Microwave-Assisted Decarbonylation of Biomass-Derived Aldehydes Using Pd-Doped Hydrotalcites

Abstract

<p>Here we report the synthesis, characterization and activity of tunable Pd-doped hydrotalcites (Pd-HTs) for the decarbonylation of furfural, hydroxymethylfurfural (HMF), aromatic and aliphatic aldehydes under microwave conditions. The decarbonylation activity reported is a notable improvement over prior heterogeneous catalysts for this process. Furfural decarbonylation is optimized in a benign solvent compatible with biomass processing - ethanol, under relatively mild conditions and short reaction times. HMF selectively affords excellent yields of furfuryl alcohol with no humin formation, but longer reaction can also afford furan via tandem alcohol dehydrogenation and decarbonylation. Yields of substituted benzaldehydes are related to calculated Mulliken charge of the carbonyl carbon. The activity and selectivity differences can be traced to loading-dependent differences in Pd speciation on the catalysts. Poisoning studies show inverse correlation between Pd loading and metal leaching: Pd-HTs with lowest Pd loading, which consist of highly dispersed and oxidized Pd species, operate heterogeneously with negligible metal leaching. Recycling experiments are consistent with this trend, offering potential for further optimization to improve robustness.</p>

Decarbonylative Olefination of Aldehydes to Alkenes

“…Recently we reported the high activity of heterogeneous catalysts based on Pd-doped hydrotalcites (Pd-HTs) for selective decarbonylation of aldehydes. 4 In the course of this study we observed that a,b-unsaturated aldehydes decarbonylate faster than aromatic and saturated aliphatic aldehydes. Given that hydortalcites, composed of metal hydroxide sheets sandwiched by anions and water, have basic sites, they can promote aldol condensation.…”