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Chemistry, Chemical and Biological Engineering, NSF Engineering Research Center for Biorenewable Chemicals, Ames Laboratory

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Submitted Manuscript

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ACS Catalysis




Catalyst deactivation resulting from the hydrothermal leaching of sulfonic acid residues and the deposition of carbonaceous residues were studied using condensed phase flow reactor experiments along with state-of-the-art solid-state NMR. Several commercially available sulfonic acid-containing heterogeneous Brønsted acids were compared by measuring the rates of sulfonic acid breakdown at hydrothermal flow conditions of 160 oC. Amberlyst 45 was found to show higher hydrothermal stability when compared to both Nafion and Amberlyst 15, with <10% loss in acidity after 48 h. The dehydration reaction of fructose to hydroxymethylfurfural (HMF) was used as a model system to compare deactivation rates from carbon deposition (fouling) to those from sulfur leaching, and deactivation from fouling was shown to be dramatically faster than that from sulfonic acid leaching alone. Fouling rates were then investigated in greater detail by comparing the influence of several factors including reactant, solvent, residence time, and feed concentration. The only successful approach to minimize fouling was the use of a polar aprotic solvent (DMSO) with dilute (50 mM) reactant streams. In aqueous systems operating the reactor in a regime with low conversion conditions (short residence times) does not significantly improve the longevity of the catalyst. Spent catalysts were characterized using 13C solid-state NMR spectroscopy enhanced by dynamic nuclear polarization (DNP). Additionally, in situ 1H and 13C high-resolution magic angle spinning (HR-MAS) solid-state NMR spectroscopy was used to investigate the solvent influence at the catalyst interface. The HR-MAS NMR studies showed that in polar aprotic solvents, the increased acidity leads to greater selectivity towards HMF; more importantly, that the dehydration products do not readily adhere to the surface in DMSO, in contrast to their behavior in water. The results demonstrate that more active and longer-lived acid catalysts could be obtained by tuning the solvent and surface polarity to allow for efficient desorption of products, thereby reducing the catalyst deactivation that occurs due to fouling.


This document is the unedited Author’s version of a Submitted Work that was subsequently accepted for publication in ACS Catalysis, copyright © American Chemical Society after peer review. To access the final edited and published work see DOI: 10.1021/acscatal.9b03455. Posted with permission.

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American Chemical Society



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