Insights into the Preference of CO2 Formation from HCOOH Decomposition on Pd Surface: A Theoretical Study

The mechanism of HCOOH decomposition on Pd(111) surface leading to the formation of CO2 and CO has been systematically investigated to identify the preference of CO2 or CO as the dominant product. Here, we present the main results obtained from periodic, self-consistent density functional theory calculations. Four possible pathways of HCOOH decomposition, initiated by the activation of the O–H, C–H, and C–O bonds of HCOOH, as well as the activation of simultaneous C–H and C–O bonds of HCOOH, have been proposed and discussed. Then, the effects of coadsorbed H2O and its coverage on the decomposition of HCOOH have been also considered. Our results show that CO2 is preferentially formed as the dominant product of HCOOH decomposition on Pd(111) surface via a dual-path mechanism, which involves both the carboxyl (trans-COOH) and formate (bi-HCOO) intermediates, along with alternative bond-breaking possible steps in those intermediates. The dehydrogenation of HCOOH on Pd surface is a vital process for CO2 formation. Further, the coadsorbed H2O and its coverage play an important role in the decomposition of HCOOH, and the preferred catalytic pathway of CO2 formation is qualitatively dependent on surface H2O coverage. Therefore, our results would at the microscopic level provide insights into the mechanism, energetics, and possible reactive intermediates of HCOOH decomposition regarding the preference of CO2 formation as the dominant product for the catalytic reactions involving HCOOH and for a direct HCOOH fuel cell on Pd system.