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1.
The adsorption and surface reactions of acetonitrile and acetonitrile-oxygen gas mixture were studied on TiO2-supported Au catalysts at 300–673 K. FTIR spectra show different kinds of molecularly adsorbed CH3CN:acetonitrile can be bonded to weak Lewis acid sites (2295 cm−1), to strong Lewis acid sites (2337 cm−1) of titania; it can be coordinated linearly through the lone electron pair of the N atom on Au sites and η2 (C,N) CH3CN species can be formed on Au particles. CH3CN dissociates on Au sites, the resulting CN(a) can be oxidized in small extent by lattice oxygen and in a greater extent by gaseous oxygen into NCO surface species. The
formation of other products (CH3NH2, H2, CO2, CH4, C2H4 and CO) was demonstrated and discussed. 相似文献
2.
Hadjiivanov Konstantin Concepción Patricia Knözinger Helmut 《Topics in Catalysis》2000,11(1-4):123-130
Adsorption of NO on vanadia–titania samples pre-subjected to different reduction treatments has been studied by FTIR spectroscopy.
When the NO adsorption is performed at 85 K on oxidized samples, antisymmetric NONO species, typical for V5+ sites, are detected and characterized by bands at 1779 and 1686 cm−1. At ambient temperature, however, adsorption is negligible and only with time reactive adsorption occurs producing NO+ (2120 cm−1), nitro/nitrato species (bands in the 1650–1100 cm−1 region) and weakly adsorbed NO (broad band at 1915 cm−1). Adsorption of NO at ambient temperature on reduced samples results in the formation of two types of species: (i) V4+(NO)2 dinitrosyls characterized by νs(NO) and νas(NO) at 1903–1880 and 1769–1753 cm−1, respectively, and (ii) V3+(NO)2 complexes, which give rise to νs(NO) at 1834–1822 cm−1 and νas(NO) at 1697–1685 cm−1. At low temperature the dinitrosyls are transformed into species in which more than one (NO)2 dimer is attached to one cationic site. Addition of O2 to NO, preadsorbed on reduced vanadia–titania samples, results in a fast oxidation of the V3+(NO)2 species, whereas the V4+(NO)2 complexes are more stable and do not disappear completely in the presence of oxygen. The results obtained suggest that NO
is a convenient probe molecule for the analysis of the oxidation state of vanadium in vanadia–titania catalysts. To prevent
oxidation of reduced vanadium sites, low equilibrium pressures of NO and registration of the IR spectrum soon after the NO
admission are recommended.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
It was demonstrated that, in contrast to previous results, an NCO surface complex does form on Au/TiO2 catalysts in the high-temperature reaction of NO + CO. By means of Fourier transform infrared spectroscopy two new absorption bands at 2285 and 2105-2210 cm-1, not observed in separate adsorption of reacting gases, were detected during the catalytic reaction. The former is attributed to Au-NCO and the latter to Ti-NCO species. It was assumed that, similar to the case of supported Pt metals, NCO is primarily formed on Au crystallites and then spills over onto titania. This idea was strengthened by the results obtained following the adsorption of HNCO on the catalyst and on the support. 相似文献
4.
L. R. Dugan B. W. Beadle A. S. Henick 《Journal of the American Oil Chemists' Society》1949,26(12):681-685
Summary A study has been made of the infrared absorption spectra of autoxidized methyl linoleate in samples ranging from PV 1 to PV
940 m.e./kg. Principal changes occur in the frequency range 3400–3550 cm−1 where bonded−OH groups absorb and at 1650–1775 cm−1 where >c=0 groups absorb.
Two maxima were observed in oxidized samples in the −OH absorption range: one sharp and distinct at 3467–70 cm−1 which increased in intensity with increase in PV and a broad band which increased with increasing PV until it resolved into
a true maximum at 3430 cm−1. Reduction of typical oxidized samples with KI reagent resulted in disappearance of the 3430 cm−1 band and appearance of a new band above 3500 cm−1. The band at 3430 cm−1 was attributed to −OOH groups associated by hydrogen bridging. The band at 3467 cm−1 and the band appearing above 3500 cm−1 were attributed to −OH groups, the band at the higher frequency resulting directly from reduction of a hydroperoxide.
Absorption due to ketone and aldehyde carbonyl groups appeared only as an indefinite shoulder on the band due to the ester
carbonyl. These were resolved by using the intensity of the sample with PV 1 as Io and that for the oxidized samples as I. A plot of Log Io/I then revealed three maxima. These indicate the presence of two and possibly three carbonyl containing substances other
than the ester carbonyl in autoxidized methyl linoleate.
Absorption in the two critical frequency ranges of fractions of autoxidized methyl linoleate eluted from an adsorption column
correlate with interpretations made from ultraviolet absorption studies of the same substances.
This paper reports research undertaken in cooperation with the Quartermaster Food and Container Institute for the Armed Forces
and has been assigned number 211 in the series of papers approved for publication. The views or conclusions contained in this
report are those of the authors. They are not to be construed as necessarily reflecting the views or indorsement of the Department
of the Army.
Presented at the Fall Meeting of the American Oil Chemists’ Society, New York, Nov. 17, 1948. 相似文献
5.
《Journal of Catalysis》1999,181(1):165-169
In situFourier transform infrared spectroscopy has been used to observe the species deposited on Co-ZSM5 during the decomposition of nitromethane. At 553 K deactivation commences after 60 min. This is accompanied by the formation of bands due to NCO species between 2150 and 2300 cm−1and the sudden development of a very strong band at 1662 cm−1. The latter band can be assigned to the s-triazine compound, melamine, and/or derivatives of it, which cause deactivation by blocking zeolite channels. The most likely chemistry is an initial dehydration of nitromethane to isocyanic acid (HNCO) which forms melamine by reaction with ammonia derived by hydrolysis of HNCO. Cyanuric acid, the cyclic trimer of HNCO, may be an intermediate in the process. 相似文献
6.
Xiao Zhang Zhenfeng He Guangquan Li Yujian Zhang Guowen Li 《Journal of Polymer Research》2010,17(2):255-263
A simple strategy to achieve molecular recognition in water is to make the polymers self-organized into nanospheres which
could incorporate the functional groups containing hydrogen bonding sites into hydrophobic-lipophilic regions. A novel amphiphilic
polymer, Poly(polyoxyethylene-600)-oxy-5-(6-(1-thymine)hexyl)) isophthaloyl (PPETHI), has been synthesized. The PPETHI polymer
could self-organize into nanospheres in dilute aqueous solution, which were 150–300 nm in diameter as estimated by SEM. The
isophthaloyl with side hexyl thymine of the polymer self-organized into hydrophobic regions and the PEG surrounded it. Molecular
recognition between thymine in PPETHI polymer and adenine substrate has been studied by FT-IR. The FT-IR studies demonstrate
that C4=O of thymine has recognized with N-H of adenine through complementary nucleobases. It shows that the typical characteristic
band at 3,352 cm−1 of N-H stretching vibration of adenine shifted to 3,373 cm−1 and the band at 1,685 cm−1 of C4=O of thymine shifted to 1,680 cm−1. To confirm the formation of hydrogen bonds, the N-H band at 3,373 cm−1 and C4=O band at 1,680 cm−1 have retrieved to 3,312 cm−1 and 1,685 cm−1 respectively upon heating to 115 °C or higher by means of variable temperature FT-IR. The formations of hydrogen-bonds between
thymine in the polymer and adenine substrate in nanospheres were confirmed. It could enhance their interaction and loading
capacity. 相似文献
7.
Long-term behavior of oil-based varnishes and paints I. Spectroscopic analysis of curing drying oils
Jacky Mallégol Jean-Luc Gardette Jacques Lemaire 《Journal of the American Oil Chemists' Society》1999,76(8):967-976
The curing of drying oils at 60°C has been investigated by Fourier transform infrared spectroscopy and Fourier transform Raman
analysis of linseed oil and poppyseed oil. In the first step, hydroperoxides are formed (broad vibration band centered around
3425 cm−1) with concomitant conjugation and cis-trans isomerization of the double bonds (disappearance of cis bands at 3011 and 716 cm−1, appearance of trans conjugated and trans nonconjugated bands at 987 and 970 cm−1). The subsequent decomposition of hydroperoxides in the presence of oxygen leads to the formation of alcohols (nitrite band
at 779 cm−1 after nitrogen monoxide treatment), aldehydes (bands at 2810 and 2717 cm−1 in gas phase), ketones (saturated and unsaturated at 1720 and 1698 cm−1, respectively), carboxylic acids (saturated and unsaturated acid fluorides identified at 1843 and 1810 cm−1 after SF4 treatment), and peresters or γ-lactones (near 1770 cm−1). A rapid decrease in the double-bond concentration is recorded when curing continues, and the formation of epoxides, characterized
by a vibration band at 885 cm−1, is observed. Thermolysis experiments have suggested the proposal of a reaction of addition of peroxyl radicals on the conjugated
double bonds as a probable mechanism. This mechanism explains both the rapid disappearance of conjugated double bonds and
the formation of epoxides as intermediate products observed in the initial step of curing. 相似文献
8.
Ching-Shiun Chen Jarrn-Horng Lin Hsiu-Wei Chen Chien-Yuan Wang 《Catalysis Letters》2005,105(3-4):149-155
FT-IR spectra of the co-adsorption of benzene and CO have been performed to identify the preferred adsorption sites of hydrogen
and benzene on a Pt/SiO2 catalyst for hydrogenation of benzene. Results of CO adsorbed on atop sites on Pt/SiO2 includes: an α peak at 2091 cm−1, a β peak at 2080 cm−1 and a γ peak at 2067 cm−1 indicating three kinds of adsorption sites for dissociative hydrogen on Pt/SiO2. The site of lowest CO stretching frequency offers stronger adsorbates–metal interaction for benzene and hydrogen. Hydrogen
binding on the site of lowest CO stretching frequency before benzene adsorption significantly enhances the reaction rate of
benzene hydrogenation. 相似文献
9.
Infrared spectra of adsorbed CO have been used as a probe to monitor changes in Pt site character induced by the coking of
Pt/Al2O3 and Pt–Sn/Al2O3 catalysts by heat treatment in heptane/hydrogen. Four distinguishable types of Pt site for the linear adsorption of CO on
Pt/Al2O3 were poisoned to different extents showing the heterogeneity of the exposed Pt atoms. The lowest coordination Pt atoms (ν(CO)
< 2030 cm−1) were unpoisoned whereas the highest coordination sites in large ensembles of Pt atoms (2080 cm−1) were highly poisoned, as were sites of intermediate coordination (2030–2060 cm−1). Sites in smaller two‐dimensional ensembles of Pt atoms (2060–2065 cm−1) were partially poisoned, as were sites for the adsorption of CO in a bridging configuration. The addition of Sn blocked
the lowest coordination sites and destroyed large ensembles of Pt by a geometric dilution effect. The poisoning of other sites
by coke was impeded by Sn, this effect being magnified for Cl‐containing catalyst. Oxidation or oxychlorination of coked catalyst
at 823 K followed by reduction completely removed coke from the catalyst surfaces.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
Adsorption of N2 on NaY zeolites at 85 K and equilibrium pressures higher than 1 kPa results in the formation of geminal dinitrogen complexes
characterized by an IR band at 2333.5 cm−1 (2255.4 cm−1 after adsorption of 15N2). With decreasing equilibrium pressure the complexes tend to loose one N2 ligand, thus forming linear species characterized by an IR band at 2336.8 cm−1 (2258.7 cm−1 after adsorption of 15N2). All species disappear completely after evacuation. Co-adsorption of N2 and CO revealed that the dinitrogen complexes are formed on Na+ cations. The changes in the concentrations of the linear and geminal N2 species with the changes in the equilibrium pressure are excellently described by equations of adsorption isotherms proposed
earlier for mono- and di-carbonyls.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
Zishan H. Khan Shamshad A. Khan Numan Salah Sami Habib S. M. Abdallah El-Hamidy A. A. Al-Ghamdi 《Nanoscale research letters》2010,5(9):1512-1517
We report the electrical and optical studies of thin films of a-Ga
x
Se100−x
nanorods (x = 3, 6, 9 and 12). Thin films of a-Ga
x
Se100−x
nanorods have been synthesized thermal evaporation technique. DC electrical conductivity of deposited thin films of a-Ga
x
Se100−x
nanorods is measured as a function of temperature range from 298 to 383 K. An exponential increase in the dc conductivity
is observed with the increase in temperature, suggesting thereby a semiconducting behavior. The estimated value of activation
energy decreases on incorporation of dopant (Ga) content in the Se system. The calculated value of pre-exponential factor
(σ0) is of the order of 101 Ω−1 cm−1, which suggests that the conduction takes place in the band tails of localized states. It is suggested that the conduction
is due to thermally assisted tunneling of the carriers in the localized states near the band edges. On the basis of the optical
absorption measurements, an indirect optical band gap is observed in this system, and the value of optical band gap decreases
on increasing Ga concentration. 相似文献
12.
Flavio H. Oliveira Marly E. Osugi Fabiana M. M. Paschoal Demetrius Profeti Paulo Olivi Maria Valnice Boldrin Zanoni 《Journal of Applied Electrochemistry》2007,37(5):583-592
The generation of active chlorine on Ti/Sn(1−x)Ir
x
O2 anodes, with different compositions of Ir (x = 0.01, 0.05, 0.10 and 0.30 ), was investigated by controlled current density electrolysis. Using a low concentration of
chloride ions (0.05 mol L−1) and a low current density (5 mA cm−2) it was possible to produce up to 60 mg L−1 of active chlorine on a Ti/Sn0.99Ir0.01O2 anode. The feasibility of the discoloration of a textile acid azo dye, acid red 29 dye (C.I. 16570), was also investigated
with in situ electrogenerated active chlorine on Ti/Sn(1−x)Ir
x
O2 anodes. The best conditions for 100% discoloration and maximum degradation (70% TOC reduction) were found to be: NaCl pH 4,
25 mA cm−2 and 6 h of electrolysis. It is suggested that active chlorine generation and/or powerful oxidants such as chlorine radicals
and hydroxyl radicals are responsible for promoting faster dye degradation. Rate constants calculated from color decay versus
time reveal a zero order reaction at dye concentrations up to 1.0 × 10−4 mol L−1. Effects of other electrolytes, dye concentration and applied density currents also have been investigated and are discussed. 相似文献
13.
The nature of the Keggin ions of tungstophosphoric acid interacting with Ce0.5Zr0.5O2 solid solution has been investigated. The vibrational study shows additional IR features at 1051 and 957 cm−1 which are correlated to the primary Keggin anions interacting with Lewis sites involving Ce4+ and Zr4+ ions, and thus affecting the P–O and W=Oterminal bonds. The IR study indicates the formation of interfacial Ce4+–O–W and Zr4+–O–W bonds. The chemisorbed Keggin molecular layers on Ce0.5Zr0.5O2 show activity towards conversion of acetophenone to styrene by Meerwein–Ponndorf–Verley reduction followed by dehydration.
The activity is correlated with the relative intensities of IR peaks at 1051 and 957 cm−1 of the perturbed Keggin molecular layers. 相似文献
14.
Akira Yamakata Taka-aki Ishibashi Kan Takeshita Hiroshi Onishi 《Topics in Catalysis》2005,35(3-4):211-216
The present account describes how photochemical reactions over metal oxides are traced by time-resolved infrared (IR) absorption
spectroscopy. The ac-coupled amplification of the IR signal allows detection of transient absorbance changes as small as 10−6 with a time resolution of 50 ns. Band-gap excited electrons in TiO2 and NaTaO3 present a structureless absorption of IR light from 3000 to 1000 cm−1. Reaction-perturbed decay of this absorption evidences the assignment to photoexcited electrons, not to holes. The efficiency
of the water splitting reaction on NaTaO3-based catalysts correlates with the quantity of electrons detected by the IR absorption. A short-lived intermediate state
of 2-propanol oxidation on TiO2 is identified by its vibrational band at 1640 cm−1 superposed on the structureless absorption of electrons. Ru dye (N3) on a TiO2 film is irradiated with a 532-nm light pulse to simulate dye-sensitized solar cells. The neutralization rate of dye cations
and the decay rate of electrons injected in the film are quantified, leading to a three-state model which describes the relaxation
of injected electrons. These results demonstrate the ability of this method in tracing photochemical kinetics over metal oxides. 相似文献
15.
Gaia Piazzesi Daniele Nicosia Mukundan Devadas Oliver Kröcher Martin Elsener Alexander Wokaun 《Catalysis Letters》2007,115(1-2):33-39
The adsorption of HNCO on Fe-ZSM5 was investigated in detail by DRIFT spectroscopy and compared to the adsorption on H-ZSM5,
Al2O3, SiO2, Fe2O3/Al2O3 and Fe2O3/SiO2. At 150 °C, HNCO adsorbs dissociatively on Fe-ZSM5 producing principally isocyanate species (–NCO) adsorbed on Al and Fe
sites. In the presence of water the hydrolysis of the –NCO groups to NH3 was observed. Comparison of the DRIFT results with measurements of the catalytic activity of coated cordierite monoliths
suggests that –NCO groups are likely intermediate species in the hydrolysis of HNCO over Fe-ZSM5. 相似文献
16.
Raúl A. Comelli 《Catalysis Letters》2008,122(3-4):302-309
Potassium and acid ferrierites were impregnated with boron species by wet and incipient wetness techniques. All samples display
a medium-intensity band at 3,450–3,470 cm−1 associated to Si−OH···O groups corresponding to boron-containing units. The 1,398–1,404 cm−1 band assigned to the B–O stretching in BO3 units does not appear on boron–potassium–ferrierite prepared by wet impregnation. Catalytic performance during the linear
butene skeletal isomerization was measured. At 300 °C, boron impregnated by incipient wetness technique on acid ferrierite
reduces both linear butene conversion at a short time and isobutene yield in all time range. Boron–potassium–ferrierite prepared
by wet impregnation has a suitable acidity to promote isobutene production. At 450 °C, this sample shows the best performance,
being the isobutene yield 1.7 times higher than the acid-ferrierite one and reaching the highest isobutene selectivity (92%).
This performance is maintained with time. Both isobutene yield and by-product distribution are strongly affected by temperature;
dimer intermediates are formed. Finally, both kinds of hydroxyl groups corresponding to 3,466 and 3,635 cm−1 bands influence the isobutene production whereas BO3 sites are inactive for this reaction. 相似文献
17.
《Journal of Catalysis》2003,213(2):305-320
CO was used to probe the nature of adsorption sites on Ag/α-Al2O3 epoxidation catalysts and to investigate the effect of Cs and Cl promoters by employing diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and chemisorption measurements. In contrast to previous studies, IR absorption bands for CO chemisorbed on reduced, supported Ag crystallites were observed; however, CO adsorption occurred on only 3–7% of the total Ag surface at 300 K and coverage depended on both the pretreatment and CO pressure utilized. No irreversible CO adsorption occurred on the alumina, whereas linearly bonded CO was the dominant species on the metallic Ag sites. After a 30-min purge, the bands due to these chemisorbed forms of CO decreased in intensity while a band due to bridge-bonded CO increased in intensity, which implies that CO reoriented as the surface concentration of CO decreased. In the presence of Cs, similar behavior was observed and the band intensity of the bridge-bonded CO increased. After reduction at 673 K, cesium suboxides appeared to be formed based on the formation of carbonyl complexes at 2028, 1950, and 1869 cm−1. On reduced Ag catalysts, electronic effects of Cs and Cl were observed and adsorbed CO gave a lower frequency, i.e., 2018 and 2009 cm−1 for Cs-promoted samples reduced at 473 and 673 K, respectively, due to an increase in the electron density on surface Ag atoms, while this band occurred at a higher frequency of 2129 cm−1 with a CsCl-promoted Ag catalyst due to a net decrease in the electron density on surface Ag atoms. After CO adsorption on O-covered Cs-promoted and CsCl-promoted catalysts, a band between 1520 and 1491 cm−1 existed which was assigned to a COO− stretching mode in a carbonate species formed on composite AgCsxOy sites. These studies with CO provide evidence that reduction at 673 K following a calcination step can lead to redistribution of Cs atoms. 相似文献
18.
The conformational changes of quenched isotactic polypropylene (iPP) during stepwise heating have been carefully studied by
in situ Fourier-transform infrared (FT-IR) spectroscopy. Analysis of the corresponding spectra shows that the mechanism of
the extension of short helix into long one happens. Furthermore, it is easier for short helix at 998 cm−1 band to extend into long one than that of short helix at 973 cm−1 band. Meanwhile, for the higher order regularity band at 841 cm−1, the melting-recrystallization seems to occur. However, the number of the higher order regularity band at 1220 cm−1 hardly remains change, which shows the limited increment of the higher order regularity band for quenched iPP in the whole
heating process. In summary, two proposed mechanisms, the extension of short helix into long one and the melting-recrystallization
of the long helix, happen during stepwise heating, which may give us new insights on the mesomorphic-to-monoclinic phase transition
mechanism of quenched iPP from a molecular structure viewpoint. 相似文献
19.
N. Guillet L. Roué S. Marcotte D. Villers J. P. Dodelet N. Chhim S. Tré Vin 《Journal of Applied Electrochemistry》2006,36(8):863-870
Cobalt tetramethoxyphenyl porphyrin (CoTMPP) adsorbed on a high area carbon support (Vulcan XC72-R) and heat-treated at 900 °C under inert atmosphere was studied as electrocatalyst for the reduction of O2 to H2O2 in acid medium. Experiments performed on rotating ring-disc electrode (RRDE) and gas diffusion electrode (GDE) show that the catalyst performance depends on the cobalt loading, going through a maximum at 0.2 wt. % Co. For higher cobalt loadings, a growing part of oxygen is reduced into water, decreasing therefore the selectivity of the catalyst. These results are interpreted in terms of a further reduction of H2O2 on Co-based catalytic sites before leaving the catalytic layer. For a GDE polarized at −150 mV vs. saturated calomel electrode (SCE) and loaded with 0.9 μg cm−2 of 0.2 wt. % Co-based catalyst, a H2O2 production rate of 300 μmol h−1 cm−2 was obtained which is five times higher than the H2O2 production rate measured with Vulcan. In these conditions, the selectivity of the Co-based catalyst for H2O2 production is 92%. The good agreement observed between RRDE and GDE results confirms the relevance of using RRDE experiment for screening these non-precious metal catalysts for further GDE applications. 相似文献
20.
Fourier transform infrared (FTIR) spectroscopy provides a simple and rapid means of detecting lard blended with chicken, lamb,
and cow body fats. The spectral bands associated with chicken, lamb, and cow body fats and their lard blends were recorded,
interpreted, and identified. Qualitative differences between the spectra are proposed as a basis for differentiating between
the pure animal fats and their blends. A semiquantitative approach is proposed to measure the percent of lard in blends with
lamb body fat (LBF) on the basis of the frequency shift of the band in the region 3009–3000 cm−1, using the equation y=0.1616x+3002.10. The coefficient of determination (R
2) was 0.9457 with a standard error (SE) of 1.23. The percentage of lard in lard/LBF blends was also correlated to the absorbance
at 1417.89 and 966.39 cm−1 by the equations y=0.0061x+0.1404 (R
2=0.9388, SE=0.018) and y=0.004x+0.1117 (R
2=0.9715, SE=0.009), respectively. For the qualitative determination of lard blended with chicken body fat (CF), the FTIR spectral
bands in the frequency ranges of 3008–3000, 1418–1417, 1385–1370, and 1126–1085 cm−1 were employed. Semiquantitative determination by measurement of the absorbance at 3005.6 cm−1 is proposed, using the equation y=0.0071x+0.1301 (R
2=0.983, SE=0.012). The percentage of lard in lard/GF blends was also correlated to the absorbance at 1417.85 cm−1 (y=0.0053x+0.0821, with R
2=0.9233, SE=0.019) and at 1377.58 cm−1 (y=0.0069x+0.1327, with R
2=0.9426, SE=0.022). For blends of lard with cow body fat (CBF) bands in the range 3008–3006 cm−1 and at 1417.8 and 966 cm−1 were used for qualitative detection. The equation y=−0.005x+0.3188 with R
2=0.9831 and SE=0.0086 was obtained for semiquantitative determination at 966.22 cm−1. 相似文献