Following Molecules through Reactive Networks: Surface Catalyzed Decomposition of Methanol on Pd(111), Pt(111), and Ni(111)

Abstract

We present a model of the surface kinetics of the dehydrogenation reaction of methanol on the Pd(111), Pt(111), and Ni(111) metal surfaces. The mechanism consists of 10 reversible dehydrogenation reactions that lead to the final products of CO and H2. The rate coefficients for each step are calculated using ab initio transition state theory that employs a new approach to obtain the symmetry factors. The potential energies and frequencies of the reagents and transition states are computed using plane wave DFT with the PW91 exchange correlation functional. The mechanism is investigated for low coverages using a global sensitivity analysis that monitors the response of a target function of the kinetics to the value of the rate coefficients. On Pd(111) and Ni(111), the reaction COH → CO + H is found to be rate limiting, and overall rates are highly dependent upon the decomposition time of the COH intermediate. Reactions at branches in the reaction network are also particularly important in the kinetics. A stochastic atom-following approach to pathway analysis is used to elucidate both the pathway probabilities in the kinetics and the dependence of the pathways on the values of the key rate coefficients of the mechanisms. On Pd(111) and Ni(111) there exists significant competition between the pathway containing the slow step and faster pathways that bypass the slow step. A discussion is given of the dependence of the model target’s probability density function on the chemical pathways.

A cuboctahedral platinum (Pt79) nanocluster enclosed by well defined facets favours di-sigma adsorption and improves the reaction kinetics for methanol fuel cells

“…A recent study43 on Pt(111) surface shows that it prefers to bind at the bridge position with binding energy -3.39 eV. However, study on cluster surface shows that *CHOH is stable at the top position with adsorption energy of -3.79 eV which is in close agreement with our calculated adsorption energy (-3.67 eV) of *CHOH at the top edge position 18 .…”

“…Elongation of C-O bond occurs from 1.22 Å to 1.29 Å, suggesting the change of hybridisation on the carbon centre. Surprisingly, *CHO intermediate calculated to be most stable at the edge position by 0.08 eV than the bridge position though the adsorption energy is higher at the bridge position.Previously Kramer et al43 reported that formyl binds most preferably through C-atom at the top site of the Pt(111) surfaces, with adsorption energy of -2.29 eV whereasDesai et al 19 reported that formyl prefers to adsorb in a di-sigma manner with the adsorption energy -2.45 eV. Gomes et al45 found that formyl adsorbed at the bridge site through C-atom with binding energy of -2.61 eV.…”

Catalytic Effect of Hydrogen Bond on Oxhydryl Dehydrogenation in Methanol Steam Reforming on Ni(111)

“…Notice that the direct barrier of H 3 COH* dehydrogenation shown Figure 1 is about 91 kJ/mol. In comparison, the barrier was found to range from 39 to 75 kJ/mol in a few early studies [16,37,38]. The difference, due to various factors such as the use of different functionals, surface slab model and transition state search methods, is quite substantial, but is also seen in similar cases.…”

“…Also based on DFT calculations, Krajčí et al demonstrated the CO/CO 2 selectivity of MSR on many alloys, e.g., PdZn, PtZn and NiZn [13]. Chen et al [14], Lausche et al [15], and Kramer et al [16] studied the selectivity of the dehydrogenation of methanol on Cu(110), Ni(100) and Ni(111), respectively. MSRs on Pt [16], Pd [16], Pt 3 Ni alloy [17], Pt-Skinned PtNi Bimetallic Clusters [18] and Co [19] have also been investigated.…”

A density functional theory study of methanol dehydrogenation on the PtPd 3 (111) surface

“…3d) with the adsorption energy of 0.333 eV ( Table 2). This adsorption mode was generally accepted as the stable configuration [57,58], in which the carbon located on top of Pt atom and the oxygen situated over adjacent Pt atom. The closed-shell electronic configuration of CH 2 O resulted in a weak interaction with PtPd 3 (111) [27,59].…”