(540f) Selective Hydrogenation of Acrolein over Single Atom Alloy Catalysts

The creation of atomically uniform sites in heterogeneous catalysis remains a challenge for the catalysis community. One such possibility would be the creation of an isolated metal atom in a matrix of another element, termed by Sykes et al as a single atom alloy (SAA). [1]

Pd-Ag alloy catalysts with very dilute amounts of Pd have been synthesized. EXAFS results confirmed that at very low concentration of Pd (as low as 0.01 wt %), Pd was completely dispersed as isolated atoms in Ag nanoparticles. Activity was improved by the presence of these isolated Pd atoms due to the creation of sites with lower activation energy for H₂ dissociation. In addition, for the same particle size, the 0.01%Pd/8%Ag alloy nanoparticles exhibited higher selectivity than their monometallic counterparts[2], suggesting that the Pd atom may act as a site for the favorable bonding of the acrolein molecule for facile hydrogenation of the aldehyde functionality. It is also seen the method of preparation is critical to obtaining highly disperse atoms of the active metal in the nanoparticles. For example, co-impregnation of the metal salts is more conducive to obtain a highly dispersive alloying metal compared to sequential impregnation. We are also extending our study using organic precursors instead of inorganic precursors for catalyst synthesis. EXAFS showed synthesis of Pd-Ag catalysts using Silver acetylacetonate, and Palladium acetylacetonate have led to larger particle size which are more selective towards allyl alcohol. [2] In addition, the effect of using different organic solvents (acetone, toluene, benzene, ethanol, chloroform) on particle size, selectivity and activity is studied for the catalysts made using organic precursors. 

References:

(1)   G. Kyriakou, M.B. Boucher, A.D. Jewell, E.A. Lewis, T.J. Lawton, A.E. Baber, H.L. Tierney, M. Flytzani-Stephanopoulos, E.C.H. Sykes, Science 2012,335, 1209.

(2)   H. Wei, C. Gomez, J. Liu, N. Guo, T. Wu, R. Lobo, C.L. Marshall, J.T. Miller, R. Meyer, J. Catal. 2012, 298, 18.