Role of the support and chloride during the purification of 1-pentene in alkyne/alkene streams over Pd catalysts

BACKGROUND Pd nanoparticles over different supports were evaluated during the alkyne selective hydrogenation of medium chain (C-7 and C-5) and the 1-pentene purification at mild operational conditions (150 kPa and 303 K). The role of support and chloride was investigated; gamma-Al2O3, gamma-Al2O3 modified with Mg, CaCO3 and activated carbon were used as supports, and PdCl2 as precursor salt. The classical Lindlar catalyst was used as reference. RESULTS Surface acidity of supports, active sites dispersion and surface species (MgO, PdxClyOz and/or functional groups) can favor or disfavor the desorption of 1-alkene during the purification of 1-pentene stream. The smallest particle sizes (3.8-10.0 nm) favor the dissociative adsorption of hydrogen over Pd degrees active sites, promoting good catalytic behavior. The best synthesized catalysts are Pd/Al-Mg and Pd/Ca, and their high selectivity (>= 90%) is favored by the presence of superficial acidic Lewis sites. On the contrary, lower selectivity (74-80%) is assessed on catalysts with Bronsted acidic sites (Pd/Al and Pd/RX3) that favored the undesired overhydrogenation or isomerization reactions. CONCLUSION The geometric and electronic properties of the support have a major influence on the activity and selectivity of the catalysts. Low loaded Pd catalysts supported on Al2O3-Mg and CaCO3 (Pd/Al-Mg, Pd/Ca) can be used for the purification of medium or large terminal alkenes at mild reaction conditions as an alternative to the toxic Lindlar commercial catalyst. (c) 2021 Society of Chemical Industry (SCI).

Automated summary

The surface acidity, active site dispersion, and surface species have significant effects on the desorption of 1-alkene during 1-pentene purification. Catalysts with smaller particle sizes, such as Pd/Al-Mg and Pd/Ca, exhibit high selectivity due to the presence of superficial acidic Lewis sites, while catalysts with Bronsted acidic sites show lower selectivity due to undesired reactions.