Size Effects of Ni Particles on the Cleavage of C–H and C–C Bonds toward Hydrogen Production from Cellulose

Hydrogen production from cellulose via aqueous-phase reforming (APR) has aroused increasing attention, but its efficiency remains challenging. Layered double oxide (LDO)-supported Ni particle has been reported as an efficient catalyst for H 2 production from cellulose in our previous work: basic sites on LDO play an important role in H 2 production by activating O–H bonds, which facilitates the cleavage of C–H and C–C bonds on Ni particles. The interfacial Ni δ+ sites further increase H 2 yield by promoting the water–gas shift (WGS) reaction. Here, this work modulates the size of Ni particles by tailoring the Ni content in Ni-containing layered double hydroxides (LDHs), and the effects of Ni particle size on the H 2 production have been investigated. The dependence of C–H and C–C cleavage on the size of Ni particle has been revealed. It has been found that a smaller Ni particle possesses lower electron density, thus significantly accelerating the C–H cleavage after the rupture of O–H bonds. But the C–C cleavage is inhibited due to lack of electron-rich adjacent Ni 0 sites on smaller Ni particles, resulting in severe coke formation. Increasing the Ni particle size favors the C–C cleavage. As a result, the H 2 yield demonstrates a “volcanic” dependence on the Ni particle size. Also, this work further confirms the role of interfacial Ni δ+ sites in facilitating CO removal by WGS reaction and suppressing the methanation of CO and/or CO 2 especially on larger Ni particles.