4.8 Article

Interface of Ni-MgCr2O4 Spinel Promotes the Autothermal Reforming of Acetic Acid through Accelerated Oxidation of Carbon-Containing Intermediate Species

Journal

ACS CATALYSIS
Volume 13, Issue 7, Pages 4560-4574

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/acscatal.2c06190

Keywords

acetic acid; autothermal reforming; hydrogen; spinel; DFT

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Ni-Mg-Cr catalysts with Cr2O3 or MgCr2O4 supports were prepared and evaluated in ATR for hydrogen production from acetic acid. The Ni0.25Mg0.75CrO3.5+/-delta catalyst with MgCr2O4 support showed higher catalytic performance, achieving stable conversion rate of acetic acid near 100% and hydrogen yield of 2.64 mol-H2/mol-HAc during a 40-hour ATR test with no significant coking. Mg modification led to the formation of a stable MgCr2O4 support with high specific surface area for HAc adsorption and transformation.
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 Cr2O3 or MgCr2O4 were prepared by the sol-gel method and evaluated in ATR. The results indicated that as compared to the Ni-Cr2O3 catalyst, the Ni0.25Mg0.75CrO3.5 +/-delta catalyst with MgCr2O4 support presented higher catalytic performance: the conversion rate of acetic acid was stable near 100%, with hydrogen yield reaching 2.64 mol-H2/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 MgCr2O4 spinel support with a high specific surface area for adsorption and transformation of HAc; however, for catalysts with excessive Mg addition, namely, Ni0.43Mg2.56CrO4.5 +/-delta and Ni0.69Mg5.31CrO7.5 +/-delta, 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, Ni4-MgCr2O4 presents a low energy barrier for the overall transformation path and a high stabilization of reaction intermediates; furthermore, as compared to Ni4-Cr2O3, oxidation of C* species by O* and OH* is significantly accelerated on Ni4-MgCr2O4 due to the considerably decreased energy barriers, thus eliminating carbon deposition and improving catalytic activity.

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