The deactivation of a ZnO doped ZrO2-SiO2 catalyst in the conversion of ethanol/acetaldehyde to 1,3-butadiene

Article abstract of DOI:10.1039/c8ra06757k

A deactivation study on the ethanol/acetaldehyde conversion to 1,3-butadiene over a ZnO promoted ZrO₂-SiO₂ catalyst prepared by a sol-gel method was performed. The samples were characterized by N₂ adsorption-desorption isotherms, scanning electron microscopy (SEM), NH₃ temperature programmed desorption (NH₃-TPD), X-ray powder diffraction characterization (XRD), thermogravimetric analyses (TGA), Fourier transform infrared resonance (FT-IR), ¹³C magic-angle spinning nuclear magnetic resonance (¹³C NMR) and X-ray photoelectron spectroscopy (XPS). The pore structure characteristics and surface acidity of Zn_0.5-Zr-Si catalysts were largely decreased with time-on-stream and no crystal structure was formed in the used catalyst, indicating that the deactivation was caused by carbon deposition. Two main types of carbon deposition were formed, namely low-temperature carbon deposition with the oxidation temperature of around 400 °C and high-temperature carbon deposition with the oxidation temperature of 526 °C. The carbon species were mainly composed of graphitized carbon, amorphous carbon, carbon in C-O bonds and carbonyls. The deactivated catalyst could be regenerated by a simple oxidation process in air. Adding a certain amount of water into the feed had a positive effect on reducing the carbon deposition.

Full text of DOI:10.1039/c8ra06757k

Sound Convergence Zones Formed by Reflection from the Sea
Boꢀom in an Incomplete Sound Channel*
†
Peng Zhang1,2, Zhenglin Li1, , Lixin Wu1, Renhe Zhang1, Jixing Qin1
1State Key Laboratory of Acoustics, Institute of Acoustics, Chinese Academy of Sciences, Beijing 100190, China.
2College of Electronic Electrical and Communication Engineering, University of Chinese Academy of Sciences, Beijing 100049, China.
lzhl@mail.ioa.ac.cn
ABSTRACT
1 INTRODUCTION
e seafloor has a significant influence on sound propagation in
deep water in the context of an incomplete sound channel. Using
data collected during an experiment in the South China Sea, we
study seafloor reflection effects on sound propagation in a range
dependent environment. e experiment phenomenon is
different from the convergence phenomenon in the deep sound
channel, also referred to as the SOFAR channel. We observe that
the spatial variation of bathymetry contributes to the formation
of the seafloor reflection convergence zone in advance, and the
sound intensity in some areas of the shadow zone is significantly
increased. Due to seafloor reflection, there are two seafloor
reflection convergence zone within 60 km of the propagation
track, in which the gains of the acoustic energy can exceed 10
dB. High sound intensity areas are also observed in the shadow
zone near 11 km and 51 km at some depths. In addition, the gain
of the second convergence zone is higher than that of the first
convergence zone when the receiving depth is the same as the
source depth. In the first convergence zone, as the receiving
depth increases, the arrival structure tends to become
complicated, and the multipath effect becomes more obvious.
Numerical analysis based on the parabolic equation and ray
theory is carried out to explain the physical mechanism of the
seafloor reflection convergence zone. e study result is
meaningful for the performance analysis of sonar in complex
deep-water environments.*
Convergence zones of the sound field are formed by
variations of the sound speed profile and water depth, which is
an important acoustic characteristic in deep water. Prior to the
twenty-first century, a series of sound propagation experiments
were conducted to elucidate the issues of convergence effect.
Hale [1] observed a strong convergence zone effect in a deep
water experiment in the early 1960s. Ray theory [2], wave theory
[3,4] and extended theories [5] were applied to study the
convergence zone over the next few decades. These theories
profoundly revealed the mechanisms of sound propagation and
could accurately predict the location of the convergence zone.
Discussions in these research papers focused on sound
propagation in typical SOFAR channels. In the far field of the
SOFAR channel, the influence of the sea floor can be ignored
because most rays are reflected by sea water before touching the
seafloor. But in an incomplete channel, the sound field is mainly
formed by sound waves reflected from the seabed. The
characteristics of seabed sediment therefore become important
factors affecting sound propagation.
Applying the theory of reversal point convergence zone,
Zhang Renhe [6] calculated the seafloor reflection coefficient of
the minimum glancing angle under the negative gradient profile
environment. However, the acoustic characteristics of the seabed
were not directly described in this paper. In addition, the
theoretical calculation does not match the experimental results
with regard to the location and gain of the convergence zone.
Wang Gang et al. [7] applied the WKBZ normal wave method to
study the seafloor reflection convergence zone under the deep
sea negative gradient depth profile. Fan Peiqin et al. [8]
simulated rapid distance prediction of the seafloor reflection
convergence zone by using environment statistical data and the
characteristic parameter calculation model. Many researchers
have looked at the effects of acoustic propagation in range-
dependent underwater environments, such as the reflection
blocking effect of the seamount [9], acoustic propagation lows
along uneven bottoms [10], and down-slope enhancement effects
[11].
KEYWORDS
convergence zone, boꢀom reflection, multipath structure
ACM Reference format:
Peng Zhang, Zhenglin Li, Lixin Wu, Renhe Zhang, and Jixing Qin. 2018.
Sound Convergence Zones Formed by Reflection from the Sea Boꢀom in
an Incomplete Sound Channel. In e 13th ACM International Conference
on Underwater Networks & Systems (WUWNet’18), December 3–5, 2018,
Shen zhen, China , (Eds.). ACM, New York, NY, USA, Article , 5 pages.
hꢀps://doi.org/10.1145/3291940.3291985
In this paper, sound propagation experiment data collected in
the South China Sea is used to analyze the characteristics of the
convergence zone formed by bottom reflection under the
incomplete channel environment with variation of bathymetry.
Numerical analysis based on the parabolic equation combined
with ray theory is carried out to calculate the arrival time of the
pulse arrival structure as well as the eigenrays and explain the
Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without
fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this
notice and the full citation on the first page. Copyrights for components of this work owned by others than ACM
must be honored. Abstracting with credit is permitted. To copy otherwise, or republish, to post on servers or to
redistribute to lists, requires prior specific permission and/or a fee. Request permissions from Permissions@acm.org.
WUWNet'18, December 3–5, 2018, Shenzhen, China
© 2018 Association for Computing Machinery.
ACM ISBN 978-1-4503-6193-4/18/12…$15.00
https://doi.org/10.1145/3291940.3291985

WUWNet’18, December 2018, Shenzhen, China
Peng Zhang et al.
physical causes of the seafloor reflection convergence
phenomenon.
speed at the depth of the deep source, which is close to the speed
of sound near the bottom. For the range larger than 10 km, the
sound speed near the seabed is much smaller than that of the
source depth. Thus, the sound reflection from the sea bottom
cannot be ignored.
2 SOUND PROPAGATION IN THE
INCOMPLETE CHANNEL
2.1 Description of the Experiment
In April 2018, a comprehensive experiment was carried out
by the State Key Laboratory of Acoustics, Chinese Academy of
Sciences in the South China Sea. One of the main purposes was
to study sound propagation characteristics in the complex deep
water environment. The sound source was towed by the
experiment’s ship away from a receiving vertical line array
(VLA). The VLA consisted of 20 hydrophones placed from 85 m
to 3400 m with an unequal depth space. The sensitivities of the
hydrophones were -170 dB, and the sampling rate of the signal
was 16 kHz. The acoustic source was towed at a speed of 4 knots,
transmitting a hyperbolic frequency modulated (HFM) signal
with a frequency range from 250 Hz to 350 Hz. The depth of the
towed transducer was about 150 m, and the emission source
level was 192 dB.
Fig. 2 Sound speed profile during the experiment.
2.2 Experimental Results
The bathymetry along the propagation track is shown in Fig.
1. We can see there is a small seamount with a height of 500 m
within 20 km of the propagation track and the topography is
undulating. The sea bottom in the range from 20 km to 60 km is
relatively flat.
xn (t)
Assume that
denotes the signal received by one of the
hydrophones on the VLA.
(1)
xn (t) = X ()H(r, z;)exp(-it)d

where
is the spectrum of original acoustic emission
X()
signals and
is the transfer function of sound channel
H(r, z;)
from source to receiver. The pulse compression method is used
to improve the signal-to-noise ratio (SNR)
xc (t) = X( )exp(-it)d
) 2 H(r, z;
(2)

The fast Fourier transform (FFT) operation is then applied to
obtain the spectrum of at -th frequency bin. The measured
i
Xi
spectra are averaged in the frequency bandwidth (100 Hz) of the
signal, and the average energy of the signal is expressed as
nf2
2
1
2
Fig. 1 The bathymetry along the propagation track.
(3)
E( f0 ) 
X
i

F2 nf nf 1inf
s
2
1
1
During the experiment, the sound speed profile of seawater
was measured every 10 km using a conductivity temperature
depth (CTD) and expendable bathythermograph (XBT). The
sound speed profile change at different distances is small, and
the sound speed profile at the receiving position is shown in Fig.
2. The maximum measured depth of the sound speed profile is
1200 m, so the sound speed profile below 1200 m is taken from
the data base. We see that it is a typical incomplete deep water
sound channel. The channel axis is located near the depth of
1100 m. The sound speed at the deepest part of the seabed is
1515 m/s, which is less than the sound speed of 1539 m/s near
the sea surface. The black dots indicate the depth of the 20 VLA
hydrophones, the blue dotted line indicates the depth of the
towed sound source, and the solid blue line indicates the sound
where
is the central frequency,
is the sampling rate,
Fs
f0
nf1
and
are the numbers at the start and end frequency for the
nf2
frequency band, respectively. Then the transmission loss (TL)
can be denoted as
(4)
TL( f )  SL( f )(10lg E( f ) M  E )


0
0
0
v
C
where
is the source level of the transducer,
is the
SL( f0 )
Mv
sensitivity of the hydrophones, and
represents the
EC
increasing energy of the pulse compression filter.
Finally, the two-dimensional TL along the experiment track is
shown in Fig. 3. It is clear that two distinct convergence zones
2

Sound Convergence Zones Formed by Reflection from the Sea
Bottom in an Incomplete Sound Channel
WUWNet’18, December 2018, Shenzhen, China
can be observed over a distance of 60 km, which are located near
20 km and 40 km, respectively. At the same time, two more
obvious acoustic enhancement areas can be observed around 11
km and 51 km.
obvious convergence zones within 60 km of the real bathymetry.
Some rays are reflected from the seamount and converge at 20
km, which is the reason for the formation of the first
convergence zone. Some of the direct-arrival rays and rays from
the first convergence zone are reflected from the sea bottom, and
then they arrive near the sea surface at around 40 km, which
leads to the formation of the second reflection convergence zone.
To quantitatively analyze the experimental phenomena, Fig. 5
shows the TLs comparisons at two typical receiving depths (85 m
and 145 m). We can further confirm that two convergence zones
appear near 20 km and 40 km. The gains of the two convergence
zones can be achieved at more than 10 dB, and the sound
intensity of the second convergence zone at the depth of 145 m
and 42 km distance is higher than that at the first convergence
zone at the same receiving depth. In addition, there are also two
areas with high sound intensity near 11 km and 51 km at the
depth of 145 m, where the gain is less than those of the two
convergence zones. However, there is only one acoustic
enhancement zone at 11 km and 85 m receiving depth, and the
sound intensity enhancement zone cannot be observed at 51 km.
The calculated results are consistent with the experimental
results.
Fig. 3 Two dimensional experimental TLs
Fig. 4 Numerical TLs results from RAM-PE model.
The parabolic equation method (RAM-PE [10,11]) is used to
calculate TLs to analyze the experimental phenomena. Selections
of the central frequency and bandwidth of the sound source are
the same as the experiment ones, with the frequency interval of
10 Hz and the frequency point number of 11. A two-layer fluid
bottom model is selected with a sediment thickness of 20 m,
sediment sound speed of 1499 m/s, and sediment density of 1.36
g/cm3 (according to the sampling results), and the infinite
basement has a sound speed of 1650 m/s and density of 1.8 g/cm3.
The
attenuation
coefficients
are
chosen
as
0.517( f /1000)1.07 dB/
[12]. Because the hydrophone
placed under the channel axis is sparse in the experiment, the TL
in Fig. 3 is not smooth due to the interpolation. So the receiving
depth below the channel axis is increased in PE calculation, and
the numerical TLs results are shown in Fig. 4.
Comparing Fig. 3 with Fig. 4, we can see that the numerical
results are consistent with the experimental TL. There are two
Fig. 5 Comparison of experimental TLs and numerical TLs,
where(a)-(b) for the receivers at 85 m and 145 m,
respectively.
3

WUWNet’18, December 2018, Shenzhen, China
Peng Zhang et al.
line that is only refracted by sea water and is not reflected by
either bottom or surface.
3 THEORETICAL EXPLANATION
To explain the seafloor reflection convergence phenomenon
observed during the experiment, ray theory is used for analysis.
Following the principle of reciprocity, Fig. 6 shows the sound
rays’ traces at two different receivers. The black dot at 0 km
indicates the source depth, and the black dotted line indicates a
receiver depth of 150m. In Fig. 6, the rays reflected by the sea
surface and seabed reflection (many times) are depicted by the
blue-green line, the rays reflected by the sea bottom (only once)
are depicted by the red line, and the blue line indicates a sound
The sound speed near the sea bottom is close to that near the
source depth. Except for a few small glancing angles, most other
sound ray traces cannot be refracted before reaching the sea
bottom and will be reflected by the seafloor, which is consistent
with the simulation results in Fig. 6. We can see a large number
of sound rays arriving near 11 km, 20 km, and 40 km at the two
receiving depths, corresponding to the high intensity area and
the two seafloor reflection convergence zones in Fig. 5. We find
that the grazing angles of the sound rays reaching the second
Fig. 6 Ray traces at two different receivers, (a) for 85m and (b) for 150m. Black dots mark the source depth, and the black
dashed line indicates the receiver depth at 150m.
Fig. 7 Comparison of eigenrays and arrival structures at different receiver depths in the first bottom reflection convergence
zone: (a) for the receiver depth at 85 m, (b) for the receiver depth at 1008 m, and (c) for the receiver depth of 3021 m.
4

[3] Brekhovskikh L M, Lysanov Yu P. 2003. Fundamentals of Ocean Acoustics
(3rd. ed.). Springer, New York, NY.
[4] Williams A O, Horul W. 1967. Axial focusing of sound in the SOFAR channel.
J. Acoust. Soc. Am 41(1), 189-198.
[5] Zhang RH. 1980. Turing-point convergence zones in underwater sound
channel(Ⅰ) A normal-mode theory. Acta Acust 1 30-42.
[6] Zhang RH, Sun GC, Lei LY, Zhou JL. 1985. Turing-point convergence zones in
the deep sea with negative velocity gradient. Acta Acust 2, 93-96.
[7] Wang G. 1995. On the study of turning-point convergence-zones formed by
sound reflection from the sea bottom in deep ocean. Master's thesis. Institute
of Acoustics, Chinese Academy of Sciences, Beijing, China.
convergence zone are smaller than those of the first convergence
zone, and the seafloor reflection loss for the rays with smaller
glancing angles is smaller, which causes a higher gain in the
second convergence zone. Some rays arrive at the range of 51
km for the receiver depth of 145m, which is refracted by the
water and forms a relatively high acoustic intensity region. But
those refracted rays cannot arrive at the receiver depth of 85 m
because the sound speed at 85 m is much greater than that near
the bottom.
[8] Fan PQ, Da LL, Li YY. 2013. The research of reflected convergence zones range
computing method in deep ocean. Tech. Acoust 32(6), 71-72
Comparing the ray traces for two different depths in Fig. 6,
the existence of the seamount contributes to the formation of the
seafloor reflection convergence zone in advance. Fig. 7 shows the
eigenrays and arrival structure at different receiver depths (85 m,
1008 m, and 3021 m) in the first reflection convergence zone (20
km). We find that the range of the seafloor reflection area
becomes larger as the receiver depth increases, and arrival
structures tend to become more complicated.
[9] Li W, Li ZL, Zhang RH. 2015. The effects of seamounts on sound propagation
in deep water. Chin Phys Lett 32(6), 103-106.
[10 Hu ZG, Li ZL, Zhang RH, Ren Y, Qin JX, He L. 2016 Sound propagation in
]
deep water with a sloping bottom. Acta Phys. Sin. 65(1), 221-229
[11 Qin JX, Zhang RH, Luo WY, Wu LX, Jiang L, Zhang B. 2014. Two-dimensional
sound propagation over a continental slope. Acta Acust 39(2) 145-153.
[12 Li Z, Li F. 2010. Geoacoustic inversion for sediments in the South China Sea
based on a hybrid inversion scheme. Chin J Ocean Limnol, 28(5),990-995.
[13 Jensen F, Kuperman W, Porter M, and Schmidt H. 2011 Computational Ocean
Acoustics (2nd. ed.). Springer, Berlin.
]
]
]
4 CONCLUSIONS
In April 2018, a propagation experiment was conducted in the
South China Sea, with a towed sound source and VLA. The
observed phenomenon is quite different from the convergence
phenomenon in the typical deep water environment. Numerical
analysis based on the parabolic equations combined with ray
theory was carried out to explain the formation mechanism of
the seafloor reflection convergence zone in deep water with a
complex seafloor environment. The experimental and numerical
results show that changes in seabed topography greatly
influence the formation and propagation characteristics of the
seafloor reflection convergence zone within the range of the
direct-arrival sound area. As the sea depth becomes gradually
shallower with increasing distance, the convergence zone under
the SOFAR channel is destroyed. Two obvious seafloor reflection
convergence structures are observed at distances of 20 km and
40 km, in which the gain is up to 10 dB. Some high sound
intensity areas are formed in the shadow zone due to the
reflection of the sea floor or the refraction of seawater. When the
source and receiver are located at the same depth, the gain of the
second convergence zone is higher than that of the first
convergence zone, which is caused by the decrease in the bottom
reflection energy loss and the increase in the number of arriving
rays. In the first reflection convergence zone, as the receiver
depth increases, the multipath effect is more obvious. The results
are meaningful for SONAR performance analysis.
ACKNOWLEDGMENTS
e authors thank all the staff for participating in the
experiment conducted in South China Sea in 2018.
is project is supported by the National Natural Science
Foundation of China (Grant Nos. 11434012, 41561144006,
11874061).
REFERENCES
[1] Hale F E. 1961. Long-Range Sound Propagation in the Deep Ocean. J. Acoust.
Soc. Am 33(4), 456-464
[2] Urick R J. 1965. Caustics and Convergence Zones in Deep-Water Sound
Transmission. J. Acoust. Soc. Am 38(2), 348-358.