Sequential Reactions Directed by Core/Shell Catalytic Reactors

Abstract

Millimeter-sized reactor particles made of permeable polymer doped with catalysts arranged in a core/shell fashion direct sequences of chemical reactions (e.g., alkyne coupling followed by hydrogenation or hydrosilylation followed by hydrogenation). Spatial compartmentalization of catalysts coupled with the diffusion of substrates controls reaction order and avoids formation of byproducts. The experimentally observed yields of reaction sequences are reproduced by a theoretical model, which accounts for the reaction kinetics and the diffusion of the species involved.

Nanoparticle–Loaded Aerogels and Layered Aerogels Cast from Sol–Gel Mixtures

“…Looking forward, we also suggest that alcogels and aerogels comprising layers doped with different catalytic NPs could find uses in directing multistep catalytic reactions whereby the reaction substrates migrate through and react sequentially on the different layers 16. Finally, we note that the solution‐based method for casting NP‐doped alco/aerogels is also compatible with molding techniques,27 (see Figure 5b,c), potentially enabling the printing of microstructures for uses in aerogel‐based optical devices3, 28 or sensors 10…”

“…Our procedure does not require solvent exchange to transfer the NPs into precursor gels,14 or the chemical reduction/vapor deposition of metal precursors to form NPs in porous silica15 (such post‐treatments usually lead to the poor control of NP size and limit the loading of NPs to ∼25 wt%14). Since our method is based on the casting of sol–gel‐NP mixtures, it can readily produce multilayered aerogel monoliths comprising different types of NPs (here, Au, Ag, Pd) that could be useful in multistep catalysis 16…”

Synthesis of palladium colloids within polydimethylsiloxane and their use as catalysts for hydrogenation

“…Trapp et al used gas chromatography columns coated with Pd colloids in siloxane polymers to study the kinetics of hydrogenation reactions [7,18], and Fritsch et al designed a reactor with Pd trapped within a PDMS membrane for catalyzing the hydrogenation of acetophenone [17] and the hydrodechlorination of chlorobenzene [19]. Madiera, Mendes and others used a PDMS membrane containing Pd for the hydrogenation of propylene and propyne gas [16,20], and Wei et al used Pd nanoparticles in core-shell PDMS structures to hydrogenate diynes [11]. In these studies, the PDMS-encapsulated Pd colloids were prepared by a variety of techniques.…”

“…In these studies, the PDMS-encapsulated Pd colloids were prepared by a variety of techniques. Wei et al added preformed Pd colloids to the PDMS before cross-linking the polymer via hydrosilylation [11]. Trapp, Fritsch, and others generated Pd colloids in situ during the hydrosilylation cross-linking of the PDMS as silicon-hydrogen (silane) bonds reduced Pd(II) to Pd(0) [7,18,19].…”

“…Pd colloids have been incorporated into polymers [7][8][9][10][11][12][13][14], and encapsulation of colloids within polymeric vessels effectively increases the overall size of the solid catalytic pieces [11]. This makes the catalyst easier to remove from the reaction mixture and thereby minimizes loss to the environment and may also increase cost savings.…”