(225f) Cinnamaldehyde Hydrogenation in A Continuous GLASS Capillary Reactor with Immobilized Palladium Nanoparticles

Selective hydrogenation of α,β-unsaturated aldehydes is of great importance in fine chemicals production. Multi-phase hydrogenation of cinnamaldehyde has attracted a great deal of research attention because the hydrogenation products are widely used in production of perfume, food additives, and pharmaceutical intermediates [1]. It is desirable to design catalytic processes to selectively hydrogenate cinnamaldehyde to specific products for economic and environmental purposes. In our work, we have synthesized palladium nanoparticles (Pd NPs) via a polyol reduction method [2], with polyvinylpyrrolidone (PVP) as stabilizer. Transmission electron microscopy (TEM) characterization shows that the Pd NPs are uniformly distributed with a diameter of 7.5±1.0 nm. The catalytic reaction system was constructed by immobilizing the prepared Pd NPs onto the surface of a glass capillary microreactor via a previously developed protocol [3]. The successful catalyst deposition was confirmed by X-ray photoelectron spectroscopy (XPS). The reactivity of the Pd NPs was evaluated in the glass capillary microreactor with continuous atmospheric hydrogen supply, and the products were analyzed by gas chromatography (GC) [4].  Less than 3% of cinnamaldehyde was hydrogenated in a blank glass capillary under similar reaction conditions. In comparison, glass capillary microreactors with immobilized Pd NPs achieved 100% conversion in 15 min, and maintained such reactivity for the following eight (8) hours. The reaction products include 3-phenyl-propionaldehyde and 3-phenyl-prop-2-en-1-ol, corresponding to the reduction of C=C and C=O bonds, respectively. The Pd catalysts consistently gave a high selectivity of C=C bond reduction (85%) at complete conversion, with the selectivity of C=O bond reduction maintained at about 15%.  This system has the potential to provide an important tool for efficient and rapid evaluation of catalytic nanoparticles and a controllable continuous reaction mode to produce desirable intermediate products.

  References

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2. F. Tao, M. Grass, Y. Zhang, D. Butcher, F. Aksoy, S. Aloni, V. Altoe, S. Alayoglu, J. Renzas, C. Tsung, Z. Zhu, Z. Liu, M. Salmeron, G.Somorjai. JACS articles. Vol. 132(2010), pp. 8697-8703.
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4. R. Lin, X. Ma, R. Ofoli. Selective hydrogenation of cinnamaldehyde in glass capillary microreactors with immobilized nanoparticles. In preparation.