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1.
The catalytic behavior of Al-promoted sulfated zirconia for n-butane isomerization at low temperature in the absence of H2 and at high temperature in the presence of H2 was studied. The addition of Al enhances the activity and stability of the catalysts for reaction at 250°C and in the presence
of H2 significantly. After on stream for 120 h, the n-butane conversion of the catalyst containing 3 mol% Al2O3 keeps steadily at 88% of its equilibrium conversion and no observable trend of further deactivation has been observed. The
difference in behavior of the promoted and unpromoted catalysts at low and high temperature is associated with a change of
reaction mechanism from bimolecular to monomolecular. Experimental evidence is presented to show that the promoting effect
of Al is different from that of the transition metals. Microcalorimetric measurements of NH3 adsorption on catalysts reveal that the remarkable activity and stability of the Al-promoted catalysts are caused by an enhancement
in the number of acid sites effective for the isomerization reaction.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
2.
《Applied catalysis》1989,46(1):103-112
The catalyst deactivation in the isomerization of n-butane was studied on H-mordenite and ZrO2 promoted by SO2−4 ion. The deactivation of H-mordenite was the result of coke deposition on the catalyst pores and the deactivation of ZrO2/SO2−4 resulted from the decrease in the oxidation state of sulphur in the surface complex. The reoxidation of sulphur, producing again the SO2−4 ion, led to the recovery of the catalytic activity of ZrO2/SO2−4 and coke burning resulted in the recovery of the H-mordenite activity. 相似文献
3.
The influence of promoters, potassium and samarium, on molybdenum supported over MgO–γ‐Al2O3 catalyst has been investigated in the oxidative dehydrogenation of propane. The acidities of catalysts were determined by temperature‐programmed desorption of NH3 and by decomposition of 2‐propanol. The K‐promoted catalyst showed the lower acidity followed by the Sm, whereas the unpromoted sample showed the highest acidity. The higher the acid character of the catalyst, the lower the selectivity to propene. Redox properties determined from EPR spectra change with the addition of the promoter. A parallelism between Mo6+ reducibility and catalytic activity was found. This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
Juan M. Campelo Rupak Chakraborty Jose M. Marinas Antonio A. Romero 《Catalysis Letters》1998,54(1-2):91-93
Pinacol (2,3‐dimethyl‐2,3‐butanediol) conversion over AlPO4 (Al/P = 1) and γ‐Al2O3 catalysts proceeded in two parallel reaction pathways with formation of 2,3‐dimethyl‐1,3‐butadiene (by 1,2‐elimination) and
3,3‐dimethyl‐2‐butanone (by rearrangement), the latter being the main reaction product. The activity was in accordance with
the surface acidity data as measured versus cyclohexene skeletal isomerization reaction. Thus, AlPO4 showed the highest activity (almost total conversion at 523 K). The 1,2‐elimination/rearrangement ratio depended on the type
of catalyst used and diene formation increased with reaction temperature. Moreover, pinacolone was a reaction intermediate
for diene production.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
V-containing catalysts supported on Al2O3, modified with varying amounts of ZrO2, were prepared by impregnation method. Dehydrogenation of ethylbenzene with CO2 was run over these catalysts in a fixed-bed downflow stainless steel reactor. Compared with pure Al2O3 support, a small amount of ZrO2 in the support led to a significant increase in catalytic activity. Partial reduction of vanadium oxides and carbon deposition were the main reasons for the decreased catalytic activity. 相似文献
6.
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
7.
María A. Vicerich Viviana M. Benitez María A. Sánchez Catherine Especel Florence Epron Carlos L. Pieck 《加拿大化工杂志》2020,98(3):749-756
Alumina and silica-alumina supported Ru-Pt catalysts were evaluated for the ring opening of naphthenes. Pt, Ru, and Ru-Pt catalysts were prepared by the impregnation of inorganic precursors over γ-alumina and silica-alumina supports. The catalysts were evaluated by temperature programmed reduction (TPR), pyridine temperature programmed desorption (TPD), CO-FTIR, and by test reactions of 33DM1B isomerization, cyclohexane dehydrogenation, cyclopentane hydrogenolysis, and the ring opening of decalin. The strong interaction between the metals (Pt-Ru) was attributed to their reductions occurring simultaneously. The acidity and strength of the acid sites of the monometallic Ru catalyst were higher than those of the monometallic Pt catalyst. The total acidity (Lewis and Brønsted) and the strength of the acid sites were higher for the silica-alumina supported catalysts. The silica-alumina catalysts had 10 times more Brønsted acidity than the γ-alumina ones and an increased activity and selectivity to decalin ring opening products. Supported monometallic Ru had the best performance for the ring opening reaction. 相似文献
8.
The conversion of benzene-containing gasoline fractions on the bifunctional Pt/SO 4 2? -ZrO2-Al2O3 catalytic system with different compositions of the support is studied. Using the results from hydroisomerization of a heptane-benzene model mixture, it is shown that a system with 67.8 wt % of aluminum oxide in its support has the best catalytic properties. For the IBP-85°C industrial benzene-containing fraction (23.7 wt % of benzene), it is established that the given catalyst ensures the complete removal of arenes from the benzene-containing fraction while raising its research octane number by 2.2–3.3 points and retaining a high yield of liquid products at levels of 98.7 wt % and higher. 相似文献
9.
Bhogal Sangeeta Sharma Gaurav Kumar Amit Sharma Shweta Naushad Mu. Alam Manawwer Stadler Florian J. 《Topics in Catalysis》2020,63(11-14):1272-1285
Topics in Catalysis - In the present study, Ag2O–Al2O3–ZrO2 based trimetallic oxide nanocatalyst was designed using simple microwave assisted reduction method. It was characterized... 相似文献
10.
Size-controlled Pd nanoparticles (PdNPs) were synthesized in aqueous solution, using sodium car-boxymethyl cellulose as the stabilizer. Size-controlled PdNPs were supported onα-Al2O3 by the incipient wetness impregnation method. The PdNPs onα-Al2O3 support were in a narrow particle size distribution in the range of 1-6 nm. A series of PdNPs/α-Al2O3 catalysts were used for the selective hydrogenation of acetylene in ethylene-rich stream. The results show that PdNPs/α-Al2O3 catalyst with 0.03%(by mass) Pd loading is a very effective and sta-ble catalyst. With promoter Ag added, ethylene selectivity is increased from 41.0%to 63.8%at 100 °C. Comparing with conventional Pd-Ag/α-Al2O3 catalyst, PdNPs-Ag/α-Al2O3 catalyst has better catalytic performance in acety-lene hydrogenation and shows good prospects for industrial application. 相似文献
11.
By using SSITKA (steady‐state isotopic transient kinetic analysis), n‐butane (n‐C4) isomerization on sulfated zirconia (SZ) has been studied for the first time at the site level. Accurate measures of the
average residence time and the concentration of the most active surface intermediates leading to isobutane (iso‐C4) were able to be determined. As has previously been observed, a fast initial deactivation of the catalyst followed by a slow
steady‐state deactivation was observed over 400 min time‐on‐stream (TOS). It was shown that even though a large amount (∼100
μmol/g) of n‐C4
was adsorbed on the catalyst, the concentration of active surface intermediates leading to iso‐C4
was only ∼10 μmol/g at 30 min TOS. The continuous decrease in
indicated that the decrease in catalytic activity was due to loss of active sites. An increase in the average residence time
of active surface intermediates leading to iso‐C4
was observed only between 30 and 100 min TOS. This suggests a possible presence of two types of active sites for n‐C4 isomerization on SZ under the reaction condition studied. It is suggested that the more‐active sites contributed to the high
initial activity, while the majority of active sites after 100 min TOS were the less active sites.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
12.
《Ceramics International》2017,43(3):3292-3297
Using freeze casting and pressureless infiltration methods, we prepared lamellar Al−Si−Mg/Al2O3−ZrO2 composites with initial ceramic loading of 30 vol% and different Al2O3:ZrO2 weight ratios (Al2O3:ZrO2=1:9, 3:7, 5:5, 7:3 and 9:1). The resultant composites inherited the lamellar structure of the Al2O3−ZrO2 scaffolds, and the thickness of both metal and ceramic layers showed a trend of first increase and then decrease with increasing Al2O3 content. During pressureless infiltration, multiple chemical reactions took place between ZrO2 and the Al−12Si−10Mg alloy and the main reaction products were (Al1−m, Sim)3Zr, Al2O3 and ZrSi2 phases. The degree of the reaction depended on the ZrO2 content in the ceramic composition. In general, the compressive strength of the composites decreased with increasing Al2O3 content, but three-point bending strength showed a first decrease and then increase. When Al2O3:ZrO2=1:9, the compressive and bending strength of the composites reached about 997±60 MPa and 426±10 MPa, respectively. A simple model was proposed to illustrate the fracture mode and toughening mechanism of the composites. 相似文献
13.
MgO−Al2O3−Cr2O3 refractories of increased corrosion resistance for nonferrous metallurgical furnaces
I. D. Kashcheev V. P. Semyannikov V. E. Gel’fenbein V. M. Bibaev T. V. Yarushina V. P. Konygin 《Refractories and Industrial Ceramics》1998,39(1):31-35
The paper sums up a study that had as its objective to develop MgO−Al2O3−Cr2O3 refractories of increased corrosion resistance for harsh service conditions. The refractories thus developed, designated PShKhM-1 and PShKhM-2, have better high-temperature strength and abrasion resistance than PKhS refractories manufactured commercially. The experimental refractories will enhance the durability of furnace and converter linings, extend their campaigns, step up their productivity, and reduce consumption of refractories and repair costs. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 1, pp. 33–37, January, 1998. 相似文献
14.
Iron‐promoted sulfated zirconia catalysts have been characterized by Mössbauer spectroscopy and XPS before and after catalytic test for the isomerization of n‐butane. The data obtained by Mössbauer spectroscopy show that iron is present in the fresh catalysts at the surface of zirconia both as isolated cations and small ferric oxide particles. The diameters of these particles do not exceed 4 nm. The characterization of the catalysts by Mössbauer spectroscopy after 20 and 120 min of reaction shows no apparent reduction of the iron cations. However, the analysis of the peak of Fe 3d3/2 in the XPS spectra shows that iron has been partially reduced in the used catalysts. These apparently contradictory results could be explained by the study of a pre‐reduced catalyst by both techniques. This study shows first that the Fe3+ cations in the particles can be reduced into Fe2+ and reoxidized at room temperature, and second that the reduction observed by XPS corresponds to the departure of the O2 re‐adsorbed at room temperature under air, occurring when the catalysts are placed under vacuum. All the data obtained seemed to confirm that the loss of the promoting effect of iron during the catalytic reaction may partially be due to the irreversible reduction of the iron species susceptible to undergo such reduction. 相似文献
15.
16.
The effects of oxidation/reduction regeneration treatments, with and without 1,2-dichloropropane present as a chlorinating agent, on the structure of Pt(3%)–Sn(4.5%)/Al2O3 catalysts have been correlated with selectivities for butane/H2 reactions. Particles of Pt0 fin Cl-free catalysts were partly covered by Sn0, but retained exposed ensembles of Pt atoms which were active for isomerisation, hydrogenolysis and dehydrogenation reactions, the latter becoming dominant at high reaction temperatures. Coking reduced Pt ensemble size and, hence, also favoured high selectivities for dehydrogenation as hydrogenolysis and isomerisation sites became poisoned. In contrast, the addition of 1,2-dichloropropane in an oxychlorination step before reduction promoted 1:1 Pt0–Sn0 alloy formation after reduction, the proportion of the total Pt in alloy being enhanced by increasing 1,2-dichloropropane concentration and oxychlorination temperature. The alloy surfaces were inactive for isomerisation and hydrogenolysis reactions, giving dehydrogenation as the sole catalytic reaction. 相似文献
17.
W. H. Cassinelli L. S. F. Feio J. C. S. Araújo C. E. Hori F. B. Noronha C. M. P. Marques J. M. C. Bueno 《Catalysis Letters》2008,120(1-2):86-94
The effect of the addition of CeO2 or La2O3 on the surface properties and catalytic behaviors of Al2O3-supported Pd catalysts was studied in the steam reforming of methane. The FTIR spectroscopy of adsorbed CO and the Pd dispersion
suggest the partial coverage of Pd0 by ceria or lanthana species. This could lead to the formation of an adduct MPd
x
O (M = Ce or La) at the surface of the metal crystallites. The addition of ceria or lanthana resulted in an increase of the
turnover rate and specific rate for steam reforming of methane. One possible explanation if that the Pd0*Pdδ+O–M interfacial species (M = Ce or La) are oxidized by H2O or CO2, promoting the O* transfer to the metal surface. This could facilitate the removal of C* species from the metal surface,
resulting in the increase of specific reaction rate and increase of the accessibility of CH4 to metal active sites. 相似文献
18.
n‐hexane was reacted on two Pt–Sn/Al2O3 catalysts, one prepared by coimpregnation (T) the other by using a bimetallic PtSn complex precursor (N). Both catalysts produced isomers, methylcyclopentane fragments and benzene, the aromatic selectivity being higher on catalyst
N. The hydrocarbon entities remaining after reaction were removed by hydrogen treatment. They contained methane, C2–C5 fragments (not observed on Pt, thus unique for PtSn) and benzene. The possible state and composition of chemisorbed carbonaceous
entities during reactions are discussed. More hydrocarbons, including slightly more methane could be hydrogenated off from
catalyst N of lower dispersion. The higher overall activity of catalyst N in the presence of more than one C per surface Pt points to its higher coke tolerance.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
《Catalysis communications》2011,13(15):1448-1451
Co3O4/NP-ZrO2, Co3O4/NP-CeO2 and Co3O4/NP-Ce0.8Zr0.2O2 catalysts were prepared via a reverse microemulsion/incipient wetness impregnation (RM–IWI) method. The catalytic properties for CO preferential oxidation (CO PROX) reaction in H2-rich stream were investigated. The Co3O4/NP-Ce0.8Zr0.2O2 catalyst with 1.8 wt.% Co3O4 loading has exhibited higher catalytic activity than that of the other two catalysts. The higher catalytic activity might be attributed to the combination effect of the highly dispersed cobalt oxide, the improvement in CeO2 reducibility due to ZrO2 incorporation in CeO2 structures, and the strong cobalt oxide-support interaction. 相似文献
20.
1 wt% Au/Fe2O3 catalyst was prepared by a co‐precipitation method. The structure of the sample in the as prepared, oxidized and reduced
states was investigated by means of X‐ray photoelectron spectroscopy (XPS), transition electron microscopy (TEM), electron
diffraction (ED) and X‐ray diffraction (XRD). The structure of the samples after various treatments and their activity in
the CO oxidation were compared. The results show the stability of the gold particle size during the treatments. However, after
oxidation, a slight shift in the Au 4f binding energy towards lower values points to the formation of an electron‐rich state
of the metallic gold particles compared to that revealed in the as prepared sample. Simultaneously, a goethite phase in the
Fe2O3 support is present, which is not observed in the “as prepared” and reduced samples. In the reduced sample the presence of
a crystalline maghemite‐c phase indicates a change in the support morphology. In the CO oxidation the oxidized sample shows
the highest activity and it might be the result of the cooperative effect of goethite, FeO and the electron‐rich metallic
gold nanoparticles. We suggest that a structural transformation occurs along the gold/support perimeter during the treatments
and we propose a possible mechanism for the effect of the oxidation treatment.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献