Methanation Suppression and Hydrogen Production Enhancement in Methanol Steam Reforming by K-Doped Ru/CeO2 Catalyst

Methanol steam reforming is a popular technology for hydrogen production, but it usually suffers from the methanation side reaction and low hydrogen yield. Herein, a novel K-doped Ru/CeO2 catalyst was proposed to suppress methanation and enhance hydrogen production. The Ru-5K/CeO2 catalyst doped with 5 wt % K achieves 100% methanol conversion, a 0.578 mol·g–1·h–1 hydrogen production rate, and 66.4% hydrogen selectivity at 450 °C, with only 3.6% CH4, which is much better than other Ru–K/CeO2 catalysts. Under the same conditions, Ru/CeO2 and Ru-10K/CeO2 only achieve 0.268 mol·g–1·h–1 and 0.224 mol·g–1·h–1 hydrogen production rates, 64.1% and 64.5% hydrogen selectivity, respectively. The promotion effect and mechanism of K doping on the methanation suppression of Ru/CeO2 catalysts in the methanol steam reforming process were investigated in detail. Characterization and experimental results show that suitable K doping in the Ru/CeO2 catalyst enhances the metal–carrier interactions and induces the formation of abundant oxygen vacancies at the same time. And the hydrogen atom dissociation and water–gas shift reactions on the catalyst surface are promoted significantly. Additionally, in situ DRIFTS characterization presents that the Ru-5K/CeO2 catalyst dominates the formation of the bridged carbonyl (Ru-CO-K) intermediate. This inhibits methane formation due to the interaction between Ru and K, and strengthens the connection of CO generated by methanol decomposition. The increase in K leads to the formation of abundant oxygen vacancies in CeO2, which promotes the dissociation of water to form hydroxyl groups and hydrogen and facilitates the water–gas shift reaction. The conversion of bridged carbonyl groups to CO2 and H2 is also accelerated, and methane formation through this dual regulatory mechanism is thus inhibited. This work offers fresh perspectives and a useful reference for hydrogen production, contributing to the ongoing discussion on the role of alkali metals in promoting methanol steam reforming.