Single atom catalysts have been found to exhibit superior selectivity over nanoparticulate catalysts for catalytic reactions such as hydrogenation due to their single-site nature. However, improved selectively is often accompanied by loss of activity and slow kinetics. Here we demonstrate that neighboring Pd single atom catalysts retain the high selectivity merit of sparsely isolated single atom catalysts, while the cooperative interactions between neighboring atoms greatly enhance the activity for hydrogenation of carbon-halogen bonds. Experimental results and computational calculations suggest that neighboring Pd atoms work in synergy to lower the energy of key meta-stable reactions steps, i.e., initial water desorption and final hydrogenated product desorption. The placement of neighboring Pd atoms also contribute to nearly exclusive hydrogenation of carbon-chlorine bond without altering any other bonds in organohalogens. The promising hydrogenation performance achieved by neighboring single atoms sheds light on a new approach for manipulating the activity and selectivity of single atom catalysts that are increasingly studied in multiple applications.
2022 Oct 17
Surface water H-bonding network is key controller of selenate adsorption on  α-alumina: An Ab-initio study.” Journal of Colloid and Interface Science, 617, Pp. 136-146. Publisher's VersionAbstract. 7/2022. “
Selenate adsorption onto metal oxide surfaces is a cost-effective method to remove the toxin from drinking water systems. However, the low selectivity of metal oxides requires frequent sorbent replacement. The design of selective adsorbents is stymied because the surface factors controlling selenate adsorption remain unknown. We calculate adsorption energies of selenate on the (0 1 2) α-Al2O3 surface using density functional theory to unravel the physics that controls adsorption. Our model is validated against experiment by correctly predicting selenate removal efficiency as a function pH. We find that the selenate adsorption energy on the anhydrous α-Al2O3 surface is surprisingly anti-correlated with the fully solvated adsorption energy; therefore, the direct interaction between adsorbate and sorbent is eliminated as the controlling mechanism. Rather, the change in number of surface hydrogen bonds after adsorption is the factor most correlated with the adsorption energy (R2 > 0.8); and is thus determined to be the factor controlling selenate adsorption. We find that pH affects adsorption by controlling the number of surface protons available for H-bonding to selenate. This work demonstrates that adsorption prediction should not be made based on gas phase sorption energies and suggests that surface engineering which increases surface protonation may be an effective strategy for increasing selenate sorption.
Neighboring Pd single atoms surpass isolated single atoms for selective hydrodehalogenation catalysis.” Nat Commun, 30, 12(1), Pp. 5179.Abstract. 8/30/2021. “