Investigation on the Catalytic Performance of Hydrogen Boride for Formic Acid

抄録

With the increasingly serious environmental and resource issues, traditional fossil fuels are gradually unable to meet our needs. Therefore, finding alternative green energy has become an important development direction. Formic acid (FA) is a multifunctional molecule that can be converted into various valuable substances. Two catalytic conversion reactions of formic acid are known: (1) dehydration reaction: HCOOH → CO + H₂O and (2) dehydrogenation reaction: HCOOH → H₂ + CO₂. Dehydration reaction can bring us CO, which can be used as a fuel and also plays an important role in the chemical industry and synthesis. Dehydrogenation reactions can generate H₂, which has received widespread attention and research in recent years as the most representative clean energy source.

Catalysts play an important role in various conversion reactions, and different catalytic reactions depend on different types of catalyst. The two-dimensional nano sheet materials obtained by the stripping of layered materials, owing to their large surface area and special electronic state, are expected to be used in various fields such as catalysts and electronic devices. In our laboratory, the hydrogen boride sheet (HB) was experimentally prepared by using strong acidic cation exchange resin to exfoliate and exchange the magnesium ions of layered material MgB₂ with protons.¹ The structure and special electronic state of HB make it promising as a new type of non-metallic two-dimensional layered catalyst.

In previous studies in our laboratory, it has been proved that hydrogen boride (HB) sheets play a role as a solid acid catalyst^{2, 3} and the sheets are chemically stable against water.⁴ Therefore, HB is expected to have a catalytic effect on the dehydration reaction of FA. In this study, the effect of HB on the catalytic conversion of FA will be investigated.

Firstly, we investigated the thermal decomposition characteristics of FA and found that FA undergoes a weak self-decomposition reaction starting from 260 °C. Then prepared HB sheets were loaded into a fixed bed reactor. As pre-treatment, the sample was heated at 300 °C in argon gas environment for 1 hour and cooled to room temperature, testing within the range of 120 - 300 °C with the introduction of FA.

We found that the conversion of FA began at 120 °C after the addition of HB, and CO was selectively generated with high conversion within the high-temperature range. The W/F (weight of catalyst / ethanol flow rate) was changed by adjusting the FA flow rate. It was found that under different W/F conditions, the product selectivity did not change significantly, But the conversion rate has changed within the low temperature range. The small amount of generation of CH₄ during the 1 μl/min experiment may be due to the large amount of hydrogen released by HB during the initial heating period which may convert CO to CH₄. After a period of time, the HB sheet reached a stable state and no CH₄ was generated (0.5 μl/min and 2 μl/min experiment). This means that FA is likely to be converted to CO with a conversion of over 90% and a selectivity of 100% under the catalysis of HB. And continuous stability tests have proven the good catalytic stability of HB. Our experimental results show that HB has good catalytic performance for the dehydration reaction of formic acid. In the presentation, detail reaction features will be shown.

References:

1) H. Nishino, et al., J. Am. Chem. Soc. 139 (2017) 13761.

2) A. Fujino, et al., ACS Omega. 4 (2019) 14100-14104.

3) A. Fujino, et al., Phys. Chem. Chem. Phys. 23 (2021) 7724-7734.

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