Structural investigation of solid-acid-promoted Pd/SDB catalysts for ethylacetate production from ethanol

Catalyzed by styrene-divinylbenzene copolymer (SDB)-supported Pd (Pd/SDB) c atalysts, ethyl acetate can be formed from water-containing ethanol via con comitant partial oxidation and esterification reaction, The partial oxidati on reaction is carried out over palladium clusters on the catalysts. The es terification reaction is catalyzed by protons formed from the spontaneous d issociation of acetic acid and can be enhanced by addition of solid acid ca talysts. To investigate the nature of solid acid in promoting the catalytic properties of Pd/SDB catalysts, extended X-ray absorption fine structure ( EXAFS) and inductively coupled plasma optical emission (ICP) spectroscopy w ere used to characterize the reaction-induced morphology change of Pd clust ers and metal loss. After the reaction, there is no evidence of palladium o xide formation, suggesting that the oxidation reaction takes place via the adsorbed oxygen. In addition, concomitantly with Pd leaching, increase of a verage Pd cluster size was observed. Pd-Pd coordination number increases fr om 3.0 to 7.9 and the Pd content decreases from 1.0 to 0.55 wt %. Addition of acid catalysts reduces leaching and growth of Pd clusters. This effect i ncreases with an increase in acid-to-Pd catalyst ratio of the mixed catalys ts. As the acid-to-Pd catalyst ratio increases from 1.0 to 4.0, Pd-Pd coord ination number decreases from 7.2 to 6.5 and the Pd content increases from 0.63 to 0.71 wt %.