catalysts
Article
Dehydrogenation of Formic Acid to CO
2
and H
2
by
Manganese(I)–Complex: Theoretical Insights for Green and
Sustainable Route
Tiziana Marino * and Mario Prejanò
Citation: Marino, T.; Prejanò, M.
Dehydrogenation of Formic Acid to
CO
2
and H
2
by
Manganese(I)–Complex: Theoretical
Insights for Green and Sustainable
Route. Catalysts 2021, 11, 141.
https://doi.org/10.3390/catal11
010141
Received: 4 January 2021
Accepted: 16 January 2021
Published: 19 January 2021
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Dipartimento di Chimica e Tecnologie Chimiche, Università della Calabria, Ponte P. Bucci cubo 14 C, Arcavacata
di Rende, CAP 87036 Cosenza, Italy; mario.prejano@unical.it
* Correspondence: tiziana.marino65@unical.it; Tel.: +39-0984492085
Abstract: In this work, a detailed computational study on a recently synthetized Mn(I)-dependent
complex [(
tBu
PNNOP)Mn(CO)
2
]
+
is reported. This species promotes the dehydrogenation of formic
acid to carbon dioxide and hydrogen. The here proposed catalytic cycle proceeds through the
formation of stabilized adduct between [(
tBu
PNNOP
tBu
)Mn(CO)
2
]
+
and formate and the progressive
release of CO
2
and H
2
, mediated by the presence of trimethylamine. In order to evaluate the influence
of the environment on the catalytic activity, different solvents have been taken into account. The
computed barriers and the geometrical parameters account well for the available experimental data,
confirming the robustness of the complex and reproducing its good catalytic performance. Outcomes
from the present investigation can stimulate further experimental works in the design of new more
efficient catalysts devoted to H
2
production.
Keywords: CO
2
;H
2
; formic acid; transition state; DFT
1. Introduction
The increasing need for new and sustainable energetic resources represents one of
the most important challenges characterizing the current century [1,2]. Indeed, fossil fuels,
gas, coal and nuclear energy are still widely used, but environmentally dangerous, energy
sources [2–5]. The intensive use of fossil fuels, for example, has been directly linked to
the increasing level of CO
2
and greenhouse gas emissions, dramatically influencing the
climate changes [3].
For these reasons, in the last fifty years, the interest devoted to possible “green”
alternatives, like the use of sunlight-, wind- and water-based energies [6], have been
increased, but, despite their promising efficiency, different technical issues are related to
them and in particular to the storage of energy vectors on large scale [7].
One of the possible solutions is represented by the so-called sustainable hydrogen
economy [8–11]. In this route, indeed, the electricity is converted in a secondary chemical
energy carrier that can be used on demand [12–16]. The combustion of H
2
in the presence
of O
2
, in devices like fuel cells, formally produces electricity and H
2
O, a green product.
On the other hand, the H
2
is not present on earth and it can be obtained/stored from/in
organic compounds, like methanol and formic acid (FA) [17–19]. In particular, since its
chemical-physical properties and its involvement in chemical industries and biomass
production, the FA is believed a promising species for the hydrogen economy [1,2,20,21].
The dehydrogenation of FA, which generates CO
2
and H
2
, (Scheme 1) is usually mediated
by metal-containing catalysts.
Catalysts 2021, 11, 141. https://doi.org/10.3390/catal11010141 https://www.mdpi.com/journal/catalysts