Catalytic studies of supported Pd-Au catalysts



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Texas A&M University


Although Pd-Au high-surface area catalysts are used in industry to improve activity and selectivity, a thorough understanding of the nature of these enhancements is lacking. A molecular-level understanding of catalytic reactions under actual reaction conditions is the ultimate goal. This thesis is mainly focused on the application of Pd-Au supported catalysts for vinyl acetate synthesis and CO oxidation reactions using highsurface area catalysts. We have attempted to improve the conventional Pd-Au based catalyst by synthesizing novel acetate-based and polymer-based catalysts. The corresponding catalytic reactivity and selectivity were measured and compared to conventional Pd-Au based catalyst systems. Subsequent characterization was performed using characterization techniques, such as, X-ray diffraction (XRD) and transmission electron microscopy (TEM). From our bimetallic catalytic studies, it was evident that the addition of Au to Pd leads to increased reactivity and selectivity. This surface modification is an important factor in the altered reaction kinetics for vinyl acetate (VA) synthesis and CO oxidation reactions. Promoted and unpromoted Pd-Au/SiO2/K+ catalyst were used for VA synthesis and the effect of pre-adsorbed O2, acetic acid and the role of oxygen were explored. The VA reaction rate of novel acetate-based Pd-Au/SiO2 catalyst was 3.5 times higher than conventional Pd-Au catalysts. Also, 100% selectivity was obtained for acetate-based Pd-Au/SiO2 at 130 oC and the VA formation rate was comparable to that of conventional Pd-Au catalysts. Therefore, the acetate-based Pd-Au/SiO2 catalyst seems very promising and can be explored further. Also, Pd(1):Au(4)/SiO2 catalysts demonstrate 100% CO conversion at much lower temperatures (90 oC) compared with other Pd-Au based catalysts. Furthermore, we were successful in obtaining sufficient CO oxidation activity with increased metal loading (5 wt%) and these catalysts did not deactivate under above-ambient reaction temperature conditions, which make 1:4 Pd- Au/SiO2 catalyst a good candidate for further exploration in CO oxidation reactions.