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

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.

Mullite-like SmMn2O5-Derived Composite Oxide-Supported Ni-Based Catalysts for Hydrogen Production by Auto-Thermal Reforming of Acetic Acid

“…Because of the interaction between Ni and Sm 2 O 3 -MnO in the 15NSM catalysts, the phase transition from m-Sm 2 O 3 to c-Sm 2 O 3 during the ATR reaction was effectively suppressed, which can be proved by XRD, and stability of the catalyst was improved. Meanwhile, over the Ni/Sm 2 O 3 -MnO active centers, the Mn 3+ species donated electrons to Sm 3+ and Ni 2+ , and the electron exchange via Mn 3+ + Sm 3+ ↔ Mn 4+ + Sm 2+ promoted the formation of surface oxygen vacancies in 15NSM, which effectively promoted the migration of active oxygen species O* and accelerated the gasification of carbon precursor C* (C* + O*→CO, CO* + O*→CO 2 ) [ 59 , 60 , 61 ], thus inhibiting coke formation, as shown in TG/DTA, SEM and the proposed Scheme 1 . In addition, due to the electron donation effect of the Mn species, a relatively stable surface Ni content was maintained throughout the reaction.…”

Synthesis and advantages of spinel-type composites

“…Then, reactions such as hydrolysis and condensation will occur in the formed transparent sol system. 90,91 Through the sol changing into a gel and a calcination process, the final products are finally obtained. Precipitation and microemulsion are two typical liquid-phase synthesis methods, which can obtain specific products by adding the precipitant to mixed solutions with different contents or by mixing two kinds of immiscible solvents with the addition of a surfactant, respectively.…”

Hydrogen Production through Distinctive C−C Cleavage during Acetic Acid Reforming at Low Temperature

“…Acetic acid-water reforming has become a research hotspot for hydrogen production. [18,19] Acetic acid is a green liquid fuel which could be produced from biomass fermentation, pyrolysis and liquefaction. As exhibited in Scheme 1, hydrogen could be produced from sustainable biomass through microbial direct fermentation or indirect method, such as ethanol and acetic acid reforming.…”