SUPPORTING INFORMATION. Room Temperature Activation of Methane and. Interactions on C-H Bond Cleavage

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1 SUPPORTING INFORMATION Room Temperature Activation of Methane and Dry Reforming with CO 2 on Ni-CeO 2 (111) Surfaces: Effect of Ce 3+ Sites and Metal-Support Interactions on C-H Bond Cleavage Pablo G. Lustemberg, Pedro J. Ramirez, Zongyuan Liu, Ramón A. Gutiérrez, David G. Grinter, Javier Carrasco, Sanjaya D. Senanayake, José A. Rodriguez,,, and M. Verónica Ganduglia-Pirovano, Instituto de Física Rosario (IFIR, CONICET-UNR) Bv 27 de Febrero 21bis, S2EZP Rosario, Santa Fe, Argentina Facultad de Ciencias, Universidad Central de Venezuela, Caracas 12-A, Venezuela Department of Chemistry State University of New York Stony Brook, NY 1179, USA CIC Energigune, Albert Einstein 8, 151 Miñano, Álava, Spain Chemistry Department, Brookhaven National Laboratory, Upton, NY 11973, USA Instituto de Catálisis y Petroleoquímica (ICP-CSIC), C/Marie Curie 2, 289 Madrid, Spain rodrigez@bnl.gov; vgp@icp.csic.es S1

Theoretical Models The interaction of Ni

The nature of the support has been varied from

x (111), and fully Ce2 O3 (1) reduced (Figure

= 1/2 d) CeO2-x: Θ = 1/ss c) CeO2-x: Θ = 3/

Ce2O3 /2 TL CeO2 Θ=2 Θ=1 g) h) i) Ce2O3 Figure

models: (a) CeO2 (111), (b g) CeO2 x (111) with

two, (e) three, and (f) four subsurface oxygen

(g-h) corresponds to (g) one and (h) two Ce2 O3

red/green, Ce+ in white and Ce3+ in gray.

The models for the defective CeO2 x (111)

stable structures in ref 1 with one surface or

three and four subsurface the parameter Θ = Nv

defect concentration, where Nv and N are the

2 Theoretical Models The interaction of Ni species on a ceria support has been modeled. The nature of the support has been varied from stoichiometric, CeO2 (111), to partially, CeO2 x (111), and fully Ce2 O3 (1) reduced (Figure S1). CeO2: Θ = a) CeO2-x: Θ = 1/s b) CeO2-x: Θ = 1/2 d) CeO2-x: Θ = 1/ss c) CeO2-x: Θ = 3/ CeO2-x: Θ = 1 f) e) 1 QL Ce2O3 /2 TL CeO2 2 QL Ce2O3 /2 TL CeO2 Θ=2 Θ=1 g) h) i) Ce2O3 Figure S1: Top and side views of the ceria surface models: (a) CeO2 (111), (b g) CeO2 x (111) with (b) one surface oxygen vacancy, (c) one, (d) two, (e) three, and (f) four subsurface oxygen vacancies. (g-h) corresponds to (g) one and (h) two Ce2 O3 quatrilayers on a 2TL-thick CeO2 (111), and (i) Ce2 O3 (1). Surface/subsurface oxygen atoms are depicted in red/green, Ce+ in white and Ce3+ in gray. Those oxygen atoms in deeper layers are blue. The models for the defective CeO2 x (111) surfaces (Figures S1b f) correspond to the most stable structures in ref 1 with one surface or subsurface oxygen vacancy, as well as with two, three and four subsurface vacancies. the parameter Θ = Nv /N has been introduced as a measure for the defect concentration, where Nv and N are the number of surface plus sub-surface vacancies in the reduced layer and the total number of atoms in a non-reduced oxygen layer of the same cell, respectively. S2

3 The removal of all subsurface O atoms from CeO 2 (111), resulting in the O surf -Ce 3+ -O vac - O Ce 3+ -O-... stacking of the five outermost layers (Figures S1f), is stabilized by.3 ev upon a reconstruction with a change in the stacking of the second O layer (Figures S1g). The resulting structure corresponds to 1 quintuple layer (QL) of hexagonal (A-type) Ce 2 O 3 on 2 trilayers (TL) of CeO 2 (111) (cf. Figure S1i). Moreover, we have considered deeper reductions (Θ = 2) with a 2 QL/2 TL Ce 2 O 3 /CeO 2 (111) model (Figures S1h), and the fully reduced (A-type) Ce 2 O 3 (1) surface (Figure S1i). Table S1 presents the calculated averaged defect formation energies, which agree with those previously published. 1 The results correspond to high-spin states; the energy difference between high-spin states and any other spin state is known to be small (less than.1 ev). 2,3 Table S1: Averaged Oxygen Vacancy Formation Energy (E v in ev) at the CeO 2 (111) Surface and Ce 2 O 3 /CeO 2 Systems N v Θ vacancy type E v (ev) a 1 1/ surface / subsurface /2 subsurface / subsurface subsurface QL Ce 2 O 3 /2 TL CeO 2 (111) QL Ce 2 O 3 /2 TL CeO 2 (111) 2.3 a High-spin configuration. The adsorption of Ni atoms was considered on all models of ceria supports, exploring several adsorption sites and different spin multiplets with total magnetization, M (M = N α N β, difference between the number of spin-up and spin-down electrons); hereafter adsorption sites are referred to as Ni Calculated DOS and local magnetic moments were inspected in order to determine electron configurations. In addition, three dimensional (3D) pyramidal Ni clusters were adsorbed on the clean, 1 QL Ce 2 O 3 /CeO 2 (111) and Ce 2 O 3 (1) supports. S3

4 Interaction of Methane with Ni-CeO 2 (111) at Room Temperature. Figure S2: Ni 2p 3/2 XPS spectra collected after exposing a Ni/CeO 2 (111) surface to 1 Torr of methane at 3K with subsequent heating to 5 K. The coverage of Ni on ceria was.15 ML. The spectra observed after heating to 5 K was very similar to that recorded before dosing methane (Figure 1 in main text). Figure S3: Ni 2p 3/2 XPS spectra collected before and after exposing a Ni/CeO 2 (111) surface to 1 Torr of methane at 3K. The coverage of Ni on ceria was.15 ML. S

5 Interaction of Ni Species with Ceria Surfaces. A. Ni 1 Adsorption on CeO 2 (111). An isolated Ni atom exhibits a s 2 3d 8 electronic configuration. From the different starting geometries considered as possible adsorption sites with total magnetization M =, 2, or, we find that the O-hollow site where two Ni s electrons are transferred from Ni to the ceria support, yielding Ni 2+ (s 3d 8 ) and two Ce 3+ species, is the most stable site (Ni in agreement with previous work (Table S2 and Figure Sa). The Ce 3+ species appear as two split-off states of the Ce f band right below the Fermi level in the density of states (DOS), as shown in Figure S5a. Note that forcing a M = state at this site (Ni results in the spin flip of the transferred electrons with a negligible change in the adsorption energy (Table S2). The change in energy accompanying spin flips will be consistently small in all Ni/ceria systems considered. However, the location of the Ce 3+ centers with respect to the Ni site, will have in general a larger effect (cf., e.g., Figures Sa and b and Table S2). Table S2: Adsorption Energy (E in ev) of a Ni Atom on Various Sites of the CeO 2 (111) Surface with Different Locations of Ce 3+ Ions and Different Total Magnetizations (M = N α N β ) site O-hollow O-bridge O-top M Ce 3+ Ni no. spin spin oxi. state elec. conf. E s 3d a s 3d a a s 3d s 3d a s 3d a 2 a 1 1+ s 3d s 3d s 3d s 3d s 3d 8.9 Ce-bridge s 3d Ce-top s 3d 1.97 b 2 2 s 2 3d 8.55 b a-b Similar geometries but with individual spins flipped and/or different Ni electron configuration. Only one is shown in Figure S. Moreover, the transfer of only one electron from Ni to the support, resulting in Ni 1+ and one Ce 3+ species, could result in either the s 1 3d 8 (M = ) or the s 3d 9 (M = 2) electron configuration, but the former has not been obtained. The most stable site for Ni 1+ adsorption is the O-bridge site (Ni Figure Sc), but it is less stable than the Ni site by about. ev (Table S2). S5

Neutral Ni atoms with concomitant zero values for the spin density at all sites, i.e., s 3d1 (M = ) were stabilized at the O-top, Ce-bridge, and Ce-top sites (Figures Sf, i and j, respectively).

Table S2). Moreover, forcing M = 2 at the Ce-top site resulted in Ni species having the s2 3d8 electron configuration, i.e., no electron pairing and spin quenching, which are the least stable.

j) i) Figure S: Adsorbed Ni at different sites on the CeO2 (111) surface. The labelling Nioxi.state @site.m corresponds to that in Table S2. Ni2+@O-hollow.

2 3 Density (States/eV) Density (States/eV) 3 Total DOS Ni d-state PDOS 3+ Ce f-states PDOS 2 1-5 - -3-2 -1 E - EFermi (ev) 1 2-7 Ni@O-top.

6 Neutral Ni atoms with concomitant zero values for the spin density at all sites, i.e., s 3d1 (M = ) were stabilized at the O-top, Ce-bridge, and Ce-top sites (Figures Sf, i and j, respectively). The adsorption energies of the and are lower than that of the most stable site by about 1.7 ev, whereas that of is lower by about 2.7 ev (cf. Table S2). Moreover, forcing M = 2 at the Ce-top site resulted in Ni species having the s2 3d8 electron configuration, i.e., no electron pairing and spin quenching, which are the least stable. O-hollow. a) d) c) b) O-bridge. O-top.2 O-top. e) O-bridge.2a O-bridge.2 O-hollow.a f) O-top. g) Ce-bridge. h) Ce-top. j) i) Figure S: Adsorbed Ni at different sites on the CeO2 (111) surface. The labelling corresponds to that in Table S2. Ni2+@O-hollow. Total DOS Ni d-state PDOS 3+ Ce f-states PDOS (b) Ni1+@O-bridge.2 3 Density (States/eV) Density (States/eV) 3 Total DOS Ni d-state PDOS 3+ Ce f-states PDOS E - EFermi (ev) Ni@O-top. 3 Total DOS Ni d-state PDOS (c) Density (States/eV) (a) E - EFermi (ev) E - EFermi (ev) 1 2 Figure S5: Density of states for Ni1 /CeO2 (111) system for (s 3d8 ) (a) (s 3d9 ) (b), and (s 3d1 ) (c). The labelling corresponds to that in Table S2. The red (blue) filled curves are the projected density of states (PDOS) onto the d (f) orbitals of Ni (Ce3+ ) atoms. The energy zero is the Fermi level. B. Ni1 Adsorption on CeO2 x (111) with Surface Oxygen Vacancies, Θ = 1/. S6

7 From the different starting geometries considered as possible adsorption sites with total magnetization M =, 2,, or 6 (Table S3), we find that the oxygen vacancy site, O v -hollow, where two Ni s electrons are transferred from Ni to the support, yielding Ni 2+ (s 3d 8 ) and two Ce 3+ species (Figure S6a), is the most stable site (Ni v -hollow.6). Moreover, Ni 2+ species can also be stabilized at O-hollow and bridge sites (Figures S6d and g), but are less stable than at the vacant site by about.3 and.7 ev, respectively (Table S3). Forcing M = 2 and states at the O v -hollow site yields negatively charged Ni 1 (s 2 3d 9 ) and Ni 2 (s 2 3d 1 ) species, respectively. They result from the transfer of one and two Ce 3+ f 1 electrons to Ni states, respectively. Ni v -hollow.2 (Figure S6b) and Ni v -hollow. (Figure S6c) are less stable than Ni v -hollow.6 by about 2.2 and 2.5 ev, respectively (Table S3). Table S3: Adsorption Energy (E in ev) of a Ni Atom on Various Sites of the (2 2)- CeO 2 x (111) Surface with One Surface and Subsurface Vacancy and Different Total Magnetizations (M = N α N β ) site O v-hollow O-hollow O-bridge M Ce 3+ Ni no. spin a spin oxi. state elec. conf. E One Surface Vacancy 2 s 2 3d s 2 3d , s 3d , 2 1+ s 3d , s 3d , 1+ s 3d s 3d O-top 3 2, 1+ s 3d O-Ce-bridge 2, s 3d , 1+ s 3d O v-hollow O-hollow O-bridge O-top One Subsurface Vacancy 2, s 3d , 1+ s 3d , 2 2+ s 3d , 1+ s 3d , 2 2+ s 3d , 1+ s 3d , 2 2+ s 3d , s 3d , 1+ s 3d Ce 3+ -top 2, 2 s 2 3d 8.2 a The spin pairs indicate the number of the Ce 3+ f 1 electrons and orientation of their spins in the second, and in the fifth atomic layers. S7

8 Ni O V -hollow.6 Ni O V -hollow.2 Ni O V -hollow. a) b) c) d) Ni O-hollow.6 Ni O-hollow. Ni O-bridge. Ni O-bridge.6 Ni O-top. e) f) g) h) Ni O-Ce-bridge. i) O-Ce-bridge. j) Figure S6: Adsorbed Ni at different sites on the (2 2)-CeO 2 x (111) surface with one surface vacancy, Θ = 1/. The labelling Ni corresponds to that in Table S3. Moreover, Ni 1+ species with the s 3d 9 electron configuration are stabilized at the O- hollow, O-bridge, O-top and O-Ce-bridge sites (Figure S6e, f, h, and i), but are less stable than Ni v -hollow.6 within. to 1.6 ev (Tables S3). Additionally, Ni 1+ with the s 1 3d 8 electron configuration can also be stabilized at the O-top site (Ni not shown), although with a reduced binding by a factor of two as compared to the most stable Ni species. Finally, Ni species with the s 3d 1 electron configuration can be formed at the O-Cebridge site (Figure S6j) with a binding that is lower than the most stable Ni v -hollow.6 by approximately 1.7 ev (Tables S3). C. Ni 1 Adsorption on CeO 2 x (111) with Subsurface Oxygen Vacancies, Θ = 1/. In the most stable vacancy configuration at Θ = 1/ (cf. Table S1), the stability of oxidized Ni v -hollow.6, Ni v -hollow. (Figures S7a and b) and Ni species (Figure S7d) was found to be comparable (Tables S3). Forcing M =, 2 and states at the O-hollow site yields Ni (s 3d 9 ) species which are less stable than Ni by about 1.1 to 1.5 ev, depending on the location the Ce 3+ f 1 electrons and orientation of their spins (not all structures listed/shown in Table S3/Figure S7). Moreover, Ni 1+ species can also be stabilized at O-bridge sites (Figure S7f), but are less stable than Ni v -hollow. by about 1 ev (Table S3). Additionally, Ni species at the O v -hollow, O-top sites and Ce 3+ -top sites (Figures S7c, h, and j) are less stable than the Ni site by approximately.2, 1.6, and 3.1 S8

Ni 2+ @ O v -hollow.6 a) b) Ni 1+ @ O v -hollow. c) Ni @ O v -hollow. d) Ni 2+ @ O-hollow.6 e) Ni + @ O-hollow.2 f) Ni + @ O-bridge. g) Ni 2+ @ O-bridge.

Figure S7: Adsorbed Ni at different sites on the (2 2)-CeO 2 x (111) surface with one subsurface vacancy, Θ = 1/. The labelling Ni oxi.state @site.

At the two former sites, Ni species have the s 3d 1 electron configuration, whereas at the latter, the s 2 3d 8. D.

Ni 2+ @O v -hollow species with the highest possible total magnetization are the most stable species (Figure S8a, Tables S).

Actually, at O-bridge sites, the oxidation state of the most stable Ni species is +1 (Table S), but are less stable than Ni 2+ @O v -hollow.8 by about.

Moroever, forcing M = at the O-bridge site yields Ni @O-bridge. (s 3d 1 ) species which are less stable than Ni 2+ @O v -hollow.8 by about 1 ev.

9 Ni O v -hollow.6 a) b) Ni O v -hollow. c) O v -hollow. d) Ni O-hollow.6 e) Ni O-hollow.2 f) Ni O-bridge. g) Ni O-bridge.6 h) O-top.2 i) Ni O-top. j) Ce 3+ -top. Figure S7: Adsorbed Ni at different sites on the (2 2)-CeO 2 x (111) surface with one subsurface vacancy, Θ = 1/. The labelling Ni corresponds to that in Table S3. ev, respectively (Table S3). At the two former sites, Ni species have the s 3d 1 electron configuration, whereas at the latter, the s 2 3d 8. D. Ni 1 Adsorption on CeO 2 x (111) with Subsurface Oxygen Vacancies, Θ = 1/2. Ni v -hollow species with the highest possible total magnetization are the most stable species (Figure S8a, Tables S). Ni 2+ species could also be stabilized at O-bridge sites (Figure S8e), but are less stable than Ni v -hollow.8 by about 1.5 ev (Table S). Actually, at O-bridge sites, the oxidation state of the most stable Ni species is +1 (Table S), but are less stable than Ni v -hollow.8 by about.5 ev. The stability of Ni 1+ species at O-bridge and O v -hollow sites is comparable within.1 ev. Moroever, forcing M = at the O-bridge site yields (s 3d 1 ) species which are less stable than Ni v -hollow.8 by about 1 ev. Additionally, Ni could be stabilized at the O-top, O-Ce-bridge and Ce-bridge sites (Figures S8g, h, and j), but are less stable than the site by approximately.7,.9, and.7 ev, respectively (Table S). E. Ni 1 Adsorption on CeO 2 x (111) with Subsurface Oxygen Vacancies, Θ = 3/. Ni 2+ species could only be stabilized on top of a vacancy site (Ni v -hollow.1, Figure S9a) and are the most stable species (Tables S5). Similar stability have Ni 1+ species with the s 3d 9 electron configuration at O-bridge sites (Figure S9c). Moreover, such Ni 1+ species S9

Table S: Adsorption Energy (E in ev) of a Ni Atom on

Subsurface Vacancy and Different Total Magnetizations (M

state 1+ 2+ 2, 2 3, 2, 2 3 5 3, 2 2, 2 6 5 6 5 site M Ov

5 6 O-bridge 6 8 5 6 O-top a O-Ce-bridge Ce-bridge E elec.

f1 electrons and orientation of their spins in the

8 a) c) b) Ni2+ @ O-bridge.8 Ni+ @ O-top. f) e) Ni+ @ Ce.

d) Ni @ O-top.a g) Ni @ Ce-bridge. j) Ni+ @ O-bridge.

10 Table S: Adsorption Energy (E in ev) of a Ni Atom on Various Sites of the (2 2)CeO2 x (111) Surface with Two Subsurface Vacancy and Different Total Magnetizations (M = Nα Nβ ) Ce3+ spina 3, 2, 2 spin 2 Ni oxi. state , 2 3, 2, , 2 2, site M Ov -hollow 8 no. 5 6 O-bridge O-top a O-Ce-bridge Ce-bridge E elec. conf. s 3d9 s 3d s 3d1 s 3d9 s 3d s 3d9 s 3d , 2 3, 2 1+ s 3d1 s 3d , 2 3, 2 1+ s 3d1 s 3d a The spin pairs indicate the number of the Ce3+ f1 electrons and orientation of their spins in the second, and in the fifth atomic layers. Ov-hollow.8 a) c) b) O-bridge.8 O-top. f) e) Ce.O-bridge.6 i) O-bridge. Ov-hollow. d) O-top.a g) Ce-bridge. j) O-bridge.6 O.Ce-bridge. h) Ce-bridge.6 k) Figure S8: Adsorbed Ni at different sites on the (2 2)-CeO2 x (111) surface with two subsurface vacancies, Θ = 1/2. The labelling corresponds to that in Table S. S1

could also be stabilized at O-hollow and O-top sites (Figures S7b and d), but are less stable than at the O-bridge site by about 1. and.9 ev, respectively (Table S5).

Table S5: Adsorption Energy (E in ev) of a Ni Atom on Various Sites of the (2 2)- CeO 2 x (111) Surface with Three Subsurface Vacancy and Different Total Magnetizations (M = N α N β ) site M Ce 3+ Ni

11 a The spin pairs indicate the number of the Ce 3+ f 1 electrons and orientation of their spins in the second, and in the fifth atomic layers.

Ni 2+ @ Ov-hollow.1 a) Ni + @ O-hollow.8 b) c) Ni + @ O-bridge.8 d) Ni + @ O-top.6 Ni @ Ce-bridge.

As mentioned above, upon removal of all subsurface oxygen atoms (Θ = 1), a surface reconstruction stabilizes 1QL of Ce 2 O 3 on 2 TL CeO 2 (111), having only reduced Ce 3+ cations in the two

11 could also be stabilized at O-hollow and O-top sites (Figures S7b and d), but are less stable than at the O-bridge site by about 1. and.9 ev, respectively (Table S5). Ni 1+ species with the s 1 3d 8 electron configuration have a significantly reduced binding (not shown). Table S5: Adsorption Energy (E in ev) of a Ni Atom on Various Sites of the (2 2)- CeO 2 x (111) Surface with Three Subsurface Vacancy and Different Total Magnetizations (M = N α N β ) site M Ce 3+ Ni no. spin a spin oxi. state elec. conf. E O v-hollow 1 8, 2 2+ s 3d O-hollow 8 7, 3 1+ s 3d O-bridge 8 7, 3 1+ s 3d O-top 6 7, 3 1+ s 3d Ce-bridge 8 6, 2 2 s 2 3d a The spin pairs indicate the number of the Ce 3+ f 1 electrons and orientation of their spins in the second, and in the fifth atomic layers. Ni species could only be stabilized at the Ce-bridge site with the s 2 3d 8 electron configuration(figure S9e), but are less stable than the most stable Ni 2+ /Ni 1+ species by about 1. ev (Table S5). Ni Ov-hollow.1 a) Ni O-hollow.8 b) c) Ni O-bridge.8 d) Ni O-top.6 Ce-bridge.8 e) Figure S9: Adsorbed Ni at different sites on the (2 2)-CeO 2 x (111) surface with three subsurface vacancies, Θ = 3/. The labelling Ni corresponds to that in Table S5. F. Ni 1 Adsorption on 1 QL and 2 QL Ce 2 O 3 /2 TL CeO 2 (111), and Ce 2 O 3 (1). As mentioned above, upon removal of all subsurface oxygen atoms (Θ = 1), a surface reconstruction stabilizes 1QL of Ce 2 O 3 on 2 TL CeO 2 (111), having only reduced Ce 3+ cations in the two outermost cerium layers. Ni ceria charge transfer to a Ce + ion in a deeper layer stabilizes Ni 1+ species at O-bridge sites (Figure S1a and Table S6). Ni 2+ species do not form. At the O-top sites, Ni δ+ species (δ < 1) are stabilized (Figure S1b), accompanied by the partial reduction of a Ce + ion in the third cerium layer, Ce ( δ)+. Ni species are less stable than Ni by about.8 ev. Additionaly, Ni species (s 3d 1 ) could S11

12 1 QL Ce2O3 / 2 TL CeO2 (111) O-top.8 + O-bridge.1 a) Ce-bridge.8 c) b) 2 QL Ce2O3 / 2 TL CeO2 (111) O-hollow.16 d) O-bridge.17 O-top.16 f) e) Ce2O3 (1) O-hollow.2 O-bridge.2 h) g) O-top.2 i) Ce-bridge.2 j) Ce3+-top.2 k) Figure S1: Adsorbed Ni at different sites on the (2 2)-1 QL and 2 QL Ce2 O3 on 2 TL CeO2 (111) and the Ce2 O3 (1) surfaces. The labelling corresponds to that in Table S6. Partially reduced Ce( δ)+ ions are pink. S12

13 Table S6: Adsorption Energy (E in ev) of a Ni Atom on Various Sites of the (2 2)- 1 QL and 2 QL Ce 2 O 3 on 2 TL CeO 2 (111) and the (2 2)-Ce 2 O 3 (111) Surfaces and Different Total Magnetizations (M = N α N β ) site M a Ce 3+a Ni E no. spin b spin oxi. state a elec. conf. a 1 QL Ce 2 O 3 /2 TL CeO 2 (111) O-bridge s 3d O-top δ+ 3d 1 δ 1.6 Ce-bridge s s 3d QL Ce 2 O 3 /2 TL CeO 2 (111) O-hollow s 3d O-bridge δ+ s 3d 1 δ 2.1 O-top s 3d Ce 2 O 3 (1) O-hollow s 3d O-bridge s 3d O-top s 3d Ce-bridge s 3d Ce 3+ -top s 3d 1.16 a In same cases a partial Ni to ceria charge transfer, δ, accompanied by the partial reduction of a Ce ion, Ce ( δ)+ is observed. The local magnetization of partially oxidized/reduced Ni/Ce ions adjusts to the total magnetization, M. b The number of the Ce 3+ f 1 electrons and orientation of their spins in the outermost cerium layers with a maximum of four per layer. only be stabilized at Ce-bridge sites (Figure S1c) with an adsoption energy comparable to that of Ni species (Table S6). Increasing the thickness of the reduced Ce 2 O 3 overlayer from 1 to 2 QL, partially hinders the Ni ceria charge transfer. At the O-bridge site where Ni 1+ were stable for 1 QL, Ni δ+ species became most stable (Table S6). Finally, for the fully reduced Ce 2 O 3 (1) surface, no metal ceria charge transfer can take place and the most stable Ni species sit on O-bridge sites (Figure S1c). G. Ni Adsorption on CeO 2 (111), 1 QL Ce 2 O 3 /2 TL CeO 2 (111), and Ce 2 O 3 (1). In previous work, a pyramidal cluster was found to be the ground state structure for the adsorption of Ni species on the CeO 2 (111) surface. The most stable site is on-top of a subsurface oxygen (Figure S11a). We recall that the adsorption of a Ni atom on CeO 2 (111) results in the Ni ceria transfer of two electrons and the formation of Ni 2+ species. Ni species also reduces the ceria support upon adsorption with the formation of two Ce 3+ ions. These two electrons are transferred from the Ni atoms forming the pyramid base. These three Ni atoms are partially oxidized (3 Ni.66+ ), whereas that at the pyramid top remains unaffected, reflecting a rapid decay of the metal-support interactions (Table S7). Upon further reducing the support, from 1 QL Ce 2 O 3 /2 TL CeO 2 (111) to Ce 2 O 3 (1), S13

the Ni ceria charge transfer becomes hindered with the Ni /Ce 2 O 3 (1) species being metallic (Table S7).

free Ni atoms) of a Pyramidal Ni Cluster on the (2 2) CeO 2 (111), 1 QL Ce 2 O 3 /2TL CeO 2 (111), and Ce 2 O

state b CeO 2 (111) 6 2 2 Ni, 3 Ni.66+ 3.67 1 QL Ce 2 O 3 /2TL CeO 2 (111) 12 9 3 Ni, 3 Ni.33+ 3.

13 a The number of the Ce 3+ f 1 electrons and orientation of their spins in the outermost cerium layers with

CeO 2 (111) 1 QL Ce 2 O 3 / / 2 TL CeO 2 (111) a) b) c) Ce 2 O 3 (1) Figure S11: Top and side views of the

14 the Ni ceria charge transfer becomes hindered with the Ni /Ce 2 O 3 (1) species being metallic (Table S7). Table S7: Adsorption Energy (E in ev/atom w.r.t. free Ni atoms) of a Pyramidal Ni Cluster on the (2 2) CeO 2 (111), 1 QL Ce 2 O 3 /2TL CeO 2 (111), and Ce 2 O 3 (111) Surfaces with Total Magnetization M = N α N β Ce Surface M 3+ Ni E no. spin a no. unpaired spins oxi. state b CeO 2 (111) Ni, 3 Ni QL Ce 2 O 3 /2TL CeO 2 (111) Ni, 3 Ni Ce 2 O 3 (1) Ni 3.13 a The number of the Ce 3+ f 1 electrons and orientation of their spins in the outermost cerium layers with a maximum of four per layer. b The Ni at the top is always Ni. CeO 2 (111) 1 QL Ce 2 O 3 / / 2 TL CeO 2 (111) a) b) c) Ce 2 O 3 (1) Figure S11: Top and side views of the most stable structures for Ni clusters on the (2 2) (a) CeO 2 (111) surface, (b) 1 QL Ce 2 O 3 /2TL CeO 2 (111), and (c) Ce 2 O 3 (111) surfaces. References (1) Murgida, G. E.; Ganduglia-Pirovano, M. V. Phys. Rev. Lett. 213, 11, (2) Da Silva, J.; Ganduglia-Pirovano, M.; Sauer, J.; Bayer, V.; Kresse, G. Phys. Rev. B 27, 75, (3) Keating, P. R. L.; Scanlon, D. O.; Watson, G. W. J. Phys.: Condens. Matter 29, 21, 552. () Carrasco, J.; Barrio, L.; Liu, P.; Rodriguez, J. A.; Ganduglia-Pirovano, M. V. J. Phys. Chem. C 213, 117, S1

The Low Temperature Conversion of Methane to Methanol on CeO x /Cu 2 O catalysts: Water Controlled Activation of the C H Bond

The Low Temperature Conversion of Methane to Methanol on CeO x /Cu 2 O catalysts: Water Controlled Activation of the C H Bond Zhijun Zuo, a Pedro J. Ramírez, b Sanjaya Senanayake, a Ping Liu c,* and José