Fuel Oxidation Catalytic Dehydrogenation Reaction Mechanism Under Palladium

Catalytic reaction is one of the most important research topics of the world, especially the reaction at the solid/liquid junction of the metal surface is even more poplar one. In present work, the density functional theory(DFT) has been employed to compute the reaction pathways of formic acid and methanol decomposition on the catalyst surface. This research has great potential of the fuel cells. In this paper, the calculations of the reaction at the metal/liquid interface are performed with the density functional theory(DFT) and the generalized gradient approximation(GGA). We study the different reaction barriers of organic matter decomposition at the catalyst surface to determine the feasibility of different reaction pathways. Specific studies are as follows:⑴In present work, we use Vienna Ab-initio Simulation Package(VASP) to build the model of formic acid absorbed at Pd/H2 O interface in order to investigate the different of the formic acid decomposition at catalytic surface. We optimized the reactant, an intermediate, transition state, and the configuration of product, and investigate the different configurations and reaction pathways of formic acid oxidation at Pd/H2 O interface. In this paper, we optimized the reactants and products based on the level of the same group, and calculate absorption energies of formic acid at three-layer slabs of Pd(111) surface. Finally, we determined the transition states and intermediates for various systems. The following conclusions:The result suggests that hydrogen bond has a great influence for the formic acid adsorbs at the H2O/Pd(111) interface. Because the hydrogen bond by water and formic acid can change the adsorption configurations. We investigate the decomposition pathways of formic acid. The findings confimed C-OH bond splitting is much difficult than C-H bond splitting at the H2O/Pd(111) interface. The result shows that only one reasonable pathway is C-H bond splitting at the H2O/Pd(111) interface.⑵This work combines density functional theory(DFT) slab calculations to simulate the reactions of formic acid decomposition at H2O/Pd(111) interface in the presence of the proton and formate for the first time. Results suggest that C-H bond and C-OH bond have become a sensitive structure when the proton present in the solution. The barrier energy of C-OH bond splitting in the presence of the proton is lower 1.6eV than C-OH bond breaking in the clean solution. And then, the proton of the C-H bond absorbed to the Pd surface. H2 O and CO2 are produced directly. The C-OH bond splitting is much easier when the proton and formate present in the solution, but the barrier energy of C-H bond splitting is much higher than reaction at clean Pd/H2 O interface. We analyze the charge density of each environment, and results suggest that the electron cloud of formate affects the charge density of formic acid to make the C-OH bond cleavage. It showed the reaction pathways of CO and CO2 is a competitive relationship.⑶In present work, we use the density functional theory to investigate the decomposition pathways of methanol on Pd(111) surface in neutral and alkaline medium. And we optimized the reactant, an intermediate, transition state, and the configuration of product. The findings confirmed both pathways(OCH2OH- → OCH2O2- → HCOO- and OCH2OH- → HCOOH→ HCOO-) were all feasible owing to the low barrier or even non-barrier for any elementary reaction involved in. We study the pathway of HCOO- dehydrogenation. The results showed that formaldehyde can be decomposed by this reaction channel into CO: H2CO→CHO→CO. It verified that both CO and HCOO- were produced during CH3 OH oxidized on Pd electrode in basic condition and proved that the proposed mechanism was reasonable.