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A prolific catalyst for dehydrogenation of neat formic acid.

Celaje JJ, Lu Z, Kedzie EA, Terrile NJ, Lo JN, Williams TJ - Nat Commun (2016)

Bottom Line: While many catalysts exist for both formic acid dehydrogenation and carbon dioxide reduction, solutions to date on hydrogen gas release rely on volatile components that reduce the weight content of stored hydrogen and/or introduce fuel cell poisons.These are avoided here.The catalyst utilizes an interesting chemical mechanism, which is described on the basis of kinetic and synthetic experiments.

View Article: PubMed Central - PubMed

Affiliation: Donald P. and Katherine B. Loker Hydrocarbon Institute and Department of Chemistry, University of Southern California, Los Angeles, California 90089-1661, USA.

ABSTRACT
Formic acid is a promising energy carrier for on-demand hydrogen generation. Because the reverse reaction is also feasible, formic acid is a form of stored hydrogen. Here we present a robust, reusable iridium catalyst that enables hydrogen gas release from neat formic acid. This catalysis works under mild conditions in the presence of air, is highly selective and affords millions of turnovers. While many catalysts exist for both formic acid dehydrogenation and carbon dioxide reduction, solutions to date on hydrogen gas release rely on volatile components that reduce the weight content of stored hydrogen and/or introduce fuel cell poisons. These are avoided here. The catalyst utilizes an interesting chemical mechanism, which is described on the basis of kinetic and synthetic experiments.

No MeSH data available.


Related in: MedlinePlus

Gas eluent stream infrared spectrum.The figure shows that compared to a prepared sample with 10 p.p.m. CO in air, the gaseous products from dehydrogenation of neat formic acid saturated in sodium formate contain <10 p.p.m. CO.
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f2: Gas eluent stream infrared spectrum.The figure shows that compared to a prepared sample with 10 p.p.m. CO in air, the gaseous products from dehydrogenation of neat formic acid saturated in sodium formate contain <10 p.p.m. CO.

Mentions: To be useful in fuel cells, FA decomposition must be selective for H2 and CO2 over H2O and CO, because CO is a poison for polymer electrolyte membrane (PEM) fuel cell catalysts such as platinum. The composition of gas produced from our conditions was determined by gas chromatography, which showed only H2 and CO2 (1:1 ratio) and no detectable CO (<1 part per thousand) (Supplementary Fig. 3). However, further analysis of the product gas by infrared spectroscopy revealed that when the reaction is conducted using neat FA, CO is observed at a concentration near the detection limit of the gas chromatography (Supplementary Fig. 4). It is known that neat FA decomposes in the presence of concentrated acid39 or at high temperatures to form H2O and CO4041. We therefore hypothesized that much of the CO produced in our reaction conditions may be formed by thermal, uncatalysed decomposition pathways. Thus, we performed the dehydrogenation in the presence of a portion of water (10 v%), and observed that under these conditions the CO in the bulk gaseous products is <10 p.p.m. by infrared spectroscopy (Supplementary Fig. 5). Moreover, we hypothesized that the thermal decomposition of neat FA might be suppressed by running the reaction using higher sodium formate loading. Indeed, heating 1 ml of neat FA in 26 mg of the iridium precatalyst and 900 mg of sodium formate (50 mol%) to 90 °C for 2 h yields a product mixture with less than 10 p.p.m. CO (Fig. 2). A similarly low level of CO is observed when dehydrogenation is performed at 70 °C for 6 h (Supplementary Fig. 6). While these strategies for CO minimization are known in the FA literature, this collection of demonstrations enables practitioners to select the level of humidity and CO content in the reaction's gas eluent stream simply by adjusting the water and base loading in the FA supply. The optimum of these parameters might be different for any particular fuel cell application, but the reaction affords flexibility to adjust them.


A prolific catalyst for dehydrogenation of neat formic acid.

Celaje JJ, Lu Z, Kedzie EA, Terrile NJ, Lo JN, Williams TJ - Nat Commun (2016)

Gas eluent stream infrared spectrum.The figure shows that compared to a prepared sample with 10 p.p.m. CO in air, the gaseous products from dehydrogenation of neat formic acid saturated in sodium formate contain <10 p.p.m. CO.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4834634&req=5

f2: Gas eluent stream infrared spectrum.The figure shows that compared to a prepared sample with 10 p.p.m. CO in air, the gaseous products from dehydrogenation of neat formic acid saturated in sodium formate contain <10 p.p.m. CO.
Mentions: To be useful in fuel cells, FA decomposition must be selective for H2 and CO2 over H2O and CO, because CO is a poison for polymer electrolyte membrane (PEM) fuel cell catalysts such as platinum. The composition of gas produced from our conditions was determined by gas chromatography, which showed only H2 and CO2 (1:1 ratio) and no detectable CO (<1 part per thousand) (Supplementary Fig. 3). However, further analysis of the product gas by infrared spectroscopy revealed that when the reaction is conducted using neat FA, CO is observed at a concentration near the detection limit of the gas chromatography (Supplementary Fig. 4). It is known that neat FA decomposes in the presence of concentrated acid39 or at high temperatures to form H2O and CO4041. We therefore hypothesized that much of the CO produced in our reaction conditions may be formed by thermal, uncatalysed decomposition pathways. Thus, we performed the dehydrogenation in the presence of a portion of water (10 v%), and observed that under these conditions the CO in the bulk gaseous products is <10 p.p.m. by infrared spectroscopy (Supplementary Fig. 5). Moreover, we hypothesized that the thermal decomposition of neat FA might be suppressed by running the reaction using higher sodium formate loading. Indeed, heating 1 ml of neat FA in 26 mg of the iridium precatalyst and 900 mg of sodium formate (50 mol%) to 90 °C for 2 h yields a product mixture with less than 10 p.p.m. CO (Fig. 2). A similarly low level of CO is observed when dehydrogenation is performed at 70 °C for 6 h (Supplementary Fig. 6). While these strategies for CO minimization are known in the FA literature, this collection of demonstrations enables practitioners to select the level of humidity and CO content in the reaction's gas eluent stream simply by adjusting the water and base loading in the FA supply. The optimum of these parameters might be different for any particular fuel cell application, but the reaction affords flexibility to adjust them.

Bottom Line: While many catalysts exist for both formic acid dehydrogenation and carbon dioxide reduction, solutions to date on hydrogen gas release rely on volatile components that reduce the weight content of stored hydrogen and/or introduce fuel cell poisons.These are avoided here.The catalyst utilizes an interesting chemical mechanism, which is described on the basis of kinetic and synthetic experiments.

View Article: PubMed Central - PubMed

Affiliation: Donald P. and Katherine B. Loker Hydrocarbon Institute and Department of Chemistry, University of Southern California, Los Angeles, California 90089-1661, USA.

ABSTRACT
Formic acid is a promising energy carrier for on-demand hydrogen generation. Because the reverse reaction is also feasible, formic acid is a form of stored hydrogen. Here we present a robust, reusable iridium catalyst that enables hydrogen gas release from neat formic acid. This catalysis works under mild conditions in the presence of air, is highly selective and affords millions of turnovers. While many catalysts exist for both formic acid dehydrogenation and carbon dioxide reduction, solutions to date on hydrogen gas release rely on volatile components that reduce the weight content of stored hydrogen and/or introduce fuel cell poisons. These are avoided here. The catalyst utilizes an interesting chemical mechanism, which is described on the basis of kinetic and synthetic experiments.

No MeSH data available.


Related in: MedlinePlus