Influence of LaNiO3 Shape on Its Solid-Phase Crystallization into Coke-Free Reforming Catalysts

Article abstract of DOI:10.1021/acscatal.6b00673

Shape-controlled LaNiO₃ nanoparticles were prepared by modified hydrothermal and precipitation routes resulting in cubes, spheres, and rods. The solid-phase crystallization of LaNiO₃ into its active catalyst form, Ni/La₂O<

Full text of DOI:10.1021/acscatal.6b00673

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Article
3
Influence of LaNiO shape on its solid-phase
crystallization into coke-free reforming catalysts
Sarika Singh, Daria Zubenko, and Brian A. Rosen
ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.6b00673 • Publication Date (Web): 26 May 2016
Downloaded from http://pubs.acs.org on May 31, 2016
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Influence of LaNiO shape on its solid-phase
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crystallization into coke-free reforming catalysts
1
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1*
Sarika Singh , Daria Zubenko , Brian A. Rosen
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1
. Department of Materials Science and Engineering, Tel Aviv University, 55 Haim
Levanon Street, Ramat Aviv 6139001, ISRAEL
*barosen@post.tau.ac.il
ABSTRACT: Shape-controlled LaNiO nanoparticles were prepared by modified
3
hydrothermal and precipitation routes resulting in cubes, spheres, and rods. The solid-
phase crystallization of LaNiO into its active catalyst form, Ni/La O , was found to
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be highly dependent on the shape and structure of the parent nanoparticle. Factors
+
2
such as the crystallization pathway and Ni -ion depletion are considered as key
factors influencing the final material. Catalysts derived from LaNiO spheres and rods
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were found to be free of carbon accumulation after 100 hours of reforming while
those derived from cubes showed excessive carbon accumulation and signs of
sintering. All the three catalysts are characterized by X-ray diffraction (XRD),
scanning electron transmission microscopy (SEM), transmission electron microscopy
(TEM), hydrogen temperature-programmed reduction (TPR) and thermogravimetric
analyses (TGA). The presence of defects, particularly stacking faults within the
Perovskite, may impact the reduction pathway and subsequent catalytic properties.
Stable and active catalysts can therefore be designed and tuned by controlling the sape
and structure of Perovskite precursors.
KEWWORDS: Perovskite, Shape control, Dry reforming of methane, Solid phase
crystallization, Carbon formation, Defects
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1. INRODUCTION:
The exploitation and control of structure in methane reforming catalysts remains a
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significant challenge to chemists and engineers worldwide. Currently, methane
conversion catalysts are limited by their ability to resist surface carbon accumulation,
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sintering, and unwanted oxidation. These mechanisms are detrimental to catalyst
lifetime and have prevented processes such as methane dry reforming from large scale
industrialization. All of these deactivation mechanisms are highly influenced by the
strength of the interaction between the active catalyst and its support, as well as the
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,5
size and shape of the active catalyst phase. The use of wetness impregnation and
solution-phase crystallization as ways to disperse the active catalyst (e.g. Ni) onto a
high surface-area support generally leads to weak and superficial catalyst-support
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interactions. These weak interactions result in a high susceptibility to sintering, poor
redox properties, and carbon accumulation. Solid-phase crystallization of well-
ordered materials has been proposed to be an effective single-step method for forming
catalysts with strong metal-support interactions. So far, investigation of this method
has largely focused on bulk and supported Perovskites (ABO ) as the parent phase
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and the influence of non-stoichiometric formulations on the ability to exsolve metal
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(B-atom) crystals.
These studies revealed that A-site deficiencies in conjunction
with oxygen vacancies beyond a limiting concentration (δ,lim) destabilized the
Perovskite structure sufficiently such that the B-atom would exsolve in order to
maintain the original stoichiometry shown below in Equation 1.
A BO
→ (1-α)(ABO ) + αB
(1)
1
-α
3-δ,lim
3- δ
This work investigates how shape-control of the parent LaNiO Perovskite
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nanoparticle can be exploited to imbue a favorable size and spatial distribution of
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exsolved Ni crystals, a strong catalyst-support interaction, and provide for coke- and
sinter-free catalytic methane oxidation. We show how selection of parent particle
shape can lead to differences in methane conversion and carbon resistance over
several orders of magnitude. These results are considered in light of how depletion
within the parent Perovskite nanoparticle and the pathway taken during crystallization
influences the final material to enable sustainable and intelligent catalyst design.
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2
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. RESULTS AND DISCUSSION
.1 Parent Perovskites and catalytic activity
Modified hydrothermal and chemical precipitation methods were used in order to
synthesize LaNiO nanoparticles with a cubic, quasi-spherical (hereafter referred to as
3
“spheres” for simplicity), and rod morphologies. Cubic particles became porous after
calcination, the final step in the Perovskite synthesis, and are not the result of
spherical particles sintered together (Figure S1). Figure 1 shows SEM micrographs
of fresh cube-, sphere-, and rod-shaped Perovskites as well as the XRD pattern for
both fresh and spent catalysts after 100 hours of methane dry reforming. X-ray
diffraction of the fresh sample shows that the obtained materials were 97% Perovskite
and 3% nickel (II) oxide (NiO) (Figure S2) in all cases. Table 1 shows the
characteristic structural parameters for each system. Statistics about the size
distribution of the parent Perovskites and exsolved Ni particles were measured by
analyzing approximately 200 particles over many TEM images using Image J analysis
software. Details about the crystal size distribution of all three shapes can be found in
Figures S3, S4, and S5.
Here, methane dry reforming was selected as the probe reaction as it is the most
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susceptible to carbon accumulation. The methane dry reforming reaction proceeds
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via Equation 2, ideally producing a 1:1 product ratio, which is favorable for
downstream processing into synthetic fuels.
CH + CO ↔ 2CO + 2H
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(2)
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For each system, solid-phase crystallization was carried out by heating the LaNiO3
nanoparticles in a 50% hydrogen atmosphere and resulted in Ni nanoparticles
supported by La O . XRD patterns of spent catalyst revealed that no Perovskite phase
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remained after reduction, but that the particles maintained the shape of their parent
after crystallization.
Figure 1: (left) Scanning electron micrographs of fresh cube-, sphere- and rod-shaped
LaNiO nanoparticles. (right) XRD patterns for all three shapes showing both fresh
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LaNiO and spent catalysts after 100 h of methane reforming.
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Table 1: Geometric data for the Perovskites and the Ni crystals exsolved from a
Perovskite of a particular shape
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LaNiO
shape
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LaNiO
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Phase composition
BET surface area
Avg. Perovskite
Size (nm)
367
Avg. Ni Crystal Size
2
(m /g)
(nm)
Cubes
Rhombohedral – 58%
Cubic – 42%
10.44
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Spheres
Rods
Rhombohedral – 65%
Cubic – 35%
10.69
9.20
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Rhombohedral – 100%
109 (L) x 38 (H)
XRD also reveals that the La O support was converted to the oxycarbonate
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La O CO phase after exposure to CO from the dry reforming process. Such a
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conversion has been found to be beneficial as the oxycarbonate is an excellent
oxidizing agent to gasify accumulated carbon at the catalyst-support interface.
Figure 2 shows how the dry reforming of methane proceeded over Ni/La O catalysts
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derived from cube-, sphere-, and rod-shaped parent Perovskites. Crystallographic data
and size distribution statistics in Figures 1 and 2 allowed us to estimate the methane
-1
-1
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turnover number to be 0.5 s , 0.21 s , and 0.35 s for the cubes, spheres, and rods
respectively. These numbers match well with turnover numbers for other industrial
-1
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dehydrogenation reactions carried out at 650 °C (generally between 0.05 s and 1 s ).
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Figure 2: (a) Methane conversion, (b) carbon dioxide conversion, and (c) H :CO
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Perovskites for dry reforming of methane at 650 °C, 1:1:8 CH :CO :Ar, and a gas-
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hourly space velocity of 125,000 mL/(g ∙h).
cat
The reaction was carried out at 650°C where carbon accumulation is highly favored
thermodynamically. Nikoo et al. calculated the equilibrium conversion for methane
dry reforming while considering solid carbon formation using the Gibbs free-energy
minimization technique employing the Soave-Redlich-Kwong (SRK) equation-of-
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state. At 650°C, the equilibrium conversions of CH and CO were calculated to be
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5% and 55% respectively. By contrast, a similar calculation by Yanbing et al. did not
consider solid carbon formation and reported the equilibrium conversion of CH and
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CO to be 60% and 75% respectively. The equilibrium H :CO product ratio using
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this later model was calculated to be 80%. Our measured conversions and product-
ratio for the rods, on which no accumulated carbon was detected, agree well with the
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thermodynamic model that did not consider solid carbon formation. The equilibrium
conversions of both CH and CO for the cubes were larger (CO more than CH ) than
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calculated by Yanbing, suggesting that the decomposition of CO and CO via
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Equations 3 and 4 is mostly responsible for the excess carbon formation on the
cubes.
2CO ↔ C + CO2
(3)
(4)
CO + 2H ↔ C + 2H O
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Fresh catalyst derived from the cube Perovskites were subjected to a mixture of CO,
CO , and H at 650°C and showed significant carbon accumulation (Figure S6) after
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0 hours, supporting this coking mechanism. The larger CO conversion compared to
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CH can also be attributed the reverse water-gas shift reaction (Equation 5) and the
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ability for the basic lanthanum oxide support to dissociate CO , which exhibits acidic
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character.
CO + H ↔ H O + CO
(5)
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.2 Sensitivity of performance to Perovskite structure
Figures 3a shows an SEM image of the catalyst derived from a cubic Perovskite
particle. EDX measurements confirm that each face of the cubic Perovskite exsolved
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0-70 Ni particles ranging in size from 15-35nm. Figure 3b shows a TEM image of
the same particle after 100 hours of dry reforming. Severe carbon accumulation is
shown on the surface of the cubes, present as both graphite and multi-walled carbon
nano-tubes (MWCNTs). The growth of the MWCNTs proceeds largely by the tip-
growth mechanism, where carbon accumulates within the Ni crystal, proceeds to grain
boundaries, and ultimately begins forming a MWNT which detaches and lifts the Ni
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particle from its support. This mechanism has been reported to be characteristic of
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large Ni particles which are prone to carbon accumulation and have weaker
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interactions with their support.
By contrast, HR-TEM imaging (Figures 3c-f) shows that Ni particles exsolved from
sphere- and rod- shaped Perovskites are buried tightly into their supports. Dashed
lines in the HR-TEM images clearly show the interface of the Ni crystal with the
La O CO support and that it is firmly buried within the support. Ni crystals were
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identified by measuring the lattice spacing and/or energy dispersive spectroscopy
EDS) analysis (Figure S5). The small size and strong interaction between the Ni
(
particles and the support for the spheres and rods enabled methane reforming to
proceed for 100 hours with no detectable form of carbon accumulation in the spent
samples as the tip-growth mechanism was unable to proceed. By comparison, carbon
accumulation on the cubes was so large that the weight of carbon in the spent sample
was almost 4 times the weight of the original catalyst (Figure S7). The fact that the
methane conversion rate on the cube-derived catalyst was stable throughout the entire
test period, despite severe coking, means that most of the area of the Ni crystals was
still exposed to the gas phase. In this case, we would expect complete deactivation of
this material once the surface and pores become completely blocked to the gas-
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phase. SEM images of spent catalysts derived from Perovskite cubes, spheres, and
rods are shown in Figure S8.
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Figure 3: (a) SEM image of cubic Perovskite after solid phase crystallization via
reduction in 50% hydrogen/argon. (b) TEM image of spent catalyst derived from cube
Perovskite where tip-growth MWCNT is shown lifting a nickel crystal off of the
surface. (c) TEM image of a nickel crystal exsolved from a Perovskite sphere (d) HR-
TEM of the same (e) TEM image of a nickel crystal exsolved from a Perovskite rod
(f) HR-TEM image of the same. Yellow and red dashed lines show the edge of the
support and Ni crystal respectively to emphasize the how socketing provides a strong
catalyst-support interaction.
We observed that the weak catalyst-support interaction found with the cubes was not
simply a function of Ni crystal size, as previously thought. The Ni crystal lifted from
the surface of the cube in Figure 3b is about 30nm. The Ni particle size distribution
for the spheres and rods (Figures S3, S4 and S5) showed that 5-10% of the Ni
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crystals exceeded this size, yet no MWCNT growth or lifting was observed. The
source of this added stability is likely connected to the solid-phase crystallization
pathway.
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There is significant confusion in the literature about which reduction pathway LaNiO3
takes to form the final Ni/La O phase, or what factors influence the reduction
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pathway. Moreover, papers that confirm a particular pathway rarely mention the
alternatives, or give insight as to why seemingly similar materials would give
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different reduction profiles.
In one such pathway, LaNiO reduction takes place as
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a 3-step process as shown below:
0
4LaNiO + 2H → La Ni O + Ni + 2H O
(6)
(7)
(8)
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La Ni O + 3H → La NiO + 2Ni + La O + 3H O
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La NiO + H → Ni + La O + H O
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An alternative 2-step mechanism is also reported:
LaNiO + H → La Ni O + H O
2
(9)
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0
La Ni O + 2H → 2Ni + La O + 2H O
(10)
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Figure 4: Temperature programmed reduction (TPR) of the cube-, sphere-, and rod-
shaped LaNiO parent nanoparticles in 5% H in N at heating rate of 10K/min.
3
2
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Figure 4 shows temperature programmed reduction (TPR) of all three Perovskite
shapes and revealed that the cubes were reduced via the 2-step pathway whereas the
spheres and rods were reduced by the 3-step mechanism. Although not universally
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true, TPR peaks observed in the reduction of LaNiO have been shown to be
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associated with individual reduction events.
The key difference in distinguishing
between the 2 pathways using TPR is comparing the ratio of the area under the second
peak to that of the first. For the 2-step mechanism, the second peak should have an
area 2x larger than the first peak, and for the 3-step mechanism the second peak
should have an area 1.5x larger than the first. After deconvolution, we found that the
area ratio for the cubes (2-step mechanism) was 1.85, and the area ratio for the
spheres and rods (3-step mechanism) was 1.52 and 1.49 respectively. Furthermore,
the molar hydrogen uptake in all three cases matched the expected stoichiometric
values for complete Ni reduction, namely 1.5 moles of H for every mole of LaNiO .
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+
2
In all cases, the final reduction peak represents the reduction of Ni to metallic Ni.
The position of the final reduction peak shows that the Ni crystals exsolved from the
cubic parent had a weaker interaction with their support and came about from the
La Ni O phase. By comparison, Ni exsolution from the Spinel phase via the 3-step
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mechanism was observed at higher temperatures, suggesting that Ni crystals formed
by this route are more stable. To emphasize this point, rod-shaped parent particles
with a Spinel structure were synthesized and showed no carbon accumulation after
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0h (Figure S9). This result also corroborates the strongly socketed Ni-crystals
observed in TEM, and the lack of tip-growth carbon accumulation on the sphere- and
rod-derived catalysts.
We suggest that the reason that the cube Perovskites took the 2-step pathway and
spheres and rods took the 3-step pathway is linked to structural defects, specifically
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stacking faults and dislocations. The 3-step pathway goes through a series of
Ruddlesden-Popper (RP) structures which are naturally layered; by comparison, the 2-
step mechanism involves a "defective" Perovskite. Features such as stacking faults
may be precursory to the formation of the layered RP structure and force the transition
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down the 3-step pathway.
Figures 5a and 5c show HR-TEM images of fresh
cube- and rod-shaped Perovskites respectively, along with their diffraction patterns.
Compared to the cubes, the diffraction pattern for the rods shows a pattern of
featureless streaks, typical of a faulted structure. Figures 5b and 5d show an inverse
FFT of the (012) plane for both the cubes and the rods. The arrows in Figure 5d
indicate the location of stacking faults in the rods, a feature absent in the cubes.
Stacking faults were distinguished from dislocations by rotation of the sample in the
TEM.
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[
012]
Figure 5: (a) HRTEM image of a LaNiO cube with the diffraction pattern the of
boxed region inset in the upper left corner (b) inverse FFT of the (012) diffraction
regions (c) HRTEM image of a LaNiO with the diffraction pattern the of boxed
region inset in the upper left corner (d) inverse FFT of the (012) diffraction regions
where arrows indicate possible stacking faults and (e) crystal model of rod-shaped
Perovskites showing the La-Ox/Ni-Ox stacking in the (012) direction where faults are
observed; La-green, Ni-white, O-red, (012) plane shown in orange.
3
3
We therefore see that defects can impact the phase from which the final Ni reduction
step occurs. This effect, in addition to the Ni crystals size, plays an important role in
the ultimate stability of the catalyst.
An additional characteristic providing stability to the catalyst is resistance against Ni-
particle sintering. This can be achieved by strong Ni-support interactions in addition
23
to limiting the proximity of surface Ni crystals. When the characteristic dimensions
+2
of the parent Perovskite particle are small, depletion of Ni within the lattice during
solid-phase crystallization can play an impactful role.
Such depletion regions can be shown to be 3-D in nature, since unidirectional
diffusion of Ni-ions cannot account for the size of exsolved Ni crystals. For example,
the rod-shaped Perovskites synthesized in this work had an average thickness of 38
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nm and the Ni crystals exsolved on their surface had an average diameter of 12.5 nm.
A spherical Ni crystal with this diameter contains approximately 25,000 unit cells of
FCC Ni (100,000 Ni atoms). The Perovskite rods were found to be composed entirely
of the rhombohedral phase with a lattice parameter of 5.45Å. With the unidirectional
diffusion condition, the Perovskite would be able to supply at most 38,000 Ni atoms
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to the growing crystal (= max number of LaNiO unit cells underneath the nickel
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crystal throughout the thickness of the rod, 1 Ni atom / cell) accounting for only 1/3
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of the Ni crystal size. As a result, Ni transport during the crystallization process
necessarily occurs in 3 dimensions. The resulting depletion regions should also extend
in 3 dimensions (e.g. hemispheres) as depicted in Figure 6. Such hemispherical
depletion may limit the lateral proximity that one growing Ni crystal can have with its
neighbor in Perovskites whose depletion regions are comparable to the dimensions of
the parent particle. This mechanism is advantageous for resistance against sintering as
the exsolved particles are separated by some minimum distance at the time of their
creation in a process limited by depletion.
+
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were small relative to the size of its parent particle, this region could be replenished
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by Ni ions deeper in the bulk and the second nickel crystal could exsolve in close
proximity to the first.
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Figure 6: (Top-left) Schematic diagram of Ni particle formation and growth of
+
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hemispherical Ni depletion regions within a rod shaped LaNiO particle. The large
3
depletion regions, being on the same length scale as the parent particle, helps to
maintain an even size and distance between exsolved particles as new particles cannot
form over regions depleted of Ni ions. (Bottom-left) schematic diagram of Ni particle
formation in a parent Perovskite where the Ni-ion depletion region is small relative to
the Perovskite size. This permits the depletion regions to be regenerated by Ni-ions
deeper in the bulk and for Ni particles to form in closer proximity, making them
susceptible to sintering. (right) TEM image showing well-spaced and spherical Ni
particles formed from a rod-shaped Perovskite.
Small lateral distances between exsolved Ni-crystals in conjunction with a weak Ni-
support interaction (as observed with the Ni-crystals exsolved from the cubes) can
lead to sintering. Sintering of Ni particles on the cubes is evidenced in this work by
the larger Ni crystals, their highly non-spherical morphology, and the many instances
of close proximity from Figure 1.
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The superiority of the rods over the spheres for catalytic activity is likely due to the
fact that the Ni particles exsolved from the rods are both higher in number and smaller
in size. Highly anisotropic Perovskites with a large number of defects may therefore
be an ideal parent nanoparticle design because it gives rise to reforming catalysts
which provide a large number of stable nickel crystals capable of resisting sintering
and carbon accumulation.
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. CONCLUSIONS
Hydrothermal and chemical precipitation routs were adopted for synthesis of cube-,
sphere- and rod-shaped LaNiO nanoparticles. Utilization of spheres and rods as the
3
parent LaNiO shape was found to be highly promising for application in the dry
3
reforming of methane at 650°C. By contrast, catalysts derived from the cubes
exhibited extreme amounts of carbon accumulation and evidence of Ni particle
sintering. The rod and sphere like Perovskite exhibited excellent catalytic activity
with no carbon formation even after 100 h. Stacking faults in the parent Perovskite are
suggested play a key role in determining the reduction pathway taken by the parent
Perovskite nanoparticle in order to form the final catalyst phase. The remarkable
stability of the spheres and rods is explained by small size and high stability of the
exsolved Ni crystals brought about by the 3-step reduction pathway. Utilization of
high-aspect ratio parent shapes (e.g. rods) may prove to be an ideal structure as many
Ni crystals can be formed whose minimum separation distance is influenced by ion-
depletion during the reduction phase.
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4
. MATERIALS AND METHODS
.1 Synthesis of shape controlled LaNiO nanostructures
3
A facile co-precipitation route was adopted to synthesize well dispersed spherical
LaNiO perovskite nanoparticles. In a typical synthesis, 0.433 gm of La(NO ) .6H O
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and 0.290 gm of Ni(NO ) .6H O were dispersed in 80 mL of Milli-Q water in a round
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bottle flask by ultra-sonication for 5 min. Afterwards, 20 mL NaOH solution (0.3 gm
NaOH pearls in 20 mL Milli-Q water) were directly added into 80 mL solution
mixture. The solution mixture quickly turned turbid, and formation of greenish-white
precipitate is instantly observed. Finally, 100 mL solution mixture was kept on hot
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plate under continuous stirring and solution temperature was raised at 60 C in
refluxing conditions for 4h. The obtained sample was centrifuged, washed 4-5 times
0
with Milli-Q water and ethanol. The sample was dried at 70 C overnight and calcined
0
at 650 C for 2h to obtain finally black powder sample of LaNiO .
3
The only the difference in the synthesis procedure of the rods was the addition of
surfactant and the adding manner of NaOH. Briefly, a solution was prepared by
dissolving 0.433 gm La(NO ) .6H O and 0.290 gm Ni((NO ) .6H O in 100 mL Milli-
3
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2
3 2
2
Q of water in the round bottle flask. Then, 150 mg of polyvinyl pyrrolidone (PVP)
surfactant was added in the solution mixture to tune the size of particles. Afterwards,
10 mM NaOH is added drop by drop into the solution mixture to maintain pH 12
under constant stirring. Finally, the solution was kept on heating mantle with a
0
magnetic stirrer under refluxing conditions at 75 C for 6h. The resulted product was
centrifuged, washed 4-5 with Milli-Q water and ethanol. The solid sample was dried
0
0
at 70 C overnight and calcined at 800 C for 2h to obtain finally black powder sample
of LaNiO3.
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A well-defined cube shape LaNiO was synthesized by hydrothermal method reported
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elsewhere. In the typical hydrothermal synthesis, 0.433 gm of La(NO ) .6H O and
3 3
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.290 gm Ni(NO ) .6H O, 0.3 gm were dissolved in 70 mL Milli-Q water. Then, 0.30
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gm PVP and 0.375 gm of glycine was added in the solution mixture. The pH of
solution mixture was adjusted to 7.7 by NH solution. The solution mixture are
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transferred to Teflon-lined stainless steel autoclave and heated at 180 C temperature
for 12h. The product is collect by centrifugation and washed with 4-5 times with
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to form nanocube of LaNiO3.
4
.2 Characterization techniques
X-ray diffraction (XRD) patterns were recorded on a Scintag – powder diffractometer
equipped with liquid nitrogen cooled germanium solid state detector with Cu Kα
radiation. X-ray photoelectron analysis (XPS) analysis were performed on a 5600
AES/XPS system (PHI, USA) using Al Kα (h = 1486.6 eV) as the excitation source.
The scanning electron micrographs were taken by Quanta 200 FEG (field-emission
gun) Environmental Scanning Electron Microscope (ESEM). The transmission
@
electron micrographs (TEM) were taken by Field Emission TEM (Tecnai F20,
Philips) operated at 200KV. Thermo-gravimetric analyses (TGA) were carried out by
TGA 2950 thermogravimetric analyzer. The surface area and temperature program
reduction (TPR) were recorded by ChemBET Quantachrome instruments. Prepared
Perovskites were placed in a quartz tube (11mm OD) fixed between two pieces of
quartz wool. Dry reforming performance of each catalyst was tested on an identical
2
surface area of Perovskite (0.3 m ) under the same gas hourly space velocity 25,000
mL/(g∙h). Prior to dry reforming catalysis, the Perovskite nanoparticles were heated to
8
00 °C for 1 hour in 5 vol% H atmosphere in order to drive the solid-phase
2
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crystallization process. The resultant material, Ni/La O , was then cooled to 650 °C
2
3
and the catalytic reaction was initiated by feeding mixture of CH and CO with a
4
2
molar ratio of unity over the catalyst. The conversion of methane and carbon dioxide
into carbon monoxide and hydrogen was monitored using an SRI gas chromatograph
fitted with MS-13X and Haysep-C packed columns. Hydrogen was detected using a
nitrogen carrier and an TCD detector. CO , CO, and CH were detected by and FID
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detector with a methanizer placed directly upstream.
SUPPORTING INFORMATION
SEM images of cubes before and after calcination, TEM micrographs of fresh LaNiO3
and spent cubes, spheres and rods, size distribution of LaNiO and Ni crystals, TGA
3
plots of spent cube, sphere and rod.
AUTHOR CONTRIBUTIONS
BAR conceived of the idea and planned the experiments. SS carried out the catalytic
testing, and all materials analysis with the help of DZ. BAR drafted the manuscript
with critical comments provided by SS and DZ.
ACKNOWLEDGEMENTS
BAR would like to acknowledge the Israeli Department of Energy (Grant# 215-11-
0
33) for partial funding. SS would like to thank the Israeli Planning and Budgeting
Committee (PBC) for partial funding. The authors want to thank Dr. Yuri Rosenberg
for collection of the XRD data, Dr. George Levi and Prof. Amit Kohn and for
assistance with TEM imaging, and Prof. Noam Eliaz for the use of laboratory space.
The authors also want to thank Gil Hayoun for assisting with the construction of the
experimental assemblies.
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*
*TABLE OF CONTENT FIGURE**
6
2x46mm (96 x 96 DPI)
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