Photon Factory Activity Report 2016 #34 (2017) B

BL-7A/2015C213

C K-edge XANES analysis of coke on CoMo catalysts used in HDS unit using feedsof LGO mixed with heavy fuel oil blendstocks
Nobuharu Kimura1*, Yoshimu Iwanami1, Ryutaro Koide1, Kenta Amemiya2
1
JX Nippon Oil & Energy Corporation, 8 Chidoricho, Naka-ku, Yokohama, 231-0815, Japan2
Photon Factory, 1-1 Oho, Tsukuba, 305-0801, Japan
1 Introduction
To ensure the most effective use of petroleum resources,
efficient techniques must be developed for converting
blendstocks of heavy fuel oil to diesel fuel oil. However,when a mixture of light gas oil (LGO) and light cycle oil(LCO), a heavy fuel oil blendstock, is fed into an oil
refinery's hydrodesulfurization (HDS) unit to produce
diesel fuel, the CoMo (Cobalt-Molybdenum) catalyst in
the HDS unit is rapidly deactivated (Fig. 1). In contrast,
when the feed is LGO mixed with residue desulfurization
gas oil (RDS-GO), another heavy fuel oil blendstock, thecatalyst is deactivated slowly. With this in mind, wefocused on the coke, or carbonaceous matter, that forms
around the active species, namely MoS2, on the catalyst
surface during the HDS reaction and is thought to be theprimary cause of deactivation of gas oil HDS catalysts.
[1]
In this study, we investigated the chemical states of themass%, and those used for the RDS-GO-containing
mixed feed were around 4–5 mass%.
Before the XANES measurements, the catalysts weresubjected to Soxhlet extraction (using toluene) for 12hours to remove the oil on them and then ground into
powders. The powdered catalysts were then fixed on anindium plate, which was mounted on the sample plate that
goes in the XAFS instrument. The XANES measurements
were conducted in total electron yield mode on station
BL-7A at the Photon Factory.
3 Results and Discussion
Figures 2 and 3 show the C K-edge XANES spectra ofspent CoMo catalysts used for different times on stream
in the HDS unit of a bench scale plant, using LCOcontaining mixed feed and RDS-GO-containing mixed
feed. Two sharp peaks were observed at 285 eV andaround 288 eV and a broad peak was also observed
around 292 eV in the XANES spectra of all spent
catalysts. The spectra were normalized at the peak around
292 eV. Aromatic compounds and basic nitrogencompounds in the feeds have been reported as potential
causes of coking. [2] Therefore, the peak observed at 285
eV was assigned to the 1s −> π* transition of the sp2
carbon atoms in aromatic compounds, and that at around
292 eV was assigned to the 1s −> σ* transition.
Meanwhile, the peak observed around 288 eV may be dueto the alkyl groups in the aromatic compounds or thepresence of oxygen-containing or nitrogen-containingfunctional groups.
It was found that the peak heights of the 1s −> π*Fig. 1: Deactivation behaviour of catalyst for two
different feeds (bench-scale plant).
coke formed on spent CoMo catalysts from an HDS unit
by way of C K-edge XANES measurements in order tounderstand the mechanism of catalyst deactivation when
the HDS feed is LGO mixed with heavy fuel oil
blendstocks such as LCO and RDS-GO.
2 Experiment
For the C K-edge XAFS measurements, we preparedspent aluminum oxide-supported CoMo catalysts which
had been used for 160, 500, 1000 and 2300 hours onstream in the HDS unit of a bench scale plant, using feeds
consisting of LGO mixed with 15 vol% of either LCO orRDS-GO. The carbon concentrations in the catalysts used
for the LCO-containing mixed feed were around 5–8Fig. 2: C K-edge XANES spectra of spent CoMo
catalysts for LCO mixed feed.

Photon Factory Activity Report 2016 #34 (2017) B

transition peaks were clearly different depending on thecompounds in the coke that formed on the catalyst
became more polycyclic as the time on stream increased.
In contrast, the peak height ratio (π* / σ*) of the catalyst
used with the RDS-GO-containing mixed feed increasedmuch less than that of the catalyst used with the LCOcontaining mixed feed as the time on stream increased,with the exception of an outlying data point at the 1000hour mark. This suggests that the aromatic compounds inthe coke on the catalyst were less likely to become
polycyclic as the time on stream increased.
These results suggest that the chemical state of the coke
forming on a catalyst will differ depending on the feed
used in the HDS reaction, and this affects the catalystdeactivation behavior.
This study was supported by the Japan Petroleum
Energy Center (JPEC) under the sponsorship of theMinistry of Economy, Trade and Industry (METI) ofJapan.

Fig. 3: C K-edge XANES spectra of spent CoMo
catalysts for RDS-GO mixed feed.
times on stream for the catalysts used with both the LCOcontaining mixed feed and RDS-GO-containing mixed
feed. Therefore, we focused on the 1s −> π* transition
peak at 285 eV in order to elucidate the chemical states ofthe coke formed on the spent CoMo catalysts during theHDS reaction.
The peak height ratio of the 1s −> π* transition peak to
the 1s −> σ* transition peak was determined by the heightof each peak. [3] The peak height ratio (π* / σ*) wasviewed as a measure of the degree of polycyclization of
the aromatic compounds in the coke on the spent catalyst.
The higher the peak height ratio (π* / σ*), the higher we
expect the degree of polycyclization of the aromaticcompounds to be.
The relationship between the time on stream and thepeak height ratio (π* / σ*) for the spent catalysts usedwith the LCO-containing mixed feed and the RDS-GOcontaining mixed feed is shown in Fig. 4. Figure 4 showsthat the peak height ratio (π* / σ*) increased with thetime on stream for the spent catalyst used with the LCOcontaining mixed feed. This suggests that the aromaticFig. 4: Relationship between the time on stream
and the peak height ratio (π*/σ*) in theXANES of spent catalysts.

References[1] T. Amano et al., Jpn. J. Appl. Phys., 52, 41304 (2013).
[2] E. Furimsky et al., Energy Fuel, 9, 439 (1995).
[3] Y. Muramatsu et al., Advances in X-Ray Chemical
Analysis 43, 425 (2012).
* kimura.nobuharu@jxgr.com