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Carbon-free H₂ production from ammonia triggered at room temperature with an acidic RuO₂/?-Al₂O₃ catalyst.

ABSTRACT: Ammonia has been suggested as a carbon-free hydrogen source, but a convenient method for producing hydrogen from ammonia with rapid initiation has not been developed. Ideally, this method would require no external energy input. We demonstrate hydrogen production by exposing ammonia and O₂ at room temperature to an acidic RuO₂/?-Al₂O₃ catalyst. Because adsorption of ammonia onto the catalyst is exothermic, the catalyst bed is rapidly heated to the catalytic ammonia autoignition temperature, and subsequent oxidative decomposition of ammonia produces hydrogen. A differential calorimeter combined with a volumetric gas adsorption analyzer revealed a large quantity of heat evolved both with chemisorption of ammonia onto RuO₂ and acidic sites on the ?-Al₂O₃ and with physisorption of multiple ammonia molecules.

SUBMITTER: Nagaoka K

PROVIDER: S-EPMC5409452 | biostudies-literature | 2017 Apr

REPOSITORIES: biostudies-literature

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Carbon-free H2 production from ammonia triggered at room temperature with an acidic RuO2/γ-Al2O3 catalyst.

Nagaoka Katsutoshi K Eboshi Takaaki T Takeishi Yuma Y Tasaki Ryo R Honda Kyoko K Imamura Kazuya K Sato Katsutoshi K

Science advances 20170428 4

Ammonia has been suggested as a carbon-free hydrogen source, but a convenient method for producing hydrogen from ammonia with rapid initiation has not been developed. Ideally, this method would require no external energy input. We demonstrate hydrogen production by exposing ammonia and O2 at room temperature to an acidic RuO2/γ-Al2O3 catalyst. Because adsorption of ammonia onto the catalyst is exothermic, the catalyst bed is rapidly heated to the catal ...[more]

PMID: 28508046

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Project description:A better fundamental understanding of the plasma-catalyst interaction and the reaction mechanism is vital for optimizing the design of catalysts for ammonia synthesis by plasma-catalysis. In this work, we report on a hybrid plasma-enhanced catalytic process for the synthesis of ammonia directly from N2 and H2 over transition metal catalysts (M/Al2O3, M = Fe, Ni, Cu) at near room temperature (?35 °C) and atmospheric pressure. Reactions were conducted in a specially designed coaxial dielectric barrier discharge (DBD) plasma reactor using water as a ground electrode, which could cool and maintain the reaction at near-room temperature. The transparency of the water electrode enabled operando optical diagnostics (intensified charge-coupled device (ICCD) imaging and optical emission spectroscopy) of the full plasma discharge area to be conducted without altering the operation of the reactor, as is often needed when using coaxial reactors with opaque ground electrodes. Compared to plasma synthesis of NH3 without a catalyst, plasma-catalysis significantly enhanced the NH3 synthesis rate and energy efficiency. The effect of different transition metal catalysts on the physical properties of the discharge is negligible, which suggests that the catalytic effects provided by the chemistry of the catalyst surface are dominant over the physical effects of the catalysts in the plasma-catalytic synthesis of ammonia. The highest NH3 synthesis rate of 471 ?mol g-1 h-1 was achieved using Ni/Al2O3 as a catalyst with plasma, which is 100% higher than that obtained using plasma only. The presence of a transition metal (e.g., Ni) on the surface of Al2O3 provided a more uniform plasma discharge than Al2O3 or plasma only, and enhanced the mean electron energy. The mechanism of plasma-catalytic ammonia synthesis has been investigated through operando plasma diagnostics combined with comprehensive characterization of the catalysts using N2 physisorption measurements, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), NH3-temperature-programmed desorption (TPD), and N2-TPD. Four forms of adsorbed NH x (x = 0, 1, 2, and 3) species were detected on the surfaces of the spent catalysts using XPS. It was found that metal sites and weak acid sites could enhance the production of NH3 via formation of NH2 intermediates on the surface.

Dataset Information

Carbon-free H₂ production from ammonia triggered at room temperature with an acidic RuO₂/?-Al₂O₃ catalyst.

Publications

Carbon-free H<sub>2</sub> production from ammonia triggered at room temperature with an acidic RuO<sub>2</sub>/γ-Al<sub>2</sub>O<sub>3</sub> catalyst.

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Dataset Information

Carbon-free H2 production from ammonia triggered at room temperature with an acidic RuO2/?-Al2O3 catalyst.

Publications

Carbon-free H<sub>2</sub> production from ammonia triggered at room temperature with an acidic RuO<sub>2</sub>/γ-Al<sub>2</sub>O<sub>3</sub> catalyst.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets

Carbon-free H₂ production from ammonia triggered at room temperature with an acidic RuO₂/?-Al₂O₃ catalyst.