Abstract
Efficient dehydrogenation of cycloalkanes under mild conditions is the key to large-scale application of cycloalkanes as a hydrogen storage medium. In this paper, a series of active metals loaded on nitrogen-doped carbon (M/CN, M = Pt, Pd, Ir, Rh, Au, Ru, Ag, Ni, Cu) were prepared to learn the role of active metals in cycloalkane dehydrogenation with cyclohexane as the model reactant. Only Pt/CN, Pd/CN, Rh/CN and Ir/CN can catalyze the dehydrogenation of cyclohexane under the set conditions. Among them, Pt/CN exhibited the best catalytic activity with the TOF value of 269.32 h−1 at 180 °C, followed by Pd/CN, Rh/CN and Ir/CN successively. More importantly, the difference of catalytic activity between these active metals diminishes with the increase in temperature. This implies that there is a thermodynamic effect of cyclohexane dehydrogenation with the synthetic catalysts, which was evidenced by the study on the activation energy. In addition, the effects of molecular structure on cycloalkane dehydrogenation catalyzed by Pt/CN were studied. The results reveal that cycloalkane dehydrogenation activity and hydrogen production rate can be enhanced by optimizing the type, quantity and position of alkyl substituents on cyclohexane.
Highlights
Hydrogen is considered to be a promising alternative for widely used fossil fuels, because it has a high calorific value and is pollution-free [1,2]
We explored the role of metal (Pt, Pd, Rh and Ir) nanoparticles supported on nitrogen-doped carbon (CN) for cycloalkane dehydrogenation under wet–dry multiphase conditions with cyclohexane as the model reactant
The results reveal that the addition of a10methyl or ethyl group can improve the dehydrogenation activity of cycloalkanes, and the methyl group is more conducive to cycloalkane dehydrogenation than the ethyl group
Summary
Hydrogen is considered to be a promising alternative for widely used fossil fuels, because it has a high calorific value and is pollution-free [1,2]. Nanomaterials 2021, 11, 2846 limitation in C-H bond cleavage, which can obtain high cycloalkane conversion and high hydrogen purity at low temperatures around 200 ◦ C [18,19]. This technology is accompanied by a low hydrogen production rate under mild conditions, which remains a key challenge in large-scale applications. Pt-based catalysts with excellent dehydrogenation performance under mild conditions (around 200 ◦ C) have been intensively studied for cycloalkane dehydrogenation [18,19,20,21,22,23,24]. The effects of type, quantity and position of alky substituents on cyclohexane for cycloalkanes dehydrogenation were investigated with Pt/CN as the model catalyst
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