Clean Hydrogen from Aqueous Water−Gas Shift Reaction at Near-Ambient Temperature

Abstract

Clean hydrogen generation from water using CO as the reducing agent is demonstrated in an aqueous water–gas shift reaction (AWGS) under ambient conditions. The aqueous phase water–gas shift reaction proceeds at 40 °C and 3 atm, with formic acid as the intermediate. Formic acid produced by a CO hydration reaction is subsequently dehydrogenated to yield H₂ and CO₂. The CO hydration step with a small positive ΔG° is enabled by elevating the CO partial pressure and using an aqueous [RuEDTA(CO)]⁻ catalyst prepared by dissolving the precursor [RuHEDTA(Cl)]K·2H₂O. The complex ion [RuEDTA(CO)]⁻ is denoted as the hydration catalyst (hyCat). Formic acid dehydrogenation is carried out over the heterogeneous catalyst PtRuBiO_x confined in a dehydrogenation reaction chamber. The use of a two-chamber reactor for the AWGS reaction provides isolation of the product hydrogen from the gas reactants, thus conveniently producing hydrogen with little or no CO. Using the two-chamber AWGS reactor, rates are measured at CO partial pressures of 3–11 atm and different [RuHEDTA(Cl)]K·2H₂O concentrations up to 5 mM. A model combining liquid-film transport and enzyme kinetics is proposed for the two-step AWGS reaction to fit the available data.