Promoting mechanism of alkali for aqueous phase reforming of bio-methanol towards highly efficient production of COx-free hydrogen

Abstract

Transforming the poisonous CO generated on the active metal sites promptly is essential for Ni-based catalyst applying in aqueous-phase reforming (APR) of biomass-derived oxygenated hydrocarbons, e.g. methanol, due to its low water-gas-shift (WGS) activity. Here, we used alkali modifier in the APR of methanol (APRM) with a Ni@NC catalyst and explored the promotion mechanism of alkali in depth. Compared with the performance of APRM over the Ni@NC catalyst without using any alkali, the hydrogen production rate increased to 8 times higher (from 33.4 to 265.4 μmolH2/gcat./s), while the CO selectivity decreased drastically (from 26.8% to 0.1%) after adding KOH at 220 °C. Through IR and XRD analysis of the produced potassium salts, it was found that the KOH mainly directly reacted with the CO produced from methanol dehydrogenation forming HCOOK, which eliminated the poisonous effect of CO on the active Ni sites and promoted methanol dehydrogenation remarkably. Besides, a small amount of KOH reacted with CO2 and promoted the WGS, by which in situ stabilization of CO2 was realized, reducing carbon emission. As a result, COx-free hydrogen at a high production rate was achieved, with HCOOK, the precursor for the important hydrogen carrier formic acid, as a side product.