Size Effects of Ni Particles on the Cleavage of C–H and C–C Bonds toward Hydrogen Production from Cellulose
Jian Zhang, Yanru Zhu, Zhe An, Xin Shu, Xiaodan Ma, Hongyan Song, Wenlong Wang, Jing He
Abstract
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.