Towards continuous deoxygenation of acetic acid catalyzed by recyclable mono/bi/trimetallic zeolite catalysts

A series of mono (Ni, Cu, Co), bi (NiCu, NiCo, CuCo), and trimetallic (NiCuCo) mordenite supported catalysts were characterized and evaluated for the continuous, near-atmospheric pressure, thermal deoxygenation of acetic acid. Acetic acid was selected as a model reactant due to its abundance in both biomass pyrolysis upgrading streams and its analogous structure to carboxylic acids found in vegetable oil upgrading streams. Surface area and metal loading were nearly constant for all studied catalysts, allowing an in-depth direct comparison of the metallic activity for reaction pathways including gasification, decarboxylation, decarbonylation, hydrodeoxygenation, and ketonization. In the absence of Ni or in the absence of H-2, the observed catalytic activity was low. Results from the bimetallic samples at 400 degrees C highlighted the importance of Ni for H-2 activation and Co for the simultaneous promotion of hydrodeoxygenation and gasification. A nearly linear correlation between the Ni content and the conversion of acetic acid was observed at 400 degrees C. Cryogenic argon isotherms revealed the location of metal sites within the mordenite pore, further emphasizing the impact of confining environments on the deoxygenation of bio-derived compounds. TGA, TPR, and TPD studies provided information on catalyst stability, reducibility, and acidity, respectively. HRTEM indicated that agglomerates formed under the studied reaction conditions. The fresh Ni/MOR catalyst, under differential conversion conditions, was stable for similar to 24 h at 460 degrees C, for an additional similar to 20 h upon regeneration at 460 degrees C, and for an additional 30 h upon regeneration at 500 degrees C. Long-exposure activity was observed in the Ni/MOR catalyst, favoring hydrodeoxygenation and decarbonylation for at least 70 h under integral conversion conditions. In the bimetallic NiCo/MOR catalyst, Co stabilized Ni active sites in a co-located configuration which promoted hydrodeoxygenation, but also promoted gasification, and eventually lead to coking/lower conversion. (C) 2021 Elsevier Inc. All rights reserved.

Automated summary

The study revealed the importance of Ni for H-2 activation and Co for simultaneous promotion of hydrodeoxygenation and gasification. A linear correlation between Ni content and acetic acid conversion was observed. Additionally, cryogenic argon isotherms indicated the location of metal sites within the mordenite pore.