High-performance metal-base bifunctional catalysts (Ni_xMg_y-MMO) for aqueous phase reforming of methanol to hydrogen

Reforming methanol in an aqueous phase is of great interest, including the water–gas shift (WGS) reaction for converting the CO formed from the dehydrogenation of methanol (DM) to CO₂ and promoting hydrogen gas production by 50%. Ni-based catalysts are highly active for catalyzing the involved dehydrogenation reaction but perform poorly at the low temperature range for the WGS reaction. In this work, metallic Ni-catalytic sites supported on basic mixed metal oxides (Ni_xMg_y-MMO), prepared from NiMgAl layered double hydroxide (LDH) precursors, were applied for the first time in the aqueous phase reforming of methanol (APRM). The Ni₃Mg₁-MMO catalyst demonstrated outstanding catalytic performance with a high hydrogen production rate of 167.2 μmol_H2/g_cat./s and a low CO selectivity of 1.9% at the temperature of 240 °C. These are among the best literature results for the APRM catalyzed by Ni-based catalysts. Compared to the neutral Ni@NC catalyst, the metal-base bifunctional Ni₃Mg₁-MMO catalyst significantly boosts the WGS process, reducing the CO selectivity and enhancing the APRM. The structure-performance studies of the Ni_xMg_y-MMO catalysts in the reactions of DM, WGS, and APRM showed that the intrinsic activity for DM increases significantly as the Ni particle size decreases, while WGS and APRM reactions are dominantly improved by the medium basic property that originated from Mg-O pairs. As a result, the intrinsic activity of the catalysts in APRM also decreases as the Ni particle size increases. These new findings are transferable to the design of efficient metal-base bifunctional catalysts for reactions similar to WGS and APRM.