7 research outputs found
Mechanistic insights to drive catalytic hydrogenation of formamide intermediates to methanol via deaminative hydrogenation
Amine-promoted hydrogenation of CO2 to methanol typically proceeds via a formamide intermediate when amines are used as additives or if the hydrogenation is performed in carbon capture solvents. The catalysts used for the hydrogenation of the formamide intermediate dictate the selectivity of the products formed: 1) Deoxygenative hydrogenation (C–O bond cleavage) resulting in N-methylation of amine and deactivation of the solvent, 2) Deaminative hydrogenation (C–N bond cleavage) resulting in formation of methanol and regeneration of the solvent. To date, catalytic reductions of CO2 with amine promoters suffer from poor selectively for methanol which we attribute to the limiting formamide intermediate, though to date, the conditions that favor C–N cleavage have yet to be fully understood. To better understand the reactivity of the formamide intermediates, a range of heterogenous catalysts were used to study the hydrogenation of formamide. Well-known gas phase CO2 hydrogenation catalysts catalyze the hydrogenation of formamide to N-methyl product via C–O bond cleavage. However, the selectivity can be readily shifted to selective C–N bond cleavage by addition of an additive with sufficient basicity for both homogenous and heterogeneous catalytic systems. The base additive shifts the selectivity by deprotonating a hemiaminal intermediate formed in situ during the formamide hydrogenation. This prevents dehydration process leading to N-methylated product, which is a key capture solvent deactivation pathway that hinders amine use in carbon capture, utilization, and storage (CCUS). The findings from this study provide a roadmap on how to improve the selectivity of known heterogenous catalysts, enabling catalytic reduction of captured CO2 to methanol
Hydrogen storage in liquid hydrogen carriers: recent activities and new trends
Efficient storage of hydrogen is one of the biggest challenges towards a potential hydrogen economy. Hydrogen storage in liquid carriers is an attractive alternative to compression or liquefaction at low temperatures. Liquid carriers can be stored cost-effectively and transportation and distribution can be integrated into existing infrastructures. The development of efficient liquid carriers is part of the work of the International Energy Agency Task 40: Hydrogen-Based Energy Storage. Here, we report the state-of-the-art for ammonia and closed CO2-cycle methanol-based storage options as well for liquid organic hydrogen carriers
Manganese-Catalyzed Sequential Hydrogenation of CO<sub>2</sub> to Methanol via Formamide
MnÂ(I)-PNP pincer catalyzed sequential
one-pot homogeneous CO<sub>2</sub> hydrogenation to CH<sub>3</sub>OH by molecular H<sub>2</sub> is demonstrated. The hydrogenation
consists of two partsî—¸N-formylation
of an amine utilizing CO<sub>2</sub> and H<sub>2</sub>, and subsequent
formamide reduction to CH<sub>3</sub>OH, regenerating the amine in
the process. A reported air-stable and well-defined Mn-PNP pincer
complex was found active for the catalysis of both steps. CH<sub>3</sub>OH yields up to 84% and 71% (w.r.t amine) were obtained, when benzylamine
and morpholine were used as amines, respectively; and a TON of up
to 36 was observed. In our opinion, this study represents an important
development in the nascent field of base-metal-catalyzed homogeneous
CO<sub>2</sub> hydrogenation to CH<sub>3</sub>OH
Conversion of CO<sub>2</sub> from Air into Methanol Using a Polyamine and a Homogeneous Ruthenium Catalyst
A highly
efficient homogeneous catalyst system for the production
of CH<sub>3</sub>OH from CO<sub>2</sub> using pentaethylenehexamine
and Ru-Macho-BH (<b>1</b>) at 125–165 °C in an ethereal
solvent has been developed (initial turnover frequency = 70 h<sup>–1</sup> at 145 °C). Ease of separation of CH<sub>3</sub>OH is demonstrated by simple distillation from the reaction mixture.
The robustness of the catalytic system was shown by recycling the
catalyst over five runs without significant loss of activity (turnover
number > 2000). Various sources of CO<sub>2</sub> can be used for
this reaction including air, despite its low CO<sub>2</sub> concentration
(400 ppm). For the first time, we have demonstrated that CO<sub>2</sub> captured from air can be directly converted to CH<sub>3</sub>OH
in 79% yield using a homogeneous catalytic system
Efficient Reversible Hydrogen Carrier System Based on Amine Reforming of Methanol
A novel hydrogen storage system based
on the hydrogen release from
catalytic dehydrogenative coupling of methanol and 1,2-diamine is
demonstrated. The products of this reaction, <i>N</i>-formamide
and <i>N</i>,<i>N</i>′-diformamide, are
hydrogenated back to the free amine and methanol by a simple hydrogen
pressure swing. Thus, an efficient one-pot hydrogen carrier system
has been developed. The H<sub>2</sub> generating step can be termed
as “amine reforming of methanol” in analogy to the traditional
steam reforming. It acts as a clean source of hydrogen without concurrent
production of CO<sub>2</sub> (unlike steam reforming) or CO (by complete
methanol dehydrogenation). Therefore, a carbon neutral cycle is essentially
achieved where no carbon capture is necessary as the carbon is trapped
in the form of formamide (or urea in the case of primary amine). In
theory, a hydrogen storage capacity as high as 6.6 wt % is achievable.
Dehydrogenative coupling and the subsequent amide hydrogenation proceed
with good yields (90% and >95% respectively, with methanol and <i>N</i>,<i>N</i>′-dimethylethylenediamine as
dehydrogenative coupling partners)
Formic Acid As a Hydrogen Storage Medium: Ruthenium-Catalyzed Generation of Hydrogen from Formic Acid in Emulsions
Formic
acid is decomposed to H<sub>2</sub> and CO<sub>2</sub> in
the presence of RuCl<sub>3</sub> and triphenylphosphines in an emulsion.
In situ formed ruthenium carbonyls, such as [RuÂ(HCO<sub>2</sub>)<sub>2</sub>(CO)<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub>] (<b>1</b>), [RuÂ(CO)<sub>3</sub>(PPh<sub>3</sub>)<sub>2</sub>] (<b>2</b>), and [Ru<sub>2</sub>(HCO<sub>2</sub>)<sub>2</sub>(CO)<sub>4</sub>(PPh<sub>3</sub>)<sub>2</sub>] (<b>3</b>), and a large cluster,
involving a Ru<sub>12</sub> core, were identified and structurally
characterized from the reaction mixtures. The catalytic activity of
the mono and binuclear complexes was also investigated and it was
found that [Ru<sub>2</sub>(HCO<sub>2</sub>)<sub>2</sub>(CO)<sub>4</sub>(PPh<sub>3</sub>)<sub>2</sub>] (<b>3</b>) shows high stability
even at elevated temperatures and pressures and its activity is 1
order of magnitude lower than those measured for the mononuclear complexes.
It was also attempted to use [RuÂ(HCO<sub>2</sub>)<sub>2</sub>(CO)<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub>] (<b>1</b>) as a catalyst
for the hydrogenation of CO<sub>2</sub> to formic acid under neutral
conditions. Although the reduction of CO<sub>2</sub> did not take
place, the conversion of [RuÂ(HCO<sub>2</sub>)<sub>2</sub>(CO)<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub>] (<b>1</b>) to an unexpected
carbonate, [RuÂ(CO<sub>3</sub>)Â(CO)<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub>]·H<sub>2</sub>O was observed
Iridium-Catalyzed Continuous Hydrogen Generation from Formic Acid and Its Subsequent Utilization in a Fuel Cell: Toward a Carbon Neutral Chemical Energy Storage
This study represents a notable step
toward a potentially carbon
neutral energy storage solution based on formic acid as a hydrogen/energy
carrier. A catalytic system derived from IrCl<sub>3</sub> and 1,3-<i>bis</i>(2′-pyridyl-imino)-isoindoline (IndH) in the presence
of aqueous sodium formate showed high selectivity and robustness for
hydrogen generation from formic acid (FA) at 90–100 °C
under both high and moderate pressure conditions suppressing the formation
of CO impurity. Being a solid substance, the catalyst can be recovered
by a simple filtration, if necessary. Furthermore, addition of neat
formic acid is sufficient to reuse the catalyst and maintain a constant
flow of H<sub>2</sub> and CO<sub>2</sub> mixture and the stable performance
of a coupled fuel cell. The easy to recycle catalyst did not show
any loss of activity after 20 days of continuous use, and similar
activity was observed even a year after the original preparation.
The reactor for formic acid decomposition provided a one to one ratio
of a H<sub>2</sub>/CO<sub>2</sub> mixture that was coupled to a hydrogen/air
proton exchange membrane (PEM) fuel cell to demonstrate a stable and
continuous conversion of chemical energy to electricity. This integrated
system embodies the first example of an indirect formic acid fuel
cell, which can function, without the requirement of applying inert
conditions and feed gas purification, for extended periods of time