Abstract
It is well known that Pd based catalyst deactivate during formic-acid decomposition in aqueous phase at mild temperatures. This study reports on a kinetic study of formic acid decomposition over Pd/γ-Al2O3 catalysts including the effect of traces of oxygen, as well as pretreatment of the catalysts and supported by in-situ Attenuated Total Reflection Infrared Spectroscopy experiments. The results show that deactivation of Pd/γ-Al2O3 catalysts can be suppressed by adding traces of oxygen. This is assigned to removal of adsorbed CO, poisoning the Pd surface, via oxidation to CO2. The activity of the catalyst during operation is maintained, promoting the H2 production compared to operation in absence of any oxygen. Clearly, oxygen oxidizes CO preferentially over H2 under the condition that the oxygen concentration is kept below 0.1 vol% in this study. Further increasing the oxygen concentration further increases conversion rate of formic-acid but also decreases the hydrogen yield significantly because formic acid oxidation and/or consecutive H2 oxidation become dominating. The results of this study are important because the effect of traces of oxygen from ambient has not been considered in most of the reports in literature.
Highlights
In times of fossil fuel resources shortage and concern about CO2 emissions, the search for alternative and sustainable energy sources has become more pressing than ever
This study reports on the influence of the oxygen concentration on rate, selectivity and deactivation in formic-acid decomposition over Pd catalysts
Note that the differences in the shape of the profiles are caused by the fact that the liquid phase can be considered as a batch reactor, the formic-acid concentration is converted with a decreasing rate in time
Summary
In times of fossil fuel resources shortage and concern about CO2 emissions, the search for alternative and sustainable energy sources has become more pressing than ever. Hydrogen has attracted an increasing level of attention as an important energy vector and may play a significant role in power distribution in the future. Many molecules have been proposed as hydrogen carriers, e.g. ammonia [1], methanol [2], methane [3] as well as higher hydrocarbons [4]. Another option is formic-acid which can be produced from CO2 and green hydrogen [5,6,7], resulting in a carbon-neutral process. Formic-acid is a significant by-product from biomass conversion. This work focusses on using liquid-phase formic-acid as a hydrogen storage material
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