Role of Catalyst Support's Physicochemical Properties on Catalytic Transfer Hydrogenation over Palladium Catalysts

Abstract

Catalytic transfer hydrogenation (CTH) is a promising reaction for valorisation of bio‐based feedstocks via hydrogenation without needing to use H2. Unlike standard hydrogenation, CTH occurs via dehydrogenation (DHD) of a hydrogen donor (H‐donor) and hydrogenation (HYD) of a substrate. Therefore, the “ideal” CTH catalyst must balance the catalysis of both reactions to maximize the hydrogen transfer between H‐donor and substrate with minimal H2 loss to gas (high atom efficiency). Additionally, the H‐donor must be highly stable to prevent secondary reactions with the substrate. Herein we study the impact of the catalyst's properties on CTH of guaiacol using bicyclohexyl, a liquid organic hydrogen carrier, as a H‐donor. The reaction was promoted by palladium dispersed on three typical support materials (γ‐Al2O3, MgO, and SiO2). The performance of these catalysts in the conversion of bicyclohexyl and guaiacol was evaluated, allowing to estimate the H‐transfer efficiency, as well as the potential for recycling the spent H‐donor (bicyclohexyl). The apparent activation energies for DHD of bicyclohexyl and HYD of guaiacol revealed that slow DHD combined with fast HYD, as is the case with Pd/MgO, favours hydrogen transfer efficiency and selectivity towards hydrogenated products. In addition, an investigation of the DHD of bicyclohexyl and HYD of guaiacol independently showed that the affinity between the organic molecules and the support significantly impacts CTH. Indeed, Pd/SiO2 was highly active for both reactions individually and almost inactive for CTH. Consequently, these findings highlight the importance of the interaction between solvent‐substrate‐support in designing catalysts for transfer hydrogenation.

Conceptual Process Design, Techno-Economics, and Greenhouse Gas Analysis of Furfuryl Alcohol Production via Transfer Hydrogenation

“…With the increasing demand for safer chemical processes and replacement of fossil-based feedstocks with biobased ones, − the interest in using CTH to upgrade biomass-derived molecules has seen considerable growth in recent years. − Several CTH reactions have been investigated, such as (i) γ-valerolactone from levulinic acid, (ii) furfuryl alcohol (FFA) from furfural, (iii) hydrodeoxygenation of guaiacol, and (iv) hydrogenation of 5-HMF . While most of the experimental work has focused on isopropanol (IPA) as a hydrogen donor, , other donor sources such as ethanol, glycerol, and even hydrocarbons , have been shown to effectively provide hydrogen during CTH reactions. Nevertheless, there is a lack of consistency around which hydrogen donor should be used and the advantages and disadvantages of each molecule in this process.…”