Definitive experimental proof for catalytic pathways and active sites during the low-temperature water-gas shift reaction remains elusive. Herein, we combine spectroscopic, kinetic and computational analyses to address the decades-long mechanistic controversy by studying the reverse water-gas shift over Pd/Al2O3. Isotopic transient kinetic analysis established the minor role of the formate intermediate, whereas hydrogen titration experiments confirmed the intermediacy of carboxyl. The ability to decouple the parallel formate and carboxyl pathways led to the identification of a distinct active site that exhibits regio- and chemoselective hydrogen addition to CO2 to yield the carboxyl intermediate. The metastable active site is formed in situ, resulting in hydroxylation of the metal–support interface and electronic restructuring. Atomistic simulations of the active site electronic structure and mechanistic landscape provided a framework that is consistent with experimental observations. Our study highlights the dynamic creation of a coordinatively unsaturated metal site caused by substrate adsorption on an adjacent support site.
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The data that support the plots in this paper and other findings of this study are available from the corresponding author on reasonable request.
Reddy, G. K. & Smirniotis, P. G. in Water-Gas Shift Reaction (eds Reddy, G. K. & Smirniotis, P. G.) Ch. 1 (Amsterdam, 2015).
Ratnasamy, C. & Wagner, J. P. Water-gas shift catalysis. Cat. Rev. 51, 325–440 (2009).
Álvarez, A. et al. Challenges in the greener production of formates/formic acid, methanol, and DME by heterogeneously catalyzed CO2 hydrogenation processes. Chem. Rev. 117, 9804–9838 (2017).
Wang, X., Shi, H., Kwak, J. H. & Szanyi, J. Mechanism of CO2 hydrogenation on Pd/Al2O3 catalysts: kinetics and transient DRIFTS-MS studies. ACS Catal. 5, 6337–6349 (2015).
Senanayake, S. D. et al. Probing the reaction intermediates for the water–gas shift over inverse CeOx/Au(111) catalysts. J. Catal. 271, 392–400 (2010).
Graciani, J. et al. Highly active copper-ceria and copper-ceria-titania catalysts for methanol synthesis from CO2. Science 345, 546 (2014).
Wang, L. C., Tahvildar Khazaneh, M., Widmann, D. & Behm, R. J. TAP reactor studies of the oxidizing capability of CO2 on a Au/CeO2 catalyst—a first step toward identifying a redox mechanism in the reverse water–gas shift reaction. J. Catal. 302, 20–30 (2013).
Kalamaras, C. M., Panagiotopoulou, P., Kondarides, D. I. & Efstathiou, A. M. Kinetic and mechanistic studies of the water–gas shift reaction on Pt/TiO2 catalyst. J. Catal. 264, 117–129 (2009).
Goguet, A., Meunier, F. C., Tibiletti, D., Breen, J. P. & Burch, R. Spectrokinetic investigation of reverse water-gas-shift reaction intermediates over a Pt/CeO2 catalyst. J. Phys. Chem. B 108, 20240–20246 (2004).
Meunier, F. C., Goguet, A., Hardacre, C., Burch, R. & Thompsett, D. Quantitative DRIFTS investigation of possible reaction mechanisms for the water–gas shift reaction on high-activity Pt- and Au-based catalysts. J. Catal. 252, 18–22 (2007).
Bunluesin, T., Gorte, R. J. & Graham, G. W. Studies of the water-gas-shift reaction on ceria-supported Pt, Pd, and Rh: implications for oxygen-storage properties. Appl. Catal. B 15, 107–114 (1998).
Ding, K. et al. Identification of active sites in CO oxidation and water-gas shift over supported Pt catalysts. Science 350, 189 (2015).
Fu, Q., Saltsburg, H. & Flytzani-Stephanopoulos, M. Active nonmetallic Au and Pt species on ceria-based water-gas shift catalysts. Science 301, 935 (2003).
Yang, M. et al. A common single-site Pt(ii)–O(OH)x–species stabilized by sodium on “active” and “inert” supports catalyzes the water-gas shift reaction. J. Am. Chem. Soc. 137, 3470–3473 (2015).
Rhodes, C., Hutchings, G. J. & Ward, A. M. Water-gas shift reaction: finding the mechanistic boundary. Catal. Today 23, 43–58 (1995).
Gokhale, A. A., Dumesic, J. A. & Mavrikakis, M. On the mechanism of low-temperature water-gas shift reaction on copper. J. Am. Chem. Soc. 130, 1402–1414 (2008).
Li, Y., Chan, S. H. & Sun, Q. Heterogeneous catalytic conversion of CO2: a comprehensive theoretical review. Nanoscale 7, 8663–8683 (2015).
Madon, R. J. et al. Microkinetic analysis and mechanism of the water-gas shift reaction over copper catalysts. J. Catal. 281, 1–11 (2011).
Kattel, S., Yan, B., Yang, Y., Chen, J. G. & Liu, P. Optimizing binding energies of key intermediates for CO2 hydrogenation to methanol over oxide-supported copper. J. Am. Chem. Soc. 138, 12440–12450 (2016).
Aranifard, S., Ammal, S. C. & Heyden, A. On the importance of the associative carboxyl mechanism for the water-gas shift reaction at Pt/CeO2 interface sites. J. Phys. Chem. C 118, 6314–6323 (2014).
Rodriguez, J. A. et al. Water-gas shift reaction on a highly active inverse CeOx/Cu(111) catalyst: unique role of ceria nanoparticles. Angew. Chem. Int. Ed. 48, 8047–8050 (2009).
Yang, Y., Evans, J., Rodriguez, J. A., White, M. G. & Liu, P. Fundamental studies of methanol synthesis from CO2 hydrogenation on Cu(111), Cu clusters, and Cu/ZnO(0001). Phys. Chem. Chem. Phys. 12, 9909–9917 (2010).
Sun, K., Kohyama, M., Tanaka, S. & Takeda, S. Reaction mechanism of the low-temperature water–gas shift reaction on Au/TiO2 catalysts. J. Phys. Chem. C 121, 12178–12187 (2017).
Hong, Q.-J. & Liu, Z.-P. Mechanism of CO2 hydrogenation over Cu/ZrO2(212) interface from first-principles kinetics Monte Carlo simulations. Surf. Sci. 604, 1869–1876 (2010).
Rodriguez, J. A., Ping, L., Jan, H., Jaime, E. & Manuel, P. Water-gas shift reaction on Cu and Au nanoparticles supported on CeO2(111) and ZnO(0001): intrinsic activity and importance of support interactions. Angew. Chem. Int. Ed. 46, 1329–1332 (2007).
Rodriguez, J. A. et al. Activity of CeOx and TiOx nanoparticles grown on Au(111) in the water-gas shift reaction. Science 318, 1757 (2007).
Mudiyanselage, K. et al. Importance of the metal–oxide interface in catalysis: in situ studies of the water–gas shift reaction by ambient-pressure X-ray photoelectron spectroscopy. Angew. Chem. Int. Ed. 52, 5101–5105 (2013).
Zhai, Y. et al. Alkali-stabilized Pt–OHx species catalyze low-temperature water-gas shift reactions. Science 329, 1633 (2010).
Bruix, A. et al. A new type of strong metal–support interaction and the production of H2 through the transformation of water on Pt/CeO2(111) and Pt/CeOx/TiO2(110) catalysts. J. Am. Chem. Soc. 134, 8968–8974 (2012).
Lykhach, Y. et al. Counting electrons on supported nanoparticles. Nat. Mater. 15, 284 (2015).
Williams, W. D. et al. Metallic corner atoms in gold clusters supported on rutile are the dominant active site during water–gas shift catalysis. J. Am. Chem. Soc. 132, 14018–14020 (2010).
Chen, Y. et al. Identifying size effects of Pt as single atoms and nanoparticles supported on FeOx for the water-gas shift reaction. ACS Catal. 8, 859–868 (2018).
Guo, Y. et al. Low-temperature CO2 methanation over CeO2-supported Ru single stoms, nanoclusters, and nanoparticles competitively tuned by strong metal–support interactions and H-spillover effect. ACS Catal. 8, 6203–6215 (2018).
Lin, L. et al. In situ characterization of Cu/CeO2 nanocatalysts for CO2 hydrogenation: morphological effects of nanostructured ceria on the catalytic activity. J. Phys. Chem. C 122, 12934–12943 (2018).
Bobadilla, L. F., Santos, J. L., Ivanova, S., Odriozola, J. A. & Urakawa, A. Unravelling the role of oxygen vacancies in the mechanism of the reverse water–gas shift reaction by operando DRIFTS and ultraviolet–visible spectroscopy. ACS Catal. 8, 7455–7467 (2018).
Xu, M. et al. Insights into interfacial synergistic catalysis over Ni@TiO2–x catalyst toward water–gas shift reaction. J. Am. Chem. Soc. 140, 11241–11251 (2018).
Zhao, K., Wang, L., Calizzi, M., Moioli, E. & Züttel, A. In situ control of the adsorption species in CO2 hydrogenation: determination of intermediates and byproducts. J. Phys. Chem. C. 122, 20888–20893 (2018).
Yang, S.-C. et al. Synergy between ceria oxygen vacancies and Cu nanoparticles facilitates the catalytic conversion of CO2 to CO under mild conditions. ACS Catal. 8, 12056–12066 (2018).
Schilling, C. & Hess, C. Elucidating the role of support oxygen in the water–gas shift reaction over ceria-supported gold catalysts using operando spectroscopy. ACS Catal. 9, 1159–1171 (2019).
Wang, Y.-G., Mei, D., Glezakou, V.-A., Li, J. & Rousseau, R. Dynamic formation of single-atom catalytic active sites on ceria-supported gold nanoparticles. Nat. Commun. 6, 6511 (2015).
He, Y. et al. Size-dependent dynamic structures of supported gold nanoparticles in CO oxidation reaction condition. Proc. Natl Acad. Sci. USA 115, 7700 (2018).
Wang, X., Shi, H. & Szanyi, J. Controlling selectivities in CO2 reduction through mechanistic understanding. Nat. Commun. 8, 513 (2017).
Lyons, T. W. & Sanford, M. S. Palladium-catalyzed ligand-directed C–H functionalization reactions. Chem. Rev. 110, 1147–1169 (2010).
Herron, J. A., Scaranto, J., Ferrin, P., Li, S. & Mavrikakis, M. Trends in formic acid decomposition on model transition metal surfaces: a density functional theory study. ACS Catal. 4, 4434–4445 (2014).
Saavedra, J., Doan, H. A., Pursell, C. J., Grabow, L. C. & Chandler, B. D. The critical role of water at the gold-titania interface in catalytic CO oxidation. Science 345, 1599 (2014).
Flytzani-Stephanopoulos, M. Gold atoms stabilized on various supports catalyze the water–gas shift reaction. Acc. Chem. Res. 47, 783–792 (2014).
Hammer, B. & Nørskov, J. K. Electronic factors determining the reactivity of metal surfaces. Surf. Sci. 343, 211–220 (1995).
Abild-Pedersen, F. et al. Scaling properties of adsorption energies for hydrogen-containing molecules on transition-metal surfaces. Phys. Rev. Lett. 99, 016105 (2007).
Henkelman, G., Uberuaga, B. P. & Jonsson, H. A climbing image nudged elastic band method for finding saddle points and minimum energy paths. J. Chem. Phys. 113, 9901–9904 (2000).
Koros, R. M. & Nowak, E. J. A diagnostic test of the kinetic regime in a packed bed reactor. Chem. Eng. Sci. 22, 470 (1967).
Yang, Y. et al. Design and operating characteristics of a transient kinetic analysis catalysis reactor system employing in situ transmission Fourier transform infrared. Rev. Sci. Instrum. 77, 094104 (2006).
Wuttke, S. et al. Discovering the active sites for C3 separation in MIL-100(Fe) by using operando IR. Spectrosc. Chem. Eur. J. 18, 11959–11967 (2012).
VandeVondele, J. et al. QUICKSTEP: fast and accurate density functional calculations using a mixed Gaussian and plane waves approach. Comput. Phys. Commun. 167, 103–128 (2005).
Perdew, J. P., Burke, K. & Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 77, 3865–3868 (1996).
Grimme, S., Antony, J., Ehrlich, S. & Krieg, H. A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H–Pu. J. Chem. Phys. 132, 19 (2010).
Lippert, G., Hutter, J. & Parrinello, M. A hybrid Gaussian and plane wave density functional scheme. Mol. Phys. 92, 477–487 (1997).
VandeVondele, J. & Hutter, J. Gaussian basis sets for accurate calculations on molecular systems in gas and condensed phases. J. Chem. Phys. 127, 9 (2007).
Goedecker, S., Teter, M. & Hutter, J. Separable dual-space Gaussian pseudopotentials. Phys. Rev. B 54, 1703–1710 (1996).
Bengtsson, L. Dipole correction for surface supercell calculations. Phys. Rev. B 59, 12301–12304 (1999).
Mei, D. H. et al. Highly active and stable MgAl2O4-supported Rh and Ir catalysts for methane steam reforming: a combined experimental and theoretical study. J. Catal. 316, 11–23 (2014).
Szanyi, J. & Kwak, J. H. Dissecting the steps of CO2 reduction: 1. The interaction of CO and CO2 with γ-Al2O3: an in situ FTIR study. Phys. Chem. Chem. Phys. 16, 15117–15125 (2014).
Szanyi, J. & Kwak, J. H. Dissecting the steps of CO2 reduction: 2. The interaction of CO and CO2 with Pd/γ-Al2O3: an in situ FTIR study. Phys. Chem. Chem. Phys. 16, 15126–15138 (2014).
Rubasinghege, G., Ogden, S., Baltrusaitis, J. & Grassian, V. H. Heterogeneous uptake and adsorption of gas-phase formic acid on oxide and clay particle surfaces: the roles of surface hydroxyl groups and adsorbed water in formic acid adsorption and the impact of formic acid adsorption on water uptake. J. Phys. Chem. A 117, 11316–11327 (2013).
Deacon, G. B. & Phillips, R. J. Relationships between the carbon-oxygen stretching frequencies of carboxylato complexes and the type of carboxylate coordination. Coord. Chem. Rev. 33, 227–250 (1980).
Tong, S. R., Wu, L. Y., Ge, M. F., Wang, W. G. & Pu, Z. F. Heterogeneous chemistry of monocarboxylic acids on alpha-Al2O3 at different relative humidities. Atmos. Chem. Phys. 10, 7561–7574 (2010).
This work was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences and performed at the Environmental Molecular Sciences Laboratory, which is a US Department of Energy Office of Science User Facility located at Pacific Northwest National Laboratory. Pacific Northwest National Laboratory is a multi-program national laboratory operated for the US Department of Energy by Battelle. Computational resources were provided by a user proposal at the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility. N.N. would like to thank O. Y. Gutierrez for critical feedback during the final stage of the manuscript’s preparation.
The authors declare no competing interests.
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Nelson, N.C., Nguyen, MT., Glezakou, VA. et al. Carboxyl intermediate formation via an in situ-generated metastable active site during water-gas shift catalysis. Nat Catal 2, 916–924 (2019). https://doi.org/10.1038/s41929-019-0343-2
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