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; γ-Al 2 O 3 , γ-Al 2 O 3 modified with Mg, CaCO 3 and activated carbon were used as supports, and PdCl 2 as precursor salt. The classical Lindlar catalyst was used as reference.RESULTS: Surface acidity of supports, active sites dispersion and surface species (MgO, Pd x Cl y O z 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 Al 2 O 3 -Mg and CaCO 3 (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.

No abstract

Pyrolysis gasoline (PyGas) is an unstable byproduct of the pyrolysis of naphtha and other hydrocarbons for the production of olefins. PyGas is stabilized by hydrogenation at mild conditions. The hydrogenation of styrene to ethylbenzene is considered a model test reaction for studying the selectivity of the catalysts because it has the slowest rate of conversion. The catalytic activity and selectivity of two bimetallic coimpregnated Pd-Ni catalysts supported on γ-alumina were assessed and compared to those of a commercial monometallic Pd catalyst (AXENS LD265). The laboratory-prepared catalysts had different metal content and Pd:Ni atomic ratios (1:1 and 1:7). Catalytic tests of selective hydrogenation of styrene to ethylbenzene were made in a batch stirred tank reactor and in a continuous fixed bed trickle bed reactor. The sulfur resistance of the bimetallic catalysts in semicontinuous condition, was assessed by means of the same operational conditions using thiophene as a model poison compound. The support, Pd-Ni coimpregnated catalysts and LD265 commercial catalysts were further characterized by N 2 chemisorption,