Nanostructured supported palladium catalysts—Non-oxidative methane coupling

The Pd on α-Al2O3 catalysts with Pd particles in the low nanometer range have been prepared by a sonochemical reduction and a colloidal method, respectively. The two catalysts differ in their particle size, the widths of their particle size distributions and the amount of carbon incorporation in the Pd lattice.The adsorptive properties of the Pd/Al2O3 samples are different as a result of the different preparation methods. The methane adsorption capacity of that sample with smaller particles is lower than that of the catalyst with larger particles and the energy of activation is nearly doubled. DRIFTS and TPD results of CO adsorption supported by transmission electron microscopy data indicate that the PdSON catalyst with smaller and more homogeneous particles than PdCOL is highly dispersed which influences the coupling-hydrogenolysis process.The catalytic activity evidenced the formation of different adspecies during methane coupling and chemisorption on both catalysts. During the hydrogenation the carbon adspecies formed mainly methane at low adsorption temperatures. The significant amount of adsorbed methane at 773 K is governed by the highly active coordination unsaturated sites at the surface.

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► Pd on α-Al2O3 catalysts were prepared by sonochemical and colloidal methods.
► The PdSON with smaller and homogeneous particles than PdCOL is highly dispersed.
► Chemisorption of CH4 in the temperature range 473–773 K, followed by hydrogenation.
► Activity evidenced different adspecies during methane coupling and chemisorption.
► Carbon adspecies evidenced different C phases, which are reactive.