Hydrogen Production from Formaldehyde and Paraformaldehyde in Water under Additive-Free Conditions: Catalytic Reactions and Mechanistic Insights

Abstract

Efficient catalytic systems based on arene-Ru(II) complexes bearing bisimidazole methane-based ligands were developed to achieve additive-free hydrogen generation from formaldehyde and paraformaldehyde in water. Our findings inferred the influential role of bis-imidazole methane ligands in the observed catalytic performance of the studied catalysts. Among the screened complexes, [(η 6 -p-cymene)RuCl(L)] + Cl − ([Ru]-2) (L = 4,4′-((2-methoxyphenyl)methylene)bis(2-ethyl-5-methyl-1H-imidazole) outperformed others to generate hydrogen gas from paraformaldehyde in water with an exceptionally high turnover number (TON) of >20,000. A detailed mechanistic pathway for hydrogen gas generation from formaldehyde has been proposed on the basis of identified several crucial catalytic intermediate species involved in the hydrogen production process.

Diruthenium Catalyst for Hydrogen Production from Aqueous Formic Acid

“…In the coming decades, the global energy demand is expected to continue to rise. As a result, accepting the challenge of providing sustainable energy to the world will be critical in the near future. − In this regard, hydrogen is considered to be an efficient chemical energy carrier that can meet the rising energy demand by reducing greenhouse gas emissions. , In this direction, liquid organic hydrogen carriers (LOHCs) carrying a high gravimetric content of hydrogen, such as methanol (12.5 wt % H 2 ), formaldehyde (8.4 wt % H 2 ), and formic acid (4.4 wt % H 2 ), can provide a solution for the safe storage and transportation of hydrogen gas. − Among these LOHCs, formic acid (53 g of H 2 /L), which is a simple C1 carboxylic acid found in nature or can be easily produced in the laboratory, can release hydrogen gas in the presence of an appropriate catalyst under mild reaction conditions. , …”

Ruthenium-Catalyzed Transformation of Ethylene Glycol for Selective Hydrogen Gas Production in Water

“…At the industrial scale, hydrogen is produced by methane reforming, aqueous-phase reforming, and steam reforming of fossil fuels, which are highly energy-intensive processes with the emissions of greenhouse gases. On the other hand, with the intervention of a suitable catalyst, hydrogen can be produced from several promising and potential small organic molecules such as methanol, − formic acid, − formaldehyde, ,− and other polyols. − …”

“…Recently, Maji et al employed a Mn-PNP complex for EG reforming to GA and H 2 as a byproduct at 140 °C in t AmOH in 12 h. 53 Therefore, it is evident from these reports that most heterogeneous catalysts work well at high temperature, while homogeneous catalysts are primarily explored in nonaqueous solvents. Recently, we also developed and explored several efficient catalysts for lowtemperature hydrogen production from methanol, 16 formic acid, 20,21 formaldehyde, 25 glycerol, 27 and others under water-based conditions. We envisioned that the dehydrogenation of EG may lead to the selective production of hydrogen gas along with the generation of formic acid as a valuable byproduct.…”

C−N Bond Formation Using Paraformaldehyde as C1 Source – Recent Advances

“…[15][16][17][18] Paraformaldehyde is a kind of solid formaldehyde with high formaldehyde content, which can be turned into formaldehyde vapour at higher temperatures, so it is easy to take part in various reactions instead of high-concentration formaldehyde. [19][20][21] Paraformaldehyde possesses the advantages of cheap price, perfect reliability, mild poison, easy to operate and transport. [22][23][24] Therefore, the use of paraformaldehyde as a source of C1 to participate in the conversion reaction in organic synthesis has attracted more and more attention.…”

“…Paraformaldehyde is a kind of solid formaldehyde with high formaldehyde content, which can be turned into formaldehyde vapour at higher temperatures, so it is easy to take part in various reactions instead of high‐concentration formaldehyde [19–21] . Paraformaldehyde possesses the advantages of cheap price, perfect reliability, mild poison, easy to operate and transport [22–24] .…”