Mechanistic study of HCOOH hydrogenation on Cu-based catalysts: Formaldehyde as H-donor for H2O formation

In pursuing low-carbon activity, the development of liquid fuels other than gasoline becomes urgent. Methanol (CH 3 OH), as a C1 green chemical, is discovered to achieve low exhaust emissions as an alternative biofuel for engines. In addition to CO 2 or CO gas, formic acid (HCOOH) has been acknowledged as CH 3 OH building block·H 2 O, as a byproduct in CH 3 OH synthesis, can be treated as a promoter for methoxy (H 3 CO) hydrogenation to enhance CH 3 OH selectivity; however, its generation appears to be difficult. In the present work, we propose a new mechanism for H 2 O generation for HCOOH-to-CH 3 OH conversion using H 2 CO as H-atom donor to OH group on non-confined and UiO-66 confined Cu 16 cluster. As demonstrated, H 2 CO achieves to lower the formation barrier of H 2 O, which is found to promote H 3 CO hydrogenation on Cu 16 @UiO-66 when it is used as H-atom donor. For HCOOH-to-CH 3 OH conversion, UiO-66 confinement effect is mainly reflected on Cu 16 stabilization by curbing cluster aggregation. • A novel reaction mechanism proposed for H 2 O formation on non-confined and UiO-66-confined Cu clusters. • The mechanism is more effective than OH disproportionation pathway. • H 2 O is further demonstrated to promote H3CO hydrogenation for HCOOH-to-CH 3 OH conversion.