Transformation of CO2 to Formic Acid or Formate Over Heterogeneous Catalysts
Although heterogeneously catalytic CO2 hydrogenation to formate was discovered 100 years ago, only recently important progress has been achieved. This chapter covers the most recent reported heterogeneous catalysts using Ni, Pd, Ru, Ir, and Au. The cataly
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Transformation of CO2 to Formic Acid or Formate Over Heterogeneous Catalysts
Abstract Although heterogeneously catalytic CO2 hydrogenation to formate was discovered 100 years ago, only recently important progress has been achieved. This chapter covers the most recent reported heterogeneous catalysts using Ni, Pd, Ru, Ir, and Au. The catalyst design and catalytic performance are described. Traditional supports such as carbon, alumina, silica, and titania are widely used. Cooperative effect of metals and supports is one important factor for the design of effective catalyst. Novel catalysts based on nanoporous material or nanoparticle and covalent framework are attractive due to their high activity.
Keywords CO2 hydrogenation Heterogeneous catalyst Formic acid Formate Immobilization Support
Heterogeneous catalysts can be reused repeatedly because they can be easily separated from the reaction mixture by simple filtration. They are environmentally benign and can be easily operated in continuous processes. In addition, the use of heterogeneous catalysts in molecule transformation makes the product separation easier. In 1914, heterogeneous CO2 hydrogenation to formate was first observed [1]. However, using heterogeneous catalysts for formate or formic acid (FA) synthesis from CO2 have only recently attracted renewed attention [2], although many kinds of heterogeneous catalysts were prepared and used to reduce CO2 to formic acid during the past decades. In this chapter, we introduce the most recent progress of CO2 transformation to formic acid with heterogeneous catalysts. It is classified according to different metal catalysts applied.
3.1
Nickel-Based Catalyst
The synthesis of FA from carbon dioxide with a heterogeneous catalyst was reported in 1935 by Farlow and Adkins [3]. The reaction was carried out using Raney® nickel as catalyst in the presence various amines and under 200–400 atm overall hydrogen pressure and 80–150 °C. In addition, amine was added to shift the thermodynamic equilibrium toward product formation (Eq. 3.1). © The Author(s) 2018 W.-H. Wang et al., Transformation of Carbon Dioxide to Formic Acid and Methanol, SpringerBriefs in Green Chemistry for Sustainability, https://doi.org/10.1007/978-981-10-3250-9_3
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3 Transformation of CO2 to Formic Acid …
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Raney nickel, 80 ºC, 1 h
CO 2 + H2 6 MPa
EtOH, 1-Ph-2-aminopropanol
HCOOH•Base
ð3:1Þ
55% yield
14 MPa
In 2006, Takahashi et al. studied the reduction of CO2 through a hydrothermal method to explore the selective formation of organic compounds [4]. They were able to form FA selectively at 300 °C when K2CO3 was employed as a CO2 source in the presence of Fe-powder, Ni-powder, and water (Eq. 3.2).
HCO3-
+ H2O Ni-powder, Fe-powder 300 °C, 6 h
HCO2-
ð3:2Þ
In 2016, Huo et al. reported the unsupported hydrogenation of carbonates to FA in aqueous phase for the first time [5]. The hydrogenation was catalyzed by nanoporous nickel (NiNPore), which was found to exhibit significant catalytic activity during the reduction of NaHCO3. FA w
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