Ketonization of hexanoic acid to diesel-blendable 6-undecanone on the stable zirconia aerogel catalyst

Article abstract of DOI:10.1016/j.apcata.2015.09.008

The ketonization of hexanoic acid, which can be prepared by the fermentation of sugars, was performed in an effort to obtain the diesel-blendable high-carbon-number ketone 6-undecanone in this study. Based on observations of the leaching of highly active base catalysts, magnesium oxide and manganese oxide, the stable amphoteric solid catalyst zirconia was selected for the acid-rich reaction environment. A high-surface-area zirconia aerogel was prepared, which successfully ketonized hexanoic acid to 6-undecanone with high conversion, 72.3%, and high selectivity, 92.6%. The further optimization of the porous structures of zirconia led to possibly improved mass transfer with approximately 35 nm of pores, which improved the catalytic activity of zirconia.

Full text of DOI:10.1016/j.apcata.2015.09.008

Accepted Manuscript
Title: Ketonization of hexanoic acid to diesel-blendable
6-undecanone on the stable zirconia aerogel catalyst
Author: Yunsu Lee Jae-Wook Choi Dong Jin Suh
Jeong-Myeong Ha Chang-Ha Lee
PII:
S0926-860X(15)30141-1
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.apcata.2015.09.008
APCATA 15540
To appear in:
Applied Catalysis A: General
Received date:
Revised date:
Accepted date:
23-6-2015
20-8-2015
8-9-2015
Please cite this article as: Yunsu Lee, Jae-Wook Choi, Dong Jin Suh, Jeong-
Myeong Ha, Chang-Ha Lee, Ketonization of hexanoic acid to diesel-blendable 6-
undecanone on the stable zirconia aerogel catalyst, Applied Catalysis A, General
http://dx.doi.org/10.1016/j.apcata.2015.09.008
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Ketonization of hexanoic acid to diesel-blendable 6-undecanone on the stable zirconia aerogel
catalyst
Yunsu Lee,a,b Jae-Wook Choi,a Dong Jin Suh,a,c,d Jeong-Myeong Ha,*,a,c,e Chang-Ha Leeb
aClean Energy Research Center, Korea Institute of Science and Technology, Seoul 02792, Republic
of Korea
bDepartment of Chemical and Biomolecular Engineering, Yonsei University, Seoul 03722,
Republic of Korea
cGreen School (Graduate School of Energy and Environment), Korea University, Seoul 02841,
Republic of Korea
dDepartment of Green Process and System Engineering, Korea University of Science and
Technology, Daejeon 34113, Republic of Korea
eDepartment of Clean Energy and Chemical Engineering, Korea University of Science and
Technology, Daejeon 34113, Republic of Korea
*Corresponding author. Tel.: +82 2 958 5837; fax: +82 2 958 5209.
E-mail address: jmha@kist.re.kr (J.-M. Ha)
1

Graphical abstract
2

Highlights
- Highly active ketonization of hexanoic acid.
- Stable zirconia aerogel catalysts exhibited the high activity.
- Mesopores improved the catalytic activity.
3

Abstract
The ketonization of hexanoic acid, which can be prepared by the fermentation of sugars, was
performed in an effort to obtain the diesel-blendable high-carbon-number ketone 6-undecanone in
this study. Based on observations of the leaching of highly active base catalysts, magnesium oxide
and manganese oxide, the stable amphoteric solid catalyst zirconia was selected for the acid-rich
reaction environment. A high-surface-area zirconia aerogel was prepared, which successfully
ketonized hexanoic acid to 6-undecanone with high conversion, 72.3%, and high selectivity, 92.6%.
The further optimization of the porous structures of zirconia led to possibly improved mass transfer
with approximately 35 nm of pores, which improved the catalytic activity of zirconia.
Keywords: ketonization; hexanoic acid; zirconia; aerogel.
4

1. Introduction
Abundant amounts of carboxylic acids are produced during the thermolysis of biomass [1-3] and
the anaerobic fermentation of sugars [4, 5] for the preparation of drop-in fuels. Although the
carboxylic acid contains only two oxygen atoms in each molecule allowing to be converted to
paraffins and olefins, its acidity must be reduced to produce petroleum-blendable hydrocarbons.
The simple processes including decarboyxlation, decarbonylation, and deoxygenation can convert
carboxylic acids, particularly fatty acids from the plant oil, to deoxygenated hydrocarbons without
a significant loss of carbons although the high pressure hydrogen gas at the high reaction
temperatures of 250 ‒ 450 °C are required for the efficient processes [6]. Another method to
convert the carboxylic acids is the ketonization which dimerizes two carboxylic acid molecules to
one ketone molecule with the removal of one water and one carbon dioxide [7-9]. A gas-phase
reaction using solid-base catalysts has been performed for the ketonization of small molecular
weight organic acids [10-15].
In addition to the thermolysis and the anaerobic fermentation, biological processes which can be
used to prepare carboxylic acids with higher carbon numbers, including butyric acid [16, 17] and
hexanoic acid [18, 19], have been studied in the hope of preparing alternative fuels which blend
better with gasoline and diesel. Although these carboxylic acids and their corresponding alcohols
are promising as high-energy-density fuels, fuels with higher carbon numbers and with lower
oxygen-to-carbon ratios can be better blended with gasoline and diesel, and the production of fuels
with higher carbon numbers via a completely biological process have been developed [20].
However, the biological processes may not be efficient to produce these chemicals because of their
5

low productivity.
The goal of this study is to develop a heterogeneous catalyst for the efficient production of the
higher-energy-density C11 ketone from biologically produced hexanoic acid [18, 19]. Attempts
were made to avoid the possible leaching of base catalysts, and a stable amphoteric catalyst was
developed for a feasible continuous flow reaction under an acid-rich environment. The
optimization of the porous aerogel catalyst was also performed to find the ketonization descriptor.
(Fig. 1)
2. Experimental
2.1. Preparation of catalysts
Silica-alumina (SixAlyO), alumina (Al2O3), titania (TiO2), zirconia (ZrO2), ceria (CeO2),
manganese oxide (MnOx), zirconium butoxide (Zr(OC4H9)4, 80% in butanol), methanol (99.5%),
hexanoic acid (HA, 99%), 6-undeanone (6-UDO, 98%), hexanoic anhydride (HAn, 98%), and
chloroform (99%) were purchased from Aldrich (Milwaukee, WI, USA). Magnesium oxide (MgO)
was purchased from Yakuri (Kyoto, Japan). An aqueous nitric acid solution (61%) and an aqueous
ammonia solution (28%) were purchased from Junsei (Tokyo, Japan). Zirconia xerogel and aerogel
were prepared using a sol-gel method. Amixture of zirconium butoxide dissolved in butanol (80%,
22.8 mL,), methanol (51.2 mL), DI water (3.6 mL), and aqueous nitric acid (61%, 3.6 mL) was
stirred at room temperature for 1 h. An aqueous ammonia solution (28%, 0.516 mL) was added to
6

the mixture, which was further stirred for 1 h. The mixture was aged for 6 h at 60 °C and dried by
means of supercritical CO2 drying (aerogel) or non-supercritical drying (xerogel). For the
supercritical CO2 drying process, the aged alcogel was placed in a chamber and liquid CO2 was
supplied to the chamber to be pressurized to 137 bar at room temperature. The chamber was kept
at 30 °C for 5 h to exchange methanol and water with CO2 and then kept at 70 °C and 137 bar for
3 h. CO2 was released and the reactor was depressurized to ambient pressure, after which the
chamber was cooled to room temperature. The prepared aerogel was collected and calcined under
an air flow at 500 °C for 6 h. For the non-supercritical drying process used to prepare the xerogel,
the prepared alcogel was dried at 120 °C for 12 h and calcined under an air flow at 700 °C for 6 h.
2.2. Characterizations of catalysts
X-ray diffraction (XRD) was performed using a D/MAX-2500 diffractometer (Rigaku) with
CuK ( = 1.54056 Å). N2-physisroption was performed using an ASAP 2020 (Micromeritics).
The samples for N2-physisorption were degassed in a vacuum at 120 °C for 12 h prior to the
measurement. CO2- and NH3 temperature-programmed desorption (TPD) measurements were
performed using a BELCAT chemisorption analyzer (BEL Japan) equipped with a thermal
conductivity detector (TCD) and a mass spectrometer. For the CO2-TPD, the catalyst (~500 mg)
was heated under a He flow (30 mL/min) at 500 °C for 1 h and a CO2 flow (50 mL/min) was
introduced at 100 °C for 1 h prior to the measurement. For the NH3-TPD, the catalyst (~500 mg)
was heated under a He flow (30 mL/min) at 500 °C for 1 h and a NH3 flow (30 mL/min) was
introduced at 100 °C for 1 h prior to the measurement.
7

2.3. Fixed-bed reaction
The catalyst (0.2 g) was placed on quartz wool in a stainless steel fixed-bed reactor and pretreated
at 500 °C under a N2 flow for 4 h. HA (0.8 g/h) was fed using an LC pump and mixed with a N2
flow (40 mL/min) before being supplied to the reactor. The weight-hourly space velocity (WHSV)
was adjusted to 4 h-1 by manipulating the amount of catalyst. The obtained mixture of gas products
was cooled to -2 °C and the liquid products were collected using a 20-cm-long 15-mL separator.
The collected liquid products were mixed with 2-propanol (internal standard) and diluted with
chloroform, which were quantified using a GC-FID (Hewlett-Packard 5890 series gas
chromatograph equipped with 60 m 0.25 m HP-5 capillary column).
3. Results and Discussion
3.1. Ketonization of hexanoic acid on the metal oxide catalysts
The ketonization of hexanoic acid was performed using several metal oxide catalysts at 360 °C
(Table 1). As reported for the ketonization of carboxylic acids with lower carbon numbers [12],
solid bases of MgO and MnO exhibited the highest conversion of hexanoic acid (HA) with the
highest selectivity to 6-undecanone (6-UDO), and other solid acids and weak bases exhibited lower
catalytic ketonization activity. A significantly large amount of hexanoic anhydride (HAn) was
obtained by the intermolecular dehydration of two HA molecules formed on poor catalysts,
including SixAlyO, Al2O3, TiO2, ZrO2, and CeO2.
8

(Table 1)
While the high catalytic ketonization activity of MgO and MnOx is attributed to the basicity in the
literature [21], we further investigated the origin of the catalytic activity using certain
characterization methods. The most active MgO and MnOx, with very low BET surface areas and
negligible pore volumes (Table 2), excluding the beneficial effects of highly dispersed MgO and
MnOx particles on the catalytic activity, exhibited the higher basicity (by CO2-TPD) compared to
TiO2, ZrO2, and CeO2 (Table 2 and Fig. S1). The less active SixAlyO and Al2O3 exhibited the
unusually large quantities of desorbed CO2 in the CO2-TPD results, which can be attributed to their
high surface areas.
(Table 2)
In addition to the basicity, the high activity of MgO and MnOx, despite their low BET surface areas,
is attributed to the homogenous reaction which took place on the dissolved MgO and MnOx.
During the continuous flow reaction, we frequently observed plugging or a significant pressure
drop for the highly active MgO and MnOx, most likely because of the leaching of the catalysts.
The catalyst powder exhibited physical changes, including the formation of gel-like sticky pastes,
and a change of the color was observed during the continuous reaction for 90 ‒ 200 h (Figs. S2
and S3). To predict the possible leaching or reconstruction of these solid-base catalysts as they
interacted with hexanoic acid, leading to homogeneous catalysis, the liquid products were
observed using ICP-AES and the spent catalysts were observed using XRD and TG. When
observed with ICP-AES, 4.33 and 5.34 g/h of Mg and Mn, respectively, dissolved in the liquid
9

products were observed during the first 25 h of operation, which indicates that MgO and MnOx
were deformed and leached during the continuous flow reaction, and a homogeneous reaction
using dissolved metal oxides occurred. The leaching of catalysts was further confirmed by
performing batch reactions at 360 °C for 6 h (Table S1), which exhibited the almost complete
leaching of Mg and Mn confirming the homogenous catalysis on MgO and MnOx.
The leaching of MgO and MnOx was further confirmed with XRD (Fig. S4). MnOx exhibited a
major transformation of face-centered cubic manganosite (MnO) [22] to other manganese oxides,
indicating that MnOx was partially dissolved in hexanoic acid and reconstructed. Although the
leaching and deforming of MgO was observed, both fresh and spent MgO exhibited a face-centered
cubic periclase structure [23] possibly because the ambient-pressure-stable periclase formed even
after the reconstruction of MgO in the acid-rich environment. Although MgO did not exhibit
significant changes in the XRD analysis, catalysis using MgO was forced to stop at 90 h because
of the significant pressure drop and plugging caused by the dissolution and re-agglomeration of
the MgO powder. These observations indicate that MgO and MnOx are not appropriate for the
heterogeneous catalytic ketonization of hexanoic acid in spite of their high catalytic activity.
3.2 Ketonization of hexanoic acid on zirconia
To avoid the homogeneous reaction by leached solid catalysts, zirconia was selected as a possible
stable ketonization catalyst because its amphoteric nature may resist the leaching under the acidic
conditions. Assuming that the observed poor activity of bulk zirconia powder could be attributed
to its low surface area (Table 2), a highly dispersed aerogel, a less dispersed xerogel, commercially
10

available zirconia, and sulfated zirconia were prepared or purchased for catalysis, and their
activities were measured as described at the experimental section (Table 3). Although the
commercially available zirconia (m-ZrO2) exhibited very poor activity and low BET surface area,
the sulfated zirconia and aerogel (ZrOx(A500)) exhibited higher conversions of HA and higher
yields of 6-UDO. Interestingly, the preferred formation of HAn was observed for the less active
m-ZrO2 and xerogel (ZrOx(X)), which exhibited lower conversion of HA.
(Table 3)
In order to find the descriptor to determine the catalytic activity of zirconia for the improved
catalysts, the crystal structures, pore structures, and acid-base properties of the catalysts were
observed. The XRD results of zirconia exhibited monoclinic ZrO2 for m-ZrO2, tetragonal ZrO2 for
S-ZrO2, and a mixture of monoclinic (minor) and tetragonal (major) ZrO2 for ZrOx(X), and
ZrOx(A500) (Fig. S5). The formation of tetragonal ZrO2 in chemically treated zirconia and the
aerogels has been reported in the literature [24]. Although the formation of tetragonal ZrO2 has
been attributed to the improved catalytic activity of zirconia in the literature [25], it is not clear
whether the crystal structure determined the catalytic activity in this study. Other than the crystal
structure, the pore structures of the zirconia catalysts were measured by means of N2-physisorption
(Table 4 and Fig. S6). S-ZrO2 and ZrOx(A500) exhibited higher BET surface areas, while m-ZrO2
and ZrOx(X) exhibited negligible BET surface areas and pore volumes. These observations
indicate that the surface area did not clearly determine the catalytic activity because S-ZrO2 with
its higher surface area did not exhibit better activity compared to ZrO2(A500).
11

(Table 4)
Along with the crystal structures and porosity, the basicity and acidity of the zirconia catalysts
were observed with CO2- and NH3-TPD measurements, respectively (Fig. S7 and Table 5),
indicating that the basicity was a good descriptor for the ketonization of zirconia. While the less
active S-ZrO2 exhibited the highest acidity because of its sulfate functionalities, the most active
ZrOx(A500) exhibited the highest basicity and high acidity. When the yield of 6-UDO,
representing the catalytic ketonization activity, was plotted on the BET surface area, CO2-
desorption, and NH3-desorption, it was clear that the basicity as measured by CO2-TPD determined
the ketonization activity, although zirconia exhibited both acidity and basicity (Fig. 2). Although
the basicity more clearly improved the ketonization activity, the synergistic effects of acids and
bases can be expected. By the possible reaction pathway (Fig. S8) [9, 26, 27], acid sites on the
catalysts also appear to contribute to the conversion of carboxylic acid to ketone.
(Fig. 2)
Along with the basicity-improved catalytic activity, the stability of ZrOx(A500) was confirmed
with an extended reaction (Fig. S9). While the selectivity to 6-UDO did not change significantly,
exhibiting results of 90 ‒ 92%, the conversion of HA continuously decreased over time, indicating
that the deactivation of ZrOx(A500) occurred. The XRD measurements did not exhibit any changes
in the crystal structures of zirconia (Fig. S10); however, the TG of spent ZrOx(A500) exhibited the
deposition of carbon on the catalyst surface (Fig. S11). Because of the carbon deposition process,
the BET surface area (82.2 to 75.1 m2/g) and the pore volume (0.59 to 0.49 cm3/g) of ZrOx(A500)
12

decreased slightly, although the pore width did not significantly change. These observations
indicate that the structure of ZrOx(A500) was very stable during the extended continuous flow
reaction and that deactivation occurred as a result of the carbon deposition, not because of the
leaching or deformation of the catalyst. The ICP-AES of liquid products confirmed the excellent
stability of ZrOx(A500), exhibiting negligible Zr (less than the detection limit of 10 ppm in the
liquid products collected for 25 h) dissolved in the liquid products, in contrast to the observations
of MgO and MnOx. The batch reaction using ZrOx(A500) also confirmed the negligible leaching
of zirconia (Table S1).
Note that the ketonization of HA on zirconia aerogel catalysts was not significantly affected by the
existence of CO2 under ambient pressure although the pressurized CO2 was reported to inhibit the
ketonization [28]. When HA was condensed to 6-UDO on ZrOx(A500) at 330 °C with co-fed CO2
([CO2]/[HA] = 7.7 (mol/mol)), the conversion of HA and the yield of 6-UDO were 32.5 and 30.5%
at WHSV = 4 h-1, respectively, which are not significantly different from those observed without
co-fed CO2, 29.8% conversion of HA and 27.9% yield of 6-UDO.
3.3 Ketonization on the zirconia aerogels with different pore structures.
While ZrOx(A500) exhibited high stability and basicity-improved activity for ketonization, its
optimization was further attempted by the thermal modification of its pore structures. Because
aerogel catalysts will give the benefit of better mass transfer during the reaction, it is important to
understand the relationship between the pore structure and the catalytic activity. Although the
adjustment of calcination temperature controlled the pore structure, the acidity per BET surface
13

area was similar to one another exhibiting 5.1 ‒ 7.0 mol/m2 (calculated by NH3-TPD results and
BET surface areas) for all zirconia except the one calcined at 1200 °C (ZrOx(A1200)) which
exhibited the negligible BET surface area (Figs. S13, S14, and Table S2). The XRD measurement
of zirconia aerogels exhibited more monoclinic and less tetragonal structures while the monoclinic
structure became more distinct at the higher calcination temperature (Fig. S15).
By manipulating the calcination temperature during the preparation of the aerogels, the zirconia
aerogel calcined at 500 °C (ZrOx(A500)), with the largest BET surface area and the smallest pore
width, exhibited the highest ketonization activity while those calcined at 1200 °C (ZrOx(A1200)),
with the smallest BET surface area and the smallest pore volume, exhibited the lowest activity
(Table 6 and Fig. 3). Because the acidity per BET surface area was not significantly different, the
catalytic activity was expected to be proportional to the BET surface area. When the yield of 6-
UDO was plotted on the BET surface area, the deviation from linearity was observed for
ZrOx(A800) and ZrOx(A600) (Fig. 4). The BJH desorption pore size distribution indicated that
ZrOx(A500) and ZrOx(A600) exhibited similar pore structures, while ZrOx(A1000) and
ZrOx(A1200) exhibited thermally destroyed pores. ZrOx(A800) was different from the others in
that it exhibited mesopores of approximately 35 nm, which are larger than those of ZrOx(A500)
and ZrOx(A600). It is reasonable to expect better gas-phase catalytic activity with larger pores,
which improve the mass transfer. Pores of zirconia aerogels in this study are mesopores exhibiting
the Knudsen diffusion whose diffusion coefficient is proportional to the pore width [29]. Although
the pores of zirconia catalysts are not uniform, we can expect the mass transfer on ZrOx(A800)
with pores of 35 nm is approximately 1.6 times faster than those on ZrOx(A500) and ZrOx(A600)
whose peak pores are approximately 20 nm. The rates of formation of 6-UDO per base site were
14

13 h-1 for ZrOx(A800) and 5.9 – 6.9 h-1 for the others except ZrOx(A1200), which may indicate
the beneficial effects of mass transfer. Therefore, the positive deviation of the catalytic activity of
ZrOx(A800) could be attributed to the better superficial catalytic activity which is obtained by the
better mass transfer through the larger pores. The slight positive deviation of ZrOx(A600) was
likely caused by the same process, although the pore size was slightly larger than that of
ZrOx(A500).
(Table 6)
(Fig. 3)
(Fig. 4)
4. Conclusions
Although the basic catalysts MgO and MnOx exhibited high catalytic activity for the ketonization
of hexanoic acid, their leaching in an acid-rich environment may not be feasible for a long-term
continuous flow reaction. High-surface-area zirconia aerogels exhibited high stability and
excellent catalytic activity under a flow of a hexanoic acid reactant, which must be appropriate for
a continuous process. With nearly identical base properties, the activity of the zirconia aerogel was
proportional to the BET surface area, although the better mass transfer with larger pores appears
to improve the catalytic activity.
15

Acknowledgements
We would like to acknowledge the financial support from the R&D Convergence Program of NST
(National Research Council of Science & Technology) of Republic of Korea/KIST (Korea Institute
of Science and Technology) (2E25402). This work was also supported by the New & Renewable
Energy Core Technology Program of the Korea Institute of Energy Technology Evaluation and
Planning (KETEP) granted financial resource from the Ministry of Trade, Industry & Energy,
Republic of Korea (No. 20143010091790).
Appendix A.
Supplementary data are available at
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acids by ketonization as a processing step in biomass conversion, J. Catal., 266 (2009) 71-78.
[29] E.L. Cussler, Diffusion, Cambridge University Press, 1997.
19

Fig. 1. Ketonization of hexanoic acid to 6-undecanone.
20

Fig. 2. Effects of the (a) surface area, (b) basicity, and (c) acidity of zirconia catalysts on the yields
of 6-UDO.
21

Fig. 3. N2-physisorption isotherms and BJH desorption pore size distributions of zirconia aerogel
catalysts prepared with different calcination temperatures.
22

Fig. 4. Yield of 6-UDO depending on the BET surface area.
23

Table 1. Catalysis results using metal oxides at 360 °C.
Reaction
temperature
(°C)
HA
conversion
(%)
6-UDO
6-UDO yield
(%)
HAn
Catalyst
selectivity (%)
selectivity (%)
SixAlyO
Al2O3
TiO2
360
15.6
63.9
22.4
28.3
20.8
37.2
87.5
90.3
10.0
1.8
31.4
76.6
66.9
78.0
64.7
1.5
360
7.9
360
14.9
4.2
ZrO2
360
9.8
2.0
CeO2
MgO
360
14.7
4.9
360
61.9
54.1
68.4
MnOx
360
75.8
0.9
24

Table 2. N2-physisorption and CO2-TPD results of the metal oxide catalysts.
Catalysts SBET (m2/g)
Vp (cm3/g)
0.75
Amount of CO2 desorbed (mol/g)
SixAlyO
Al2O3
TiO2
569
62.7
5.7
4.5
3.6
6.1
8.3
150
120
3
0.18
0.012
0.011
0.009
0.015
0.029
ZrO2
7
CeO2
MgO
5
44
15
MnOx
25

Table 3. Catalysis activity of zirconia at 360 °C.
Reaction
temperature
(°C)
HA
6-UDO
selectivity
(%)
HAn
selectivity
(%)
6-UDO yield
(%)
Catalysts
conversion
(%)
m-ZrO2
360
9.8
20.8
2.0
78.0
S-ZrO2
360
32.9
85.0
28.0
1.3
5.6
ZrOx(X)
ZrOx(A500)
360
11.6
11.4
87.5
360
74.5
92.6
68.9
0.5
26

Table 4. N2-physisorption results of the zirconia catalysts.
SMicropore measured by t-
Catalyst
SBET (m2/g)
Vp (cm3/g)
plot (m2/g)
3.1
m-ZrO2
S-ZrO2
ZrOx(X)
4.6
0.011
0.12
126.0
1.8
36.7
0.004
0.59
0.9
ZrOx(A500) 82.2
9.6
27

Table 5. Basic and acidic properties of zirconia catalysts according to a TPD analysis.
Catalyst
m-ZrO2
Amount of desorbed CO2 (mol/g)
Amount of desorbed NH3 (mol/g)
7
26
S-ZrO2
77
4
589
11
ZrOx(X)
ZrOx(A500)
172
480
28

Table 6. Ketonization results on zirconia aerogel catalysts at 360 °C.
6-UDO
SMicropore
Reaction
HA
6-UDO
6-UDO
yield
HAn
SBET
Vp
formation
Catalyst
by t-plot temperat
conversio selectivit
selectivit
y (%)
(m2/g)
(cm3/g)
per
base
(m2/g)
ure (°C)
n (%)a
y (%)
(%)a
site (h-1)
360
360
360
360
360
72.3
58.7
48.3
14.3
6.2
92.6
93.4
93.2
63.7
11.2
66.9
54.9
45.0
9.1
0.7
5.9
6.9
13
ZrOx(A500)
ZrOx(A600)
ZrOx(A800)
ZrOx(A1000)
ZrOx(A1200)
103.3
69.2
28.2
13.0
1.7
0.55
0.46
0.27
0.11
0.01
4.8
12.4
9.9
6.0
1.0
1.1
1.5
35.1
88.0
6.6
2.6
0.7
aThe error ranges: ± 1.9% for the HA conversion and ± 1.7% for the 6-UDO yield.
29