Abstract
DFT+U calculations have been utilized to explore theoretically three
potential pathways of HCHO oxidation on Co-doped
CeO2(111) with O-vacancy herein. To begin with possible
adsorption configurations and resultant adsorption strengths of HCHO on
Co-doped CeO2(111) are presented, we conclude that HCHO
adsorbed Co-doped CeO2(111) has the kinetic stability
order of Eads(Co-O-bridge) >
Eads(O-top) >
Eads(Ce-top-II) >
Eads(Ce-O-bridge) >
Eads(Ce-top-I) >
Eads(Co-top) with different adsorption locations.
O-vacancy has further constructed artificially at the surface rather
than subsurface to stimulate the catalytic activity of Co-doped
CeO2(111) because of surficial lower O-vacancy formation
energy compared to the subsurface. Based on Langmuir-Hinshelwood
mechanism in which O2 and HCHO are both co-adsorbed on
the reduced ceria surface, three resultant individual reaction products,
resulting from different pathways of HCHO oxidation on Co-doped
CeO2(111) with O-vacancy, are identified in detail
within the frame of transition state theory. It shows that, at Co-O
bridge site, HCHO is oxidized to carbonate species with reactive energy
barriers of TS1 of 0.71 and TS2 of 0.36 eV; at O top site, HCHO oxidized
to CO need to overcome barriers of TS1 of 0.55 and TS2 of 0.06 eV; while
at Ce-O bridge site, HCHO to CO2 is the most difficult
to proceed because of its highest energy barriers of TS1 of 0.96 and TS2
of 2.14 eV. We thus predict that the reaction pathway of HCHO to CO
proceeds with the lowest overall barrier on defective Co-doped
CeO2(111). These findings provide clear insight into
further exploration in formaldehyde activation processes.