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New Method for Synthesis Nano Size γ-Al2O3 Catalyst for Dehydration of Methanol to Dimethyl Ether

DOI:10.7763/IJCEA.2012.V3.172
Authors:
Omid Rahmanpour at Petroleum University of Technology
Omid Rahmanpour
Ahmad Shariati at Petroleum University of Technology
Ahmad Shariati
Mohammad Reza Khosravi-Nikou at Petroleum University of Technology
Mohammad Reza Khosravi-Nikou
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Nowadays the importance of nano-particles and their uses in different industries have attracted many researches. The materials in nano-scale show different characteristics in comparison with their bulk state. Nano-materials have potential applications in optoelectronics, catalysis, and membranes. In this paper Nano-size porous γ-alumina was successfully synthesized by precipitation method under ultrasonic vibration mixing. Sonochemistry help the nano particles to synthesis regular form. The synthesized catalyst was characterized by SEM, XRD, BET, and TPD techniques. The effect of two most important operating conditions (i.e. Temperature and WHSV) on performance of this catalyst was investigated for dehydration of methanol to dimethyl ether (DME). The optimum operating condition was at temperature of 320 º C and WHSV of 15 h-1. Index Terms—Dimethyl ether (DME), γ-alumina catalyst, Sonochemistry, Nano sized catalyst, operating conditions.
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Abstract—Nowadays the importance of nano-particles and
their uses in different industries have attracted many
researches. The materials in nano-scale show different
characteristics in comparison with their bulk state.
Nano-materials have potential applications in optoelectronics,
catalysis, and membranes. In this paper Nano-size porous
γ-alumina was successfully synthesized by precipitation method
under ultrasonic vibration mixing. Sonochemistry help the
nano particles to synthesis regular form. The synthesized
catalyst was characterized by SEM, XRD, BET, and TPD
techniques. The effect of two most important operating
conditions (i.e. Temperature and WHSV) on performance of
this catalyst was investigated for dehydration of methanol to
dimethyl ether (DME). The optimum operating condition was at
temperature of 320 ºC and WHSV of 15 h-1.
Index Terms—Dimethyl ether (DME), γ-alumina catalyst,
Sonochemistry, Nano sized catalyst, operating conditions.
I. INTRODUCTION
Dimethyl ether (DME) is an important chemical for the
production of gasoline, ethylene, aromatics and other
chemicals [1]-[5]. Its applications as a fuel or a fuel additive
for vehicles and family cooking have been studied [6], [7]. In
view of the environmental protection, the substitution of
DME for Freon as an aerosol spray and a refrigerant is being
considered [8]-[10]. From the literatures, it can be concluded,
almost all commercial DME were produced by the
dehydration of methanol using different solid-acid catalysts
such as zeolites, sillica–alumina, alumina, Al2O3–B2O3, etc.
by following reaction (Equation (1)): [11].
-1
3 3 3 2
2 C H O H C H O C H + H O (-22 .6 k j m o l )
(1)
In recent years, increasing attention has been focused on
the development of nano-sized alumina powders for
advanced engineering materials [12], [13]. Conventional
processes for synthesizing ceramic nano powder involve
mechanical synthesis, vapor phase reaction, precipitation,
and combustion and sol–gel methods [14]-16]. Catalytic
dehydration of methanol over solid-acid catalysts offers a
potential process for dimethyl ether synthesis. Several
catalysts having activity and selectivity for the catalytic
conversion of methanol to DME are known, the so called
acidic dehydration catalysts [17]-[19]. Commercially γ-Al2O3
is used to a large extent for this reaction at a temperature
range of 270 to 380 ºC.
Manuscript received January 25, 2012; revised March 23, 2012.
The authors are with the Petroleum University of Technology, Ahwaz,
Iran (e-mail: orahmanpour@gmail.com; Shariati@put.ac.ir;
mr.khosravi@put.ac.ir).
The sonochemical synthesis of nanophase materials has
the advantage that various classes of materials can be
generated simply by changing the reaction medium. So it is
worthwhile to overview the different applications, where
cavitations can be used efficient. Preparation of metal and
metal oxide nanoparticles immobilized on various materials
is one of the key researches in nanoscience and
nanotechnology, because an excellent synergy and
Bifunctional effect would be expected [20]. It is well
known that the alternative method for generating stabilized
metal nanoparticles involves synthesizing them in or on
nanoporous supports, which help define particle size and
serve to immobilize the resulting particles [21].
The aim of the present study is to find effect of
sonochemistry in particles structure and the optimum
operating condition of new nano size synthesized γ-Al2O3.
Dehydration of methanol to dimethyl ether was carried out in
the fixed bed micro reactor and the structure of solid-acid
catalysts was also studied by SEM, XRD, BET, and TPD
techniques.
II. EXPERIMENTAL
A. Catalyst Synthesis
Aluminum nitrate {Al(NO3)3-9H2O, 99.5%}(Merck),
Ammonia {NH4OH, 32%} (Merck) and deionized water
were used as starting chemicals. A transparent gel-like
precursor containing Al cations is precipitated at pH ~7.5–8.5
when ammonia (%3.2) and Al nitrate salt solutions (0.26 M)
are mixed together in 400 ml deionized water. The solution
was mixing under ultrasonic vibration and maintained at a
temperature 70 ºC for 2 h. The following chemical reactions
occurred during preparation:
3
3 3 4 4 3
Al(NO ) +3NH OH Al(OH) +3NH NO
(2)
32
Al(OH) AlOOH +H O
(3)
2 3 2
AlOOH Al O +H O
(4)
The precipitate obtained by reaction (2) was aged at a
temperature ~70 ºC helped to homogenize the gel due. The
ageing step is essential to convert Al (OH)3 to crystalline
boehmite precursor by reaction (3). The precipitate is further
processed by washing in deionized water. Then was added
300 ml ethanol to the filtered Al(OH)3 under ultrasonic
vibration for 1 h then dried in oven at ~70 ºC for 18 h.
γ -Al2O3 is produced by calcinations of dried boehmite
(AlOOH) at 550 ºC for 4 h by reaction (4).
New Method for Synthesis Nano Size γ-Al2O3 Catalyst for
Dehydration of Methanol to Dimethyl Ether
Omid Rahmanpour, Ahmad Shariati, and Mohammad Reza Khosravi Nikou
125
International
Journal of Chemical Engineering and Applications, Vol. 3, No. 2, April 2012
B. Characterization Tests of Catalyst
The crystallity of catalyst, measured by PW1840 (40 Kv,
30 Ma) X-Ray diffract meter using Cu Kα radiation source
(λ=1.54056 A°) through the range of 2θ=5°C to 90°. BET
surface area, total pore volume and average pore diameter
were determined by N2 adsorption-desorption isotherm at 77
K using NOVA 2000instrument (Quantachrome, USA). The
pore volumes were determined at a relative pressure (P/P0) of
0.99. Prior to the adsorption-desorption measurements, the
sample was degassed at 200° C in N2 flow for 3h to remove
the physically adsorbed water immediately before analysis.
The pore size distribution of the catalyst was verified by a
BJH (Barett-Joyner- Helenda) model from the adsorption
branch of the nitrogen isotherms. The acidity of the sample
was measured by temperature programmed desorption of
ammonia using BEL- CAT (type A, Japan) instrument with a
conventional flow apparatus. A 0.1 g sample was initially
degassed at 500 °C under The flow rate of 50 ml/min for 60
min at a heating rate of 10°C/min then; the sample was
cooled to 100 °C and saturated with 5% NH3/He for 30 min.
The sample was then purged with the flow for 15 min to
remove weakly and physically adsorbed NH3 on the surface
of the catalyst. After that, the sample was heated at of 10
°C/min under the flow of the carrier gas (30 ml/min) from
100 °C to 700 °C and the amount of ammonia in effluent was
measured via thermal conductivity detector (TCD).
Fig. 1. Schematic view of experimental setup
C. Methanol Dehydration Process
A schematic representation of the experimental set-up is
shown in figure 1.Vapor phase dehydration of methanol to
dimethyl ether was carried out in the fixed bed micro reactor
(stainless steel, O.D=0.75 in, length=10 in). Liquid methanol
(grade AA, 99.9% purity) was injected to the pre heater by
means of HPLC (metering) pump (working range of 0.01 to
9.99 ml/min), then evaporated in the pre heater that kept at
the constant temperature of 300 ºC. After pre-heater, the
vaporized methanol is conducted to the fix bed flow reactor.
Reactor consists of two heating zones. First zone is to raise
the feed temperature to the desirable level and the other one
to maintain the reactor surrounding at the proper temperature
to minimize heat losses and simulate an adiabatic reactor.
The down line effluent was constantly kept at temperatures
above 160°
С, to prevent condensation of the reactant and
products. The reaction temperature is changed between 270º
C
to 380º
C and for each test 1 gr of the catalyst was loaded to
the reactor. Methanol was pumped to the pre-heater before
entering the reactor. The effluent of the reactor was analyzed
with a gas chromatograph (ACME 6100, Younglin
Instrument Korea) which is equipped with nonpolar capillary
column TRB-5(95% dimethyl-5% diphenyl polsiloxane) and
a flame ionization detector (FID).
III. RESULT AND DISCUSSION
A. Phase Analysis
The XRD patterns of the new nano size synthesized
γ-alumina are shown in Figure 2 that the three peaks at
2Ө=37.8○, 2Ө=45.7○ and 2Ө=66.9○ are assigned to (311), (4
0 0) and (4 4 0) reflections of γ-Al2O3. The crystallite sizes
were also calculated using the Scherrer (Eq. (5)):
cos
K
D

(5)
where, K is a constant generally taken as ~ 0.9, λ is the
wavelength of the incident radiation, β is the full width of
diffraction peak at half maximum intensity (FWHM) and θ is
the diffraction angle. The calculated crystallite sizes were
found to be in the range of 1-2 nm for nano size synthesized
γ-Alumina. Crystal structures were very close in synthesized
γ-Alumina catalyst that can be good effect in reaction. These
close crystal layers was made under ultrasonic waves.
Fig. 2. XRD patterns of synthesized γ-Al2O3
Fig. 3. Scan electron microscopy images of γ-Al2O3 catalyst
B. SEM
Fig. 3 shows the SEM image of the synthesized γ-Al2O3
sample after calcination. The crystals of the sample reached a
porous and spongy form, and the morphology of the crystals
were regular pores and present enough volume for reaction
and increase surface area. SEM of synthesized catalyst shows
low bulk density and high bulk pores which these structures
c)
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International Journal of Chemical Engineering and Applications, Vol. 3, No. 2, April 2012
made from evaporation of ethanol under ultrasonic vibration
mixing.
C. Acidity Measurements
The TPD spectra Fig. 4 of the synthesized γ-alumina
catalyst contain an intense peak in 160°C and 320 this peak
reduced slightly in the temperature range of 200–500 ºC that
corresponds weak to medium acid sites which is attributable
to the removal of adsorbed NH3 on the catalyst surface with
low strengths and the temperature of the desorption maxima
and the acid content of the catalysts are summarized in Table
I. TCD signal shows the synthesized catalyst have medium
acid site and this peak was presented in 320 °C and strong
acid site was not seen in this signal. TCD signal shows the
synthesized catalyst have medium acid site and this peak was
presented in 320 °C and strong acid site was not seen in this
signal.
TABLE I: SUMMARY OF ACIDIC SITE MEASURED BY NH3-TPD OF
SYNTHESIZED Γ-AL2O3 CATALYST
Weak
acid sites (mmol/g)
Total
Nano size γ-Al2O3
0.883
1.07
Temperature (ºC)
170
Fig. 4. NH3-TPD profile of γ-alumina
Fig. 5. N2 adsorption and desorption isotherms of γ-Al2O3 catalyst
D. N2 Adsorption-Desorption (BET)
The N2 adsorption and desorption isotherm remains type
IV, as is seen from Fig. 5. According to IUPAC classification
[22], the hysterics loop (type H1) occurs at a relative pressure
range of p/p0 = 0.6–0.95, indicating a broad pore size
distribution with uniform size and shape. As it can be seen,
synthesized nano γ-Al2O3 catalyst show a mesoporous
structure with different pore size distributions. The surface
area, pore size distribution and pore volume data obtained for
nano size synthesized γ-Al2O3 catalyst using ammonia agent
obtained by its calcination at 550 °C for 4 h in air are
tabulated in Table II. The BJH pore size distribution curves
are reproduced in Fig. 6. The pore size distribution is wide
and pore size lies between 1 and 20 nm.
Fig. 6. BJH pore size distribution of γ-Al2O3 catalyst
TABLE II: SUMMARY OF SURFACE AREA AND PORE VOLUME OF
SYNTHESIZED Γ-AL2O3 CATALYST
Surface area
(m2 g-1)
Average pore
diameter (nm)
Pore volume
(cm3 g-1)
Nano size
γ-Al2O3
216
9.646
0.5212
E. Catalytic Activity
The reaction performance results, including methanol
conversion calculated according to (Eq. (6)) [23].
initial MeOH final MeOH final DME
MeOH
initial MeOH
n - (n +2n )
X %= 100
n
(6)
The conversion variation trend with temperature was
investigated for different weight hourly space velocities at
range of 15 to 45 hr-1 at a constant pressure of 100 kPa gauge.
As depicted in figure 7 the trend is nearly similar for different
WHSVs but the amount of methanol conversion is reduced
with increasing space velocity in the temperature range of
270 to 380 °C for synthesized γ-Alumina.
Fig. 7. Catalyst bed temperature profile over different weight hourly space
velocity
It is clear from the figure that the system reached to the
equilibrium conversion at temperature range of 310 to 340 °C
under WHSV of 15 hr-1 and by increasing WHSV, the
reaction could not meet the equilibrium conditions. The
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International Journal of Chemical Engineering and Applications, Vol. 3, No. 2, April 2012
highest conversion was resulted in temperature range of
310-340 °C. Equilibrium conversion shows acceptable result
for this nano sized catalyst.
IV. CONCLUSION
Nano-sized porous γ-Al2O3 was successfully synthesized
via a series of synthetic pathways. The calculated crystallite
sizes were 1-2 nm with surface area ~216 m2/g, average pore
diameter of 9.646 nm, and pore volume ~ 0.5212cm3/g.
According to the hysterics loop (type H1) the synthesized
nano γ-Al2O3 catalyst show a mesoporous structure.
The results showed the maximum conversion of reaction
was observed at a temperatures range of 310 to 340 °C and
WHSV of 15 hr-1 with methanol conversion of 84% for
synthesized. All of results showed that sonochemistry is a
new method for synthesized catalysts and have competitive
potential with commercial catalysts. Sonochemistry can play
major role in formation of particles and crystals structure.
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Omid Rahmanpour was born in Marand on March
14th 1985. He received her bachelor degree in
Chemical Engineering from Babol Noshirvani
University of Technology, Mazandaran, Iran, in 2009.
Now, he is studying for MS degree in Gas Engineering
Department, Petroleum University of Technology,
Ahwaz, Iran. Currently his main efforts are taken to
synthesis of γ-Al2O3/CNTs catalyst for dehydration of
methanol and other acidic catalysts.
128
International Journal of Chemical Engineering and Applications, Vol. 3, No. 2, April 2012
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  • Oct 2017
The extent of removal of heavy metal ions cadmium Cd(II) and silver Ag(I) in single and binary system by adsorption on alumina has been investigated. Adsorption experiments were performed in batch technique from synthetic solutions using high purity nano activated alumina prepared in laboratory as adsorbent for heavy metals remove. Several experimental parameters that affect the extent of adsorption of the metal ions of interest have been investigated such as adsorbent dosage, concentration of the adsorbate, contact time, agitation speed and pH of the system under study. The equilibrium nature of the adsorption of the metal ions at different concentrations has been followed by Freundlich and Langmuir adsorption isotherms. Correlation coefficients (2) derived from these plots are (0.965) for cadmium Cd(II) and (0.966) for silver Ag(I). This work proposes a cost-effective method for the efficient removal of Cd(II) and Ag(I) from aqueous solutions. The conditions required for effective removal have been optimized.
... Deepak et al., synthesized Al 2 O 3 NPs via electrochemical method and evaluated photo catalytic degradation of malachite green (MG) dye with double adsorption process to check the percentage of adsorption [10]. Omid Rahmanpour et al., synthesized Al 2 O 3 by precipitation method under ultrasonic vibration mixing [11]. ...
Photocatalytic and electrochemical sensor for direct detection of paracetamol comprising γ-aluminium oxide nanoparticles synthesized via sonochemical route
Article
Full-text available
  • Jan 2020
Aluminium oxide nano particles (Al2O3 NPs) were synthesized using simple but effective probe sonication method. The structural, photocatalytic, and electrochemical sensor properties of Al2O3 NPs were investigated by powder X-ray Powder Diffraction (PXRD), Scanning electron microscopy (SEM), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), UV–vis Spectroscopy, and Electrochemical analyzer potentiostat. The impact of sonication on the physical properties of Al2O3 NPs was elucidated. From the powder X-ray diffraction (PXRD) studies the material exhibited a face centered cubic structure and γ phase with crystallite size in the range from 6 to 16 nm. The semiconductor behavior has been confirmed from the study of energy band gap via diffuse reflectance spectroscopy (DRS). The conductivity of the samples was studied by cyclic voltammetry (CV) and Electrochemical Impedance spectroscopy (EIS) in 0.1 M HCl and 0.1 M NaOH as aqueous electrolytes. The electrode exhibited specific capacitance of 0.866 F g-1 and 0.488 F g-1 at scan rate 10 mV/s in acidic and alkaline electrolytes, respectively. EIS measurements showed reduction in the charge transfer resistance in acidic electrolyte. Modified carbon paste electrode employing γ-Al2O3 NPs has sensed Paracetamol in both acidic and alkaline electrolytes. The electrode displayed high sensitivity for paracetamol detection under varying concentrations. A linear calibration curve for paracetamol detection was obtained with a limit of detection (LOD) 2.3602 × 10⁻³ mol/L. These results confirm that the γ-Al2O3 NPs are promising electrode material for sensing paracetamol with high electrode reversibility and as an excellent photocatalyst.
Effect of catalytic hydrodynamics over microagglomerates of Mn2O3 and PdO supported on γ-χ-Al2O3 for dimethyl ether production
Article
In this study, we synthesize microagglomerates of PdO and Mn2O3 supported over γ-χ-Al2O3 via the impregnation method, for their application in the methanol dehydration to dimethyl ether, under reaction conditions of 240 °C to 290 °C and 1 pressure atm. It was determined by XRD, TEM and XPS that when PdO (Pd²⁺) is present at 3% by weight over γ-χ-Al2O3, conversions of 57% and selectiveness of 100% towards dimethyl ether can be reached at 250 °C due to at a higher density of moderate acid sites (a moderate acidity difference of 0.5276 mmol/g with respect to Mn2O3/γ-χ-Al2O3). Additionally, our theoretical and experimental results between the correlation of the textural and morphological properties of the PdO/γ-χ-Al2O3 and Mn2O3/γ-χ-Al2O3 materials with the hydrodynamics and kinetics of the reaction, showed that when PdO agglomerates with a size of ∼79.2 µm are used, higher internal mass transfer rates predominate when compared to using Mn2O3 agglomerates of a larger size, ∼124 µm. Finally, the relative stability shown by the PdO/γ-χ-Al2O3 catalyst during 10 h of reaction was correlated with its low apparent activation energy (111 kJ/mol) and with its inactive phase change of PdO measured by XPS after the reaction.
Fabrication of CoNiMo/γ-Al2O3 from waste aluminum foil to convert waste lube oil to hydrotreated oil
Article
Full-text available
  • Sep 2021
Because of the heavy metal content and other toxic chemicals, used lubricating oil remains one of the most serious environmental concerns. The target of this work is the synthesis of γ-Al2O3 from waste aluminum foil and re-refining waste lubricating oils using solvent extraction pursued by hydrotreatment. The trimetallic CoNiMo/γ-Al2O3 catalyst was prepared via a co-impregnation method. The support and tri-metallic supported alumina are characterized by N2 adsorption–desorption techniques, X-ray diffraction (XRD), Raman spectroscopy, HRTEM, and EDX. The catalyst was evaluated in the hydrotreating of extracted waste lubricating oils. The results confirmed that the solvent to oil ratio of 3 gave the higher performance with the highest percent of sludge elimination at room temperature. Hydrotreating of extracted lube oil was investigated to determine the effect of variables such as temperature, pressure, liquid hour space velocity, and hydrogen to oil feed ratio. The results indicated that the optimum conditions are (temperature 400 °C, Pressure 60 bar, 0.75 h⁻¹ LHSV). The results showed improvement of the hydrotreated waste lubricating oils properties by decreasing the refractive index from 1.480 to 1.460, the total acid number decreased from 8.164 to 0. 459, the Viscosity Index increase from 78 to 129, and the Sulfur content decreased from 6752 ppm to 543 ppm.
Quantitative evaluation of coupling effects of pore structures and metal loadings on catalytic hydrogenation of tar model reactants over sulfided NiMo/γ-Al2O3 catalysts: Role of segmented catalytic active phase volumes
Article
Currently, there is no easy-to-use method for determination of catalytic active phase volume (APV). Therefore, the current study designed a calculation method by defining APV (α → β nm) as the difference in pore volume (α → β nm) between the catalyst support and the catalyst (without taking fine structure of the catalyst into account for simplicity). This new method was successfully validated through regression analysis of 15 catalysts (R2 > 0.97). Moreover, the couplings of pore structures and metal loadings on catalytic hydrogenation of reactants were quantitatively assessed based on the calculation of APV. The promotion or inhibition effect of one compound on hydrogenation of other compounds may also vary with the couplings of metal loading and pore structure, but it wasn't taken into account in this study. The key segmented APVs (SAPVs) in various pore sections for hydroconversion of reactants were determined using a stepwise linear regression model at the 95% confidence level. The findings showed that the SAPVs in the pores with a pore size of 5–10 nm and 10–20 nm were responsible for hydroconversion of quinoline and most of the aromatic compounds, respectively. The predicted key SAPVs were consistent with the experimental observations, which demonstrated availability of the proposed APV.
Impact of Molybdenum Doping on the Structural, Optical and Dielectrical Properties of α-Al2-x MoxO3
Article
  • Apr 2021
The effects of Molybdenum (Mo) doping on the structural, optical, and electrical properties of alumina α-Al2−xMoxO3, (x = 0.02–0.14) synthesized via solid-state reaction method have been studied. X-ray diffraction (XRD) analysis confirms of single-phase hexagonal corundum structure in the range 0.06–0.14. The influence of Mo doping on the structural parameters was estimated from XRD data by applying the Rietveld profile fitting method and Fourier-transform infrared spectroscopy. XRD results revealed that replacing Al with Mo does not affect the unit cell dimensions owing to that Mo occupy the vacant sites available in the crystal structure. The electron density map revealed strong positive peaks corresponding to the position occupied by (Al/Mo) and the intensity of these peaks increases with increasing Mo doping. Optical properties revealed that the energy bandgaps (Eg) increase with increasing MoO3, due to the difference in the ionic radius of Al+3 and Mo+3. The dielectric properties indicated that the values of ε′ and tan δ increased as molybdenum concentration increased as a result of the free charges build-up at the interfaces. It was found that tanδ peak lies in the region where DC-conductivity dominates which is a clear indication of the contribution of ionic conduction to the dielectric loss.
Slurry Phase Synthesis and Utilization of Dimethyl Ether
Article
Full-text available
  • Dec 2001
Economics and Industry). The technology was imple- mented jointly by the CCUJ (Center for Coal Utilization, Japan), Taiheiyo Coal Mining Co., Ltd., and Sumitomo Metal Industries, Ltd. at a plant constructed at the Tai- heiyo Coal Mining site in Kushiro City. Construction be- gan in the summer of 1999, and operation and research commenced approximately 18 months later. A total of six continuous trials have been conducted, and operation of the plant has proven to be extremely stable, with the long- est continuous period of operation being two months. A total of approximately 400 tons of high-purity DME has been produced during these trials.
Coproduction of Methanol and Dimethyl Ether from Biomass-Derived Syngas on a Cu−ZnO−Al 2 O 3 /γ-Al 2 O 3 Hybrid Catalyst
Article
  • Jan 2008
The coproduction of methanol (MeOH) and dimethyl ether (DME) from biomass-derived synthesis gas on the coprecipitated Cu−ZnO−Al2O3/γ-Al2O3 hybrid catalysts has been investigated to overcome the equilibrium conversion of CO on the MeOH only synthetic reaction at the H2-decificient condition. Two different types of γ-Al2O3 were employed as the solid-acid component of hybrid catalyst: one prepared by a precipitation method and the other prepared by a sol–gel method. Several hybrid catalysts were prepared by the coprecipitation method in the slurry of γ-Al2O3 with the variation in the weight ratio of MeOH synthesis catalyst (Cu−ZnO−Al2O3) to solid-acid catalyst (γ-Al2O3) as well as by changing aging time during synthesis. The catalytic activity results revealed that the best yield of MeOH and DME with concomitant decrease in the CO2 formation was obtained on the hybrid catalyst containing γ-Al2O3 prepared by the sol–gel method with an aging time of 6 h. The hybrid catalysts were characterized by using the BET surface area measurements, NH3 temperature programmed desorption (NH3-TPD), scanning electron microscopy (SEM), temperature programmed reduction (TPR), and X-ray diffraction (XRD) methods. The observed catalytic properties were related to the surface area of Cu metal, dispersion of Cu−ZnO−Al2O3 particles, and reducibility and acidity of hybrid catalysts. The enhanced catalytic activity with low selectivity to CO2 is attributed to the facile reducibility of well-dispersed copper oxides at low temperatures and also to the benign acid strength of the hybrid catalysts.
The effect of micro and nano particle sizes of H-ZSM-5 on the selectivity of MTP reaction
Article
The effect of particle size on the catalytic activity of H-ZSM-5 zeolite in the methanol to propylene (MTP) reaction was investigated in a fixed-bed flow reactor under the operating conditions of T=460°C, P=1atm, and WHSV=1h−1. Nano and micro size H-ZSM-5 were prepared by reflux and hydrothermal crystallization methods, respectively. The nano and micro H-ZSM-5 were characterized using XRD, NH3–TPD, BET area, SEM and ICP–AES analytical techniques. Nano size H-ZSM-5 showed higher activity and stability compared to the micro size H-ZSM-5. Nano H-ZSM-5 was also found to have higher selectivity to propylene than the micro size H-ZSM-5.
The potential of di-methyl ether (DME) as an alternative fuel for compression-ignition engines: A review
Article
This paper reviews the properties and application of di-methyl ether (DME) as a candidate fuel for compression-ignition engines. DME is produced by the conversion of various feedstock such as natural gas, coal, oil residues and bio-mass. To determine the technical feasibility of DME, the review compares its key properties with those of diesel fuel that are relevant to this application. DME’s diesel engine-compatible properties are its high cetane number and low auto-ignition temperature. In addition, its simple chemical structure and high oxygen content result in soot-free combustion in engines. Fuel injection of DME can be achieved through both conventional mechanical and current common-rail systems but requires slight modification of the standard system to prevent corrosion and overcome low lubricity. The spray characteristics of DME enable its application to compression-ignition engines despite some differences in its properties such as easier evaporation and lower density. Overall, the low particulate matter production of DME provides adequate justification for its consideration as a candidate fuel in compression-ignition engines. Recent research and development shows comparable output performance to a diesel fuel led engine but with lower particulate emissions. NOx emissions from DME-fuelled engines can meet future regulations with high exhaust gas recirculation in combination with a lean NOx trap. Although more development work has focused on medium or heavy-duty engines, this paper provides a comprehensive review of the technical feasibility of DME as a candidate fuel for environmentally-friendly compression-ignition engines independent of size or application.
Review: Dehydration Catalysts for the Methanol/Dimethyl Ether Reaction
Article
Catalysts for the methanol/dimethyl ether reaction are reviewed with particular emphasis on the acid/base properties of the catalysts. The focus is on temperatues less than around 300°C and atmospheric pressure conditions, which correspond to potential automotive applications. Mechanisms including both dual site (acid/base) Langmiur-Hinshelwood and single site Rideal-Eley mechanisms have been postulated, with both Bronsted and Lewis acid sites involved in the dehydration reaction. Temperatures higher than about 300°C, as well as a strong surface acidity, tend to promote the further dehydration of DME to form C2-Q5 olefins and eventually hydrocarbon products in a series type reaction sequence. Methods exist, particularly in zeolites, to control the strength and type of surface acidity, and therefore the selectivity to DME.
DME synthesis from synthesis gas on the admixed catalysts of Cu/ZnO/Al2O3 and ZSM-5
Article
Na-ZSM-5 and H-ZSM-5 catalysts with three different Si/Al ratios were prepared to investigate methanol dehydration and direct DME synthesis. The acid strength of ZSM-5 increased with a decrease in the Si/Al ratios and methanol dehydration rate was maximized on H-ZSM-5(30) with the highest acid strength. The direct DME synthesis was conducted on the admixed catalysts of Cu/ZnO/Al2O3 and ZSM-5. The optimized solid acid composition on the admixed catalysts with Na-ZSM-5 for maximizing CO conversion was lowered with a decrease in the Si/Al ratio. The experimental results show that the overall DME synthesis rate can be determined by the intrinsic methanol synthesis rate on the admixed catalysts with the compositions higher than the optimized one and the overall rate can be controlled by the methanol dehydration rate on the admixed catalysts with the composition lower than the optimized one.
Sonochemical synthesis of gold nanoparticles on chitosan
Article
Au nanoparticles deposited on chitosan were readily prepared from aqueous solution of NaAuCl4 containing chitosan powder by the reaction with sonochemically formed reducing species. The average size of the formed Au particles was measured to be 22 nm with a relatively narrow size distribution, although there was no specific stabilizer for Au nanoparticles.
Concentrations of toxic heavy metals in ambient particulate matter in an industrial area of northeastern China
Article
  • Jun 2008
This paper investigates concentrations of various heavy metals in ambient particulate matter (PM) and provide evidence for prevention from air pollution. The concentrations of heavy metal components in the PM were determined by inductively coupled plasma/Mass spectrometry (ICP/MS) from September 2000 to August 2002 in a northeast industrial city in China. Concentrations of Cd, Mn, Pb, Ni, Cr and As in the PM were 9.3, 461.9, 588.7, 69.5, 205.7 and 57.4 ng/m3 in the industrial area, and 5.7, 245.5, 305.0, 31.4, 58.8 and 32.5 ng/m3 in the main road, respectively. Concentrations of these heavy metals except Cd were significantly higher in the industrial area and main road than those in the suburban area (P < 0.05 or P < 0.01). The change curves of the six heavy metal concentrations show their concentrations increased in the winter and spring, but decreased in the summer and autumn. The results indicate that concentrations of the metals in the PM are relatively high in the industrial area and main road.