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K. Anic, A. Wolfbeisser, H. Li, Ch. Rameshan, K. Föttinger, J. Bernardi, G. Rupprechter:
"Surface spectroscopy on UHV-grown and technological Ni-ZrO2 reforming catalysts: from UHV to operando conditions";
Topics in Catalysis, 59 (2016), 1614 - 1627.

Ni nanoparticles supported on ZrO2 are a prototypical
system for reforming catalysis converting
methane to synthesis gas. Herein, we examine this catalyst
on a fundamental level using a 2-fold approach employing
industrial-grade catalysts as well as surface science based
model catalysts. In both cases we examine the atomic
(HRTEM/XRD/LEED) and electronic (XPS) structure, as
well as the adsorption properties (FTIR/PM-IRAS), with
emphasis on in situ/operando studies under atmospheric
pressure conditions. For technological Ni-ZrO2 the rather
large Ni nanoparticles (about 20 nm diameter) were evenly
distributed over the monoclinic zirconia support. In situ
FTIR spectroscopy and ex situ XRD revealed that even
upon H2 exposure at 673 K no full reduction of the nickel
surface was achieved. CO adsorbed reversibly on metallic
and oxidic Ni sites but no CO dissociation was observed at
room temperature, most likely because the Ni particle
edges/steps comprised Ni oxide. CO desorption temperatures
were in line with single crystal data, due to the large
size of the nanoparticles. During methane dry reforming at
873 K carbon species were deposited on the Ni surface
within the first 3 h but the CH4 and CO2 conversion hardly
changed even during 24 h. Post reaction TEM and TPO
suggest the formation of graphitic and whisker-type carbon
that do not significantly block the Ni surface but rather
physically block the tube reactor. Reverse water gas shift
decreased the H2/CO ratio. Operando studies of methane
steam reforming, simultaneously recording FTIR and MS
data, detected activated CH4 (CH3 and CH2), activated
water (OH), as well as different bidentate (bi)carbonate
species, with the latter being involved in the water gas shift
side reaction. Surface science Ni-ZrO2 model catalysts
were prepared by first growing an ultrathin ``trilayer´´
(O-Zr-O) ZrO2 support on an Pd3Zr alloy substrate, and
subsequently depositing Ni, with the process being monitored
by XPS and LEED. Apart from the trilayer oxide,
there is a small fraction of ZrO2 clusters with more bulklike
properties. When CO was adsorbed on the (fully
metallic) Ni particles at pressures up to 100 mbar, both
PM-IRAS and XPS indicated CO dissociation around room
temperature and blocking of the Ni surface by carbon (note
that on the partially oxidized technological Ni particles,
CO dissociation was absent). The Ni nanoparticles were
stable up to 550 K but annealing to higher temperatures
induced Ni migration through the ultrathin ZrO2 support
into the Pd3Zr alloy. Both approaches have their benefits
and limitations but enable us to address specific questions
on a molecular level.

Nickel Zirconia Model catalysts Technological catalysts Carbon monoxide Methane steam reforming Methane dry reforming In situ spectroscopy Operando spectroscopy

http://dx.doi.org/10.1007/s11244-016-0678-8

http://publik.tuwien.ac.at/files/PubDat_243118.pdf