Synthesis of Pd(0) nanocatalyst using lignin in water for the Mizoroki–Heck reaction under solvent-free conditions

• Pd(0) nanospheres of 1–5 nm were synthesized and stabilized by lignin as a reducing agent and stabilizer in water at ∼100 °C.
• Lignin@Pd-NPs has been characterized by UV-vis., FT-IR, SEM, TEM, EDX, HRICP-AES and PXRD techniques.
• Lignin@Pd-NPs was an efficient catalyst for the Mizoroki–Heck reactions under solvent-free conditions with short reaction times.
• Lignin@Pd-NPs is a highly stable, heterogeneous, recoverable and recyclable catalyst upto 5–7 times with same efficiency

Palladium(0) nanospheres with an average size of 1–5 nm were synthesized and stabilized by lignin in water without any reducing agent. The lignin supported palladium(0) nanoparticles (lignin@Pd-NPs) were characterized by UV–vis., FT-IR, SEM, TEM, HRICP-AES, EDX and PXRD. Absence of the peak at 430 nm in UV–vis., spectrum confirmed the reduction of Pd(II) to Pd(0). The five characteristic peaks at (1 1 1), (2 0 0), (2 2 0), (3 1 1) and (2 2 2) corresponding to the 2θ values 40°, 46.7°, 67.9°, 81.9° and 86.9°, respectively, appeared in PXRD spectrum indicated the crystallographic planes of Pd(0) with fcc structure. The Pd(0) loaded on lignin was 0.0467 mmol/g determined by HRICP-AES and 0.89% (w/w) by EDX. The performance of lignin@Pd-NPs catalyst have been investigated for the Mizoroki–Heck CC bond formation reactions between n-butyl propene-2-enoate and halobenzenes and substituted halobenzenes in polar to highly polar solvents as well as under solvent-free conditions in the presence of organic or inorganic bases. The lignin@Pd-NPs was found to be a highly efficient catalyst to yield the desired products of up to 94% under solvent-free conditions in short reaction times. The catalyst was heterogeneous and hence recovered by filtration and reused several times in the subsequent batches of the same reaction.

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