Artificial control of olivine alteration has potential applications for both H-2 production and CO2 reduction (by mineralization and hydrogenation). To explore methods to overcome the still-constrained olivine alteration problem, olivine + spinel alteration experiments were performed with the addition of Mg-Al spinel in CO2-rich (0.5 M NaHCO3) solution under hydrothermal conditions (300 degrees C and 10 MPa). Mg-Al spinel enhanced olivine serpentinization significantly (more than 2 times), and generation of both H-2 and CO2 hydrogenation products was accelerated (up to 3 times) with >= 10 wt% Mg-Al spinel especially at the latter stage of the 72 h reaction. Mineral measurements revealed that more Al released from Mg-Al spinel was incorporated into Al-serpentine by the replacement of Fe with higher Mg-Al spinel content. Both Al and Fe incorporated into Al-serpentine were released as the reaction proceeded. Thus, H-2 production was elevated with the presence of a large amount Mg-Al spinel at the latter stage of the reaction. HCO3 played an important role in the promotion of Mg-Al spinel dissolution with the release of Al, which was stored in magnesite after being utilized. This study also suggests that the presence of Mg-Al spinel (5-20 wt%) in the starting mineral does not have significant influence on the total H-2 yield from olivine alteration over the entire operation period. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.