 108 (35) :13364-13369

[7] In situ attenuated total reflection infrared spectroscopy:: A sensitive tool for the investigation of reduction-oxidation processes on heterogeneous Pd metal catalysts [J].

Bürgi, T ;

Wirz, R ;

Baiker, A .

JOURNAL OF PHYSICAL CHEMISTRY B, 2003, 107 (28) :6774-6781

[8] In situ infrared spectroscopy of catalytic solid-liquid interfaces using phase-sensitive detection:: Enantioselective hydrogenation of a pyrone over Pd/TiO2 [J].

Bürgi, T ;

Baiker, A .

JOURNAL OF PHYSICAL CHEMISTRY B, 2002, 106 (41) :10649-10658

[9] Selective oxidation of benzyl alcohol to benzaldehyde in "supercritical" carbon dioxide [J].

Caravati, M ;

Grunwaldt, JD ;

Baiker, A .

CATALYSIS TODAY, 2004, 91-2 :1-5

[10] METAL CRYSTALLINITY EFFECTS IN ELECTROCATALYSIS AS PROBED BY REAL-TIME FTIR SPECTROSCOPY - ELECTROOXIDATION OF FORMIC-ACID, METHANOL, AND ETHANOL ON ORDERED LOW-INDEX PLATINUM SURFACES [J].

CHANG, SC ;

LEUNG, LWH ;

WEAVER, MJ .

JOURNAL OF PHYSICAL CHEMISTRY, 1990, 94 (15) :6013-6021

← 1 2 3 4 5 6 7 8 →