Density functional studies relevant to methanol steam reforming

Abstract

In this study, methanol steam reforming (MSR) on different catalytic surfaces (Cu, PdZn, Ir, Pd and Pt) have been systematically studied by density functional methods. The adsorption studies of relevant species for MSR indicate that adsorptions on Ir (100) surface are the most stable compared to the other studied surfaces with an exception for OH. The stepped Cu(221) surface facilitates the adsorption of OH, CH2O and HCOO. And the adsorption characteristics on (100) surfaces of Ir, Pt and Pd are very similar for most species.

The effects of O, N, C, and CO impurities with intermediates involved in methanol steam reforming have been systematically studied on (100) surfaces of Cu and PdZn. The impurities can change the charges of adjacent surface atoms locally on the surface. Generally, only COOH and HCOOH adsorption are affected compared to other intermediates due to hydrogen bonding.

For the kinetics studies on formaldehyde steam reforming, we found that the dominant process on Ir (100) is the dehydrogenation of formaldehyde. While the CH2O desorption is more favorable on Cu and PdZn based catalytic surfaces.

The effects of strains for methoxide decomposition were studied on PdZn (100) surface. For thermodynamics study, our results demonstrate that the most thermodynamically favorable adsorption structures for all studied adsorbates are on the slightly compressed (ΔLC=-1%) surface. According to our investigation on activation energies for strain effects, we found that expansive strain can increase the activity of the PdZn(100) surface, but reduces its selectivity at the same time.