No abstract

Various nitrogen-doped carbon materials were prepared via treatments of an activated carbon (AC) with ammonia and hydrogen peroxide, and their catalytic performance was tested for aerobic oxidation of several alcohols in ethanol. The amount and nature of doped nitrogen-species were examined by X-ray photoelectron spectroscopy to discuss the genesis of active species by nitrogen doping. The nitrogendoped AC catalysts are active for the oxidation of such alcohols as benzyl alcohol, cinnamyl alcohol, and 5-(hydroxymethyl)-2-furaldehyde, and in some cases, they are even more selective to the oxidation of the hydroxyl group compared with conventional Pt/C and Ru/C catalysts, for which coupling products with the ethanol solvent are formed at low conversion levels. Graphite-type doped nitrogen species are significant for the formation of active sites on the surface of AC. The present results demonstrate the potential of nitrogen-doped AC materials as metal-free, carbon-based catalysts useable for organic synthetic reactions.

The influence of the redox behavior of Rh/AlPO4 on automotive three-way catalysis (TWC) was studied to correlate catalytic activity with thermal stability and metal–support interactions. Compared with a reference Rh/Al2O3 catalyst, Rh/AlPO4 exhibited a much higher stability against thermal aging under an oxidizing atmosphere; further deactivation was induced by a high-temperature reduction treatment. In situ X-ray absorption fine structure experiments revealed a higher reducibility of Rh oxide (RhO x ) to Rh, and the metal showed a higher tolerance to reoxidation when supported on AlPO4 compared with Al2O3. This unusual redox behavior is associated with an Rh–O–P interfacial linkage, which is preserved under oxidizing and reducing atmospheres. Another effect of the Rh–O–P interfacial linkage was observed for the metallic Rh with an electron-deficient character. This leads to the decreasing back-donation from Rh d-orbitals to the antibonding π* orbital of chemisorbed CO or NO, which is a possible reason for the deactivation by high-temperature reduction treatments. On the other hand, surface acid sites on AlPO4 promoted oxidative adsorption of C3H6 as aldehyde, which showed a higher reactivity toward O2, as well as NO, compared with carboxylate adsorbed on Al2O3. A precise control of the acid–base character of the metal phosphate supports is therefore a key to enhance the catalytic performance of supported Rh catalysts for TWC applications.