Transferability of the SRP32-vdW specific reaction parameter functional to CHD3 dissociation on Pt(110)-(2 × 1)

Abstract

Stepped transition metal surfaces, including the reconstructed Pt(110)-(2 × 1) surface, can be used to model the effect of line defects on catalysts. We present a combined experimental and theoretical study of CHD 3 dissociation on this surface. Theoretical predictions for the initial sticking coefficients, S 0 , are obtained from ab initio molecular dynamics calculations using the specific reaction parameter (SRP) approach to density functional (DF) theory, while the measured sticking coefficients were obtained using the King and Wells method. The SRP DF used here had been previously derived for methane dissociation on Pt(111) so that the experiments test the transferability of this SRP DF to methane + Pt(110)-(2 × 1). The agreement between the experimental and calculated S 0 is poor, with the average energy shift between the theoretical and measured reactivities being 20 kJ/mol. There are two factors which may contribute to this difference, the first of which is that there is a large uncertainty in the calculated sticking coefficients due to a large number of molecules being trapped on the surface at the end of the 1 ps propagation time. The second is that the SRP32-vdW functional may not accurately describe the Pt(110)-(2 × 1) surface. At the lowest incident energies considered here, Pt(110)-(2 × 1) is more reactive than the flat Pt(111) surface, but the situation is reversed at incident energies above 100 kJ/mol.

CHD3 Dissociation on the Kinked Pt(210) Surface: A Comparison of Experiment and Theory

“…We find that the activation barriers for the different surfaces do not depend strictly linearly on the generalized coordination number, as shown in Figure S4, but rather scatter around a line, in reasonable agreement with the trend in adsorption energies of oxygen and hydrogen adsorbates on Pt nanoparticles. 22,23 The geometry of the transition state with the lowest activation barrier, also given in Table 2, more closely resembles that calculated on the stepped Pt(110)-(2 × 1) 33 surface than on the flat Pt(111) 25 surface. Table 2.…”

“…The Journal of Physical Chemistry C Article Alternatively, the structure of the Pt(210) surface may not be correctly reproduced by the SRP32-vdW functional as functionals which include van der Waals correlation do not necessarily produce the right surface geometry. 64 In recent work on Pt(110)-(2 × 1) 33 we found that the activation barrier for dissociation of CHD 3 was up to 10 kJ/mol higher when the surface structure calculated by using the SRP32-vdW functional was used compared to those obtained experimentally. 65−67 A comparison of the calculated and experimental 63 Pt(210) surface geometries can be found in Table S1.…”

“…As in previous work for CHD 3 dissociation on nickel, 15,38 platinum, 15,25,33,40 and copper surfaces, 49 we make use of the semiempirical SRP32-vdW exchange correlation functional defined as…”

“…This is consistent with results for Pt(211) which show that reactivity on the leastcoordinated step edge atom dominates 15,25,35,36,40 and on Pt(110)-(2 × 1) where most reactivity occurs on the ridge atom. 33,37 The distributions of the angles that describe the initial geometry of the CHD 3 molecule for all the trajectories (red dashed line), the initial geometry of the molecules that react (blue dashed line), and the geometry of the molecules that react at the point where the dissociating bond becomes longer than the transition state value (blue solid line) are presented in Figure 8. Panel A shows the distributions of θ, the angle between the dissociating bond and surface normal, panel B shows the distributions of β, the angle between the methyl umbrella axis and surface normal, and panel C shows the distributions of γ, the angle between the dissociating bond and the umbrella axis.…”

“…However, it underestimated the sticking coefficients for CHD 3 dissociation on Pt(110)-(2 × 1), as it failed to capture the geometry of the surface correctly which led to the calculated activation barrier being up to 10 kJ/mol too high. 33 In the present work we will compare results from King and Wells measurements and ab initio molecular dynamics (AIMD) calculations to determine whether the SRP32-vdW DF is also able to quantitatively reproduce the reactivity on the kinked Pt(210) surface. The structure of the Pt(210) surface is shown schematically in Figure 1.…”