Starting from subsurface Zr0-doped “inverse” Pd and bulk-intermetallic Pd0Zr0 model catalyst precursors, we investigated the dry reforming reaction of methane (DRM) using synchrotron-based near ambient pressure in-situ X-ray photoelectron spectroscopy (NAP-XPS), in-situ X-ray diffraction and catalytic testing in an ultrahigh-vacuum-compatible recirculating batch reactor cell. Both intermetallic precursors develop a Pd0–ZrO2 phase boundary under realistic DRM conditions, whereby the oxidative segregation of ZrO2 from bulk intermetallic PdxZry leads to a highly active composite layer of carbide-modified Pd0 metal nanoparticles in contact with tetragonal ZrO2. This active state exhibits reaction rates exceeding those of a conventional supported Pd–ZrO2 reference catalyst and its high activity is unambiguously linked to the fast conversion of the highly reactive carbidic/dissolved C-species inside Pd0 toward CO at the Pd/ZrO2 phase boundary, which serves the role of providing efficient CO2 activation sites. In contrast, the near-surface intermetallic precursor decomposes toward ZrO2 islands at the surface of a quasi-infinite Pd0 metal bulk. Strongly delayed Pd carbide accumulation and thus carbon resegregation under reaction conditions leads to a much less active interfacial ZrO2–Pd0 state.
Graphitic deposits anti-segregate into Ni 0 nanoparticles to provide restored CH 4 adsorption sites and near-surface/dissolved C atoms, which migrate to the Ni 0 /ZrO 2 interface and induce local Zr x C y formation. The resulting oxygen-deficient carbidic phase boundary sites assist in the kinetically enhanced CO 2 activation toward CO(g). This interface carbide mechanism allows for enhanced spillover of carbon to the ZrO 2 support, and represents an alternative catalyst regeneration pathway with respect to the reverse oxygen spillover on Ni-CeZr x O y catalysts. It is therefore rather likely on supports with limited oxygen storage/exchange kinetics but significant carbothermal reducibility.
Following the need
for an innovative catalyst and material design
in catalysis, we provide a comparative approach using pure and Pd-doped
LaCu
x
Mn
1–
x
O
3
(
x
= 0.3 and 0.5) perovskite
catalysts to elucidate the beneficial role of the Cu/perovskite and
the promoting effect of Cu
y
Pd
x
/perovskite interfaces developing
in situ
under model NO + CO reaction conditions. The observed bifunctional
synergism in terms of activity and N
2
selectivity is essentially
attributed to an oxygen-deficient perovskite interface, which provides
efficient NO activation sites in contact with
in situ
exsolved surface-bound monometallic Cu and bimetallic CuPd nanoparticles.
The latter promotes the decomposition of the intermediate N
2
O at low temperatures, enhancing the selectivity toward N
2
. We show that the intelligent Cu/perovskite interfacial design is
the prerequisite to effectively replace noble metals by catalytically
equally potent metal–mixed-oxide interfaces. We have provided
the proof of principle for the NO + CO test reaction but anticipate
the extension to a universal concept applicable to similar materials
and reactions.
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