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

Abstract

BACKGROUND: Pd nanoparticles over different supports were evaluated during the alkyne selective hydrogenation of medium chain (C7 and C5) and the 1-pentene purification at mild operational conditions (150 kPa and 303 K). The role of support and chloride was investigated; γ-Al2O3, γ-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° 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 Brönsted 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.