共查询到20条相似文献,搜索用时 31 毫秒
1.
Ruitenbeek M. van Dillen A.J. de Groot F.M.F. Wachs I.E. Geus J.W. Koningsberger D.C. 《Topics in Catalysis》2000,10(3-4):241-254
The mechanism of catalytic oxidation reactions was studied using in situ X-ray absorption spectroscopy (XAFS) over a 17.5
wt% V2O5/Al2O3 catalyst, i.e., at reaction temperatures and in the presence of reactants. It was found that X-ray absorption near-edge structure
(XANES) is a powerful tool to study changes in the local environment and the oxidation state of the vanadium centres during
catalytic oxidation. At 623 K, the catalyst follows the associative mechanism in CO oxidation. XAFS revealed that the Mars–van
Krevelen mechanism is operative at 723 K for CO oxidation. The extended X-ray absorption fine structure (EXAFS) results showed
that the structure of the supported V2O5 phase consists of monomeric tetrahedral (Al–O)3–V=O units after dehydration in air at 623 K. However, the residuals of the EXAFS analysis indicate that an extra contribution
has to be accounted for. This contribution probably consists of polymeric vanadate species. The structure remains unchanged
during steady-state CO oxidation at 623 and 723 K. Furthermore, when oxygen was removed from the feed at 623 K, no changes
in the spectra occurred. However, when oxygen is removed from the feed at 723 K, reduction of the vanadium species was observed,
i.e., the vanadyl oxygen atom is removed. The V3+ ion subsequently migrates into the γ-Al2O3 lattice, where it is positioned at an Al3+ octahedral position. This migration process appears to be reversible; so the (Al–O)3–V=O units are thus restored by re-oxidation.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
2.
Martin Sterrer Thomas Berger O. Diwald Erich Knözinger Alain Allouche 《Topics in Catalysis》2007,46(1-2):111-119
The adsorption properties of oxygen radicals on the surface of polycrystalline oxides can provide relevant information about
the functionality of specific surface sites in oxidation catalysis. Using electron paramagnetic resonance spectroscopy, we
investigated O2 adsorption at MgO nanocrystal surfaces which were previously enriched with O− radicals i.e. trapped hole centers. On dehydroxylated particle surfaces, two ozonide radical types O
3
−
were isolated as adsorbates and the related energies for O2 adsorption were found to be 55 ± 5 kJ mol−1 and 100 ± 5 kJ mol−1. The respective adsorption sites are assigned to hole centers trapped on oxygen terminated corners and cation vancancies,
respectively.
In addition, O
3
−
ions were also employed as probes for electron trapping sites on partially hydroxylated sample surfaces. Five types of O− radicals emerge from surface colour centre bleaching with N2O, but only two of them adsorb O2 at room temperature. A connection between the well-characterized (H+)(e-) defect – an electron trapped in close vicinity of a nearby proton [Chiesa et al. J. Phys. Chem. B 109 (2005) 7314] – and
one ozonide type which exhibits significant magnetic coupling with an adjacent proton, was established on the basis of their
production parameter dependence. Although the g tensor of an O3
− species reflects the properties of the radical itself rather than the structure of the adsorption site, the related signatures
are proposed to serve also as spectroscopic fingerprints for catalytically relevant surface anion environments. 相似文献
3.
Indonesian Roto Middle subbituminous coal was gasified in a pilot-scale dry-feeding gasification system and the produced syngas
was purified with hot gas filtering and by low temperature desulfurization to the quality that can be utilized as a feedstock
for chemical conversion. Roto middle coal produced syngas that has a typical composition of 36–38% CO, 14–16% H2, and 5–8% CO2. Particulates in syngas were 99.8% removed by metal filters at the operating temperature condition of 200–250°C. Sulfur containing
compounds of H2S and COS in syngas were also desulfurized in the Fe chelate system to yield less than 0.5 ppm level. The full stream gasification
and syngas purifying system has been successfully operated and thus can provide clean syngas for the research on the conversion
of syngas to chemicals like DME and on the future IGFC using fuel cells.
This work was presented at the 6
th
Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006. 相似文献
4.
A. Messerer 《Carbon》2006,44(2):307-324
The reaction kinetics of the oxidation and gasification of four types of model and real diesel soot (light and heavy duty vehicle engine soot, graphite spark discharge soot, hexabenzocoronene) by nitrogen oxides and oxygen have been characterized for a wide range of conditions relevant for modern diesel engine exhaust and continuously regenerating particle trapping or filter systems (0-20% O2, 0-800 ppm NO2, 0-250 ppm NO, 0-8% H2O, 303-773 K, space velocities 1.3 × 104-5 × 105 h−1). Soot oxidation and NO2 adsorption experiments have been performed in a model catalytic system with temperature controlled flat bed reactors, novel aerosol particle deposition structures, and sensitive multicomponent gas analysis by FTIR spectroscopy. The experimental results have been analyzed and parameterized by means of a simple carbon mass-based pseudo-first-order rate equation, a shrinking core model, oxidant-specific rate coefficients, Langmuir-Hinshelwood formalisms (maximum rate coefficients and effective adsorption equilibrium constants), and Arrhenius equations (effective activation energies and pre-exponential factors), which allow to describe the rate of reaction as a function of carbon mass conversion, oxidant concentrations, and temperature. At temperatures up to 723 K the reaction was driven primarily by NO2 and enhanced by O2 and H2O. Within the technically relevant concentration range the reaction rates were nearly independent of O2 and H2O variations, while the NO2 concentration dependence followed a Langmuir-Hinshelwood mechanism (saturation above ∼200 ppm). Reaction stoichiometry (NO2 consumption, CO and CO2 formation) and rate coefficients indicate that the reactions of NO2 and O2 with soot proceed in parallel and are additive without significant non-linear interferences. The reactivity of the investigated diesel soot and model substances was positively correlated with their oxygen mass fraction and negatively correlated with their carbon mass fraction. 相似文献
5.
Ethanol steam reforming was studied at 673–823 K over Pt–Ni/δ-Al2O3. Results indicate that bimetallic catalyst is resistant to coke deposition at steam-to-carbon ratios as low as 1.5 and higher
ratios are beneficial for both ethanol conversion and hydrogen formation. About 773 K is the optimum since high H2 production rates are accompanied by low CO and CH4 production rates. A power-function rate expression obtained on the basis of intrinsic rates at 673 K gives reaction orders
of 1.25 (±0.05) and −0.215 (±0.015) for ethanol and steam, respectively; the apparent activation energy is calculated as 39.3
(±2) kJ mol−1 between 673 and 723 K. 相似文献
6.
《Fuel》2007,86(1-2):194-202
Experimental investigations of the influence of excess oxygen coefficient, H2O/coal mass ratio using high-temperature steam, mean mass diameter of pulverized coal and coal size fraction on basic characteristics of coal gasification were performed. Experiments were carried out on a laboratory scale (0.09 m i.d. × 1.5 m high) coal gasification apparatus with lignite type of coal. Influence of steam was realized through comparison of results obtained from experiments with (H2O/coal = 0.287 kg kg−1) and without steam addition (H2O/coal = 0.024 kg kg−1). High values of carbon conversion, obtained both for finely ground and for coarse pulverized coal points to the easiness of lignite gasification, i.e. to its high suitability for gasification. 相似文献
7.
Hanne Rönkkönen Pekka Simell Matti Reinikainen Outi Krause 《Topics in Catalysis》2009,52(8):1070-1078
The effect of sulfur on biomass gasification gas clean-up over ZrO2, Y2O3–ZrO2 and SiO2–ZrO2 catalysts was examined. Experiments were carried out at the temperature range of 600–900 °C with sulfur free and 100 ppm
H2S containing simulated gasification gas feeds. A mixture of toluene and naphthalene was used as a tar model compound. Results
revealed that the sulfur addition affected positively on the catalyst properties mainly at 600 and 700 °C: over Y2O3–ZrO2 and ZrO2 sulfur addition improved naphthalene and ammonia conversion. However, over SiO2–ZrO2 no clear effect with H2S addition was observed. The effect of sulfur addition on the catalyst properties was connected to the formation of SO2 from H2S when oxygen was available. The intensity of the sulfur effect increased with the Lewis basicity strength of the catalysts.
This indicates that the sulfur adsorption has a role in generating new type of active sites and/or plays role in changing
the redox properties of the zirconia. Since the biomass gasification gas contains usually significant amounts of H2S the sulfur tolerance of the zirconia based catalysts is a remarkable benefit. 相似文献
8.
Effect of metal oxide additives on the catalytic performance of Ga2O3–Al2O3 prepared by the sol–gel method for the selective reduction of NO with propene in the presence of oxygen was studied. Of several
metal oxide additives, the addition of In2O3 enhanced drastically the activity of Ga2O3–Al2O3 for NO reduction by propene in the presence of H2O. In addition, the activity of In2O3‐doped Ga2O3–Al2O3 catalyst was extremely intensified by the presence of H2O below 350°C. The promotional effect of H2O was interpreted by the suppression of undesirable propene oxidation and the removal of carbonaceous materials deposited
on the catalyst surface. We also found that close interaction of In2O3 and Ga2O3 is necessary for the enhancement of activity by H2O. A lot of hydrocarbons except methane and oxygenated compounds served as good reducing agents, among which propene and 2‐propanol
were the most efficient ones. In2O3‐doped Ga2O3–Al2O3 catalyst was capable of reducing NO into N2 quite efficiently in the presence of H2O at a very high space velocity.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
Daisuke Hirabayashi Takeshi Yoshikawa Kazuhiro Mochizuki Kenzi Suzuki Yoichi Sakai 《Catalysis Letters》2006,110(3-4):269-274
Several types of calcium ferrite base catalysts (Ca/Fe = 0.33–3) for propylene (C3H6) combustion were prepared. Calcium ferrite catalyst with brownmillerite crystal structure provided catalytic activity for
C3H6 combustion in the temperature range of 250–450 °C. The brownmillerite phase (Ca2Fe2O5) was responsible for the formation of oxygen adspecies (O
2
−
) in the surface layer below 450 °C. 相似文献
10.
Thapanon Settheeworrarit Chaveng Pakawatchai Santi Maensiri Jumras Limtrakul Apinpus Rujiwatra 《Journal of Inorganic and Organometallic Polymers and Materials》2006,16(3):231-239
Summary The inorganic–organic hybrid [VIV
4O10VV
2O4] (C6H14N2)·H2O polymeric framework was prepared under mild hydrothermal conditions from a mixture of DABCO and V2O5 in deionized water with a 1:1:450 mole ratio, at neutral pH. The reaction was carried out at 180 °C for 3 days under autogenous pressure yielding phase pure crystals product. The crystal structure was studied using both powder and single crystal X-ray crystallography, revealing the structure to be of the ({UuDd}:T*)α′ type in the SP+T class and Z-T subclass. The presence of the organic cation was confirmed by FT-IR spectrum and chemical composition analysis. The structure was thermally stable up to over 400 °C, and showed ferromagnetic character at room temperature with the maximum molar susceptibility of 8.26 × 10−3 emu/mol−1 at zero applied field. 相似文献
11.
Sieghard E. Wanke 《加拿大化工杂志》1973,51(4):454-458
The oxidation of propane, over a concentration range of 0.30 to 1.04 mole % in air was investigated over a commercial diesel exhaust catalyst consisting of CuO, Cr2O3 and Pd supported on Al2O3. The rate of reaction was correlated by a first order, irreversible rate function; the resulting pre-exponential factor and activation energy were 3.15 × 107 cc/g-sec and 21.3 kcal/gmole, respectively. At high temperatures the reaction rate became influenced by pore diffusion. A temperature of 675°K was required to obtain 50% propane conversion. It was concluded that this catayst is unsuitable for catalytic mufflers on diesel buses since the measured value of diesel exhaust temperatures at the cataytic muffler inlet is significantly less than 675°K. 相似文献
12.
A relatively simple and rapid micro-gasification test has been developed for measuring gasification reactivities of carbonaceous materials under conditions which are more or less representative of an entrained gasification process, such as the Shell coal gasification process. Coal particles of < 100 μm are heated within a few seconds to a predetermined temperature level of 1000–2000 °C, which is subsequently maintained. Gasification is carried out with either CO2 or H2O. It is shown that gasification reactivity increases with decreasing coal rank. The CO2 and H2O gasification reactions of lignite, bituminous coal and fluid petroleum coke are probably controlled by diffusion at temperatures 1300–1400 °C. Below these temperatures, the CO2 gasification reaction has an activation energy of about 100 kJ mol?1 for lignite and 220–230 kJ mol?1 for bituminous coals and fluid petroleum coke. The activation energies for H2O gasification are about 100 kJ mol?1 for lignite, 290–360 kJ mol?1 for bituminous coals and about 200 kJ mol?1 for fluid petroleum coke. Relative ranking of feedstocks with the micro-gasification test is in general agreement with 6 t/d plant results. 相似文献
13.
R. G. Aivazyan V. V. Azatyan V. I. Kalachev 《Combustion, Explosion, and Shock Waves》1999,35(1):65-69
The concentration limits for flame propagation in GeH4−O2 (air) mixtures are determined over a wide range of initial pressures (0.7–100 kPa) at room temperature. Flame propagation
is found to be of a chain-thermal character and excited intermediate particles are involved in the reactions which limit the
branching rate. The gas-phase reaction products (H2O2, H2O, and H2) are determined and its is shown that the relative yields of these components and the stoichiometry, as a whole, vary with
the composition of the initial gas mixture. Chemically induced decomposition of GeH4 by a branching-chain oxidation process for oxidation of the hydride by oxygen is observed.
Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 1, pp. 72–76, January–February 1999. 相似文献
14.
Seung Jong Lee Soung Hyoun Kim Kyoung Hoon Kang Young Don Yoo Yongseung Yun 《Korean Journal of Chemical Engineering》2007,24(6):1128-1132
The Korean pilot-scale gasification facility consists of a coal gasifier, hot gas filtering system, and acid gas removal (AGR)
system. The syngas stream from the coal gasification at the rate of 100–120 Nm3/hr included pollutants such as fly ash, H2S, COS, etc. The acid gas, such as H2S and COS, is removed in the AGR system before generating electricity by gas engine and producing chemicals like Di-methyl
Ether (DME) in the catalytic reactor. A hydrolysis system was installed to hydrolyze COS into H2S. The designed operation temperature and pressure of the COS hydrolysis system are 150 °C and 8 kg/cm2. After the hydrolysis system, COS was reduced below 1 ppm at the normal operating condition. The normal designed operation
temperature and pressure of the AGR system are below 40 °C and 8 kg/cm2. Fe-chelate was used as an absorbent. H2S was removed below 0.5 ppm in the AGR system when the maximum concentration of H2S was 900 ppm. A small scale COS adsorber was also installed and tested to remove COS below 0.5 ppm. COS was removed below
0.1 ppm after the COS adsorbents such as the activated carbon and ion exchange resin.
This work was presented at the 6
th
Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006. 相似文献
15.
Daisuke Hirabayashi Takeshi Yoshikawa Kazuhiro Mochizuki Kenzi Suzuki Yoichi Sakai 《Catalysis Letters》2006,110(1-2):155-160
Several types of calcium ferrite base catalysts (Ca/Fe = 0.33–3) for propylene (C3H6) combustion were prepared. Calcium ferrite catalyst with brownmillerite crystal structure provided catalytic activity for
C3H6 combustion in the temperature range of 250–450 °C. The brownmillerite phase (Ca2Fe2O5) was responsible for the formation of oxygen adspecies (O
2
−
) in the surface layer below 450 °C. 相似文献
16.
Hakan Erer Okan Zafer Ye?ilel Orhan Büyükgüng?r 《Journal of Inorganic and Organometallic Polymers and Materials》2010,20(4):774-782
Three M(II)-squarate complexes, [Co(sq)(H2O)(Nmim)4] (1), [Zn(μ1,3-sq)(H2O)2 (Nmim)2]
n
(2) and [Cd(μ1,3-sq)(H2O)2(Nmim)2]
n
(3) (sq = squarate, Nmim = N-methylimidazole) have been synthesized and characterized by elemental, spectral (IR and UV–Vis.) and thermal analyses. The
molecular structures of the complexes have been investigated by single crystal X-ray diffraction technique. The squarate ligand
acts as two different coordination modes as a monodentate (in 1) and bis(monodentate) (O
1–
O
3
) bridging ligand (in 2, 3). The Co(II) atom has a distorted octahedral geometry with the basal plane comprised of three nitrogen
atoms of Nmim ligands and a oxygen atom of squarate ligand. The axial position is occupied by a nitrogen atom of Nmim and
one aqua ligand. The crystallographic analysis reveals that the crystal structures of 2 and 3 are one-dimensional linear chain
polymers along the c and b axis, respectively. The configuration around each metal(II) ions are distorted octahedral geometry
with two nitrogen atoms of trans-Nmim, two aqua ligands and two oxygen atoms of squarate-O1,O3 ligand. These chains are held together by the C–H···π, π···π and hydrogen-bonding interactions, forming three-dimensional network. 相似文献
17.
Young-Chan Choi Tae-Jun Park Jae-Ho Kim Jae-Goo Lee Jae-Chang Hong Yong-Goo Kim 《Korean Journal of Chemical Engineering》2001,18(4):493-498
Experimental Studies of a 1 Ton/Day coal slurry feed type oxygen blown, entrained flow gasifier have been performed with the
slurry concentration and gasifier temperature at 65% and above 1,300 ‡C, respectively. The characteristics of ash fusion temperature
with addition of CaO as a flux were investigated to maintain the proper slag tapping condition in the range of reaction temperature.
As the flux addition increased, ash fusion temperature showed a eutectic effect with the eutectic at around 20–30% CaO. In
order to analyze the gasification characteristics, the effects of O2/coal feed ratio on the product gas composition, heating value, gasifier temperature and cold gas efficiency were evaluated.
From the results, it was shown in the case of Kideco coal that the cold gas efficiency was 44–60% and the heating value was
1,700-2,200 kcal/Nm3, while Drayton coal showed a cold gas efficiency of 55–62% and a heating value of 1,800-2,200 kcal/Nm3. In the case of Datong coal, the cold gas efficiency was 38–65%, and the heating value was 2,000-2,300 kcal/Nm3. Also, the results showed that the optimal operating condition of O2/coal ratio for the three different coals was 0.9.
Presented at the Int’/Symp. on Chem. Eng. (Cheju, Feb. 8–10, 2001), dedicated to Prof. H. S. Chun on the occasion of his retirement
from Korea University. 相似文献
18.
Wen Fu Yan Zhen Ma Shannon M. Mahurin Jian Jiao Edward W. Hagaman Steven H. Overbury Sheng Dai 《Catalysis Letters》2008,121(3-4):209-218
Au/Al2O3 · xH2O and Au/TiO2/Al2O3 · xH2O (x = 0–3) catalysts were prepared by assembling gold nanoparticles on neat and TiO2-modified Al2O3, AlOOH, and Al(OH)3 supports, and their catalytic activity in CO oxidation was tested either as synthesized or after on-line pretreatment in
O2–He at 500 °C. A promotional effect of TiO2 on the activity of gold catalysts was observed upon 500 °C-pretreatment. The catalyst stability as a function of time on
stream was tested in the absence or presence of H2, and physiochemical characterization applying BET, ICP-OES, XRD, TEM, and 27Al MAS NMR was conducted. 相似文献
19.
We measured the absolute rate constants for the hydrogen peroxide oxidation of two different octyl dimethyl amines in isopropanol/water
mixtures at 23°C. The amines were 1-octyl dimethyl amine (1) and 2-ethylhexyl dimethyl amine (2); their structures were analogous to those most often encountered in commercial alkyl dimethyl amine oxide production. The
observed first-order rate constants for the disappearance of amine across a range of H2O2 concentrations (0.5–8 M) indicated that the overall rate was first-order in amine and 3/2-order in H2O2. Calculations showed k
1=0.16 M−1h−1, k
2=0.046 M−1h−1, and k
1/k
2=3.5. The rates appeared to decrease with increasing steric hindrance around the nitrogen atom. We also investigated the effect
of water on the reaction rates. When [H2O]<∼4.5 M in isopropanol, the rates increased with increasing [H2O]; for [H2O]>∼4.5 M, the rates were insensitive to [H2O]. 相似文献
20.
Philip L. Walker Shiro Matsumoto Tamotsu Hanzawa Takatoshi Muira Ismail M.K. Ismail 《Fuel》1983,62(2):140-149
Calcium is the most important in-situ catalyst for gasification of US coal chars in O2, CO2 and H2O. It is a poor catalyst for gasification of chars by H2. Potassium and sodium added to low-rank coals by ion exchange and high-rank coals by impregnation are excellent catalysts for char gasification in O2, CO2 and H2O. Carbon monoxide inhibits catalysis of the CH2O reaction by calcium, potassium and sodium; H2 inhibits catalysis by calcium. Thus injection of synthesis gas into the gasifier will inhibit the CH2O reaction. Iron is not an important catalyst for the gasification of chars in O2, CO2 and H2O, because it is invariably in the oxidized state. Carbon monoxide disproportionates to deposit carbon from a dry synthesis gas mixture (3 vol H2 + 1 vol CO) over potassium-, sodium- and iron-loaded lignite char and a raw bituminous coal char, high in pyrite, at 1123 K and 0.1 MPa pressure. The carbon is highly reactive, with the injection of 2.7 kPa H2O to the synthesis gas resulting in net carbon gasification. The effect of traces of sulphur in the gas stream on catalysis of gasification or carbon-forming reactions by calcium, potassium, or sodium is not well understood at present. Traces of sulphur do, however, inhibit catalysis by iron. 相似文献