Impact of alkali acetate promoters on the dynamic ordering of PdAu catalysts during vinyl acetate synthesis

• Deactivation of PdAu particles depends on the promoter nature MOAc (M+ = Li+, Na+, K+, Cs+).
• Pd rich PdAu particles reorder in active Pd1Au1 and less active Pd2+ species.
• Concentration of Pd2+ (inactive Pd3(OAc)6 and active M2Pd2(OAc)6) depends on M+.
• Deactivation of PdAu correlates with the concentration of inactive Pd3(OAc)6 species.
• Nature of M+ influences reordering of PdAu and therefore the overall activity.

Fresh and used alkali acetate (MOAc with M+ = Li+, Na+, K+, Cs+) promoted bimetallic PdAu catalysts were studied to investigate the impact of the alkali metal cations on the deactivation of the catalysts during vinyl acetate (VA) synthesis from ethene and acetic acid. Dynamic reordering of PdAu toward an active Pd1Au1 phase, a less active M2Pd2(OAc)6 and inactive Pd3(OAc)6 complexes determines the overall activity. Decreasing deactivation from LiOAc to CsOAc promoted PdAu can be associated with the lower concentration of inactive Pd3(OAc)6 leached from the active PdAu particles and with the lower loss of Cs+ compared to Li+ during reaction. CsOAc binds most efficiently to Pd3(OAc)6 and forms active Cs2Pd2(OAc)6, lowering the tendency to leach Cs+. Reduction of Pd in M2Pd2(OAc)6 to a mixed “Pd/M+–O” adlayer on the bimetallic PdAu particles stabilized active Pd0 on the PdAu surface maintaining the catalyst activity. Thus, increasing “Pd/M+–O” concentrations from LiOAc to CsOAc lower long-term deactivation of PdAu.

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