The Catalytic Decomposition of Nitrous Oxide and the NO + CO Reaction over Ni/Cu Dilute and Single Atom Alloy Surfaces: First-principles Microkinetic Modelling

Density functional theory calculations and microkinetic modelling reveal that well-engineered Ni/Cu dilute alloys are promising for the catalytic reduction of NO by CO.


Adsorption of N 2 O on Rh(111), Cu(111), Ni/Cu(111) SAA and Ni 2 Cu(111)
shows the six identified N 2 O adsorption structures, and Table S1 summarises the computed adsorption energies and bond lengths.

NO* -NO* repulsive interactions
To demonstrate the NO* -NO* repulsive interactions, we plot the average adsorption energy of NO* over Rh(111) for different NO* surface coverages. As seen, at increasing surface coverage the NO* binding strength diminishes (i.e. less exothermic adsorption).

Side views of the states within the N 2 O* formation and decomposition reaction pathways
The following figures show the side view of the different states that are involved in the N 2 O* formation/decomposition pathways (see Figure 2, Figure 3 and Figure 4 in the main text).
The images are for the Ni 2 Cu (111) Figure  Regarding the NO 2 * formation, we find that on Cu-based the forward barrier is always larger than 0.70 eV, while the reverse barrier (i.e. NO 2 * dissociation) is always smaller than 0.30 eV. Our data indicates that the formation of NO 2 * is neither kinetically nor thermodynamically favoured. The most stable final state for all the three surfaces is the socalled μ-N,O-nitrito adsorption mode, whose stability is experimentally confirmed on other coinage metal surfaces. 2 We also compute the adsorption energies of NO 2 * in the μ-N,O-nitrito structure on the Cu-based surfaces (Table S2). The obtained values imply that even if NO 2 * is formed on the surface its dissociation will be dramatically more favourable than its desorption, thereby corroborating our reaction mechanism, which does not take into account the formation of NO 2 *.    Figure S12 (A) and (B) shows that the selectivity peak of Ni 2 Cu(111) is unaffected by changes to the activation barrier to the formation of N 2 * (R16 in Table 2 in the main text) and the dimerization reaction (R15 in Table 2 in the main text) on Ni*. On the contrary, the peak (which appears between 950 K and 1400 K) disappears upon increasing the activation barrier for the formation of N 2 O* (R9 in Table 2 in the main text) and NO* dissociation (R8 in Table   2 in the main text) reactions on Ni*. Therefore, the selectivity spike for Ni/Cu SAA and Ni 2 Cu in Figure 7 (A) is associated only with the latter two reactions.

Sites involved in surface reactions over Ni/Cu bimetallic alloys
Several elementary events in our microkinetic model involve two sites, which may be of different type on the Ni/Cu bimetallic alloys. On the latter surfaces, the two-site reactions (see Table 2) can happen either on Cu sites, where the reactants and products are on Cu*, or on pair of sites that include both Ni* and Cu*. Table S3 tabulates the two-site events of the NO + CO reaction along with the site types whereon the reactant and product adspecies are adsorbed in our model. Table S3. Two-site events and sites where reactant and product species are adsorbed. The adsorption sites (i.e. either Ni*or Cu*) are shown in bold. Also in bold are the reaction numbers, which correspond to the numbers shown in Table 2 in the main text. Empty sites are denoted as Ni* or Cu*. For occupied sites, the adsorbate is specified followed by the site type in parenthesis.   3 Therefore, the result of microkinetic simulations will strongly depend on the performance of the selected XC functional. For example, for the NO + CO reaction, one should expect that the selectivity peak of Figure 7 (A) will be higher than 0.65 if optPBE-vdW is used. By contrast, values of 0.25 or less can be expected if the DFT-TS or BEEF-vdW are employed.