Hydrogenation reactions catalyzed by colloidal palladium nanoparticles under flow regime

Abstract

A glycerol colloidal solution of palladium nanoparticles stabilized by PVP (PdPVP, mean diameter of 2.2 ± 0.8 × 10 −9 m) was employed under flow conditions for hydrogenation reactions. After optimization, we selected the tube-in-tube flow reactor as the more suitable system for this catalytic process due to its ability to regulate the addition of hydrogen. PdPVP nanoparticles were synthesized and fully characterized ((HR)-TEM, PXRD, EA, and ICP) both in glycerol solution and at solid state. The reduction of different substrates, including nitrobenzene, 4-phenylbut-3-en-2-one, and isophorone, was achieved under relatively smooth conditions (5-7 × 10 5 Pa of H 2) in short times (<600 s). Unfortunately, the reduction of 1-dodecene was not possible due to the faster isomerization reaction. The optimal effusion of hydrogen in the colloidal phase together with the catalytic efficiency of this system is noteworthy.

Remarkable catalytic activity of polymeric membranes containing gel-trapped palladium nanoparticles for hydrogenation reactions

“…For the hydrogenation of alkene substrates, full conversion in 24 s was obtained for the indene hydrogenation, selectively reducing the conjugated C]C bond to the aromatic ring (entry 1), leading to a turnover frequency ca. three times higher than other conjugated substrates described in the literature [8]. However, for non-conjugated C]C bonds, such as 1-dodecene, lower conversion was achieved (26 % conversion after recycling 3 times (x12 s) or 36 s of residence time; entry 2) with a low chemoselectivity, mainly obtaining isomerization products (i.e.…”

“…Where V Cont is the volume of the contactor shell side (m 3 ) Q , l the volumetric flow rate of the liquid phase (m 3 ⋅s −1 ), L cont the lengh of the module (0.1 m), r Cont is the radius of the module (0.002 m), n fib the number of fibers (8), r e the external diameter of fibers (3.0⋅10 -4 m).…”

“…Furthermore, supported palladium catalysts have been largely studied and efficiently applied for synthesis of both fine [5] and bulk chemicals [6]. Especially, working under continuous flow conditions represents a sustainable tool in terms of safety, diminution of reaction time, process intensification and scale-up [7,8]. In this frame, polymeric catalytic membranes have proven to be outstanding tools for catalytic reactions in the fine chemical industry, generally working under mild conditions (< 150°C) [9][10][11][12].…”

Palladium and Copper: Advantageous Nanocatalysts for Multi-Step Transformations

“…Gómez and co-workers have vast experience in the synthesis and catalytic applications of metal nanoparticles in glycerol, where the solvent plays a key role as liquid support, enabling an efficient immobilization of metal-based NPs and easy recycling of the catalytic phase [ 110 , 111 , 112 , 113 , 114 , 115 ]. Therefore, PdNPs stabilized by cinchona-based alkaloids were prepared for the tandem synthesis of functionalized amines via reductive amination of aldehydes [ 114 ].…”

Recent Progress in Continuous‐Flow Hydrogenation

“…In 2019, Gómez and co‐workers studied the hydrogenation of nitrobenzene ( 6 ) in flow . In this reaction, three different stabilizers for the Pd catalyst were used, showing different activities (Scheme ).…”