Biobased adipic acid is a platform chemical that can be produced via the catalytic hydrogenation of muconic acid, a biomass-derived microbial intermediate. Supported Pd catalysts achieve quantitative yields of adipic acid during muconic acid hydrogenation, with a turn-over frequency (TOF) &gt;10 sec-1; however, the acidic environment promotes irreversible Pd leaching and results in nonviable process economics. Atomic layer deposition (ALD) has emerged as a promising technology to stabilize Pd active sites against leaching and sintering by applying sub-nanometer metal oxide coatings in a self-limiting, layer-by-layer fashion. ALD increases catalyst stability with each coating cycle, albeit with the tradeoff of reduced Pd accessibility. This work examines the application of Al2O3 ALD to sufficiently stabilize Pd deposited on commercial TiO2 supports during muconic acid hydrogenation. Catalyst characterization via scanning transmission electron microscopy and atom probe tomography confirm that Al2O3 ALD sufficiently deposits throughout the complex pore network of TiO2, while batch and flow reactor testing determine that sub-nanometer ALD coatings reduce Pd leaching by over two-fold and mitigate sintering at 700°C, all while retaining over 70% of the uncoated catalyst productivity. Accelerated aging results were then incorporated into techno-economic models to demonstrate the potential of ALD to lower the minimum selling price of biobased adipic acid for an “nth-generation” biorefinery through enhanced catalyst stability.

Atomic layer deposition with Al2O3 for enhanced Pd/TiO2 stability during biobased adipic acid production

256th National Meeting (2018)

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