Oxidation of Alcohols with Molecular Oxygen on Solid Catalysts

Palladium Nanoparticles Entrapped in Aluminum Hydroxide: Dual Catalyst for Alkene Hydrogenation and Aerobic Alcohol Oxidation

[reaction: see text] A new aluminum hydroxide-supported palladium catalyst (1) made by a one-pot synthesis through nanoparticle generation and gelation shows a dual catalytic activity for olefinic hydrogenation and aerobic alcohol oxidation.

Selective Oxidation of Sulfides to Sulfoxides Using 30% Hydrogen Peroxide Catalyzed with a Recoverable Silica-Based Tungstate Interphase Catalyst

Various types of aromatic and aliphatic sulfides are selectively oxidized to sulfoxides and sulfones in good to excellent yields using 30% H2O2 in the presence of catalytic amounts of a novel recoverable silica-based tungstate interphase catalyst at room temperature. The catalyst can be recovered and reused for at least eight reaction cycles under the described reaction conditions without considerable loss of reactivity. [reaction: see text]

The selective aerobic oxidation of methylaromatics to benzaldehydes using a unique combination of two heterogeneous catalysts

A unique combination of a supported cobalt complex and the first example of supported NHPI in acetic acid gives a surprisingly stable heterogeneous catalytic system for the selective aerobic oxidation of methylaromatics to benzaldehydes at atmospheric pressure.

In situ spectroscopic investigation of heterogeneous catalysts and reaction media at high pressure

In situ characterization of catalysts by means of complementary spectroscopic techniques can be regarded as the first step towards rational catalyst design. Spurred by the growing interest of catalytic reactions in supercritical fluids and by several industrial reactions traditionally performed at high pressure (>10 bar), new demands and challenges are put to in situ spectroscopic characterization of heterogeneous catalytic reactions. In this article, we discuss the development and the use of spectroscopic and related techniques suitable for elucidating such high-pressure reactions. Selected examples from phase behaviour studies with a view cell, investigations with transmission and attenuated total reflection (ATR) infrared spectroscopy as well as X-ray absorption spectroscopy (EXAFS, XANES), are presented to show the strategies, opportunities and limitations of such high pressure in situ studies. Different facets appear to be important to gain insight into catalytic reactions in supercritical fluids: the identification of the phase behaviour of the reaction mixture, the behaviour of the fluid inside the porous catalyst, the processes occurring at the solid-fluid interface, the possible dissolution of active species and, similar as in gas-solid reactions, the establishment of structure-activity relationships.

Unraveling the Surface Reactions during Liquid-Phase Oxidation of Benzyl Alcohol on Pd/Al2O3: an in Situ ATR−IR Study

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 (Pd0) even in the presence of oxygen, in agreement with the dehydrogenation mechanism of alcohol oxidation.