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1.
Jifei Jia Liwu Lin Jianyi Shen Zhusheng Xu Tao Zhang Dongbai Liang Yi Chen 《中国科学B辑(英文版)》1998,41(6):606-615
CO adsorption microcalorimetry was employed in the study of γ-Al2O3-supported Pt, Pt-Sn and Pt-Fe catalysts. The results indicated that the initial differential heat of CO adsorption of the
Pt/γ-Al2O3 catalyst was 125 kJ/mol. As CO coverage increased, the differential heat of adsorption decreased. At higher coverages, the
differential heat of adsorption decreased significantly. 60% of the differential heat of CO adsorption on the Pt/γ-N2O3 catalyst was higher than 100 kJ/mol. No significant effect on the initial differential heat was found after adding Sn and
Fe to the Pt/γ-Al2O3 catalyst. The amount of strong CO adsorption sites decreased, while the portion of CO adsorption sites with differential
heat of 60–110 kJ/mol increased after increasing the Sn or Fe content. This indicates that the surface adsorption energy was
changed by adding Sn or Fe to Pt/γ-N2O3. The distribution of differential heat of CO adsorption on the Pt-Sn(C)/γ-Al2O3 catalyst was broad and homogeneous. Comparison of the dehydrogenation performance of C4 alkanes with the number of CO adsorption sites with differential heat of 60–110 kJ/mol showed a good correlation. These results
indicate that the surface Pt centers with differential heats of 60–110 kJ/mol for CO adsorption possess superior activity
for the dehydrogenation of alkanes.
Project supported by FORD and the National Natural Science Foundation of China (Grant No. 09412302) and the Transcentury Training
Program Foundation for the Talents by The State Education Commission of China. 相似文献
2.
In Situ IR Spectroscopic Studies on Molybdenum Nitride Catalysts: Active Sites and Surface Reactions
Recent IR spectroscopic studies on the surface properties of fresh Mo2N/-Al2O3 catalyst are presented in this paper. The surface sites of fresh Mo2N/-Al2O3, both Mo+ (0<<2) and N sites, are probed by CO adsorption. Two characteristic IR bands were observed at 2045 and 2200 cm-1, due to linearly adsorbed CO on Mo and N sites, respectively. The surface N sites are highly reactive and can react with adsorbed CO to form NCO species. Unlike adsorbed CO on reduced passivated one, the adsorbed CO on fresh Mo2N/-Al2O3 behaves similarly to that of group VIII metals, suggesting that fresh nitride resembles noble metals. It is found that the surface of Mo nitrides slowly transformed into sulfide under hydrotreating conditions, which could be the main reason for the activity drop of molybdenum nitride catalysts in the presence of sulfur-containing species. Some surface reactions, such as selective hydrogenation of 1,3-butadiene, isomerization of 1-butene, and hydrodesulfurization of thiophene, were studied on both fresh and reduced passivated Mo2N/-Al2O3 catalysts using IR spectroscopy. The mechanisms of these reactions are proposed. The adsorption and reaction behaviors of these molecules on fresh molybdenum nitride also resemble those on noble metals, manifesting the unique properties of fresh molybdenum nitride catalysts. Mo and N sites are found to play different roles in the adsorption and catalytic reactions on the fresh Mo2N/-Al2O3 catalyst. Generally, Mo sites are the main active sites for the adsorption and reactions of adsorbates; N sites are not directly involved in catalytic reactions but they modify the electronic properties of Mo sites. 相似文献
3.
N. B. Shitova V. A. Drozdov P. E. Kolosov M. D. Smolikov 《Reaction Kinetics and Catalysis Letters》2000,41(5):720-728
The formation of Pt/γ-Al2O3 and Pt/C catalysts from platinum carbonyl clusters H2[Pt3(CO)6]n (n = 2, 5) is studied. The strength of interaction between clusters (strong Lewis bases) and the support and the state of platinum
in catalysts are governed by the acceptor strength of the support. The formation of a stable platinum compound with a surface
of γ-Al2O3 (strong Lewis acid) is shown for a Pt/γ-Al2O3 catalyst by the method of radial distribution functions. In a Pt/C catalyst containing the same amount of Pt supported on
a carbon material known to be a weaker acceptor, metallic platinum is formed along with surface-bonded platinum. Proceeding
from the existence of the active phase of catalysts in the form of a surface platinum complex and platinum crystallites, the
properties of catalysts are discussed in the complete oxidation of methane and the dehydrogenation of cyclohexane, as well
as the high dispersity of platinum and its thermal stability 相似文献
4.
D. N. Titov A. V. Ustyugov O. P. Tkachenko L. M. Kustov Ya. V. Zubavichus A. A. Veligzhanin N. V. Sadovskaya I. V. Oshanina L. G. Bruk O. N. Temkin 《Kinetics and Catalysis》2012,53(2):262-273
The state of the active constituents of the freshly prepared PdCl2-CuCl2/γ-Al2O3 catalyst for the low-temperature oxidation of the carbon monoxide by molecular oxygen was studied by X-ray absorption spectroscopy
(XAS), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and diffuse reflectance IR Fourier transform spectroscopy
(DRIFTS). It was shown that copper in the form of a crystalline phase of Cu2Cl(OH)3 with the structure of the mineral paratacamite and palladium chloride in an amorphous state occurred on the surface of γ-Al2O3. According to XAS data, the local environment of palladium consisted of four chlorine atoms, which formed a flat square with
an increased distance between palladium and one of the chlorine atoms. The evolution of the local environments of copper and
palladium upon a transition from the initial salts to the impregnating solutions and chlorides on the surface of γ-Al2O3 was considered. The role of γ-Al2O3 in the formation of the Cu2Cl(OH)3 phase was discussed. It was found by the DRIFTS method that linear (2114 cm−1) and bridging (1990 and 1928 cm−1) forms of coordinated carbon monoxide were formed upon the adsorption of CO on the catalyst surface. The formation of CO2 upon the interaction of coordinated CO with atmospheric oxygen was detected. Active sites including copper and palladium
were absent from the surface of the freshly prepared catalyst. 相似文献
5.
1H MAS NMR and15N NMR studies of adsorbed N2 and N2O molecules were used to characterize Br?nsted and Lewis acidic sites of unmodified γ-Al2O3 and γ-Al2O3 modified with NaOH. Changes in the concentrations of surface hydroxyls with the increase in the number of more “basic” OH
groups for NaOH/γ-Al2O3 have been found by1H MAS NMR experiments. Two different types of Lewis acidic sites in γ-Al2O3 have been revealed using15N NMR studies. The strongest sites are poisoned even at small NaOH concentrations (ca. 0.05 wt.%). Not only the number of electron-accepting sites but also their strength are supposed to decrease for modified
γ-alumina. 相似文献
6.
A series of MoO3/γ-Al2O3 catalysts with different Mo surface densities (Mo atoms/nm2) has been prepared by incipient wetness impregnation method. Structural characteristics of the prepared catalysts were investigated
by atomic absorption spectroscopy, X-ray diffraction, Fourier Transform Infrared spectroscopy, N2 adsorption at −196 °C, and temperature-programmed reduction (TPR). The catalytic activities of the prepared catalysts were
tested by cyclohexene conversion between 200 and 400 °C. XRD results indicated that molybdenum oxide species were dispersed
as a monolayer on the support up to 4.04 Mo atoms/nm2, and the formation of crystalline MoO3 was observed above this loading. FTIR and TPR results showed that molybdenum oxide species were present predominantly in
tetrahedral form at lower loading, and polymeric octahedral forms were dominant at higher loading. Cyclohexene conversion
reaction proceeded mainly through the simple dehydrogenation pathway in the studied temperature range 200–400 °C and was found
to be highly dependent on MoO3 dispersion. 相似文献
7.
Xiaohuin Liu Yong Guo Wenjie Xu Yanqin Wang Xueqing Gong Yanglong Guo Yun Guo Guanzhong Lu 《Kinetics and Catalysis》2011,52(6):817-822
The influence of the alumina support on the catalytic activity of Pt/Al2O3 catalysts in aqueous phase reforming of ethylene glycol to hydrogen was studied. The catalysts were prepared by impregnation
of γ-, δ-, and α-alumina with H2PtCl6. The highest rate of hydrogen production (452 μmol min−1 g−1) obtained with the Pt/α-Al2O3 catalyst can be related to the highest extent of dispersion of Pt on α-Al2O3. XPS, TEM-EDX and TPR-H2 measurements showed the absence of chloride-containing surface complexes in the Pt/α-Al2O3 catalyst. However, chloride-containing entities were found on the surface of Pt/γ-Al2O3 and Pr/δ-Al2O3 catalysts. When chloride ions are removed chlorinated Pt species facilitate the sintering of Pt crystallites and in this
way affect the extent of Pt dispersion. Moreover, depending upon the particular crystalline form, alumina atoms have different
coordination and alumina surfaces contain varying amounts of OH groups of different nature which affect the interaction between
Pt and the support. 相似文献
8.
V. Yu. Borovkov S. P. Kolesnikov V. I. Koval’chuk J. L. d’Itri 《Russian Chemical Bulletin》2007,56(5):863-869
Adsorption of 13C18O+12C16O mixtures on the Pt(2.9%)/γ-Al2O3, (Pt(2.6%)+Cu(2.7%))/γ-Al2O3, and (Pt(2.6%)+Cu(5.1%))/γ-Al2O3 catalysts was studied by FTIR spectroscopy. On the metallic Pt surface at coverages close to saturation, CO is adsorbed both
strongly and weakly to form linear species for which the vibrational frequencies of the isolated 13C18O molecules adsorbed on Pt are ∼1940 and ∼1970 cm−1, respectively. The redistribution of intensities of the high-and low-frequency absorption bands in the spectra of adsorbed
13C18O indicates that these linear forms are present on the adjacent metal sites. The weak adsorption is responsible for the fast
isotope exchange between the gaseous CO and CO molecules adsorbed on metal. The Pt-Cu alloys, in which the electronic state
of the surface Pt atoms characteristic of monometallic Pt remains unchanged, are formed on the surface of the reduced Pt-Cu
bimetallic catalysts. The decrease in the vibrational frequencies of the isolated C=O bonds in the isolated Pt-CO complexes
suggests that the CO molecules adsorbed on the Cu atoms affect the electronic properties of Pt.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 831–836, May, 2007. 相似文献
9.
以九水合硝酸铝(Al(NO3)3·9H2O)与正硅酸乙酯(TEOS)为前驱盐,采用溶胶-凝胶法制备一系列不同Al2O3含量的SiO2-Al2O3复合氧化物,并通过浸渍硝酸氧锆引入ZrO2,制备ZrO2/SiO2-Al2O3复合氧化物催化剂,考察催化剂在肉桂醛(CAL)MPV转移加氢中的催化性能,并结合N2物理吸附、X射线粉末衍射(XRD)、傅里叶变换红外光谱(FTIR)、NH3-程度升温脱附(NH3-TPD)、Py-原位红外(Py-IR)等技术,研究催化剂结构、织构以及表面性质与其催化性能间的构效关系.研究表明,所制备的催化剂均以L酸为主,并含有少量B酸中心,这使得加氢产物以肉桂醇(COL)为主,并含有少量1-苯丙烯-2-丙基醚(CPE).Al2O3含量不仅影响催化剂表面的酸中心数量,而且对催化剂的织构参数有较大影响.随Al2O3含量的增加,催化剂表面L酸与B酸中心均有所增加,而孔径则持续变小,这使得催化反应呈现CAL转化率先增加后减少、目标产物COL选择性先稍有减小后有所增加的趋势.在Si/Al比为2时,催化剂具有最优的催化性能,优化反应条件下,CAL转化率达96%,目标产物COL选择性达90%. 相似文献
10.
Jifei Jia Yuan Kou Liwu Lin Zhusheng Xu Tao Zhang Jianzhong Niu Dongbai Liang 《Reaction Kinetics and Catalysis Letters》1998,63(2):391-396
Pt LIII-edge XANES and EXAFS were employed to investigate the nature of Pt/γ-Al2O3, Pt−Sn/γ-Al2O3 and Pt−Fe/γ-Al2O3 catalysts. The results indicated that Pt species on these catalysts were all in the oxidized states before reduction, and
in the metallic states after reduction. The dispersity of the Pt species on the catalysts was very high after reduction. The
electronic properties of the highly dispersed Pt species were different from that of the bulk Pt in large crystallites. An
interaction between Pt and the metal-oxide modified γ-Al2O3 support is proposed. The interaction improved the dispersity of the Pt species on the catalysts and is thought to be the
reason for the enhanced activity and selectivity for dehydrogenation reactions over these catalysts. 相似文献
11.
Adsorption complexes of CO-Lewis acid sites with 3- and 5-coordinated Al3+ are modeled by the density functional method using the cluster approach. Cluster models of the site with 4-coordinated Al3+ on the surface of γ-Al2O3 and in zeolites are suggested. For these models of adsorption complexes, C-O vibration frequencies are calculated and the
energetics of CO adsorption is evaluated.
Translated fromZhurnal Struktumoi Khimii, Vol. 38, No. 5, pp. 834–839, September–October, 1997. 相似文献
12.
V. Yu. Tregubenko I. E. Udras V. A. Drozdov A. S. Belyi 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2009,83(12):2039-2044
The formation of highly imperfect γ-Al2O3 oxide prepared by calcining pseuodoboehmite and plasticized by organic acids was studied. The nature of the organic acid-aluminum
hydroxide plasticizer was found to substantially influence the degree of γ-Al2O3 structure imperfection estimated qualitatively as the difference between the X-ray structural density and effective density
with respect to helium and aluminum oxide. A high degree of imperfection caused an increase in the intensity of the absorption
band at 3775 cm−1 corresponding to OH groups localized on five-coordinate Al3+ and the concentration of Lewis acid centers. The adsorption and catalytic properties of systems based on these carriers were
studied. 相似文献
13.
Petre A. L. Auroux A. Gervasini A. Caldararu M. Ionescu N. I. 《Journal of Thermal Analysis and Calorimetry》2001,64(1):253-260
The surface properties of supported gallium oxide catalysts prepared by impregnation of various supports (γ-Al2O3, SiO2, TiO2, ZrO2) were investigated by adsorption microcalorimetry, using ammonia and water as probe molecules. In the case of acidic supports
(γ-Al2O3, ZrO2, TiO2), the acidic character of supported gallium catalysts always decreased in comparison with gallium-free supports; on very
weakly acidic SiO2, new acidic centers were created when depositing Ga2O3. The addition of gallium oxide decreased the hydrophilic properties of alumina, titania and zirconia, but increased the amount
of water adsorbed on silica. The catalytic performances in the selective catalytic reduction of NO by C2H4 in excess oxygenwere in the order Ga/Al2O3>Ga/TiO2>Ga/ZrO2>>Ga/SiO2. This order is more related to the quality of the dispersion of Ga2O3 on the support than to the global acidity of the solids.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
《Journal of molecular catalysis. A, Chemical》1999,137(1-3):287-295
The photochemical reaction of W(CO)6 with triphenylphosphine (PPh3) in the presence of γ-Al2O3 and Pd/γ-Al2O3 has been used to prepare W/γ-Al2O3 and Pd–W/γ-Al2O3 catalysts. Adsorbed mono- and disubstituted W species have been identified by FTIR spectroscopy. There is evidence of the adsorption of W(CO)6−x Lx species on both the alumina and the Pd surface. After thermal decomposition and reduction at 573 K the catalysts have been characterized by FTIR spectroscopy of adsorbed NH3, CO and NO. The retention of W and P suppresses the Lewis acidity of the alumina support. On Pd–W/γ-Al2O3, the W is present in a partially reduced state in close association with Pd. This interaction modifies the chemisorptive properties of NO relative to those of the monometallic Pd and W catalysts. In line with these observations the Pd–W/γ-Al2O3 catalyst presents an enhanced activity for NO decomposition at 473 K. 相似文献
15.
Eugenia V. Kul''ko Aleksandra S. Ivanova Anna A. Budneva Evgenii A. Paukshtis 《Reaction Kinetics and Catalysis Letters》2006,88(2):381-390
Summary Acid-base properties of aluminas prepared by thermal treatment of a hydrated CTA-product at 600°C were studied. The CTA-oxides,
representing γ-Al2O3, were shown to contain terminal and bridged OH-groups. The concentration of the terminal OH-groups in the CTA-oxides was
found to exceed their concentration in γ-Al2O3 prepared by dehydration of the “precipitated” pseudoboehmite, whereas the concentration of the bridged OH-groups in the CTA-oxides
was lower than that in γ-Al2O3 prepared from pseudoboehmite. The total concentration of the surface Lewis acid sites in CTA-oxides varies within the limits
of 2.80-4.14 mmol/m2 and is essentially above that in g-Al2O3 (2.25 mmol/m2). The distinctive feature of the CTA-oxides is that their surface contains strong Lewis acid sites with nCO = 2220 and 2238 cm-1. The total concentration of basic sites in the CTA-oxides is lower than that in g-Al2O3, however, in contrast to g-Al2O3,they contain strong basic sites with nCDCl3 = 2200 cm-1. 相似文献
16.
In this study the V2O5/-Al2O3 catalysts were prepared by the grafting method. Their Brönsted and Lewis acid sites were investigated with pyridine adsorption using infrared spectroscopic techniques. It was concluded that when the catalysts composition of the active component V2O5 increased, the supporting material -Al2O3 was covered by a monolayer of V2O5. When the amount of active component was over 11.8 wt.%, the supporting material was covered as multilayer.It was also concluded that after pyridine adsorption, the number of Lewis acid sites of V2O5/-Al2O3 catalyst decreased with increasing V2O5 content. The number of the Brönsted acid sites of the V2O5/-Al2O3 catalyst showed an increase with increasing V2O5 content and reached a maximum for the catalyst with 11.8 wt.% V2O5. Upon further increase of V2O5 content, the number of the Brönsted acid sites decreased. 相似文献
17.
M. A. Ryashentseva 《Chemistry of Heterocyclic Compounds》2006,42(8):1018-1020
In the presence of Pd-and Cr-containing catalysts applied to γ-Al2O3 or sibunite 4,5,6,7-tetrahydroindole is converted into indole. Indole was obtained in quantitative yield on sulfided 0.15–0.5%
Pd/γ-Al2O3 catalyst at 360°C and on catalysts containing 5% Cr2O3, 5% La2O3 (or 5% polirit), 1% K2O/89% γ-Al2O3 at 475–480°C.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1176–1178, August, 2006. 相似文献
18.
M. O. Kazakov A. V. Lavrenov I. G. Danilova O. B. Belskaya V. K. Duplyakin 《Kinetics and Catalysis》2011,52(4):573-578
The acidic and hydrogenating of Pt/SO42−-ZrO2-Al2O3 samples containing from 18.8 to 67.8 wt % Al2O3 as a support constituent were studied by the IR spectroscopy of adsorbed CO and pyridine, and the model reactions of n-heptane and cyclohexane isomerization on these catalysts were examined. The total catalyst activity in the conversion of
n-heptane decreased with the concentration of Al2O3; this manifested itself in an increase in the temperature of 50% n-heptane conversion from 112 to 266°C and in an increase in the selectivity of isomerization to 94.2%. In this case, the maximum
yield of isoheptanes was 47.1 wt %, which was reached on a sample whose support contained 67.8 wt % Al2O3. A maximum yield (69.6 wt %) and selectivity (93.7%) for methylcyclopentane formation from cyclohexane were also reached
on the above catalyst sample. This can be explained by lower concentrations of Lewis and Br?nsted acid sites in the Pt/SO42−-ZrO2-Al2O3 system, as compared with those in Pt/SO42−-ZrO2. The experimental results allowed us to make a preliminary conclusion that the Pt/SO42−-ZrO2-Al2O3 catalyst whose support contains 67.8 wt % Al2O3 is promising for use in the selective hydroisomerization of benzene-containing gasoline fractions in the thermodynamically
favorable process temperature range of 250–300°C. 相似文献
19.
Barbara Pacewska Olga Kluk-Płoskońska D. Szychowski 《Journal of Thermal Analysis and Calorimetry》2006,85(2):351-359
An attempt
to obtain aluminium hydroxide that could give aluminium oxides of increased
thermal stability was made. Aluminium hydroxide was precipitated during a
hydrolysis of aluminium chloride in ammonia medium. The influence of preparative
conditions, such as a dosing rate of aluminium precursor, pH, duration of
the precipitate refluxing and temperature of calcination, on the properties
of obtained hydroxides and oxides was investigated. The materials were studied
with the following methods: thermal analysis, IR spectroscopy, low-temperature
nitrogen adsorption and adsorption–desorption of benzene vapours.
Precipitated boehmites had high values of S
BET
determined from nitrogen adsorption (220–300 m2g–1),
good sorption capacity for benzene vapours, developed mesoporous structure
and hydrophilic character. It has been proved that a high pH value during
the precipitation of aluminium hydroxide favoured better crystallisation of
boehmite structure, higher temperature of its dehydroxylation into γ-Al2O3,
and delayed transformation of γ phase into α-Al2O3.
Aluminium oxides derived from the hydroxides precipitated at a high pH were
the most stable at high temperatures, and were characterised with the best
surface properties.
The online version of the original
article can be found
at 相似文献
20.
The present paper reviews in detail the different studies now being conducted by our research team concerning the ultradeep hydrodesulfurization (HDS) of dibenzothiophene (DBT) derivatives over Mo/TiO2 and Mo/TiO2–Al2O3 catalysts. First, a detailed characterization of Mo/TiO2 (P-25 Degussa, 50 m2/g) catalysts prepared by equilibrium adsorption technique shows that Mo- species are highly and uniformly dispersed on the surface of titania up to 6.6 wt% MoO3 loading. Above this value, some aggregation of Mo occurs, leading to the formation of bulk MoO3. Below 6.6 wt% MoO3 loading, the Raman spectroscopy data of the calcined samples show that the supported Mo-species possess a highly distorted octahedral MoO6 structure. TiO2–Al2O3 composites were prepared by chemical vapor deposition (CVD) using TiCl4 as a precursor. Using several characterization techniques, we demonstrated that the support composite presents a high dispersion of TiO2 over -Al2O3 without forming precipitates up to ca. 11 wt% loading. Moreover, the textural properties of the composite support are comparable to those of alumina. Under the present sulfidation conditions (673 K, 5%H2S/95%H2), Mo-species supported on TiO2 are better sulfided than on alumina, as demonstrated using XPS. This can be attributed to the relatively lower interaction between Mo-species and titania. The state of sulfide species supported on the composite support can be considered as a transition state between TiO2 and Al2O3. However, at relatively higher TiO2 loadings (ca. 11 wt%), Mo/TiO2–Al2O3 catalysts exhibit sulfidability similar to that of Mo/TiO2. The HDS tests conducted in both the laboratory and in industry show that sulfide catalysts supported on TiO2–Al2O3 (ca. 11 wt% TiO2) are more active than those supported on TiO2 or Al2O3. 相似文献