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Publications in Scientific Journals:

M. Bekheet, P. Kheyrollahi Nezhad, N. Bonmassar, L. Schlicker, A. Gili, S. Praetz, A. Gurlo, A. Doran, Y. Gao, M. Heggen, A. Niaei, A. Farzi, S. Schwarz, J. Bernardi, B. Klötzer, S. Penner:
"Steering the Methane Dry Reforming Reactivity of Ni/La2O3 Catalysts by Controlled In Situ Decomposition of Doped La2NiO4 Precursor Structures";
ACS Catalysis, 11 (2021), 43 - 59.



English abstract:
The influence of A- and/or B-site doping of Ruddlesden−Popper perovskite
materials on the crystal structure, stability, and dry reforming of methane (DRM) reactivity of
specific A2BO4 phases (A = La, Ba; B = Cu, Ni) has been evaluated by a combination of
catalytic experiments, in situ X-ray diffraction, X-ray absorption spectroscopy (XAS), X-ray
photoelectron spectroscopy (XPS), and aberration-corrected electron microscopy. At room
temperature, B-site doping of La2NiO4 with Cu stabilizes the orthorhombic structure (Fmmm)
of the perovskite, while A-site doping with Ba yields a tetragonal space group (I4/mmm). We
observed the orthorhombic-to-tetragonal transformation above 170 °C for La2Ni0.9Cu0.1O4 and
La2Ni0.8Cu0.2O4, slightly higher than for undoped La2NiO4. Loss of oxygen in interstitial sites
of the tetragonal structure causes further structure transformations for all samples before
decomposition in the temperature range of 400 °C−600 °C. Controlled in situ decomposition
of the parent or A/B-site doped perovskite structures in a DRM mixture (CH4:CO2 = 1:1) in
all cases yields an active phase consisting of exsolved nanocrystalline metallic Ni particles in
contact with hexagonal La2O3 and a mixture of (oxy)carbonate phases (hexagonal and monoclinic La2O2CO3, BaCO3). Differences
in the catalytic activity evolve because of (i) the in situ formation of Ni−Cu alloy phases (in a composition of >7:1 = Ni:Cu) for
La2Ni0.9Cu0.1O4, La2Ni0.8Cu0.2O4, and La1.8Ba0.2Ni0.9Cu0.1O4, (ii) the resulting Ni particle size and amount of exsolved Ni, and (iii)
the inherently different reactivity of the present (oxy)carbonate species. Based on the onset temperature of catalytic DRM activity,
the latter decreases in the order of La2Ni0.9Cu0.1O4 ∼ La2Ni0.8Cu0.2O4 ≥ La1.8Ba0.2Ni0.9Cu0.1O4 > La2NiO4 > La1.8Ba0.2NiO4. Simple
A-site doped La1.8Ba0.2NiO4 is essentially DRM inactive. The Ni particle size can be efficiently influenced by introducing Ba into the
A site of the respective Ruddlesden−Popper structures, allowing us to control the Ni particle size between 10 nm and 30 nm both
for simple B-site and A-site doped structures. Hence, it is possible to steer both the extent of the metal-oxide-(oxy)carbonate
interface and its chemical composition and reactivity. Counteracting the limitation of the larger Ni particle size, the activity can,
however, be improved by additional Cu-doping on the B-site, enhancing the carbon reactivity. Exemplified for the La2NiO4 based
systems, we show how the delicate antagonistic balance of doping with Cu (rendering the La2NiO4 structure less stable and
suppressing coking by efficiently removing surface carbon) and Ba (rendering the La2NiO4 structure more stable and forming
unreactive surface or interfacial carbonates) can be used to tailor prospective DRM-active catalysts.


"Official" electronic version of the publication (accessed through its Digital Object Identifier - DOI)
http://dx.doi.org/10.1021/acscatal.0c04290


Created from the Publication Database of the Vienna University of Technology.