Gas-phase oxidation of alcohols with dioxygen over Au/TiO2 catalyst: The role of reactive oxygen species

The activity of the (3% Au)/TiO2 catalyst with an average gold particle size of 3.6 ± 1.0 nm in the gas-phase oxidation of lower aliphatic alcohols (ethanol, propanol, isopropanol, and butanol) into the corresponding carbonyl compounds (acetaldehyde, propanal, acetone, and butanal) has been studied. A two-peak profile of the activity of the catalyst as a function of temperature has been observed in all of the reactions. The first peak falls within the temperature range from 120 to 130°C, while the complete conversion of the alcohols is achieved at 200–300°C. It is hypothesized that the low-temperature activity is due to the generation of a thermally unstable reactive oxygen species on the catalyst surface

Gas-phase oxidation of alcohols with O2 and N2O catalyzed by Au/TiO2: A comparative study

Gas-phase oxidation of alcohols (EtOH, PrOH, i-PrOH, BuOH) to their carbonyl derivatives was used as test reaction to elucidate the mechanism of a low-temperature catalytic activity of Au/TiO2. The reactions were carried out in the presence of molecular oxygen, nitrous oxide as well as in the absence of the gas-phase oxidants. The relative contribution of oxidative and non-oxidative dehydrogenation pathways was thus estimated. The presence of oxygen in the feed brought about to a double peak profile of catalytic activity as a function of temperature for all the alcohols. The low-temperature peak fells on 120–130 °C. In contrast, the use of N2O as an oxidant gave rise to usual profile of catalytic activity, which is similar to that of anaerobic dehydrogenation of alcohols. The results obtained allowed to suggest the mechanism of the alcohols oxidation. The low temperature peak is probably related to participation of active oxygen species, generated from O2 on the catalyst surface. Oxidation with N2O is interpreted by preliminary dehydrogenation of alcohols to corresponding carbonyl derivatives followed by H2 oxidation

Gas-phase oxidation of alcohols with O2 and N2O catalyzed by Au/TiO2: A comparative study

Gas-phase oxidation of alcohols (EtOH, PrOH, i-PrOH, BuOH) to their carbonyl derivatives was used as test reaction to elucidate the mechanism of a low-temperature catalytic activity of Au/TiO2. The reactions were carried out in the presence of molecular oxygen, nitrous oxide as well as in the absence of the gas-phase oxidants. The relative contribution of oxidative and non-oxidative dehydrogenation pathways was thus estimated. The presence of oxygen in the feed brought about to a double peak profile of catalytic activity as a function of temperature for all the alcohols. The low-temperature peak fells on 120–130 °C. In contrast, the use of N2O as an oxidant gave rise to usual profile of catalytic activity, which is similar to that of anaerobic dehydrogenation of alcohols. The results obtained allowed to suggest the mechanism of the alcohols oxidation. The low temperature peak is probably related to participation of active oxygen species, generated from O2 on the catalyst surface. Oxidation with N2O is interpreted by preliminary dehydrogenation of alcohols to corresponding carbonyl derivatives followed by H2 oxidation

Gas-phase oxidation of alcohols with dioxygen over Au/TiO2 catalyst: The role of reactive oxygen species

The activity of the (3% Au)/TiO2 catalyst with an average gold particle size of 3.6 ± 1.0 nm in the gas-phase oxidation of lower aliphatic alcohols (ethanol, propanol, isopropanol, and butanol) into the corresponding carbonyl compounds (acetaldehyde, propanal, acetone, and butanal) has been studied. A two-peak profile of the activity of the catalyst as a function of temperature has been observed in all of the reactions. The first peak falls within the temperature range from 120 to 130°C, while the complete conversion of the alcohols is achieved at 200–300°C. It is hypothesized that the low-temperature activity is due to the generation of a thermally unstable reactive oxygen species on the catalyst surface

Promoting effect of 4-dimethylaminopyridine on selective oxidation of benzyl alcohol over MoVTeNb mixed oxides

A liquid phase oxidation of benzyl alcohol with 1 atm molecular oxygen catalyzed by MoVTeNb mixed oxides has been investigated. It is demonstrated that 4-dimethylaminopyridine (DMAP) acting as a co-catalyst, notably accelerates the reaction, as well as influences the ratio of the reaction products (benzaldehyde, benzyl benzoate and benzoic acid). The findings can be interpreted in terms of the involvement of DMAP (a good enough N-nucleophile) in the process of chemo-desorption of oxygenates formed on the catalyst surface

Oxidation, oxidative esterification and ammoxidation of acrolein over metal oxides: Do these reactions include nucleophilic acyl substitution?

It is known that nucleophilic acyl substitution in the RCOX compounds with “good leaving” groups X is a fundamental and energetically favorable route to carboxylic acid derivatives. When water, alcohols and ammonia are used as nucleophiles, carboxylic acids, esters and amides (or nitriles) are obtained, respectively. On the other hand, the same products are derived from aldehydes upon their catalytic aerobic oxidation, on condition that water, alcohols and ammonia are present in the feed gas. Therefore, one can surmise that nucleophilic substitution reactions are involved intrinsically in the catalytic oxidation reactions. In agreement with this hypothesis we have shown, as an example, that the selfsame catalyst, MoVTeNb mixed oxides, enables successful oxidation, oxidative esterification and ammoxidation of acrolein. The mechanistic aspects of these reactions are considered based on established organic and general chemistry principles