Single-site heterogeneous catalysis with isolated Pd atoms was reported earlier mainly for oxidation reactions and for Pd catalysts supported on oxide surfaces. In the present work, we show that single Pd atoms on nitrogen-functionalized mesoporous carbon, observed by aberration-corrected scanning transmission electron microscopy (ac STEM), contribute significantly to the catalytic activity for hydrogen production from vapor-phase formic acid decomposition providing an increase by 2-3 times as compared to Pd catalysts supported on nitrogen-free carbon or unsupported Pd powder. Some gain in selectivity was also achieved.According to X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) studies after ex situ reduction in hydrogen at 573 K, these species exist in a
address: vvk@catalysis.ru (V.V. Kaichev).
A B S T R A C TThe methanol oxidation over highly dispersed vanadium oxide supported on TiO 2 (anatase) has been investigated by in situ Fourier transform infrared spectroscopy (FTIR), near ambient pressure X-ray photoelectron spectroscopy (NAP XPS), X-ray absorption near edge structure (XANES), and temperature-programmed reaction spectroscopy. The data were complimented with kinetics measurements in a flow reactor. It was found that at low temperatures dimethoxymethane competes with methyl formate, whereas the production of formaldehyde is greatly inhibited. FTIR shows the presence of non-dissociatively adsorbed molecules of methanol, as well as adsorbed methoxy, dioximethylene, and formate species under reaction conditions. According to the NAP XPS and XANES data, the reaction involves the reversible reduction of V 5+ cations, pointing that the vanadia lattice oxygen participates in the methanol oxidation through the classical Mars-van Krevelen mechanism. The detailed mechanism of the methanol oxidation on vanadia catalysts is discussed.
The rate of hydrogen production from vapour-phase formic acid decomposition can be increased by 1-2 orders of magnitude by doping a Pd/C catalyst with potassium ions. Surface potassium formate and/or bicarbonate species could be involved in the rate-determining step of this reaction.
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