Product selectivity and mass transport in levulinic acid transfer hydrogenation by monolithic MIL-100, MIL-88B and ZIF-8@Pd MOFs

• Published in: Frontiers in chemistry 2023-01, Vol.10, p.1087939-1087939
• Main Authors: McIntyre, Sean R, Saenz-Cavazos, Paola A, Hunter-Sellars, Elwin, Williams, Daryl R
• Format: Article
• Language: English
• Subjects: biomass conversion; Chemistry; diffusion constant; hydrogenation; mass transfer; MOF; zero-length column
• ISSN: 2296-2646; 2296-2646
• DOI: 10.3389/fchem.2022.1087939

The diffusion processes between adsorbent and adsorbate naturally play a significant role in the efficiency and selectivity of the heterogenous catalytic process. This paper considers the importance of diffusion processes in the transfer hydrogenation reaction of levulinic acid to γ-valerolactone by MIL-88B, MIL-100, and ZIF8@Pd monolithic catalysts. Over a period of five catalytic cycles, it was shown that the Fe-based catalysts can achieve similar conversions to the ZIF-8 supported Pd, with the only current limitation being the lower aqueous stability of these MOFs. Diffusion constants were calculated using the ZLC method, with micropore diffusion limitation found for ZIF-8 and MIL-100 monolithic frameworks at 2.7 x 10 and 4.6 x 10  cm  s respectively. This diffusion limitation was also confirmed by IR spectroscopy with an increasing concentration of C-H bands on the MOF substrate post-reaction. Mass transfer coefficients, also calculated by ZLC, revealed increased mass transport for the hydrophobic ZIF-8 framework, which perhaps aids in the γ-valerolactone selectivity over side products that are produced in the absence of catalytic material, as seen for MIL-88B and MIL-100 after multiple uses.