Catalysis by ultrathin
LaBO₃ (B=Co, Fe) perovskite films

@article{Shi2022,

title = {High-performance water gas shift induced by asymmetric oxygen vacancies: Gold clusters supported by ceria-praseodymia mixed oxides},

author = {Junjie Shi and Hailian Li and Alexander Genest and Weixuan Zhao and Pengfei Qi and Tao Wang and Günther Rupprechter},

doi = {10.1016/j.apcatb.2021.120789},

year  = {2022},

date = {2022-02-01},

urldate = {2022-02-01},

journal = {Applied Catalysis B: Environmental},

volume = {301},

pages = {120789},

publisher = {Elsevier BV},

abstract = {Modifying and controlling sites at the metal/oxide interface is an effective way of tuning catalytic activity, beneficial for bifunctional catalysis by reducible oxide supported \underline{metal nanoparticles}. We employed mixed ceria-praseodymia supported Au clusters for the \underline{water gas shift} reaction (WGSR). Varying the Ce:Pr ratio (4:1, 2:1, 1:4) not only allows to control the number of oxygen vacancies but, even more important, their local coordination, with asymmetrically coordinated O# being most active for water activation. These effects have been examined by X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, temperature programmed desorption/reduction (TPD/TPR), and density functional theory (DFT). Using the WGSR performance of Au/CeOx as reference, Au/Ce_{4}Pr_{1}O_{x} was identified to exhibit the highest activity, with a CO conversion of 75% at 300 °C, which is about 5-times that of Au/CeO_{x}. Au/Ce_{4}Pr_{1}O_{x} also showed excellent stability, with the conversion still being 70% after 50 h time-on-stream at 300 °C. Although a higher Pr content leads to more O vacancies, the catalytic activity showed a “volcano behavior”. Based on DFT, this was rationalized via the formation energy of oxygen vacancies, the binding energy of water, and the asymmetry of the O# site. The presented route of creating active vacancy sites should also be relevant for other heterogeneous catalytic systems.},

keywords = {P08},

pubstate = {published},

tppubtype = {article}

}

@article{Kiatsaengthong2022,

title = {Effects of Mg, Ca, Sr, and Ba Dopants on the Performance of La_{2}O_{3} Catalysts for the Oxidative Coupling of Methane},

author = {Danusorn Kiatsaengthong and Kanticha Jaroenpanon and Pooripong Somchuea and Thanaphat Chukeaw and Metta Chareonpanich and Kajornsak Faungnawakij and Hiesang Sohn and Günther Rupprechter and Anusorn Seubsai},

doi = {10.1021/acsomega.1c04738},

year  = {2022},

date = {2022-01-04},

urldate = {2022-01-04},

journal = {ACS Omega},

volume = {7},

number = {2},

pages = {1785--1793},

publisher = {American Chemical Society (ACS)},

abstract = {Oxidative coupling of methane (OCM) is a reaction to directly convert methane into high value-added hydrocarbons (C_{2+}) such as ethylene and ethane using molecular oxygen and a catalyst. This work investigated lanthanum oxide catalysts for OCM, which were promoted with alkaline-earth metal oxides (Mg, Ca, Sr, and Ba) and prepared by the solution-mixing method. The synthesized catalysts were characterized using X-ray powder diffraction, CO_{2}-programmed desorption, and X-ray photoelectron spectroscopy. The comparative performance of each promoter showed that promising lanthanum-loaded alkaline-earth metal oxide catalysts were La-Sr and La-Ba. In contrast, the combination of La with Ca or Mg did not lead to a clear improvement of C_{2+} yield. The most promising LaSr50 catalyst exhibited the highest C_{2+} yield of 17.2%, with a 56.0% C_{2+} selectivity and a 30.9% CH_{4} conversion. Catalyst characterization indicated that their activity was strongly associated with moderate basic sites and surface-adsorbed oxygen species of O_{2}^{–}. Moreover, the catalyst was stable over 25 h at a reactor temperature of 700 °C.},

keywords = {P08},

pubstate = {published},

tppubtype = {article}

}

@article{Haunold2021,

title = {LiOx-modification of Ni and Co_{3}O_{4} surfaces: An XPS, LEIS and LEED study},

author = {Thomas Haunold and Günther Rupprechter},

doi = {10.1016/j.susc.2021.121915},

year  = {2021},

date = {2021-11-01},

urldate = {2021-11-01},

journal = {Surface Science},

volume = {713},

pages = {121915},

publisher = {Elsevier BV},

abstract = {LiO_{x} was deposited at room temperature by physical vapor deposition (PVD) on polycrystalline Ni foil and Co_{3}O_{4}(111) thin film, creating uniform model systems well-suited for surface-sensitive characterization by X-ray photoelectron spectroscopy (XPS), low energy ion scattering (LEIS) or low energy electron diffraction (LEED). In the case of Ni, about 15 layers of LiO_{x} film were grown under the current conditions either stepwise or continuously, with XPS analysis indicating a deposition rate of 0.16 and 0.24 ML/min, respectively. Li 1s and O 1s spectra revealed that Li_{2}O and to a lesser extent LiOH were preferentially formed. The stability of the LiO_{x}films was examined in UHV, upon annealing at 573 K and upon hydrogen reduction at 723 K. On the more reactive Co_{3}O_{4}(111) film grown on Ir(100), the Li accommodation rate was about twice as high, at least within the first minutes of deposition. Post-deposition LEED showed an obscured cobalt oxide diffraction pattern, not unexpected in light of the LiO_{x} deposited. On both substrates, LEIS characterization of Li (≈ 103 eV) was prevented by the high background in this kinetic energy region, due to surface roughness and unspecific scattering. Still, LiO_{x} deposition was evident from the vanished LEIS signals of Ni or Co. The prepared LiO_{x}-modified surfaces may serve as starting point for the future growth of epitaxial Li_{x}CoO_{2} model systems.},

keywords = {P08},

pubstate = {published},

tppubtype = {article}

}

@article{Zeininger2021,

title = {Single-Particle Catalysis: Revealing Intraparticle Pacemakers in Catalytic H2 Oxidation on Rh},

author = {Johannes Zeininger and Yuri Suchorski and Maximilian Raab and Sebastian Buhr and Henrik Grönbeck and Günther Rupprechter},

doi = {10.1021/acscatal.1c02384},

year  = {2021},

date = {2021-07-27},

urldate = {2021-07-27},

journal = {ACS Catalysis},

volume = {11},

number = {15},

pages = {10020--10027},

publisher = {American Chemical Society (ACS)},

abstract = {Self-sustained oscillations in H_{2} oxidation on a Rh nanotip mimicking a single catalytic nanoparticle were studied by in situ field emission microscopy (FEM). The observed spatio-temporal oscillations result from the coupling of subsurface oxide formation/depletion with reaction front propagation. An original sophisticated method for tracking kinetic transition points allowed the identification of local pacemakers, initiating kinetic transitions and the nucleation of reaction fronts, with much higher temporal resolution than conventional processing of FEM video files provides. The pacemakers turned out to be specific surface atomic configurations at the border between strongly corrugated Rh{973} regions and adjacent relatively flat terraces. These structural ensembles are crucial for reactivity: while the corrugated region allows sufficient oxygen incorporation under the Rh surface, the flat terrace provides sufficient hydrogen supply required for the kinetic transition, highlighting the importance of interfacet communication. The experimental observations are complemented by mean-field microkinetic modeling. The insights into the initiation and propagation of kinetic transitions on a single catalytic nanoparticle demonstrate how in situ monitoring of an ongoing reaction on individual nanofacets can single out active configurations, especially when combined with atomically resolving the nanoparticle surface by field ion microscopy (FIM).},

keywords = {P08, TACO-associated},

pubstate = {published},

tppubtype = {article}

}