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1.
CoMo/Al2O3 catalysts were prepared by impregnating Cobalt nitrate solution into oxidic or sulfided Mo/Al2O3. The properties of CoMo/Al2O3 catalysts were characterized by XRD, TPS, oxygen chemisorption and ESR. Catalytic activity of CoMo/Al2O3 catalyst was evaluated by thiophene HDS as a probe reaction. When CoMo/Al2O3 catalyst was prepared by impregnating Cobalt nitrate solution into sulfided Mo/Al2O3, the interaction between Mo and alumina became weaker and the formation of synergic phase was facilitated. These structural
changes may explain higher HDS activity of CoMo/Al2O3 catalyst prepared by impregnating Cobalt nitrate solution into sulfided Mo/Al2O3. 相似文献
2.
MoO3/Al2O3 catalysts with eggshell Mo concentration profiles were prepared by reaction of Al2O3 extrudates or balls with slurry of MoO3 in water. The Mo concentration wave penetrating Al2O3 particles during this slurry impregnation was almost rectangular. Its height was close to the filled monolayer loading. The thickness of the shell was regulated either by impregnation time or by the MoO3 amount in the slurry. The hydrodesulfurization activity of Mo species deposited by slurry impregnation was about the same or better (depending on the Al2O3 used) as in industrial MoO3/Al2O3 catalyst. 相似文献
3.
Jae-Sung Choi Kwang-Ik Moon Young Gul Kim Jae Sung Lee Cheol-Hyun Kim David L. Trimm 《Catalysis Letters》1998,52(1-2):43-47
CO2 reforming of methane was studied over modified Ni/Al2O3 catalysts. The metal modifiers were Co, Cu, Zr, Mn, Mo, Ti, Ag and Sn. Relative to unmodified Ni/Al2O3, catalysts modified with Co, Cu and Zr showed slightly improved activity, while other promoters reduced the activity of CO2 reforming. Mn-promoted catalyst showed a remarkable reduction in coke deposition, while entailing only a small reduction
in catalytic activity compared to unmodified catalyst. The catalysts prepared at high calcination temperatures showed higher
activity than those prepared at low calcination temperature. The Mn-promoted catalyst showed very low coke deposition even
in the absence of diluent gas and the activity changed only slightly during 100 h operation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
The effect of the ratio of reactant molecular diameter to catalyst pore diameter (λ) on the restrictive diffusion under hydrodesulfurization (HDS) reactions of heavy residue oils over CoMo/Al2O3 catalysts was investigated. A series of Al2O3 with various pore structures were used as supports of CoMo sulfide. The HDS reaction was carried out in a semi-batch Carberry type reactor at 648 K and 10.3 MPa. Two empirical correlations for restrictive diffusion under HDS reaction conditions were developed depending on the value of λ. The results showed that the restrictive diffusion effect under HDS reaction conditions is severe for the lower values of λ. However, this effect seems not prominent for higher values of λ. The order of the magnitude of the effective diffusivity was in the range of 10?6-10?7 cm2/s for the sulfur-containing compounds of residue oil in CoMo/Al2O3 catalysts at 648 K. 相似文献
5.
The transformation of cyclopentanone in the presence of H2S/H2 was investigated at atmospheric pressure over a sulfided CoMo/Al2O3 catalyst. The main reaction products were cyclopentanethiol and cyclopentene, the relative amounts of which depended on the reaction temperature and on the H2S to cyclopentanone molar ratio. The best results were obtained at 220°C, with a 2.5 H2S to cyclopentanone molar ratio: under these conditions, the cyclopentanethiol molar selectivity remained at about 90%, in a range of cyclopentanone conversion of 10–70%. 相似文献
6.
Pulse studies of the interaction of CH4 and NiO/Al2O3 catalysts at 500°C indicate that CH4 adsorption on reduced nickel sites is a key step for CH4 oxidative conversion. On an oxygen-rich surface, CH4 conversion is low and the selectivity of CO2 is higher than that of CO. With the consumption of surface oxygen, CO selectivity increases while the CO2 selectivity falls. The conversion of CH4 is small at 500°C when a pulse of CH4/O2 (CH4O2=21) is introduced to the partially reduced catalyst, indicating that CH4 and O2 adsorption are competitive steps and the adsorption of O2 is more favorable than CH4 adsorption 相似文献
7.
Jae Hyun Koh Jung Joon Lee Heeyeon Kim Ara Cho Sang Heup Moon 《Applied catalysis. B, Environmental》2009,86(3-4):176-181
The deactivation of CoMo/Al2O3 in the hydrodesulfurization (HDS) of dibenzothiophene (DBT) was investigated under laboratory conditions that allowed the accelerated deposition of coke on the catalyst. The coke deposition was enhanced at low H2 pressures and when naphthalene was added to the reaction solution. Characterization of deactivated catalysts by elemental analysis (EA) and temperature-programmed oxidation (TPO) identified two types of carbonaceous species deposited on the catalysts, the reactive and the refractory species. The refractory deposit, or hard coke, was a major contributor to the deactivation and, therefore, the amounts of hard coke present on the catalyst determined the overall activity. A correlation was established in this study between the activity and the amounts of deposited hard coke based on the results of accelerated deactivation treatment. A similar relation was also observed between the two parameters when the catalyst was used in an industrial process for long periods. The above findings suggest that the reaction periods of two different scales, i.e., in laboratory and industrial processes, can be correlated with each other based on the amounts of hard coke when coking is the major mechanism of catalyst deactivation. 相似文献
8.
The potentiality of a Pt-K/Al2O3 catalyst in the simultaneous removal of particulate matter (soot) and NO
x
is investigated in this work by means of Temperature Programmed Oxidation (TPO) experiments and Transient Response Method
(TRM), and compared with Pt-Ba/Al2O3. The results point out the higher performances of K-based sample in the soot combustion as compared to the Ba-based catalyst,
and similar behaviour in the NO
x
-storage. 相似文献
9.
Mesoporous Si-SBA-15 was applied to enhance the FCC gasoline selective hydrodesulfurization (HDS) performance of conventional Co-Mo/Al2O3 catalysts and the physicochemical properties of the resulting catalyst were compared with those of Co-Mo/Al2O3 catalysts incorporated with macroporous kaolin, mesoporous Si-MCM-41 and microporous Si-ZSM-5. The selective HDS performances of all the catalysts were assessed with different FCC gasolines as feedstocks. The results showed that the HDS selectivity of the catalysts was closely related to the Mo sulfidation that depends on catalyst surface area and metal-support interaction. With the superior Mo sulfidation, the Co-Mo/Si-SBA-15-Al2O3 catalyst had the optimal HDS selectivity for not only the full-range FCC gasolines but also the heavy fractions thereof. The present article demonstrates the significance of enhancing Mo sulfidation in improving HDS selectivity and thus sheds a light on the development of highly selective HDS catalysts. 相似文献
10.
Thomas Mathew Yusuke Yamada Atsushi Ueda Hiroshi Shioyama Tetsuhiko Kobayashi 《Catalysis Letters》2005,100(3-4):247-253
The steam reforming of dimethyl ether (DME) was performed on Ga2O3–Al2O3 mixed oxides prepared by sol–gel method. Ga2O3 significantly affects the catalytic performance with respect to the DME conversion and H2 yield. The catalytic activity increases with the Ga concentration in Ga2O3–Al2O3 mixed oxides. It is very interesting that without the aid of an additional transition metal component, Ga2O3 and Ga2O3 containing Al2O3 mixed oxide system exhibit good activity in the reforming reaction. To the best of our knowledge, this is the first report that reveals the reforming ability of Ga2O3 for the production of H2 from DME and/or methanol. 相似文献
11.
An Fe2O3 (10 wt%)/Al2O3 (90 wt%) catalyst prepared by a coprecipitation method was found to be effective for dehydrogenation of ethylbenzene to produce
styrene in the presence of CO2 instead of steam used in commercial processes. The dehydrogenation of ethylbenzene over the catalyst in the presence of CO2 was considered to proceed both via a one-step pathway and via a two-step pathway. CO2 was found to suppress the deactivation of the catalyst during the dehydrogenation of ethylbenzene.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
12.
The relative acid site densities of a range of Ni-Mo/Al2O3 based catalysts were measured by the temperature-programmed desorption of tert-butylamine. The catalysts investigated possessed different surface areas and active species loadings. The effect of active species impregnation on the acidity of blank aluminas was also determined. Similarly the effect of sulphiding on catalyst acidity was also addressed. 相似文献
13.
Ni/Al2O3 catalysts were prepared by saturating gas-solid reactions as an atomic layer epitaxy (ALE) process. Vaporized Ni(acac)2 was chemisorbed on a porous alumina support, and the produced surface complex was then air treated to remove the ligand residues. The nickel content could be precisely controlled by repeating this reactor cycle. On alumina preheated at 800°C, the nickel content varied from 3 to 21 wt%, when the number of reaction cycles was increased from one to ten. The performance of the Ni-catalysts was evaluated in the gas-phase hydrogenation of toluene. The preheat temperature of alumina influenced the activity of the catalyst, and a maximum in the activity was observed for catalysts prepared from alumina preheated at 875°C. Catalysts prepared by four reaction cycles, containing about 10 wt% nickel, gave the highest utilization of nickel. 相似文献
14.
Ja Hun Kwak Do Heui Kim Tamás Szailer Charles H. F. Peden János Szanyi 《Catalysis Letters》2006,111(3-4):119-126
The NO
x
adsorption mechanism on Pt/BaO/Al2O3 catalysts was investigated by performing NO
x
storage/reduction cycles, NO2 adsorption and NO + O2 adsorption on 2%Pt/(x)BaO/Al2O3 (x = 2, 8, and 20 wt%) catalysts. NO
x
uptake profiles on 2%\Pt/20%BaO/Al2O3 at 523 K show complete uptake behavior for almost 5 min, and then the NO
x
level starts gradually increasing with time and it reaches 75% of the inlet NO
x
concentration after 30 min time-on-stream. Although this catalyst shows fairly high NO
x
conversion at 523 K, only ~2.4 wt% out of 20 wt% BaO is converted to Ba(NO3)2. Adsorption studies by using NO2 and NO + O2 suggest two different NO
x
adsorption mechanisms. The NO2 uptake profile on 2%Pt/20%BaO/Al2O3 shows the absence of a complete NO
x
uptake period at the beginning of adsorption and the overall NO
x
uptake is controlled by the gas–solid equilibrium between NO2 and BaO/Ba(NO3)2 phase. When we use NO + O2, complete initial NO
x
uptake occurs and the time it takes to convert ~4% of BaO to Ba(NO3)2 is independent of the NO concentration. These NO
x
uptake characteristics suggest that the NO + O2 reaction on the surface of Pt particles produces NO2 that is subsequently transferred to the neighboring BaO phase by spill over. At the beginning of the NO
x
uptake, this spill-over process is very fast and so it is able to provide complete NO
x
storage. However, the NO
x
uptake by this mechanism slows down as BaO in the vicinity of Pt particles are converted to Ba(NO3)2. The formation of Ba(NO3)2 around the Pt particles results in the development of a diffusion barrier for NO2, and increases the probability of NO2 desorption and consequently, the beginning of NO
x
slip. As NO
x
uptake by NO2 spill-over mechanism slows down due to the diffusion barrier formation, the rate and extent of NO2 uptake are determined by the diffusion rate of nitrate ions into the BaO bulk, which, in turn, is determined by the gas phase
NO2 concentration. 相似文献
15.
The reduction of lean NOx using ethanol in simulated diesel engine exhaust was carried out over Ag/Al2O3 catalysts in the presence of H2O and SO2. The Ag/Al2O3 catalysts are highly active for the reduction of lean NOx by ethanol but the reaction is accompanied by side reactions to
form CH3CHO, CO along with small amounts of hydrocarbons (C3H6, C2H4, C2H2 and CH4) and nitrogen compounds such as NH3 and N2O. The presence of H2O enhances the NOx reduction while SO2 suppresses the reduction. The presence of SO2 along with H2O suppresses the formation of acetaldehyde and NH3. By infrared spectroscopy, it was revealed that the reactivity of NCO species formed in the course of the reaction was greatly
enhanced in the presence of H2O. The NCO species readily reacts with NO in the presence of O2 and H2O at room temperature, being converted to N2 and CO2 (CO). Addition of SO2 suppresses the formation of NCO species and lowers the reactivity of the NCO species. However, the reduction of NOx is still
kept at high conversion levels in the presence of H2O and SO2 over the present catalysts. About 80% of NOx in the simulated diesel engine exhaust was removed at 743 K.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
XPS measurements have shown that tin oxides are more readily reduced to metallic tin by hydrogen in Ni/Al2O3 systems than on pure Al2O3. During the reductive activation of Sn doped Ni/Al2O3 catalysts, surface segregation of the dopant was observed. This finding may explain that tin enhances the selectivity of the steam reforming catalysts only when added in very low concentrations and that it acts as a poison at higher loadings. 相似文献
17.
The rates and product selectivities of the C3H6-NO-O2 and NO-H2 reactions over a Pt/Al2O3 catalyst, and of the straight, NO decomposition reaction over the reduced catalyst have been compared at 240C. The rate of NO decomposition over the reduced catalyst is seven times greater than the rate of NO decomposition in the C3H6-NO-O2 reaction. This is consistent with a mechanism in which NO decomposition occurs on Pt sites reduced by the hydrocarbon, provided only that at steady state in the lean NO
x
reaction about 14% of the Pt sites are in the reduced form. However, the (extrapolated) rate of the NO-H2 reaction at 240C is about 104 times faster than the rate of the NO decomposition reaction thus raising the possibility that NO decomposition in the former reaction is assisted by Hads. It is suggested that adsorbate-assisted NO decomposition in the C3H6-NO-O2 reaction could be very important. This would mean that the proportion of reduced Pt sites required in the steady state would be extremely small. The NO decomposition and the NO-H2 reactions produce no N2O, unlike the C3H6-NO-O2 reaction, suggesting that adsorbed NO is completely dissociated in the first two cases, but only partially dissociated in the latter case. It is possible that some of the associatively adsorbed NO present during the C3H6-NO-O2 reaction may be adsorbed on oxidised Pt sites. 相似文献
18.
Temperature-programmed desorption (TPD) and oxidation (TPO) were used to investigate the decomposition and oxidation of ethanol on Al2O3, Pd/Al2O3, and PdO/Al2O3. Ethyl--13C alcohol (CH3
13CH2OH) was adsorbed on the catalysts so that reaction pathways of the two carbons could be distinguished. Alumina was mainly a dehydration catalyst, but dehydrogenation was also observed and some carbon remained on the surface. In the presence of O2, A12O3 oxidized the decomposition products and the-carbon was oxidized faster. Ethanol, which was adsorbed on A12O3, decomposed much faster on Pd/A12O3 by diffusing to Pd and undergoing CO elimination to form CH4,13CO, H2, and surface carbon. On PdO/A12O3, the decomposition was slower than on Pd/A12O3 until lattice oxygen was extracted above 450 K; the decomposition products were oxidized by lattice oxygen. In the presence of gas phase O2, Pd/Al2O3 was an active oxidation catalyst at low temperature, but lattice oxygen had to be extracted from PdO/A12O3 before it had significant oxidation activity. 相似文献
19.
Miguel Ángel Centeno Cristina Portales Ignacio Carrizosa José Antonio Odriozola 《Catalysis Letters》2005,102(3-4):289-297
A series of low loading gold supported ceria/alumina catalysts have been prepared by the deposition–precipitation method, varying the pH of the synthesis. The catalysts were characterised by means of XRD, TEM, SBET, XRF and UV–Vis techniques, and their catalytic activity towards CO oxidation in the absence and in presence of water in the stream, were tested. It has been found that in this low loading gold catalysts, where the metallic particles are far away one from another and the oxygen transportation is not the limiting step of the reaction, the electronic properties of the ceria phase and the structure of the metal-support perimeter more than the diameter of the gold nanoparticles is the determinant factor in the catalytic performances of the solid. 相似文献
20.
Nobuyuki Ichikuni Daiya Murata Shogo Shimazu Takayoshi Uematsu 《Catalysis Letters》2000,69(1-2):33-36
Ni/Al2O3 catalysts were prepared by the spray reaction method. The NiO particles supported on NiAl2O4 were stabilized against the aggregation and converted into smaller Ni particles by H2 reduction. The Ni particles stabilized on NiAl2O4 marked anomalous high activity for CO hydrogenation, due to the stronger interaction between Ni and NiAl2O4. This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献