Abstract
Formic acid (FA) is considered as a potential durable energy carrier. It contains ~4.4 wt % of hydrogen (or 53 g/L) which can be catalytically released and converted to electricity using a proton exchange membrane (PEM) fuel cell. Although various catalysts have been reported to be very selective towards FA dehydrogenation (resulting in H2 and CO2), a side-production of CO and H2O (FA dehydration) should also be considered, because most PEM hydrogen fuel cells are poisoned by CO. In this research, a highly active aqueous catalytic system containing Ru(III) chloride and meta-trisulfonated triphenylphosphine (mTPPTS) as a ligand was applied for FA dehydrogenation in a continuous mode. CO concentration (8–70 ppm) in the resulting H2 + CO2 gas stream was measured using a wide range of reactor operating conditions. The CO concentration was found to be independent on the reactor temperature but increased with increasing FA feed. It was concluded that unwanted CO concentration in the H2 + CO2 gas stream was dependent on the current FA concentration in the reactor which was in turn dependent on the reaction design. Next, preferential oxidation (PROX) on a Pt/Al2O3 catalyst was applied to remove CO traces from the H2 + CO2 stream. It was demonstrated that CO concentration in the stream could be reduced to a level tolerable for PEM fuel cells (~3 ppm).
Highlights
Many methods to store and/or to transport energy in a green and durable way are being investigated in order to transition to an environmentally friendly economy
H2 could be chemically combined with carbon dioxide (CO2 ) to form liquid Formic acid (FA) [4], which is more stored and transported than gaseous H2 considering practical and safety issues
FA would function as an intermediate to store and to transport energy in a clean way (Figure 1)
Summary
Many methods to store and/or to transport energy in a green and durable way are being investigated in order to transition to an environmentally friendly economy. Is produced through steam reforming and water gas shift reactions rich gas streams, Equations (3) and (4) are of importance [23] Several catalysts such as noble metals supported on alumina or ceria as well as transition metals on similar supports are available [24]. CO content in the resulting gas mixture was not measured in a continuous mode, but batch experiments performed using the same reactant concentrations showed no CO traces (detection limit ~3 ppm) [7]. The CO concentration (ppm level) in the H2 + CO2 gas streams was measured as a function of the reaction temperature and FA feed flow. Quantification of such low CO concentrations (especially in CO2 -rich gas mixtures) is an extremely difficult task.
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