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}

}

@article{Shen2021,

title = {Emerging applications of MXene materials in CO_{2} photocatalysis},

author = {Jiahui Shen and Zhiyi Wu and Chaoran Li and Chengcheng Zhang and Alexander Genest and Günther Rupprechter and Le He},

doi = {10.1016/j.flatc.2021.100252},

year  = {2021},

date = {2021-07-01},

journal = {FlatChem},

volume = {28},

pages = {100252},

publisher = {Elsevier BV},

abstract = {MXene materials, a young family of two-dimensional transition-metal carbides and nitrides, hold great promise for diverse demanding applications. Recently, it was discovered that MXenes can boost the efficiency of CO_{2} photocatalysis, e.g. by accelerating the charge separation, alleviating the photocorrosion, enhancing CO_{2} adsorption and activation, and promoting the photothermal conversion capability. In this mini-review, we summarize recent developments of photocatalysts based on MXene materials for various CO_{2} reduction reactions with a focus on the role of MXenes in photocatalytic processes. Several perspectives in terms of challenges and future research in this area are also highlighted.},

keywords = {P08, pre-TACO},

pubstate = {published},

tppubtype = {article}

}

@article{Suchorski2021,

title = {Resolving multifrequential oscillations and nanoscale interfacet communication in single-particle catalysis},

author = {Yuri Suchorski and Johannes Zeininger and Sebastian Buhr and Maximilian Raab and Michael Stöger-Pollach and Johannes Bernardi and Henrik Grönbeck and Günther Rupprechter},

doi = {10.1126/science.abf8107},

year  = {2021},

date = {2021-06-18},

urldate = {2021-06-18},

journal = {Science},

volume = {372},

number = {6548},

pages = {1314--1318},

publisher = {American Association for the Advancement of Science (AAAS)},

abstract = {Metal nanoparticles used in heterogeneous catalysis can bear different facets with different reaction kinetics. Suchorski et al. used field electron microscopy with high spatial (∼2 nanometers) and time (∼2 milliseconds) resolution to study hydrogen oxidation on a curved rhodium crystal that displayed individual nanofacets. They also performed field ion microscopy of the water products. Periodic formation and depletion of subsurface oxygen blocked or allowed hydrogen adsorption, respectively, and led to oscillatory kinetics that could frequency lock between facets but at different frequencies. Surface reconstructions could also induce collapse of spatial coupling of oscillations.},

keywords = {P08, pre-TACO},

pubstate = {published},

tppubtype = {article}

}

@article{Yang2021,

title = {Co_{3}O_{4}-CeO_{2} Nanocomposites for Low-Temperature CO Oxidation},

author = {Jingxia Yang and Nevzat Yigit and Jury Möller and Günther Rupprechter},

doi = {10.1002/chem.202100927},

year  = {2021},

date = {2021-04-29},

urldate = {2021-04-29},

journal = {Chemistry A European Journal},

publisher = {Wiley},

abstract = {In an effort to combine the favorable catalytic properties of Co_{3}O_{4} and CeO_{2}, nanocomposites with different phase distribution and Co_{3}O_{4} loading were prepared and employed for CO oxidation. Synthesizing Co_{3}O_{4}-modified CeO_{2} via three different sol-gel based routes, each with 10.4 wt % Co_{3}O_{4} loading, yielded three different nanocomposite morphologies:  CeO_{2}-supported Co_{3}O_{4} layers, intermixed oxides, and homogeneously dispersed Co. The reactivity of the resulting surface oxygen species towards CO were examined by temperature programmed reduction (CO-TPR) and flow reactor kinetic tests. The first morphology exhibited the best performance due to its active Co_{3}O_{4} surface layer, reducing the light-off temperature of  CeO_{2} by about 200 °C. In contrast, intermixed oxides and Co-doped  CeO_{2} suffered from lower dispersion and organic residues, respectively. The performance of Co_{3}O_{4}- CeO_{2} nanocomposites was optimized by varying the Co_{3}O_{4} loading, characterized by X-ray diffraction (XRD) and N_{2} sorption (BET). The 16–65 wt % _{3}O_{4}− CeO_{2} catalysts approached the conversion of 1 wt % Pt/CeO2, rendering them interesting candidates for low-temperature CO oxidation.},

keywords = {P08, pre-TACO},

pubstate = {published},

tppubtype = {article}

}

@article{Rawool2021,

title = {Direct CO_{2} capture and conversion to fuels on magnesium nanoparticles under ambient conditions simply using water},

author = {Sushma A Rawool and Rajesh Belgamwar and Rajkumar Jana and Ayan Maity and Ankit Bhumla and Nevzat Yigit and Ayan Datta and Günther Rupprechter and Vivek Polshettiwar},

doi = {10.1039/d1sc01113h},

year  = {2021},

date = {2021-03-31},

urldate = {2021-03-31},

journal = {Chemical Science},

volume = {12},

number = {16},

pages = {5774--5786},

publisher = {Royal Society of Chemistry (RSC)},

abstract = {Converting CO_{2} directly from the air to fuel under ambient conditions is a huge challenge. Thus, there is an urgent need for CO_{2} conversion protocols working at room temperature and atmospheric pressure, preferentially without any external energy input. Herein, we employ magnesium (nanoparticles and bulk), an inexpensive and the eighth-most abundant element, to convert CO_{2} to methane, methanol and formic acid, using water as the sole hydrogen source. The conversion of CO_{2} (pure, as well as directly from the air) took place within a few minutes at 300 K and 1 bar, and no external (thermal, photo, or electric) energy was required. Hydrogen was, however, the predominant product as the reaction of water with magnesium was favored over the reaction of CO_{2} and water with magnesium. A unique cooperative action of Mg, basic magnesium carbonate, CO_{2}, and water enabled this CO_{2} transformation. If any of the four components was missing, no CO_{2} conversion took place. The reaction intermediates and the reaction pathway were identified by ^{13}CO_{2} isotopic labeling, powder X-ray diffraction (PXRD), nuclear magnetic resonance (NMR) and in situ attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), and rationalized by density-functional theory (DFT) calculations. During CO_{2} conversion, Mg was converted to magnesium hydroxide and carbonate, which may be regenerated. Our low-temperature experiments also indicate the future prospect of using this CO_{2}-to-fuel conversion process on the surface of Mars, where CO_{2}, water (ice), and magnesium are abundant. Thus, even though the overall process is non-catalytic, it could serve as a step towards a sustainable CO_{2} utilization strategy as well as potentially being a first step towards a magnesium-driven civilization on Mars.},

keywords = {P08, pre-TACO},

pubstate = {published},

tppubtype = {article}

}

@article{Rupprechter2021,

title = {Operando Surface Spectroscopy and Microscopy during Catalytic Reactions: From Clusters via Nanoparticles to Meso-Scale Aggregates},

author = {Günther Rupprechter},

doi = {10.1002/smll.202004289},

year  = {2021},

date = {2021-03-10},

urldate = {2021-03-10},

journal = {Small},

publisher = {Wiley},

abstract = {Operando characterization of working catalysts, requiring per definitionem the simultaneous measurement of catalytic performance, is crucial to identify the relevant catalyst structure, composition and adsorbed species. Frequently applied operando techniques are discussed, including X-ray absorption spectroscopy, near ambient pressure X-ray photoelectron spectroscopy and infrared spectroscopy. In contrast to these area-averaging spectroscopies, operando surface microscopy by photoemission electron microscopy delivers spatially-resolved data, directly visualizing catalyst heterogeneity. For thorough interpretation, the experimental results should be complemented by density functional theory. The operando approach enables to identify changes of cluster/nanoparticle structure and composition during ongoing catalytic reactions and reveal how molecules interact with surfaces and interfaces. The case studies cover the length-scales from clusters via nanoparticles to meso-scale aggregates, and demonstrate the benefits of specific operando methods. Restructuring, ligand/atom mobility, and surface composition alterations during the reaction may have pronounced effects on activity and selectivity. The nanoscale metal/oxide interface steers catalytic performance via a long ranging effect. Combining operando spectroscopy with switching gas feeds or concentration-modulation provides further mechanistic insights. The obtained fundamental understanding is a prerequisite for improving catalytic performance and for rational design.},

keywords = {P08, pre-TACO},

pubstate = {published},

tppubtype = {article}

}