Interface of Ni-MgCr<sub>2</sub>O<sub>4</sub> Spinel Promotes the Autothermal Reforming of Acetic Acid through Accelerated Oxidation of Carbon-Containing Intermediate Species
Chenyu Ding, Xiaomin Hu, Wenjing Sun, Reshalaiti Hailili, Fuxia Liao, Chenghong Shu, Jia Huang, Lihong Huang, Ning Wang
Abstract
Autothermal reforming (ATR) is an effective route for hydrogen production from acetic acid (HAc) derived from biomass. Ni-based catalysts are promising candidates for ATR due to their high activity, but coke formation hinders their practical application. To tackle this issue, a series of Ni-Mg-Cr catalysts with supports of Cr 2 O 3 or MgCr 2 O 4 were prepared by the sol–gel method and evaluated in ATR. The results indicated that as compared to the Ni-Cr 2 O 3 catalyst, the Ni 0.25 Mg 0.75 CrO 3.5±δ catalyst with MgCr 2 O 4 support presented higher catalytic performance: the conversion rate of acetic acid was stable near 100%, with hydrogen yield reaching 2.64 mol-H 2 /mol-HAc during a 40 h ATR test, while there was no obvious coking. It was found that Mg modification was prone to constituting a stable MgCr 2 O 4 spinel support with a high specific surface area for adsorption and transformation of HAc; however, for catalysts with excessive Mg addition, namely, Ni 0.43 Mg 2.56 CrO 4.5±δ and Ni 0.69 Mg 5.31 CrO 7.5±δ, low reactivity was found and was linked to constraining of Ni from the solid solution of Mg(Ni)O. Density functional theory (DFT) calculations reveal that during the ATR process, Ni 4 -MgCr 2 O 4 presents a low energy barrier for the overall transformation path and a high stabilization of reaction intermediates; furthermore, as compared to Ni 4 -Cr 2 O 3, oxidation of C* species by O* and OH* is significantly accelerated on Ni 4 -MgCr 2 O 4 due to the considerably decreased energy barriers, thus eliminating carbon deposition and improving catalytic activity.