(496e) Tandem Catalysis in a New, Solid-Phase Route to Renewable Aromatic Chemicals from Biobased Furanics

Efficient production routes for â??drop-inâ??, renewable aromatics are currently bring highly sought after due to diminishing reserves and changes in the composition of fossil fuel resources. In this light, sugar-derived furanics offer attractive alternative resources for the production of aromatic chemicals. Recently, we reported on a new three-step procedure to the synthesis of (substituted) phthalic anhydrides from biobased furanics by introducing an intermediate hydrogenation step in the classical Diels-Alder (DA) aromatization route, typically run at elevated temperatures, to address the general issue of the reversible nature of the DA addition step [1]. The hydrogenated DA adduct of, e.g. 2-methylfuran and maleic anhydride (MFMA[H]), is thermally stable and can be efficiently aromatized to give 3-methylphthalic anhydride and ortho-/meta-toluic acid in a tandem catalytic reaction using a physical mixture of acidic zeolites and Pd/C in toluene. Variation in acidity and textural properties of, e.g. H-Y zeolites, in the combined dehydration/dehydrogenation catalyst provides a handle on selectivity toward aromatic products [2]. A linear correlation exists between the yield of 3-methylphthalic anhydride and the product of the strong acid/total acidity ratio and mesopore volume of H-Y, indicating the need for a balanced catalyst acidity and porosity of H-Y zeolite.

Here, we show that the hydrogenated DA adducts can also be conveniently converted to renewable aromatics in a solid-phase reaction (i.e., without any solvent), using only H-Y zeolites [3]. The remarkable performance of these catalysts in the solid-phase can still be further enhanced upon the addition of a small amount of a dehydrogenation catalyst (e.g., 1 wt. % Pd/C or Pt/C) or by the use of bifunctional catalysts (e.g., 1 wt. % Pd/H-Y or Pt/H-Y). Monitoring the evolution of H₂, H₂O, and CO₂ as a function of temperature and time provided valuable insights into the mechanism of aromatization and decarboxylation. The effects of various experimental parameters, different concentrations of H-Y zeolites and dehydrogenation catalysts, on the reactivity of MFMA[H] were studied to effectively control the reaction rate and product selectivity. The use of Pt/H-Y (Si/Al=30) resulted in an excellent yield of 94% total aromatics, which is the highest reported to date. The bifunctional catalysts were also found highly selective for the aromatization of other hydrogenated DA furan derivatives. The development of new heterogeneous catalysts for the production of aromatic chemicals from biomass-derived furanics can therefore be guided by taking into account the influence of the acidic and textural properties of H-Y zeolites on selectivity.

[1] S. Thiyagarajan, H. C. Genuino, M. Å?liwa, J. C. van der Waal, E. de Jong, J. van Haveren, B. M. Weckhuysen, P. C. A. Bruijnincx, D. S. van Es. Substituted phthalic anhydrides from bio-based furanics: A new approach to renewable aromatics, ChemSusChem 2015, 8, 3052-3056.

[2] H. C. Genuino, S. Thiyagarajan, J. C. van der Waal, E. de Jong, J. van Haveren, D. S. van Es, B. M. Weckhuysen, P. C. A. Bruijnincx. Selectivity control in solid acid and Pd-catalyzed tandem aromatization of bio-based furanics, Manuscript in preparation.

[3] S. Thiyagarajan, H. C. Genuino, J. C. van der Waal, E. de Jong, B. M. Weckhuysen, J. van Haveren, P. C. A. Bruijnincx, D. S. van Es. A facile solid-phase route to renewable aromatic chemicals from biobased furanics, Angew. Chem. Int. Ed. 2016, 55, 1368-1371.