Insight into the Selectivity Mechanism During Formaldehyde Decomposition: Hydrogen or Methanol Production

Abstract

Formaldehyde-water decomposition is promising for hydrogen production due to high hydrogen content. Its decomposition involves complex parallel reactions, but thermodynamically usually yields methanol, not H₂. Formaldehyde decomposition has several steps, with formic acid as a key intermediate from the formaldehyde–water shift. Organometallic hydrides are crucial catalyst intermediates in both the shift and formic acid decomposition. They overcome energy barriers to react with H⁺ or CH₂(OH)₂, determining final products. DFT calculations show an organoruthenium hydride prefers H₂ production via proton coupled electron transfer (PCET), despite higher Gibbs free energy (Δ_rG) than methanol formation, because methanol production has a high-barrier step. Alkaline solvent boosts H₂ yield over organorhodium. Formaldehyde could also decompose into hydrogen over organorhodium in a medium-pressure reactor, as higher temperature facilitates methanol reforming, a novel pathway.