Fine chemical intermediates produced by selective hydrogenation of alkynes over a WPd catalyst

CECILIA R. LEDERHOS; CARLOS R. VERA; M. JULIANA MACCARRONE; FERNANDO COLOMA-PASCUAL; CAROLINA P. BETTI; MÓNICA E. QUIROGA

Beijing

Congreso; The 16 th International Congress of Catalysis (ICC 16); 2016

Some selective hydrogenation reactions dealing with the transformation of carbon-carbon triple bonds into double bond ones are a crucial step in the synthesis of a wide range of fine chemicals including vitamins, fragrances, medical drugs and many other products with a total worldwide production of more than 1000 tons per year. In this paper the effects of reactant concentration, temperature and hydrogen pressure on the activity and selectivity of a low cost WPd/Al2O3 catalyst for the selective hydrogenation of 3-hexyne into hexene were studied. Orders of reaction and the apparent activation energy were calculated.The optimal reaction temperature for the partial hydrogenation of 3-hexyne was 323 K, total conversion being practically achieved at 150 min reaction time, with a selectivity to (Z)-3-hexene of 95%. The high selectivity was attributed to the absence of the β-PdH phase, responsible for deep hydrogenation, and thepresence of electron-rich Pdd- (92% at/at) as main active sites for insertion of a single hydrogen. This is in turn associated to factors of electronic type, though the influence of geometric factors or both on the catalyticactivity, cannot be discarded. The negative reaction orders for 3-hexyne (-0.45) and hydrogen (-1.04) point to the presence of strongly inhibiting reactant adsorption effects. A moderate value of the apparent activation energy, 14.6 kJ mol-1, was regressed from the kinetic data.