I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[1828]
Open Access
Abstract: The Fischer
-Tropsch Synthesis (FTS) is an alternative route
to produce liquid fuels from a variety of
carbon feedstocks including coal and biomass. Typically iron and cobalt based catalysts have been
used for the FTS reaction, in which a mixture of CO and H
2
(syn
-gas) reacts to form hydrocarbons.
Enhanced performa
nce has been reported for iron
-based systems doped with alkali metals and
chalcogenides. Sulfides are considered a poison for most catalytic processes, but sul
fur in the form of
sul
fates (S
VI
) is found to enhance the performance of iron based catalysts tow
ards the FTS when
present at low levels.
In this study a wide range of iron based catalysts w
as
prepared
under varying synthesis conditions and
with
different dopants. The standard methods of preparation used were co-
precipitation and incipient
wetness
impregnation. A
structural
study
of
a wide range of iron based catalysts
was
carried out using
characterisation methods
such as
X-ray Absorption Fine Structure (XAFS) spectroscopy, X
-ray
Photoelectron Spectroscopy (XPS), Powder X
-ray Diffraction (PXRD),
Scanning
Electron
Microscopy (SEM), Energy Dispersive X
-ray (EDX) and
Brunner
-Emmett
-Taller surface area
determination (BET). The characterisation was performed before and after reduction of the catalysts
(under H
2
) to form the catalytically active material
s.
Before reduction, PXRD
, XPS
and quantitative analysis
identified a ha
ematite iron oxide structure (
α
-
Fe
2
O
3
) for all samples. The crystallinity of the iron o
xide materials varied
between samples
prepared
in various conditions
. The highest crystallinity
was observed for the samples synthesised at pH7, fast
titrant addition rate, at room temperature.
The same techniques
revealed changes in the iron oxide
structure after reduction. T
he catalyst
s activated
at 400
o
C were
mainly composed of
Fe
3
O
4
and
those
activated at 450
o
C were a
mixture of Fe
2+
, Fe
3+
oxides and metallic iron Fe
0
. Moreover
, the
study of
the role of alkali metals show
ed that some of the alkali promoters (K, Rb) may decrease
the effective
iron oxide reduction
temperature.
The
nitrogen adsorp
tion experiment was used to establish that iron
oxide
doped
with different promoters
had a mesopor
ous structure
with
a narrow pore size
distribution
.
The SEM analysis indicated two different types of surface
: irregularly shaped agglomerates with
smaller ro
und edged particles attached to their surface and homogenous agglomerates surfaces with
sharp edges for the samples with different promot
ers. The most homogenous were the samples with
Rb. All samples had small particles attached to the surface of larger ag
glomerates.
An
increase of the alkali metals on the su
rface after the
activation process and migration of the alkalis
to the surface with ris
ing reduction temperature
were observed using bulk and surface techniques
(XRF, EDX and XPS)
. The
differences i
n K K
-edge shape of the XANES
spectrum indicated changes
in the local structure of K
corresponding to
changes
of
coordination number around K
+
during
activation.
It was also observed that reduction influenced the sulfur species in
iron oxide catalyst.
For
all the samples prior to reduction sulfates
(SO
4
2-
) were
detected by XPS and XAFS. After
the
reduction
at 400
o
C and 450
o
C, characteristic XPS
S 2p peaks for both sulfate and sulf
ide,
were
noticed.
The sulf
ate/sulfide ratio was higher for the catalyst sam
ples
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Aug 2011
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I18-Microfocus Spectroscopy
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Open Access
Abstract: The preservation of waterlogged archaeological wooden finds, such as Henry VIII's flagship the Mary Rose[1], [2] and [3], is complicated by the biological, chemical, and mechanical changes induced from prolonged exposure to a marine environment. Of particular concern are sulfur species that form acidic compounds that attack wood4. Here we show that different sulfur compounds do not form acids at the same rate or pathway and propose a preservation strategy of applying SrCO3 nanoparticles. These nanoparticles not only neutralize problematic sulfuric acid, but also reduced sulfur compounds, such as sulfur and pyrite, which pose a long term threat. This is the first treatment that eliminates acidification at the root. Although this strategy was devised for the Mary Rose, it could be employed to preserve any archaeological organic artifact rich in problematic sulfur, from sunken ships and silk tapestries to ancient texts and parchments.
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Jul 2011
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I18-Microfocus Spectroscopy
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Jun 2011
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[1125]
Abstract: Disregulation of transition metal ions is implicated in many neurodegenerative disorders,
and altered status may both affect disease progression and hold biomarker potential. The analytical
challenges in this field often lead to isolated evidence for altered concentration, distribution, chemical or
mineral state, limiting the conclusions that can be drawn. Combining methods that are highly sensitive to
a range of these properties can give new insight.
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Mar 2011
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I18-Microfocus Spectroscopy
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Mar 2011
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I18-Microfocus Spectroscopy
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Mar 2011
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[1115]
Abstract: The influence of soil organisms on metal mobility and bioavailability in soils is not currently fully understood. We conducted experiments to determine whether calcium carbonate granules secreted by the earthworm Lumbricus terrestris could incorporate and immobilise lead in lead- and calcium- amended artificial soils. Soil lead concentrations were up to 2000 mg kg-1 and lead:calcium ratios by mass were 0.5-8. Average granule production rates of 0.39 + 0.04 mgcalcite earthworm-1 day-1 did not vary with soil lead concentration. The lead:calcium ratio in granules increased significantly with that of the soil (r2 = 0.81, p = 0.015) with lead concentrations in granules reaching 1577 mg kg-1. X-ray diffraction detected calcite and aragonite in the granules with indications that lead was incorporated into the calcite at the surface of the granules. In addition to the presence of calcite and aragonite X-ray absorption spectroscopy indicated that lead was present in the granules mainly as complexes sorbed to the surface but with traces of lead-bearing calcite and cerussite. The impact that lead-incorporation into earthworm calcite granules has on lead mobility at lead-contaminated sites will depend on the fraction of total soil lead that would be otherwise mobile.
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Feb 2011
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I18-Microfocus Spectroscopy
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Diamond Proposal Number(s):
[4911]
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Feb 2011
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I18-Microfocus Spectroscopy
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Jan 2011
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I18-Microfocus Spectroscopy
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Abstract: The chemistry of molybdenum species in artificial corrosion pits on 316L stainless steel was investigated using X-ray absorption spectroscopy (XANES). It was found that the K-edge spectra are consistent with the presence of an Mo(III) species. The presence of Mo(VI) polymolybdates as been proposed to explain the well-known beneficial effects of Mo in decreasing the susceptibility of stainless steel to localised corrosion, but no evidence of these species was found. High resolution measurements (with a spatial resolution of 3.5 μm in the vertical direction) through the dissolving metal interface did not detect the presence of any different Mo-containing species in the vicinity of the salt film. However, the spatial resolution was insufficient to detect the presence of submonolayer species on the dissolving metal surface that have been proposed to block active dissolution.
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Jan 2011
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