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1.
The effects of support pretreatment with nC1–C5 alcohols on the performance of Rh–Mn–Li/SiO2 catalyst in the synthesis of C2-oxygenates from syngas have been investigated by CO hydrogenation reaction, transmission electron microscopy (TEM), pulse
adsorption of CO and H2, and Fourier Transform infrared (FT-IR) spectroscopy. The catalysts prepared from the pretreated silica supports exhibited
higher space time yields of C2-oxygenates (STYC2-oxy) and selectivities towards C2-oxygenates (SC2-oxy) than that prepared from the untreated silica support. The enhancement in the hydrophobicity of the pretreated silica supports
would be favorable for increasing Rh dispersion and ratio of Rh+/Rh0 sites, therefore increasing the number of active sites, especially the active sites for CO insertion. Such variations are
responsible for the improvements in the catalytic performance of the Rh–Mn–Li/SiO2 catalyst. 相似文献
2.
Propane conversion over alumina supported Pt and Rh (1 wt% metals loading) was examined under fuel rich conditions (C3H8:O2:He = 1:2.25:9) over the temperature range 450–650 °C. Morphological characteristics of the catalyst materials were varied
by calcining at selected temperatures between 500 and 1,200 °C. X-ray diffraction and BET analysis showed the treatment generated
catalyts metals with particle sizes in the range of <10 to >500 nm, and support surface areas in the range of 20–240 m2/g. Remarkably, both Rh and Pt yielded product compositions close to equilibrium values (with high H2 and CO selectivity, complete oxygen conversion and almost complete propane conversion) so long as the metal particle size
was sufficiently low, ≲10–15 nm. In cases where the particle size was large, primarily complete oxidation rather than partial
oxidation products were observed, along with unreacted C3H8, indicative of a direct oxidation pathway in which gas-phase CO and H2 are not present as intermediate species. It is proposed that the high resistance of Rh to coarsening is largely responsible
for the observation of a higher selectivity of this material for syngas products when prepared by procedures similar to those
for Pt. Overall, the tunability of the product composition obtained over Rh and Pt via processing steps has direct significance
for the incorporation of such catalyts into the anodes of solid oxide fuel cells. 相似文献
3.
Na2WO4/Co–Mn/SiO2 catalyst was prepared and used for the simultaneous production of ethylene and syngas from CH4. A CH4 conversion of 38% and a yield of 21% for (C2H4 + CO), with a C2H4/CO/H2 ratio of 1/0.7/0.7 were obtained under the optimized conditions. 相似文献
4.
The preparation of a highly active bimetallic SiO2‐supported Rh–Co catalyst from RhCl3 and Co2(CO)8 (Rh:Co= 1 : 3 atomic ratio) has been studied by IR spectroscopy and ethylene hydroformylation, etc. Two steps are involved
in the preparative process: (1) surface‐mediated synthesis of Rh+(CO)2/SiO2 from calcined RhCl3/SiO2; (2) impregnation of Rh+(CO)2/SiO2 with a Co2(CO)8 solution followed by H2 reduction at 623 K. The IR results of reductive carbonylation of calcined RhCl3/SiO2 have been compared to those of uncalcined RhCl3/SiO2 at 373 K. In situ IR observations, extraction results and elemental analysis suggest that approximately 50% of RhCl3 are transformed to Rh2O3 on the SiO2 surface and that calcined RhCl3/SiO2 is converted to a mixture of [Rh(CO)2Cl]2 and [Rh(CO)2O2 (Os: surface oxygen) under CO at 373 K. When this SiO2‐supported mixture was submitted to impregnation with a Co2(CO)8 solution at room temperature, IR study and elemental analysis show that [Rh(CO)2Cl]2 reacts easily with Co2(CO)8 on the surface to give RhCo3(CO)12, whereas [Rh(CO)2O2 does not react with Co2(CO)8. Catalytic study in steady‐state ethylene hydroformylation shows that a catalyst thus derived is more active than a catalyst
derived from RhCo3(CO)12/SiO2 and a catalyst derived by coimpregnation of [Rh(CO)2Cl]2 and Co2(CO)8 on SiO2. This result suggests that the high rhodium dispersion of [Rh(CO)2O2 plays a crucial role in the formation of highly dispersed bimetallic Rh–Co sites.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
The V2O5 catalysts supported on TiO2–SiO2–MoO3 (TSM) prepared by the coprecipitation method were investigated for the selective catalytic reduction (SCR) of NO by NH3 at low temperatures. The V2O5/TSM catalyst with 7–13 wt% SiO2 was found to exhibit a superior SCR activity and a good sulfur tolerance at low temperatures (<250 °C). The presence of highly
active polymeric vanadates formed by the incorporation of MoO3 to TiO2–SiO2 and superior redox properties seems to enhance SCR activity, and furthermore the very lower SO2 oxidation activity due to the higher acidity leads to the remarkable improvement of sulfur tolerance. 相似文献
6.
Methanethiol has been synthesized by one‐step catalytic reaction from H2S‐content syngas on K2MoS4/SiO2 catalyst with selectivity over 95% under the optimum reaction conditions of 563 K, 2.0–3.0 MPa and 5–6% H2S content in the feed syngas. The results of XRD and XPS showed that Mo–S–K phase on the surface of the catalyst K2MoS4/SiO2 was responsible for the high activity and selectivity to methanethiol, and which may be restrained by the existence of (S–S)2- species.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
EXAFS investigations at the Rh K edge of lanthana-promoted Rh/SiO2 catalysts showed that the local environment of the Rh ions in the oxidic catalyst precursor state did not depend on the La2O3 content and resembled that of Rh2O3. No LaRhO3 formation could be detected. In the reduced state, EXAFS as well as H2 and CO chemisorption demonstrated that La2O3 increased the Rh dispersion. Covering of the Rh metal particles by La2O3 was minor, because during catalyst preparation, La was impregnated prior to Rh. 相似文献
8.
Regeneration behaviors of Fe/Si‐2 and Fe–Mn/Si‐2 catalysts for C2H6 dehydrogenation with CO2 to C2H4
Longya Xu Jinxiang Liu Hong Yang Yide Xu Qingxia Wang Liwu Lin 《Catalysis Letters》1999,62(2-4):185-189
The catalytic performance of Fe/Si‐2 and Fe–Mn/Si‐2 catalysts for conversion of C2H6 with CO2 to C2H4 was examined in a continuous‐flow and fixed‐bed reactor. The results show that the Fe–Mn/Si‐2 catalyst exhibits much better
reaction activity and selectivity to C2H4 than those of the Fe/Si‐2 catalyst. Furthermore, the coking–decoking behaviors of these catalysts were studied through TG.
The catalytic performances of the catalysts after regeneration for conversion of C2H6 or dilute C2H6 in FCC off‐gas with CO2 to C2H4 were also examined. The results show that both activity and selectivity of the Fe–Mn/Si‐2 catalyst after regeneration reached
the same level as those of the fresh catalyst, whereas it is difficult for the Fe/Si‐2 catalyst to refresh its reaction behavior
after regeneration.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
Nóra Győrffy Attila Wootsch Sándor Szabó István Bakos Lajos Tóth Zoltán Paál 《Topics in Catalysis》2007,46(1-2):57-64
Rh was deposited on to a well-characterized 3.1% Pt/SiO2 (InCat-1) parent catalyst by underpotential deposition method to obtain a model Rh–Pt bimetallic catalyst. TEM and EDS was
used to determine its mean particle size and bulk composition: the particles of ca. 3 nm contained ca. 60% Pt and 40% Rh.
The Rh–Pt catalyst was tested in methylcyclopentane (MCP) reaction between 513 K and 603 K and 60–480 Torr H2 pressure (with 10 Torr MCP). The parent Pt/SiO2 as well as a 5% Rh/SiO2 catalyst were also studied for comparison. Four subsequent treatments with O2 and H2 up to T = 673 K were applied on the bimetallic catalyst before the catalytic runs. The overall activity showed positive hydrogen
order on all samples, bimetallic Rh–Pt resulting in the lowest TOF values. Ring opening and hydrogenolysis products, as well
as unsaturated hydrocarbons were formed from MCP. The selectivity of ring opening products and fragments over Rh–Pt catalyst
was between the values observed on Pt and Rh, while the selectivity towards benzene formation was highest on the bimetallic
sample, especially at higher temperatures. “Selective” ring opening occurred on all samples, resulting mostly in 2 and 3-methylpentane
and less hexane. Different pretreatments with H2 and O2 affected slightly the dispersion values and the catalytic behavior of Rh–Pt sample. The selectivities of the Rh–Pt catalyst
being between the values observed for Pt/SiO2 and Rh/SiO2 indicates that the sample studied represented a real bimetallic catalyst, resembling both components and exhibiting at the
same time, new properties in addition to those, characteristic of Pt or Rh.
Dedicated to Konrad Hayek. 相似文献
10.
Zakaria Chajar Valérie Le Chanu Michel Primet Hélène Praliaud 《Catalysis Letters》1998,52(1-2):97-102
The selective reduction of NO by C3H8 is performed on copper-based catalysts: Cu/Al2O3, Cu/SiO2, Cu/SiO2–Al2O3 solids, fresh and hydrothermally-treated Cu-MFI with various Si/Al ratios. For all the Cu-MFI solids and for the non-zeolitic
supported-copper solids with low copper loadings, O2 promotes the reduction of NO. The C3H8–NO reaction rate correlates with the number of accessible and isolated Cun+ ions deduced from the infrared spectroscopy of adsorbed CO. When only one type of sites is detected, the FTIR spectroscopy
of adsorbed CO allows an estimation of the copper dispersion.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
C3H6 hydroformylation and CH3OH synthesis on organometallics derived (Pd + Ln)/ SiO2 and Pd/SiO2 catalysts have been studied. The activity and selectivity towards methanol in CO + H2 reaction were observed to increase for all the modified catalysts while both the hydroformylation activity and selectivity towards oxygenates in C3H6 hydroformylation decreased for the catalysts in comparison to those of Pd/SiO2. The FTIR, TPD data and characteristic catalytic properties of the catalysts studied allow to suggest that C3H6 hydroformylation on (Pd + Ln)/SiO2 catalysts occurs on monometallic Pd clusters without participation of mixed active sites and CO complexes activated thereon. 相似文献
12.
The electrochemical promotion of the CO2 hydrogenation reaction on porous Rh catalyst–electrodes deposited on Y2O3-stabilized-ZrO2 (or YSZ), an O2− conductor, was investigated under atmospheric total pressure and at temperatures 346–477 °C, combined with kinetic measurements
in the temperature range 328–391 °C. Under these conditions CO2 was transformed to CH4 and CO. The CH4 formation rate increased by up to 2.7 times with increasing Rh catalyst potential (electrophobic behavior) while the CO formation
rate was increased by up to 1.7 times with decreasing catalyst potential (electrophilic behavior). The observed rate changes
were non-faradaic, exceeding the corresponding pumping rate of oxygen ions by up to approximately 210 and 125 times for the
CH4 and CO formation reactions, respectively. The observed electrochemical promotion behavior is attributed to the induced, with
increasing catalyst potential, preferential formation on the Rh surface of electron donor hydrogenated carbonylic species
leading to formation of CH4 and to the decreasing coverage of more electron acceptor carbonylic species resulting in CO formation. 相似文献
13.
Selective oxidation of hydrogen sulfide containing excess water and ammonia over Bi-V-Sb-O catalysts
Dae-Won Park Byung-Ha Hwang Wol-Don Ju Moon-Il Kim Kyung-Hoon Kim Hee-Chul Woo 《Korean Journal of Chemical Engineering》2005,22(2):190-195
We investigated the selective oxidation of hydrogen sulfide to elemental sulfur and ammonium thiosulfate by using Bi4V2-xSbxO11-y
catalysts. The catalysts were prepared by the calcination of a homogeneous mixture of Bi2O3, V2O5, and Sb2O3 obtained by ball-milling adequate amounts of the three oxides. The main phases detected by XRD analysis were Bi4V2O11, Bi1.33V2O6, BiSbO4 and BiVO4. They showed good H2S conversion with less than 2% of SO2 selectivity with a feed composition of H2S/O2/NH3/H2O/He=5/2.5/5/60/27.5 and GHSV=12,000 h-1 in the temperature ranges of 220–260 ‡C. The highest H2S conversion was obtained for x=0.2 in Bi4V2-xSbxO11-y
catalyst. TPR/TPO results showed that this catalyst had the highest amount of oxygen consumption. XPS analysis before and
after reaction confirmed the least reduction of vanadium oxide phase for this catalyst during the reaction. It means that
the catalyst with x=0.2 had the highest reoxidation capacity among the Bi4V2-xSbxO11-y
catalysts. 相似文献
14.
Eun-Yong Ko Eun Duck Park Kyung Won Seo Hyun Chul Lee Doohwan Lee Soonho Kim 《Catalysis Letters》2006,110(3-4):275-279
The preferential CO oxidation (PROX) in the presence of excess hydrogen was studied over Pt–Ni/γ-Al2O3. CO chemisorption, X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy and temperature-programmed
reduction were conducted to characterize active catalysts. The co-impregnated Pt–Ni/γ-Al2O3 was superior to Pt/Ni/γ-Al2O3 and Ni/Pt/γ-Al2O3 prepared by a sequential impregnation of each component on alumina support. The PROX activity was affected by the reductive
pretreatment condition. The pre-reduction was essential for the low-temperature PROX activity. As the reduction temperature
increased above 423 K, the CO2 selectivity decreased and the atomic percent of Ni in the bimetallic phase of Pt–Ni increased. This catalyst exhibited the
high CO conversion even in the presence of 2% H2O and 20% CO2 over a wide reaction temperature. The bimetallic phase of Pt–Ni seems to give rise to high catalytic activity for the PROX
in H2-rich stream. 相似文献
15.
Steam reforming of ethanol, C2H5OH+H2O→2CO+4H2, was carried out over Co/Al2O3, Co/SiO2, Co/MgO, Co/ZrO2 and Co/C. The properties of the Co catalysts were greatly affected by the supports. Co/Al2O3 exhibited the highest selectivity for steam reforming of ethanol by suppression of methanation of CO and decomposition of
ethanol.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
TiO2–SiO2 mixed oxide with large pore size was synthesized by the xerogel method and it was then used to prepare the WO3/TiO2–SiO2 catalyst by an incipient wetness method. The as‐prepared WO3/TiO2–SiO2 sample was employed as the first heterogeneous catalyst in the liquid‐phase cyclopentene oxidation by aqueous H2O2, which exhibited higher selectivity (about 75%) to glutaraldehyde (GA) and, in turn, higher GA yield than the WO3/SiO2 heterogeneous catalyst and even the tungstic acid homogeneous catalyst under the same reaction conditions. The amorphous
WO3 phase was identified as the active sites and the loss of the active sites was proved to be not important. The lifetime of
the catalyst was determined and its regeneration method was proposed. The effects of various factors on the catalytic behaviors,
such as the WO3 loading, the calcination temperature, the surface acidity and the reaction media, were investigated and discussed based on
various characterizations including BET, XRD, XPS, FTIR, EXAFS and Raman spectra etc.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
17.
The relationship between the product selectivity for the NO–H2–O2 reaction and characteristics of the catalyst, Pt/ZrO2, was investigated. From the results of activity tests and characterizations, such as CO adsorption and TEM, the catalysts
with high Pt dispersions showed high NH3 selectivities, and those with significantly agglomerated Pt particles by high temperature calcination exhibited higher N2 formation. The effect of the reduction and oxidation pretreatment was also investigated. The reduced Pt sites promoted the
formation of NH3. The pretreatment condition influenced not only on the amount of accumulated nitrogen-containing species during the reaction
but also on the decomposition of ammonium nitrate, which was suspected to be an accumulated species. The decomposition of
ammonium nitrate would be involved in the NO–H2–O2 reaction. 相似文献
18.
Steam reforming (SR) and oxidative steam reforming (OSR) of ethanol were investigated over undoped and Cu, Co and Ca doped
Ni/CeO2–ZrO2 catalyst in the temperature range of 400–650 °C. The nickel loading was kept fixed at 30 wt.% and the loading of Cu and Co
was varied from 2 to 10 wt% whereas the Ca loading was varied from 5 to 15 wt.%. The catalysts were characterized by various
techniques, such as surface area, temperature programmed reduction, X-Ray diffraction and H2 chemisorption. For Cu and Co doped catalyst, CuO and Co3O4 phases were detected at high loading whereas for Ca doped catalyst, no separate phase of CaO was found. The reducibility
and the metal support interactions were different for doped catalysts and varied with the amount and nature of dopants. The
hydrogen uptake, nickel dispersion and nickel surface area was reduced with the metal loading and for the Co loaded catalysts
the dispersion of Ni and nickel surface area was very low. For Cu and Ca doped catalysts, the activity was increased significantly
and the main products were H2, CO, CH4 and CO2. However, the Co doped catalysts showed poor activity and a relatively large amount of C2H4, C2H6, CH3CHO and CH3COCH3 were obtained. For SR, the maximum enhancement in catalytic activity was obtained with in the order of NCu5. For Cu–Ni catalysts,
CH3CHO decomposition and reforming reaction was faster than ethanol dehydrogenation reaction. Addition of Cu and Ca enhanced
the water gas shift (WGS) and acetaldehyde reforming reactions, as a result the selectivity to CO2 and H2 were increased and the selectivity to CH3CHO was reduced significantly. The maximum hydrogen selectivity was obtained for Catalyst N (93.4%) at 650 °C whereas nearly
the same selectivity to hydrogen (89%) was obtained for NCa10 catalyst at 550 °C. In OSR, the catalytic activity was in the
order N > NCu5 > NCa15 > NCo5. In the presence of oxygen, oxidation of ethanol was appreciable together with ethanol dehydrogenation.
For SR reaction, the highest hydrogen yield was obtained on the undoped catalyst at 600 °C. However, with calcium doping the
hydrogen yields are higher than the undoped catalyst in the temperature range of 400–550 °C. 相似文献
19.
Hyun-Seog Roh Yong Wang David L. King Alexandru Platon Ya-Huei Chin 《Catalysis Letters》2006,108(1-2):15-19
Supported Rh catalysts have been developed for selective H2 production at low temperatures. Ethanol dehydration is favorable over either acidic or basic supports such as γ-Al2O3 and MgAl2O4, while ethanol dehydrogenation is more favorable over neutral supports. CeO2–ZrO2-supported Rh catalysts were found to be especially effective for hydrogen production. We focused on a support prepared by
a co-precipitation method having composition Ce0.8Zr0.2O2. A 2%Rh/Ce0.8Zr0.2O2 catalyst, prepared via impregnation without pre-calcination of support, exhibited the highest H2 yield at 450 °C among various supported Rh catalysts evaluated in this study. This may be due to both the strong interaction
between Rh and Ce0.8Zr0.2O2 and the high oxygen transfer rate favoring reforming of acetaldehyde instead of methane production. 相似文献
20.
Nickel niobate (NiNb2O6) supported on SiO2 was prepared by a chemical mixing method using mixed Ni and Nb citrate solutions. X-ray diffraction study showed that the NiNb2O6 compound was reduced to Ni metal and NbO2 after H2 treatment at 600 ° C, and a strong Ni-niobia interaction was induced after the decomposition of the compound: the ethane hydrogenolysis activity was suppressed severely after high temperature reduction at 600 ° C, and recovered by O2 treatment at 500 ° C followed by low-temperature reduction at 200 ° C. The selectivity of cyclohexane dehydrogenation was improved significantly by the Ni-niobia interaction, if compared with unpromoted Ni/SiO2 catalyst, and the structural change and catalytic behaviors were compared with those of Rh double oxides such as RhNbO4. 相似文献