posted on 2017-05-08, 15:49authored byBing Yang, Cong Liu, Avik Halder, Eric C. Tyo, Alex B. F. Martinson, Sönke Seifert, Peter Zapol, Larry A. Curtiss, Stefan Vajda
Size-selected
Cun catalysts (n = 3,
4, 20) were synthesized on Al2O3 thin films
using mass-selected cluster deposition. A systematic
study of size and support effects was carried out for CO2 hydrogenation at atmospheric pressure using a combination of in
situ grazing incidence X-ray absorption spectroscopy, catalytic activity
measurement, and first-principles calculations. The catalytic activity
for methanol synthesis is found to strongly vary as a function of
the cluster size; the Cu4/Al2O3 catalyst
shows the highest turnover rate for CH3OH production. With
only one atom less than Cu4, Cu3 showed less
than 50% activity. Density functional theory calculations predict
that the activities of the gas-phase Cu clusters increase as the cluster
size decreases; however, the stronger charge transfer interaction
with Al2O3 support for Cu3 than for
Cu4 leads to remarkably reduced binding strength between
the adsorbed intermediates and supported Cu3, which subsequently
results in a less favorable energetic pathway to transform carbon
dioxide to methanol.