PUBLICATIONS

Authors: Garbujo, A.; Pacella, M.; Natile, MM.; Guiotto, M.; Fabro, J.; Canu, P.; Glisenti, A.

Published on: Applied Catalysis A General Journal – 25.08.2017 – Elsevier – Amsterdam (The Netherlands)

Abstract: 

Several perovskites of the type La1-xAxCo0.5Cu0.5O3 (A = K, Sr, Ba; x = 0, 0.25, 0.5) and a Sr-doped understoichiometric one, have been prepared by citrate method aiming at application as noble metals free catalysts for automotive application. The catalysts have been characterized by BET, X-ray diffraction (XRD), Temperature Programmed Reduction (TPR), X-Ray Photoelectron Spectroscopy (XPS), and Scanning Electron Microscopy (SEM) and the effect of A-doping has been investigated. The catalytic activity was studied in model reactions (CO oxidation, CO assisted NO reduction), and in a complex three way catalysts (TWC) mixture approaching automotive exhaust composition at both stoichiometric and O2-limiting conditions and the obtained results are discussed in relation with characterization results.

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Authors: Giulia Spezzati, Yaqiong Su, Jan P. Hofmann, Angelica D. Benavidez, Andrew T. DeLaRiva, Jay McCabe, Abhaya K. Datye, Emiel J. M. Hensen

Published on: ACS Catalysis – 07.09.2017 – American Chemical Society (ACS) – Eindhoven (The Netherlands)

Abstract: 

Ceria-supported Pd is a promising heterogeneous catalyst for CO oxidation relevant to environmental cleanup reactions. Pd loaded onto a nanorod form of ceria exposing predominantly (111) facets is already active at 50 °C. Here we report a combination of CO-FTIR spectroscopy and theoretical calculations that allows assigning different forms of Pd on the CeO₂(111) surface during reaction conditions. Single Pd atoms stabilized in the form of PdO and PdO₂ in a CO/O₂atmosphere participate in a catalytic cycle involving very low activation barriers for CO oxidation. The presence of single Pd atoms on the Pd/CeO₂-nanorod, corroborated by aberration-corrected TEM and CO-FTIR spectroscopy, is considered pivotal to its high CO oxidation activity.

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Authors: Ya-Qiong Su, Jin-Xun Liu, Ivo A. W. Filot, Emiel J. M. Hensen

Published on: Chemistry of Materials-  Vol. 29, No. 21, 13.10.2017, p. 9456–9462. – American Chemical Society (ACS) – Eindhoven (The Netherlands)

Abstract: 

We carried out density functional theory calculations to investigate the ripening of Pd clusters on CeO2(111). Starting from stable Pdn clusters (n=1-21), we compared how these clusters can grow through Ostwald ripening and coalescence. As Pd atoms have a high mobility than Pd¬n clusters on the CeO2(111) surface, Ostwald-ripening is predicted to be the dominant sintering mechanism. Particle coalescence is only possible when very small clusters with less than 5 Pd at-oms are involved. These ripening mechanisms are facilitated by adsorbed CO through lowering barriers for the cluster diffusion, detachment of a Pd atom from clusters, and transformation of initial planar clusters.

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Authors: M. Václavík, M. Plachá, P. Kočí, M. Svoboda, T. Hotchkiss, V. Novák, D. Thompsett

Published on: Materials Characterization – Pages:311-318 – 04.11.2017 – Elsevier B.V. – Amsterdam (The Netherlands)

Abstract: 

Modern automobiles with internal combustion engine are equipped with several different converters of exhaust gas and a particulate filter. The size and cost of exhaust aftertreatment system can be reduced by coating the catalytically active material on or into the porous filter walls. The characterisation of filter morphology including the distribution of catalytic material inside the filter wall is a key prerequisite for the development of porous structures with optimum performance with respect to pressure loss, filtration efficiency and catalytic activity.

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Authors: Ya-Qiong Su, Ivo A. W. Filot, Jin-Xun Liu, Emiel J. M. Hensen

Published on: ACS Catalysis – Pages:75-80 – 20.11.2017 – American Chemical Society (ACS) – Eindhoven (The Netherlands)

Abstract: 

Doping CeO₂ with Pd atoms has been associated with catalytic CO oxidation, but current surface models do not allow CO adsorption. Here, we report a new structure of Pd-doped CeO₂(111), in which Pd adopts a square planar configuration instead of the previously assumed octahedral configuration. Oxygen removal from this doped structure is favorable. The resulting defective Pd-doped CeO₂ surface is active for CO oxidation and is also able to cleave the first C–H bond in methane. We show how the moderate CO adsorption energy and dynamic features of the Pd atom upon CO adsorption and CO oxidation contribute to a low-barrier catalytic cycle for CO oxidation. These structures, which are also observed for Ni and Pt, can lead to a more open coordination environment around the doped-transition-metal center. These thermally stable structures are relevant to the development of single-atom catalysts.

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Authors: P. Kočí, M. Isoz, M. Plachá, A. Arvajová, M. Václavík, M. Svoboda, E. Price, V. Novák, D. Thompsett

Published on: Catalysis Today – 21.12.2017 – Elsevier B.V. – Amsterdam (The Netherlands)

Abstract: 

This paper introduces a newly developed methodology for the pore-scale simulation of flow, diffusion and reaction in the coated catalytic filter. 3D morphology of the porous filter wall including the actual distribution of catalytic material is reconstructed from X-ray tomography (XRT) images and further validated with the mercury intrusion porosimetry (MIP). The reconstructed medium is then transformed into simulation mesh for OpenFOAM. Flow through free pores in the substrate as well as through the coated zones is simulated by porousSimpleFoam solver, while an in-house developed solver is used for component diffusion and reactions.

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Authors: Carlotto, S.; Natile, MM.; Glisenti, A.; Vittadini, A.

Published on: Catalysis Today – 21.12.2017 – Elsevier B.V. – Amsterdam (The Netherlands)

Abstract: 

The NO reduction in a CO–NO atmosphere at the Co- and Cu-doped SrTiO₃(100) surfaces is investigated by density functional theory calculations. The energy profiles for several mechanisms are computed and compared. On this basis, a rationale for the available experimental data is proposed. Oxygen vacancies formed as intermediate species in the CO oxidation process play a key role in the NO reduction. Their concentration is also relevant because, if low, formation of N₂O prevails on that of N₂, leading to an incomplete reduction. The formation of oxygen vacancies is favored by Co and Cu impurities, the latter being most effective. Overall, doping promotes the catalytic reduction of NO on SrTiO₃.

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Authors: Jin-Xun Liu,Yaqiong Su, Ivo A. W. Filot,Emiel J. M. Hensen

Published on: Journal of the American Chemical Society 2018 140 (13), 4580-4587 – 02.03.2018 – DOI: 10.1021/jacs.7b13624

Abstract: 

Resolving the structure and composition of supported nanoparticles under reaction conditions remains a challenge in heterogeneous catalysis. Advanced configurational sampling methods at the density functional theory level are used to identify stable structures of a Pd₈ cluster on ceria (CeO₂) in the absence and presence of O₂. A Monte Carlo method in the Gibbs ensemble predicts Pd-oxide particles to be stable on CeO₂ during CO oxidation. Computed potential energy diagrams for CO oxidation reaction cycles are used as input for microkinetics simulations. Pd-oxide exhibits a much higher CO oxidation activity than metallic Pd on CeO₂. This work presents for the first time a scaling relation for a CeO₂-supported metal nanoparticle catalyst in CO oxidation: a higher oxidation degree of the Pd cluster weakens CO binding and facilitates the rate-determining CO oxidation step with a ceria O atom. Our approach provides a new strategy to model supported nanoparticle catalysts.

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Authors: Jin-Xun Liu,Yaqiong Su, Ivo A. W. Filot,Emiel J. M. Hensen

Published on: Journal of Catalysis, Vol. 363, 01.07.2018, p. 154-163.

Abstract: 

The replacement of platinum group metals by non-noble metals has attracted significant attention in the field of three-way catalysis. Here, we use DFT calculations to comprehensively study NO reduction by CO and CO oxidation on Pd(1 1 1) and transition metal doped Pd(1 1 1). Whilst direct NO dissociation is very difficult on metallic Pd(1 1 1), doping with transition metals can substantially lower the reaction barrier for NO dissociation. The lowest barrier is predicted for Ti-doped Pd(1 1 1). An electronic structure analysis shows that the low barrier is due to the strong adsorption of N and O on surface sites involving Ti atoms. It relates to strong hybridization of the N and O orbitals with the half-filled d-band of the metallic surface. At the same time, the anti-bonding states are shifted above the Fermi level, which further strengthens the adsorption of N and O. A Brønsted-Evans-Polanyi relation for NO dissociation on TM-doped Pd(1 1 1) surfaces is identified. The complete reaction pathway for N₂, N₂O and CO₂ formation on Pd(1 1 1) and Ti-doped Pd(1 1 1) was considered. Besides more facile NO dissociation, the energy barrier for CO oxidation is decreased for the Ti-doped surface. Microkinetics simulations confirm that the activity and selectivity for NO reduction and CO oxidation are drastically improved after Ti doping. Our findings indicate that doping of Pd with non-noble metal can further improve the performance of three-way catalysts.

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Authors: Pacella, M.; Garbujo, A.; Fabro, J; Guiotto, M.; Xin, Q.; Natile, MM, Canu, P; Cool, P.; Glisenti, A.

Published on: Applied Catalysis B Environmental, Volume 227, 5 July 2018, Pages 446-458 – Elsevier BV, Amsterdam (The Netherlands) 

Abstract: 

In this contribution several LaCoO₃ based nanocomposites have been prepared and tested for application as Three-Way Catalytic Converters (TWC): the aim is in developing Platinum Group Metal (PGM)-free catalysts. To reach this objective we designed and realized nanocomposites in which active CuO nanoparticles are deposited on active LaCoO₃. This perovskite is active in oxidation while copper is active in reduction: catalytic bifunctionality is thus built-in via a tailor-made and controlled nanocomposition. The deposition was carried out by means of an innovative Ammonium-Driving-Deposition precipitation (ADP) procedure allowing to obtain nanocomposites in which CuO is highly dispersed on LaCoO₃. This increases the reducibility of the nanocomposites, as revealed by the TPR measurements. The deposition of copper does not alter significantly the surface composition which remains rich in lanthanum oxide/hydroxide, the main effect consisting in a slight increment of surface hydroxylation. Moreover, the copper amount on the LaCoO₃surface does not increase linearly with the nominal composition.

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