Unveiling the decomposition mechanism of formic acid on Pd/WC(0001) surface by using density function theory

Abstract

In pursuit of low-cost direct formic acid fuel cells, tungsten carbide (WC) supported Pd catalyst is considered as an ideal candidate for efficient decomposition of formic acid due to low Pd utilization and excellent performance. Herein, different adsorption configurations and active sites of the intermediates, involved in the HCOOH decomposition, on WC(0001)-supported Pd monolayer (Pd/WC(0001)) surface investigated by using density functional theory. The results reveal that trans-HCOOH, HCOO, cis-COOH, trans-COOH, HCO, CO, H2O, OH and H exhibit chemisorption on Pd/WC(0001) surface, whereas cis-HCOOH and CO2 exhibit weak interactions with Pd/WC(0001) surface. In addition, the minimum energy pathways of HCOOH decomposition are analyzed to generate CO and CO2 due to the fracture of C–H, H–O and C–O bonds. The adsorbed HCOOH, HCOO, mHCOO, cis-COOH and trans-COOH configurations exhibit dissociation rather than desorption. CO formation occurs through the decomposition of cis-COOH, trans-COOH and HCO, whereas the CO2 formation happens due to the decomposition of HCOO. It is found that the most favorable pathway for HCOOH decomposition on Pd/WC(0001) surface is HCOOH→HCOO→CO2, where the formation of CO2 from HCOO dehydrogenation determines the reaction rate. Overall, CO2 is the most dominant product of HCOOH decomposition on Pd/WC(0001) surface. The presence of WC, as monolayer Pd carrier, does not alter the catalytic behavior of Pd and significantly reduces the Pd utilization.