A DFT Study of Transition States for C−H Activation on the Ru(0001) Surface

Abstract

The transition states of the elementary reactions for the dissociation of methane on the ruthenium (0001) surface have been investigated with DFT periodic calculations and the nudged elastic band method (NEB) for 25% coverages. The calculated barriers are 85 kJ mol-1 for methane decomposition, 49 kJ mol-1 for methyl decomposition, and 16 kJ mol-1 for methylene decomposition, respectively. The decomposition of CHads requires the highest activation energy from the series with 108 kJ mol-1. Discussion concerning chemical bonding aspects of the transition states structures is provided for.

Structure and reactions of carbon and hydrogen on Ru(0001): A scanning tunneling microscopy study

“…Their calculated structure for CH+3H is indeed the same as the one we calculated, although a somewhat smaller unit cell was employed in their simulations. The authors also found a relatively high activation barrier from C+4H to CH+3H, around 70 kJ/mol or 725 meV [6]. This does not agree with our findings where CH was formed after annealing a H-covered surface to 100 and up to 260 K. Assuming a pre-exponential value of 10 13 Hz and a probability of CH formation at 100 K of 1/second (our experimental time scale), the activation energy is estimated to be approximately 260 meV.…”

“…Using theoretical calculations Ciobica et al [5,6] found that CH is the most stable species among all CH x (x=0-4). When the interaction between CH and H atoms was considered, CH+3H was found to be the most stable among CH 4 , CH 3 +H, CH 2 +2H, CH +3H and C+4H.…”

“…Although CH, CH 2 and/or CH 3 were observed after dissociative adsorption or thermal decomposition of larger hydrocarbons [7][8][9][14][15][16], only CH could be formed by the reaction of atomic carbon and hydrogen [11][12][13]16], suggesting the high stability of CH. Because CH was also theoretically found to be most stable among the CH x species on Ru [5,6], which exhibits the highest catalytic activity in Fischer-Tropsch synthesis, hydrocarbon chain-growth using CH as a primary monomer unit has been proposed [10].…”

Modeling Catalytic Reactivity in Heterogeneous Catalysis

“…r H , The rate of C ad hydrogenation depends implicitly on hydrogen pressure. For Ru(0001), the corresponding reaction energy scheme is shown in Figure 19.7 [4].…”

Density Functional Theory Study of Methyl Iodide Adsorption and Dissociation on Clean and K-Promoted β-Mo2C Surfaces

“…Since nickel is a catalyst for commercial steam reforming of methane, a lot of experimental and theoretical study is focused on the investigation of methyl groups on nickel surfaces; see, for example, ref 1. DFT calculations addressed the effect of coadsorbed iodine 2 and the decomposition pathway of CH fragments 3 as well. Taking into account that the activation of the C-H bond in methane requires high energy, while the C-I bond breaks rather easily, adsorbed methyl iodide has been used as a precursor for generation of methyl groups by thermal activation or photolysis on different metal surfaces.…”