INCAPE   05401
INSTITUTO DE INVESTIGACIONES EN CATALISIS Y PETROQUIMICA "ING. JOSE MIGUEL PARERA"
Unidad Ejecutora - UE
artículos
Título:
Kinetic Study of the Selective Hydrogenation of 3-Hexyne over W-Pd/Alumina Catalysts? Reaction Kinetics, Mechanisms and Catalysis
Autor/es:
GERARDO TORRES; MÓNICA E. QUIROGA; CAROLINA P. BETTI; CECILIA R. LEDERHOS; CARLOS R. VERA; M. JULIANA MACCARRONE; JUAN C. YORI
Revista:
Reaction Kinetics, Mechanisms and Catalysis
Editorial:
Springer Nature
Referencias:
Lugar: Budapest; Año: 2019 vol. 127 p. 259 - 281
ISSN:
1878-5190
Resumen:
Low loaded W-Pd/Alumina are relatively novel catalysts for performing the selective hydrogenation of alkynes, but there is scarce information on the working mechanism. This work studies the kinetics of the selective hydrogenation of 3-hexyne to (Z)-3-hexene over a low loaded W-Pd/Alumina catalyst. Runs at different mild reaction conditions were used for fitting a set of Langmuir-Hinshelwood models. Semihydrogenation was the prevailing reaction path, leading selectively to (Z)-3-hexene > 95%, as with classical Lindlar catalysts. Smaller amounts of (E)-3-hexene and negligible of n-hexane were detected. When considering a pseudo-homogeneous model, approximate orders in 3-hexyne and hydrogen were (2.5) and (-2.2), respectively. The latter value pointed to an important role of hydrogen chemisorption. Twelve kinetic models were fitted to the experimental data. A normal dissociative adsorption of hydrogen could not account for the high order in hydrogen, hence the adsorption of non-dissociated molecular hydrogen was also taken into account. Best fit model was the one considering adsorption of 3-hexyne as rate-limiting step, with molecular hydrogen acting as a competitor over Pdn+ sites, and with hydrogen being dissociated over other different sites: Pdˉ.Adsorption occurs by formation of two sigma bonds between the alkyne and two surface Pd metal atoms. Electron-deficient Pd species formed by the interaction of W with Pd would be sites for adsorption of hexyne and stabilization of ?spectator? molecular hydrogen. A value of 26.9 kJ mol-1 was obtained for the activation energy for 3-hexyne adsorption.