γ–Al2O3 Catalysts by First-Principles

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CO activation on Ni/#-AlO Catalysts by First Principles Calculations: From Ideal Surfaces to Supported Nanoparticles Marius-Christian Silaghi, Aleix Comas-Vives, and Christophe Copéret ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.6b00822 • Publication Date (Web): 06 Jun 2016 Downloaded from http://pubs.acs.org on June 7, 2016

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CO2 Activation on Ni/γγ−Al2O3 Catalysts by First Principles Calculations: From Ideal Surfaces to Supported Nanoparticles Marius-Christian Silaghi, Aleix Comas-Vives,* and Christophe Copéret Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 1-5, 8093 Zürich

ABSTRACT: Due to the impact human-related CO2 emissions have on global warming, the conversion of this molecule to useful products is of increasing interest. For this purpose, further understanding of the CO2 activation is needed. Ni-based catalysts are able to dissociate and convert CO2 into fuels and although these systems are generally simulated using simple slab models, real catalysts are significantly more complex. They are generally composed of nanoparticles supported on oxides, being γ-Al2O3 one of the most widely used supports. In this study, we perform ab initio simulations in order to model the CO2 activation on Ni nanoparticles supported on γ-Al2O3. Starting from ideal surface terminations, going to Ni nanoparticles (0.5-1 nm) and up to γ-Al2O3 supported Ni nanoparticles, the role of terraces, steps, edges and the support is evaluated for this chemical transformation. The metal-oxide interface provides the most active sites for CO2 activation, due to a synergistic effect between the nickel nanoparticles and the Lewis acidic sites of γ-Al2O3. KEYWORDS: CO2 Activation, Nickel, Surfaces, Nanoparticles, Alumina, Support Effects, DFT Calculations

Transforming CO2 into more valuable and useful chemicals1 is becoming increasingly important, in view of its impact on the global environment of our planet. Several reactions are able to convert CO2 to into more useful chemical feedstocks:2 Reverse Water Gas Shift, hydrogenation of CO2 to methanol3/hydrocarbons,4 or CO2 reforming5 and methanation. CO2 is highly stable (thermodynamically) and rather inert (kinetically), and therefore it is of prime importance to get further insights about CO2 activation.6 Nickel, among different transition metals,7 is able to dissociate CO2 via relatively low activation energies,8 and ab initio calculations using slab models have shown that the reaction is slightly surface sensitive, with the reactivity following the trend: Ni(110) > Ni(100) > Ni (111).9 Early experimental work demonstrated the capability of the Ni(110) surface to first molecularly adsorb and subsequently dissociate CO2 at room temperature10 Real metallic catalysts, however, contain not only terraces but also edges and steps which can be more reactive than ideal terminations11 and display different adsorption and reaction properties than extended surfaces.12 On the top of that, metallic nanoparticles are supported on high surface area oxide materials such as SiO2, ZrO2, TiO2, MgO, CeO2 and Al2O3.13 Among them, γ-Al2O3 is a widely used and essential support in heterogeneous catalysis. Indeed, the 110 termination of γ-Al2O3, contains highly acidic and reactive AlIII sites, which are able to activate H2 and CH414 and to promote the carboncarbon bond formation from CH3F and dimethyl ether to ole-

fins.15. Al2O3-based supported catalysts are the most widely used in particular in CO2 conversion processes, because of the stability of alumina towards high reaction temperatures and in the presence of steam. In addition, this support is able to adsorb CO2, and has been proposed to activate CO2 at the metalsupport boundary,16 and to influence the metal reduction state.17 Thus, for γ-Al2O3-supported Ni nanoparticles not only the metal, but also the support and the metal-oxide interface can play an essential role in CO2 activation. Here, we use density functional theory (DFT) periodic calculations in order to understand the CO2 adsorption and activation on Ni nanoparticles supported on γ-Al2O3. We evaluate the role of each component in the catalyst by using different levels of complexity: from ideal surface terminations (terraces and steps), to sub-nanometric and nanometric Ni nanoparticles (Ni13 and Ni55) and up to Ni nanoparticles supported on the (100) and 110 facets of γ-Al2O3. Previous studies also used successive levels of complexity in order to study metal supported nanoparticles. For example for the CO adsorption on Ni clusters supported on alumina18 or the study of catalytic processes on Au nanoparticles supported on TiO2.19 The CO2 adsorption and dissociation on ideal Ni(111) and stepped Ni(211) surfaces was first addressed (Figure 1). CO2 adsorption is endothermic by 20 kJ.mol-1 on the Ni(111) surface while it is exothermic by 40 kJ.mol-1 on the Ni(211) surface.9b Concerning the CO2 activation, the transition-state energies (ETS) are 60 kJ.mol-1 and 42 kJ.mol-1, respectively. The CO2 dissociation energies leading to adsorbed CO* and O* present similar thermodynamics, being –100 kJ.mol-1 and –96 kJ.mol-1 more stable than initial reactants for the Ni(111) and the Ni(211) surfaces, respectively. We then considered the CO2 reactivity on icosahedral Ni13 and Ni55 nanoparticles of ca. 0.5 and 1 nm (Figure S1), which were the most stable particles shapes for clusters containing 13 and 55 atoms, respectively20 (Figure 1, Table S1). We found that CO2 preferentially binds to edges and corners of the nanoparticles (Figure S2). Such trends, i.e. increased adsorption energies with decreasing metal atom coordination number have been previously reported for the adsorption of CO*, O*, H2O*, CHx* and several other oxygenated species on Pt 21 nanoparticles and low and high Miller indices metal surfaces22 as well as for the CO adsorption on Pd nanoparticles.23 The strongest CO2 adsorption was found for the Ni13 cluster with ‫ܧ‬௔ௗ௦ = –100 kJ.mol-1 compared to Ni55 (‫ܧ‬௔ௗ௦ = –58 kJ.mol-1) 24 (Figure S2). It is also worth mentioning that on the Ni55 cluster, the adsorption of CO2 on a Ni(111) terrace of the cluster is exothermic in contrast to the CO2 adsorption on an ideal Ni(111) surface (‫ܧ‬௔ௗ௦ = –37 kJ.mol-1 vs. +20 kJ.mol-1). Concerning the CO2 activation, the edges of the Ni13 particle are also the most reactive for the CO2 dissociation both kinetically and thermodynamically (ETS = –34 kJ.mol-1, Ediss = – 202 kJ.mol-1). Figure 1 shows the corresponding geometries.

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Table 1. CO2 adsorption energies with respect to initial reactants (Eads), O-C-O angle of chemisorbed CO2, Bader charges of the adsorbed CO2 molecule q(CO2), sum of Bader charges for all the Ni atoms of the corresponding metallic system upon CO2 adsorption q(Nin) and sum of the Bader charges of all the atoms of the γ-Al2O3 surface upon CO2 adsorption: q(γγ-Al2O3), energy of the TS (ETS), activation energy (Eact = ETS – Eads), dissociation energy of CO2 Ediss with respect to initial reactants, and reaction energy (∆ ∆E) for the CO2 dissociation: ΔE = Ediss – Eads. All the energies are in in kJ.mol-1. γ-Al2O3

Ni system

Alsurf

111 211 Ni13 ICO Ni55 ICO (edge) Ni55 ICO (111) Ni13 ICO 100 Ni55 ICO 110

Ni13 CBPT-2 Ni55 Marks

AlVc AlVd AlVa AlVc AlIVb AlIII

Eads [kJ/mol]

O-C-O

q(CO2)

q(Nin )

q(γ-Al2O3)

20 -40 -100

130 140 140

-0.60 -0.56 -0.59

0.60 0.56 0.59

-------

-58

134

-0.55

0.55

---

-148 -104 -150 -123 -169 -151

125 132 121 124 124 128

-0.93 -0.80 -0.93 -0.97 -0.97 -0.91

0.60 0.57 0.57 0.56 0.77 0.60

0.33 0.23 0.36 0.41 0.20 0.31

150 100

TS 50 Ni111

0 E [kJ/mol]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Ni211

-50 Ni 1313ICO - edge - edge

-100 -150 -200

Ni - edge 5555ICO - edge

CO2*

Ni - terrace 5555ICO - surf

CO* + O*

-250 -300

Figure 1. Energy profile (in kJ.mol-1) for the CO2 activation on the Ni(111), (terraces) and Ni(211) steps,, edges of Ni13 particles and edges and terraces of the Ni55 particle. The geometries for the CO2 activation route on the Ni13 particle are shown.

On the Ni55 particle, the CO2 activation is significantly more favored than on ideal surface terminations both on the edges (ETS = –11 kJ.mol-1, Ediss = –186 kJ.mol-1) and terraces (ETS = 29 kJ.mol-1, Ediss = –165 kJ.mol-1) (see Figure S3 for the corresponding geometries). Overall, we find that CO2 reactivity follows the trend Ni13 (edges) > Ni55 (edges) > Ni55 (111 terraces) > Ni(211) > Ni(111) (Table 1). Hence, a particle size effect is obtained for Ni13 vs. Ni55 system that can be explained based on the lower coordination number of surface Ni atoms on Ni13 with respect to Ni55 case. Bader charge analysis of the adsorbed CO2 (Table 1), shows that upon adsorption, the CO2 molecule becomes negatively charged (the sum of Bader charges of carbon and the two oxygen atoms, q(CO2) < 0), while the corresponding metallic surface or nanoparticle becomes positively charged (the sum of the Bader charges for all Ni atoms q(Nin) > 0, Table 1). This describes an electron transfer from the metallic system to CO2, similarly to what is observed in molecular chemistry upon coordination of CO2 to an electron-rich metal site, and it corresponds to an electron donation from the metallic surface/particle to the antibonding 2πu orbital.7a, 9a Similar electron transfer processes have been previously reported on Ni(111),9a

ETS [kJ/mol]

Eact [kJ/mol]

Ediss [kJ/mol]

ΔE [kJ/mol]

59 38 -34 -11 29 -51 -57 7 96 -16 -119

39 78 66 47 87 97 47 157 219 153 32

-100 -96 -202 -186 -165 -126 -133 -37 -170 -226 -262

-120 -56 -120 -128 -107 22 -29 113 -47 -57 -111

Ni11010 and stepped Ni(211) surfaces9b and on other metal and oxide7a and metal carbide surfaces.25 This electron transfer leads to CO2 bending in order to stabilize the valence orbital, as predicted by the Walsh diagram of the molecule.7a In order to obtain further insights about the possible role of the support in CO2 activation, we constructed models of Ni nanoparticles supported on γ-Al2O3. Different shapes of subnanometric Ni13 (~0.5 nm) and nanometric Ni55 (~1.0 nm) particles (Figure S1) were supported on the fully dehydroxylated (100) and (110) terminations of γ-Al2O3 (Figure S4). For the (100) surface we evaluated the same surface sites previously used for the adsorption of Pt13 and Pd13 clusters.26 At 700 °C, which are conditions typically used in CO2 reforming, the less abundant (100) surface (16%) is fully dehydroxylated while the predominant 110 surface (74%) contains only ~0.7 OH/nm2,27which is why we also considered a fully dehydroxylated surface for the latter termination. The most stable particle shapes for Ni13 and Ni55 particles on the two surfaces of γAl2O3 ((100) and (110)) are shown in Figure S5. On the (100) surface of γ-Al2O3 the particles maintain the particle shape and the binding energies per nickel for the Ni13 and Ni55 particles are equal to ‫ܧ‬ୠଵ଴଴ = –337 kJ.mol-1 and Ni55 ‫ܧ‬௕ଵ଴଴ = –387 kJ.mol-1, respectively (Figure S6). This is likely associated to the low Lewis-acidity of surface AlV (AlVa-AlVd) atoms (weak metal – support interaction).27a In contrast, on the fully dehydroxylated (110) surface, the particle shape changes significantly and is accompanied with larger binding energies per nickel, i. e. ‫ܧ‬ୠଵଵ଴ = –361 kJ.mol-1 and ‫ܧ‬௕ଵଵ଴ = –394 kJ.mol-1 for the Ni13 and Ni55 particles, respectively (Figure S6). This is due to the presence of more Lewis-acidic tri-coordinated (AlIII) and tetra-coordinated (AlIVa, AlIVb) Al atoms, which can be related to the stronger metal-support interaction.27b Ab Initio Molecular Dynamic DFT also confirmed significant particle shape deformation upon adsorption on the 110 surface of γ-Al2O3 (Figure S7). The CO2 adsorption on the Ni@γ-Al2O3 systems is significantly stronger than on the bare nanoparticles. CO2 adsorbs via an η2-configuration, with one oxygen atom bonded to a Lewisacidic surface aluminum atom (AlIII, AlIV, AlV) and the carbon bonded to the particle. Among several analyzed structures (Figure S8-S9), the most stable ones (see Figure 2a) have binding energies between –169 and –148 kJ.mol-1. The charge of the CO2 molecule in the supported nanoparticles take values between –0.80 to –0.93 |e|, while for the unsupported nanoparticles the charge of the CO2 molecule take values within to –0.55 and –0.59 |e| (Table 1, Figure 2c).

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a)

c) -40 y = 188,11x + 31,23 R² = 0,77

Ni55 ICO

-60 -80 Ni13 ICO (1) - 100

Ni55 ICO (1) - 100

b)

Eads [kJ.mol-1]

Ni13 ICO Ni13 ICO (2)

-100 -120

100

Ni55 ICO (2)

110 -140

Ni55 ICO (1) Ni13 ICO (1) cluster

Ni55 Marks

-160

Ni13 CBPT-2 Ni13 CBPT-2 - 110

Ni55 Marks - 110

-180 -1,10

-0,90

q (CO2)

-0,70

-0,50

Figure 2. a) CO2 binding in η2-configuration at the metal-support interface for Ni13/55 particles supported on a) the fully dehydroxylated (100) b) and (110) surfaces of γ-Al2O3 (Al: pink, O: red, Ni: blue, C: grey); c) CO2 binding energy of CO2 bound to nanoparticles in gas phase and the metal-support interface as a function of the charge of CO2 (q(CO2)).

This is associated with a decrease of the O-C-O angle of CO2 (Figure S10). Upon CO2 adsorption on the supported clusters, the Ni nanoparticles as a whole (q(Nin) transfer charge to CO2, getting depleted in charge with values in the range of +0.6 |e| to +0.8 |e|. Thus, the additional negative charge transferred to CO2 on the supported nanoparticles must come from the support, which indeed gets depleted in charge: the sum of the charges of all the atoms of the support (γ-Al2O3) is positive, taking values within: +0.23-0.41. Thus, when CO2 adsorbs on the supported nanoparticles, it gets more negatively charged than on the metallic surfaces or nanoparticles, due to the additional charge transfer from both the metallic particles and the support. Recently, similar electron shuttle processes at the interface of gold adatoms supported on thin MgO films have been found to activate CO2 and reduce it to oxalate species at the oxide-metal interface.28 Subsequently, we evaluated the CO2 cleavage on the Ni13/Ni55 nanoparticles supported on the (100) and the (110) surfaces of γ-Al2O3 (see Figure 3 for the corresponding energy profiles). For the CO2 activation on the Ni13 particle supported on the (100) γ-Al2O3 surface, we located two pathways for the CO2 activation, one taking place on the particle and another one taking place on the metal-support interface (Figure S11 a). In both cases the stability of the corresponding transition-state (ETS= –51 and –57 kJ.mol-1) as well as the dissociation energy (Ediss = –121 and –126 kJ.mol-1) are similar (Table 1). For this surface, the transition-state energy is also lower than for the bare Ni13 particle. Nevertheless, the dissociation energy of CO2 is found to be more favorable for the latter case (Ediss = –202 kJ.mol-1). For Ni55 particle supported on the (100) surface of γAl2O3, we only located CO2 activation steps on the metalsupport interface, with one oxygen of CO2 bonded to one Al of the support and the carbon of CO2 bonded to a Ni atom in direct contact with the surface (see Table 1 and Figure S11a; Eads: –150 kJ.mol-1) or to a Ni atom one plane above (Eads: –123 kJ.mol-1). When the carbon of CO2 is adsorbed on Ni in direct contact to the surface, CO2 activation is endothermic (Ediss: -37 kJ.mol-1) with a rather energy demanding transition-state (ETS: 7 kJ.mol-1). Conversely, when the carbon of CO2 is initially adsorbed on a Ni atom on one plane above the support, the CO2

cleavage is significantly more exothermic than for the previous case (Ediss: –170 kJ.mol-1). a) 150 100 50

E [kJ/mol]

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TS

0

Ni 13ICO 13 - 100 (1)

-50

Ni 55ICO (3) 55 - 100

-100

Ni 13CBPT2 13 - 110 (5

-150

Ni 55MD (6) 55 - 110

-200

CO2*

-250 -300

CO* + O*

b)

Figure 3 a) Energy profile for the CO2 activation on the Ni13 and Ni55 clusters supported on the (100) and the (110) surface of γ-Al2O3. b) Geometries for the CO2 cleavage on the Ni55 particle supported on the 110 surface of γAl2O3.

However, the latter pathway displays the most unfavorable TS of all analyzed systems (ETS: 96 kJ.mol-1). Such unfavorable kinetics towards CO2 cleavage can be explained by the too close proximity of CO* and O* in the transition-state (rC-O = 1.769 Å), which was found to inversely correlate with the stability of the transition-states among all the evaluated supported structures (see Figure S13). Also, the regularly shaped and

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symmetric Ni clusters on the (100) surface γ-Al2O3, are probably not able to easily adapt (in the transition state structures). Finally, the surface Al atoms of the (100) surface are probably not acidic enough and hence the adsorption of O* on the metalsupport interface is not significantly stabilized. On the 110 termination of γ-Al2O3 (Figure 3) the CO2 dissociation presents the most favorable thermodynamics among all the evaluated systems: Ediss: –226 and Ediss: –262 kJ.mol-1 for Ni13 and Ni55, respectively (see Table S4 and Figure S12 for all the evaluated possibilities). However, the supported Ni13 particle has a transition-state energy similar to the one found for Ni13 particle (ETS = –16 kJ.mol-1 vs. –34 kJ.mol-1) probably because the oxygen is not stabilized by the nickel particle at the transition state (se Figure S11). Conversely, the CO2 activation on the interface between the Ni55 cluster and the 110 surface of γ-Al2O3 is the most favored one (ETS = –116 kJ.mol-1), due to the binding of the O* atom both to the highly acidic AlIII surface site and the metallic particle (see the corresponding geometry in Figure 3b). Strong metal support interactions were also proposed for the water gas shift reaction catalyzed by CeO2(111) supported Pt nanoparticles. Valence photoemission and DFT results suggested that the support induced electronic perturbations to the Pt particle that favored the ability of the metal to cleave the O-H bonds of water.30 For all supported clusters, we found that there is a linear decrease in the activation energy EA with increasing the C-O distance in the corresponding transition-state (rC-O(TS)) (see Figure S13 a). Based on the calculated energetics for all systems reported in Table 1, we evaluated the possible “BrønstedEvans-Polanyi” (BEP) relationship between the activation energy of CO2 (Eact in Table 1) and the reaction energy of the CO2 dissociation (∆E in Table 1) (see Figure S14). Eact is defined as the energy difference between the energy of the transition state corresponding to the CO2 dissociation (ETS in Table 1) and the energy of adsorbed CO2 (Eads in Table 1). ∆E is defined as the energy difference between the system where CO2 is dissociated as CO and O (Ediss in Table 1) and the energy of adsorbed CO2 (Eads in Table 1). While the BEP relationship holds for the unsupported metallic nanoparticles, it does not hold for all the evaluated systems (Figure S14). These results suggest that for the reactions occurring on metal-support interfaces, BEP relationships are not as clear as for metallic systems, which points out the importance of the local environment. Thus, transitionstates should be calculated explicitly. However, we do observe product-like transition states in all cases. For the supported nanoparticles, the interface helps separating the CO* and O* species in the transition state, resulting in lower activation energies. Such an energetic dependency on the CO* and O* distance is also observed for the energy of the CO2 dissociation (Figure S13 b). If both CO* and O* are too close in the final configuration there is electrostatic repulsion between both species, resulting in a less favorable CO2 dissociation. In summary, our results show that when considering only the metal (Ni), the CO2 adsorption strength and reactivity increases in the order Ni(111) < Ni(211) < Ni55 < Ni13 where the edges of nanoparticles, especially of sub-nanometric ones, are the most reactive. When CO2 adsorbs on Ni nanoparticles supported on γ-Al2O3, the binding energy is significantly higher than on the bare nanoparticles, which is attributed to an increased electron transfer from both the nanoparticle and the support to the CO2 molecule. The role of the metal-support interface in CO2 cleavage is allowing further separation in the transition-state between CO* and O*, stabilizing the latter species. Whether this adsorbed O* is catalytically active or leads to OH* formation under H2 atmosphere and thus to deactivation is still an open question, which needs being further explored in the future. The most active route towards CO2 activation was found to occur on the interface between the Ni55 particle and the 110 surface of γ-Al2O3, since it has the lowest activation energy (32

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kJ mol-1 and the most favored thermodynamics for the CO2 dissociation (Ediss = -262 kJ mol-1), highlighting the role the support can play in favoring the CO2 cleavage. This work provides further understanding on the support effects in heterogeneous catalysis and that significant metal-strong interactions provide more favorable routes, opening the path for the design of more active metal/oxide interfaces towards the CO2 activation.

ASSOCIATED CONTENT Computational Details DFT calculations were performed by means of the Vienna ab initio simulation package (VASP)31 (version 5.2) employing the PW91 functional.32 Further details on the calculations can be found in the SI.

Supporting Information Further details on the calculations, the construction of the models and all the evaluated pathways can be found in the ESI.

AUTHOR INFORMATION Corresponding Author [email protected]

Notes The authors declare no competing financial interests.

ACKNOWLEDGMENT The authors thank the Swiss National Foundation (Ambizione project PZ00P2_148059) and the SCCER Heat and Electricity Storage for financial support. REFERENCES 1. (a) Wang, W.; Wang, S.; Ma, X.; Gong, J., Chem. Soc. Rev. 2011, 40, 3703-3727; (b) Sakakura, T.; Choi, J.-C.; Yasuda, H., Chem. Rev. 2007, 107, 2365-2387. 2. (a) Kondratenko, E. V.; Mul, G.; Baltrusaitis, J.; Larrazabal, G. O.; Perez-Ramirez, J., Energy Environ. Sci. 2013, 6, 3112-3135; (b) Porosoff, M. D.; Yan, B.; Chen, J. G., Energy Environ. Sci. 2016, 9, 6273. 3. (a) Hansen, J. B.; Højlund Nielsen, P. E., Methanol Synthesis. In Handbook of Heterogeneous Catalysis, Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim, Germany, 2008; (b) Behrens, M.; Studt, F.; Kasatkin, I.; Kühl, S.; Hävecker, M.; Abild-Pedersen, F.; Zander, S.; Girgsdies, F.; Kurr, P.; Kniep, B.-L.; Tovar, M.; Fischer, R. W.; Nørskov, J. K.; Schlögl, R., Science 2012, 336, 893-897; (c) Graciani, J.; Mudiyanselage, K.; Xu, F.; Baber, A. E.; Evans, J.; Senanayake, S. D.; Stacchiola, D. J.; Liu, P.; Hrbek, J.; Sanz, J. F.; Rodriguez, J. A., Science 2014, 345, 546-550; (d) Liu, C.; Yang, B.; Tyo, E.; Seifert, S.; DeBartolo, J.; von Issendorff, B.; Zapol, P.; Vajda, S.; Curtiss, L. A., J. Am. Chem. Soc. 2015, 137, 8676-8679; (e) Grabow, L. C.; Mavrikakis, M., ACS Catal. 2011, 1, 365-384. 4. Centi, G.; Perathoner, S., Catal. Today 2009, 148, 191-205. 5. Pakhare, D.; Spivey, J., Chem. Soc. Rev. 2014, 43, 7813-7837. 6. Toda, Y.; Hirayama, H.; Kuganathan, N.; Torrisi, A.; Sushko, P. V.; Hosono, H., Nat Commun 2013, 4: 2378. 7. (a) Freund, H. J.; Roberts, M. W., Surf. Sci. Rep. 1996, 25, 225-273; (b) Ko, J.; Kim, B.-K.; Han, J. W., J. Phys. Chem. C 2016, 120, 3438-3447. 8. (a) Ferreira-Aparicio, P.; Guerrero-Ruiz, A.; Rodrı́guezRamos, I., Appl. Catal. A 1998, 170, 177-187; (b) Foppa, L.; Silaghi, M.C.; Larmier, K.; Comas-Vives, A., J. Catal. 2016, in press doi:10.1016/j.jcat.2016.02.030; (c) Catapan, R. C.; Oliveira, A. A. M.; Chen, Y.; Vlachos, D. G., J. Phys. Chem. C 2012, 116, 20281-20291.

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SYNOPSIS TOC The CO2 activation on Ni supported on γ-Al2O3 has been evaluated by first principles, accounting for the role of terraces, steps, edges, finite particles and the metal-support interface for this chemical transformation. The metaloxide interface is the most active towards CO2 activation, highlighting the importance support effects can have in heterogeneous catalysis.

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