Hydrothermal Reduction of NaHCO₃ into Formate with Protein-Based Biomass over Pd/γ-Al₂O₃ Nanocatalysts

Abstract

CO2/HCO3 – reduction with a renewable reductant has a promising potential for tackling the CO2 problem, but achieving high efficiency is still a challenge. Herein, protein-based biomass as the renewable reductant is found to achieve efficient NaHCO3 reduction under hydrothermal conditions. With the Pd/γ-Al2O3 nanocatalyst, the efficiency of NaHCO3 reduction reached 49.0% with l-alanine (the model compound of protein) as the reductant, which was attributed to the superior hydrogen activation property of Pd and the enhanced adsorption of NaHCO3 on the Pd/γ-Al2O3 surface. Furthermore, the mechanism study revealed that the reductive −NH2 group in protein fulfilled NaHCO3 reduction, which was moderately oxidized to N2 (not NO2 – or NO3 –) as the ultimate product, indicating additional merits of amending the natural nitrogen cycle and eliminating the burden of disposing toxic nitrite/nitrate. The universality of the proposed strategy was also examined with the direct use of protein and protein-based biomass of microalgae as the reductant. With efficient NaHCO3 reduction being achieved, this strategy of NaHCO3 reduction by protein-based biomass could provide a novel and sustainable approach to CO2 conversion and also a potential method of amending the anthropogenic-imbalanced nitrogen cycle.

CO2 reduction into formic acid under hydrothermal conditions: A mini review

“…Yang et al 61 found the yield of formic acid always maintained at ~7% even the water filling ratio raised to 45% when using 2‐pyrrolidone as a reductant. The same phenomenon also occurred when amino‐based reductant L‐alanine was used to generate formic acid from hydrothermal CO 2 reduction , in which the formic acid yield is near ~45% even though Pt/γ‐Al 2 O 3 was added to promote this process 62 …”

“…Moreover, they found that substitutional groups on −NH 2 oxidation could have a steric effect on the production of formate from HCO 3 − . 62 The benzene containing amino-based substance like L-lysine had a weaker ability for HCO 3 − reduction with only 19.2% yield of formate, which was even less than a half of the yield (51.2%) with glycine as reductant. DFT calculation revealed that the steric hindrance had a negative impact on the dehydrogenation of the amino group, in which 2.53 eV energy barrier for rate-determining step of L-lysine was required that is significantly higher than the value of 1.5 eV for glycine.…”

“…Effect of water filling on formic acid yield with different catalysts or reductants 19,25,29,30,61,62 enhance the dissolution of gaseous CO 2 in water improved the yield of formic acid to 5.5%. In contrast, when HCO 3 − was used as a carbon source, a 43% yield of formic acid was observed.…”

“…After the formation of a nitro compound, nitrobutyric acid is formed through intramolecular attack or nucleophilic attack of OH − to γ‐hydroxybutyric acid in an alkaline reaction system where the free NO 2 − reacts with NH 4 + to form N 2 to complete the whole reaction. Moreover, they found that substitutional groups on −NH 2 oxidation could have a steric effect on the production of formate from HCO 3 − 62 . The benzene containing amino‐based substance like L‐lysine had a weaker ability for HCO 3 − reduction with only 19.2% yield of formate, which was even less than a half of the yield (51.2%) with glycine as reductant.…”

Production of Nitrogen‐Containing Compounds via the Conversion of Natural Microalgae from Water Blooms Catalyzed by ZrO2

“…showed that protein‐based microalgae could also reduce CO 2 emissions, and the microalgae themselves could be converted into value‐added chemicals, such as organic acids and N‐substituted lactams. Utilizing the nitrogen source in protein‐based biomass can also reduce the consumption of fossil fuels [13] . Therefore, it is of great significance to study the use of nitrogen‐rich natural microalgae to produce value‐added nitrogen‐containing compounds [1c,14] .…”