Selective hydrogenation of furanic aldehydes using Ni nanoparticle catalysts capped with organic molecules

- Ni NPs capped with organic molecules showed high activity for selective hydrogenation.
- The surface organic molecules suppressed over-hydrogenation unlike uncapped Ni NPs.
- The size effect of capped and uncapped Ni NPs was estimated.
- The capped Ni NP catalysts can be reused up to 5 times without loss in activity.
- The absence of Ni ensemble sites on the capped Ni NPs was confirmed by in-situ IR.

Ni nanoparticles were synthesized by a colloidal method in the presence of organic surface-capping agents and used to catalyze the selective hydrogenation of unsaturated furanic aldehydes to furanic alcohols. The effects of the Ni nanoparticle size and surface organic layer were evaluated. Of the 3.7, 5.1, 6.8, and 10.4 nm Ni nanoparticles tested in selective furfural (FFR) hydrogenation to furfuryl alcohol (FFA), the 6.8 nm Ni nanoparticles exhibited the highest yield because access to the surface sites on the smaller and larger nanoparticles was blocked by the densely packed organic layer and by their agglomeration due to magnetic attraction, respectively. The capped Ni nanoparticles exhibited a high FFA yield of 96%, whereas significant over-hydrogenation was observed when uncapped calcined Ni/SiO2 catalysts with similarly sized Ni nanoparticles were employed. Steric hindrance of the Ni surface induced by the organic surface layer led to selective FFR hydrogenation to FFA. The capped Ni nanoparticles could be reused repeatedly without a significant loss in the FFA yield. They also exhibited high selectivity (>90%) in the hydrogenation of other unsaturated furanic aldehydes to their corresponding alcohols.

70