Adsorption and decomposition of formic acid on Pd/Au(111) system: a DFT study

L.A. MEIER; N. CASTELLANI

Montevideo

Congreso; 42do Congreso de Químicos Teóricos de Expresión Latina (QUITEL 2016; 2016

Universidad de la República. Uruguay

Hydrogen(H2) is a source of alternative energy for portable electronicdevices. A large number of materials can store hydrogen. One of them is formicacid (HCOOH) that recently has gained great interest due to its high ambienttemperature stability, easy storage and transport. There are two ways for thedecomposition of HCOOH: i) the dehydrogenation (HCOOH → CO2 + H2),ii) the dehydration (HCOOH → CO + H2O). In the dehydrogenation reaction, it is possible toobtain in a first step formate or carboxylic ions from adsorbed formic acid,and subsequently, in a second step these ions are dehydrogenated to give CO2.The results reported in this workare based on the DFT (Density Functional Theory) formalism and were implementedby means of VASP (Vienna Ab-initio Simulation Program) [1]. Repeated slabsrepresenting the Pd(111) and Au(111) surfaces contain four layers of atoms and a vacuum gap in the normal direction. Thewidth of this gap was optimized to minimize the interaction between slabs.For the Pd/Au(111) system a rhombohedralPd cluster was considered. The HCOOH adsorption was studied in two different orientations:horizontal and perpendicular to the surface, noting that the perpendicularorientation is the more stable. Later dehydrogenation via formation of formateion (HCOO-) and the carboxylic ion (COOH-) was analyzed bydetermining the transition states. After a first dehydrogenation (See Fig. 1),preliminary results allow us to infer the presence of a very low or negligibleenergy barrier for the formation of CO2 from COOH- adsorbedon Pd(111) and Pd4/Au(111) systems.