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1.
James C. W. Chien Jiun-Chen Wu Chi-I Kuo 《Journal of polymer science. Part A, Polymer chemistry》1982,20(8):2019-2032
The chemical composition of a MgCl2-supported, high-mileage catalyst has been determined at every stage of its preparation. Ball milling of MgCl2 with ethyl benzoate (EB) resulted in the incorporation of 95% of the EB present to give MgCl2·EB0.15. A mild reaction with a half-mole equivalent of p-cresol (PC) at 50°C for 1 h resulted in near quantitative retention of p-cresol by the support. The composition is now approximately MgCl2·EB0.15P?0.5. Addition of an amount of AlEt3 corresponding to half-mole equivalent of p-cresol liberated one mole of ethane per mole of p-cresol, thus signaling quantitative reaction between the two components. The support contains on the average one ethyl group per Al. Further reaction with TiCl4 resulted in the incorporation of titanium of approximately 8, 38, and 54% in the oxidation states of +2, +3, and +4, respectively. The ratio of Al to Ti in the catalyst lies in the range of 0.5–1.0. Only 19% of all the Ti+3 species in the catalyst can be observed by electron paramagnetic resonance (EPR); these are attributable to isolated Ti+3 complexes. The remaining EPR silent Ti+3 species are believed to be bridged to another Ti+3 by Cl ligands. The total Cl content is equal to the sum of 2 × Mg + 3 × Al + 3.5 × Ti. Most of the p-cresol moiety apparently disappeared from the support, leaving much of ethyl benzoate in the catalyst. Activation with AlEt3/methyl-p-toluate complex reduces 90% of the Ti+4 in the catalyst to lower oxidation states. The ester apparently moderates the alkylating power of AlEt3 to avoid excessive formation of divalent titanium sites. There appears to be a constant fraction of 1/4–1/5 of the titanium which is isolated and the remainder is in bridged clusters independent of the oxidation states of titanium. 相似文献
2.
James C. W. Chien Takashi Nozaki 《Journal of polymer science. Part A, Polymer chemistry》1991,29(4):505-514
Hydrogen (pH2 = 72 torr) increases the rate of propylene polymerization by a MgCl2/ethyl benzoate/p-cresol/AlEt3/TiCl4-AlEt3/methyl-p-toluate catalyst (CW-catalyst) by two-to three-fold which corresponds closely with the increase in the number of active sites as counted by radiolabeling with tritiated methanol. The oxidation states of titanium in decene polymerizations by the CW-catalyst were determined as a function of time of polymerization (tp). In the absence of H2, all [Ti+n] for n = 2, 3, 4 remain constant during a batch polymerization. In the presence of H2 and within 5 min of tp, [Ti+2] decreases by an amount, corresponding to 15% of the total titanium and [Ti+3] increases by the same amount, while [Ti+4] is not changed. Therefore, three-fourths of the H2 activation result from oxidative addition processes. The remaining one-fourth of the H2 activation may be attributed to the activation of previously deactivated Ti+3 ions by hydrogenolysis. Monomer converts some of the EPR silent Ti+3 sites to EPR observable species resulting in their activation. 相似文献
3.
James C. W. Chien Siegfried Weber Youliang Hu 《Journal of polymer science. Part A, Polymer chemistry》1989,27(5):1499-1514
A precise method for the determinations of Ti+2, Ti+3 and Ti+4 was developed. The CW-procatalyst before activation contains mostly Ti+4 ions with 6% Ti+3 and 4% Ti+2 ions. Activation with AlEt3 alone at room temperature reduced all the titaniums to lower valence states consisting of 71% Ti+3 and 29% Ti+2. Reduction is incomplete when methyl-p-toluate was present as external Lewis base during activation: at 25°C the distribution of Ti+4 : Ti+3 : Ti+2 is 36% : 25% : 38%; the distribution at 50°C is 37% : 22% : 40%. Aging of the activated catalyst caused little or no changes in the distribution of [Ti+n]; whereas the catalytic activity decays rapidly with aging. The aged catalysts have polymerization activity comparable to the decreased activity of the catalyst during a polymerization. The [Ti+n] was determined for the CW-catalyst during the course of a decene polymerization; they were found to be Ti+4 : Ti+3 : Ti+2 = 30% : 27% : 43%, which did not change with polymerization time. These results suggest that the reducibility of Ti+4 species by AlEt3 or 3AlEt3/MPT to different valence states is predicated by their structures. These species do not undergo further changes in their oxidation states during either aging or polymerization. Their decays probably involve nonreductive metathesis reactions like those known for zirconium alkyls. Possible structures for the stereospecific and nonspecific sites are proposed. 相似文献
4.
James C. W. Chien Youliang Hu 《Journal of polymer science. Part A, Polymer chemistry》1989,27(3):897-913
Superactive Ziegler–Natta catalysts have been prepared from a soluble MgCl2·2-ethyl hexanol adduct in the presence of organic esters through reactions with TiCl4 and activated with AlEt3/phenyltriethoxy-silane. Electron paramagnetic spectra (EPR) were used to elucidate the nature and amount of those Ti+3 ions not bridged to another Ti+3 ion; the chlorine bridged Ti+3 ions are EPR silent. The EPR spectra were attributed to two rhombic Ti+3 sites with principal values for the g-tensors (1.967, 1.949, 1.915; and 1.979, 1.935, 1.887). The total amount of the EPR species, obtained by double integration of the EPR spectra, is in close agreement with the concentration of isospecific catalytic sites determined by radiotagging. This suggests that the nonspecific sites are EPR silent. When o-phthalic ester was present during the catalyst synthesis, there appears an EPR signal at the free electron g-value. This signal was attributed to a Ti+3 phthalate species with resonance stabilization and spin delocalization; it is absent in the catalysts made in the presence of monoesters such as ethyl benzoate. The effects of monomer, O2, H2O, and I2 on the EPR spectra were investigated. The changes in the EPR spectral intensity and the total Ti+3 ions, the latter determined by redox titrations during a polymerization or catalyst aging, are described. The results were extensively compared with those observed for supported Ziegler–Natta catalyst prepared with crystalline MgCl2. 相似文献
5.
James C. W. Chien Tsunle Ang 《Journal of polymer science. Part A, Polymer chemistry》1987,25(4):1011-1026
Polymerizations of decene-1 were carried out from 0° to 70° at A/T = 167 and [M] = 0.75 M initiated by 0.17, 0.34, and 0.69 mM of Ti contained in the MgCl2/ethylbenzoate/p-cresol/AlEt3/TiCl4-AlEt3/methyl-p-toluate catalyst. The rate of polymerization is directly proportional to the catalyst concentration. About 12% of the Ti in the catalyst is initially active at 50°; they are 1.4%, 8.8%, and 9.4% at 0°, 25°, and 70°, respectively. The changes of Rp with temperature parallels the variations in the active site concentration. The decline of Rp with time has second-order plots with slopes which are inversely proportional to the catalyst concentration, but the rate constants for these deactivations are nearly the same for decene and propylene polymerizations. These results strongly support a mechanism of deactivation involving two adjacent sites in the catalyst particle surfaces. The rate constants of propagation and of chain transfer to AlEt3, the energetics for these processes, and MW and MW distribution data have been obtained. 相似文献
6.
7.
James C. W. Chien Jiun-Chen Wu Chi-I. Kuo 《Journal of polymer science. Part A, Polymer chemistry》1983,21(3):725-736
Fourier transform infrared (FTIR) spectra were obtained for a typical MgCl2-supported, high-mileage catalyst for propylene polymerization. When ball-milling MgCl2 with ethyl benzoate (EB), the latter is incorporated into the support (I) by Lewis acid-base complexation involving both oxygen atoms of the ester. Reaction of (I) with p-cresol (PC) resulted in a material (II) that contains all the characteristic IR bands of PC. The reaction of (II) that contains all the characteristic IR bands of PC. The reaction of (II) with AlEt3 (TEA) resulted in (III) whose spectrum supports the reaction observed by product analysis and NMR spectroscopy. There was no evidence of any reaction between TEA and EB. Further reaction of (III) with an excess of TiCl4 caused substantial removal of the p-cresol moiety as shown by the diminution of its characteristic bands. Finally, activation with 3TEA-1MT (methyl-p-toluate) complexes gave spectra that revealed the presence of MT in the activated catalyst without any visage of p-cresol moiety. The nondestructive FTIR method, however, is not quantitative. Quantitative analysis of the organic components in the support materials (I), (II), and (III) and the catalysts was accomplished by hydrolysis of the inorganic components, extraction with ether, and analysis by gas chromatography. The results are in good agreement with composition deducted from elemental analysis and substantiate the FTIR conclusions. 相似文献
8.
Probing the Coordinative Unsaturation and Local Environment of Ti3+ Sites in an Activated High‐Yield Ziegler–Natta Catalyst
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Elena Morra Prof. Elio Giamello Prof. Sabine Van Doorslaer Giuseppe Antinucci Dr. Maddalena D'Amore Prof. Vincenzo Busico Prof. Mario Chiesa 《Angewandte Chemie (International ed. in English)》2015,54(16):4857-4860
The typical activation of a fourth generation Ziegler–Natta catalyst TiCl4/MgCl2/phthalate with triethyl aluminum generates Ti3+ centers that are investigated by multi‐frequency continuous wave and pulse EPR methods. Two families of isolated, molecule‐like Ti3+ species have been identified. A comparison of the experimentally derived g tensors and 35,37Cl hyperfine and nuclear‐quadrupole tensors with DFT‐computed values suggests that the dominant EPR‐active Ti3+ species is located on MgCl2(110) surfaces (or equivalent MgCl2 terminations with tetra‐coordinated Mg). O2 reactivity tests show that a fraction of these Ti sites is chemically accessible, an important result in view of the search for the true catalyst active site in olefin polymerization. 相似文献
9.
James C. W. Chien Chi-I Kuo 《Journal of polymer science. Part A, Polymer chemistry》1985,23(3):731-760
Two methods were used in an attempt to determine by radioquenching the active site concentration, [Ti*], in a MgCl2 supported high activity catalyst. For the reactions of tritium labelled methanol, the kinetic isotope effects were first determined: kH/kT = 1.63 for the total polymer and 1.67 for the isotactic polypropylene fraction. Polymerizations were quenched with an excess of isotopic CH3OH after various lengths of time, at different A/T (amount of AlEt3 with 0.33 equivalent of methyl-p-toluate to amount of Ti in the catalyst) ratios, and temperatures. From the known specific activity of tritium in CH3OH and radioassay of the polymer, value of the total metal polymer bond, [MPB], can be obtained. [MPB] increases linearly with polymerization time. Extrapolation to t = 0 gives [MPB]0, which should be close to [Ti*] because chain transfer with aluminum alkyls to produce Al–P bonds is negligible during very early stage of the polymerization. The values of [MPB]0 range from 7–30% of the total Ti; the number of MPB is nearly equally distributed in the amorphous and isotactic fractions of polypropylene in most runs. The rate of incorporation of radioactive CO into polymers produced by the MgCl2 supported high mileage catalyst is far slower than that claimed by some investigators for TiCl3 type catalysts. There is an initial rapid phase of incorporation of CO which lasts for about 1 hr of contact time. The subsequent rate of CO incorporation steadily declines, yet there is no constant maximum value of radioactivity even after 48 h of reaction in the absence of monomer. Radioquenching of polymerizations with CO was also performed at several temperatures and A/T ratios. In all cases, the maximum [Ti–P] was reached after 30–40 min of polymerization, whereas the maximum rates of polymerization, Rp,m, occurred within 3–10 min. In fact, the rate of polymerization decays to a small fraction of Rp,m after 30–40 min. Furthermore, this maximum value of [Ti–P] remains constant until the end of polymerization (t = 90 min). Therefore, isotopic CO is not reacting with the initially formed active sites Ti1*, but only with those sites, Ti2*, which predominate during the later stage of polymerization. 相似文献
10.
James C. W. Chien Tsunle Ang 《Journal of polymer science. Part A, Polymer chemistry》1987,25(3):919-934
Decene-l was polymerized with the MgCl2/ethylebenzoate/p-cresol/AIEt3/TiCl4-AlEt3/methyl-p-toluate catalyst at 50° using an A/T ratio of 167 and a range of monomer concentration. The concentration of the two kinds of active sites are [Ti] = 12% and [Ti] = 4% of the total titanium. The rate constants of propagation are 24 M?1 s?1. Chain transfers to AIEt3, monomer, and by β-hydride elimination have rate constant values of 1.7 × 10?3 M?1 s?1, 1.34 × 10?2 M?1 s?1, and 1.7 × 10?2 s?1, respectively. Poly(decene-l) have relatively narrow MW which are unchanged during the course of a polymerization. Therefore, the active site concentrations in the CW catalyst for propylene and decene polymerization are identical and their rate constant values agree within a factor of 2. However, the rate of decene polymerization depends on fractional order of monomer concentration and decreases with the increase of activator concentration. Furthermore, the formation of metal polymer bonds has a rate independent of these concentrations. These kinetic behaviors are a manifestation of absorption processes of these species which are not seen in propylene polymerizations. 相似文献
11.
James C. W. Chien Youliang Hu 《Journal of polymer science. Part A, Polymer chemistry》1987,25(10):2881-2892
Hydrogen has been found earlier to increase the initial rate of polymerization by MgCl2/EB/PC/AlEt3/TiCl4-AlEt3/MPT, CW-catalyst (+Bi, +Be) (EB, ethyl benzoate; PC, p-cresol; MPT, methyl-p-toluate), but decays more rapidly as compared to polymerizations in the absence of H2. In this study the effect of H2 was studied when either the internal Lewis base, EB Bi, or the external Lewis base, MPT Be, or both are deleted from the CW-catalyst. H2 does not affect the stereospecificity of all the catalysts, but causes a slight increase of polymer yield, whereas the yield is virtually unchanged by H2 for the catalysts activated with Be. Unlike the catalyst (+Bi, +Be) where H2 increases active site concentrations [Ti*] about threefold, it affects [Ti*] negligibly when Be is absent. The rate constants of propagation is about the same with or without H2 for the CW-catalyst (+Bi, –Be) or (–Bi, –Be); the same statement can be said about the rate constant of chain transfer with AlEt3 or with H2. Hydrogen increases the rate of catalyst site deactivation for the various catalysts in the order of(+Bi, +Be) > (–Bi, –Be) > (+Bi, –Be). 相似文献
12.
James C. W. Chien Phillipe Bres 《Journal of polymer science. Part A, Polymer chemistry》1986,24(8):1967-1988
The effect of external Lewis base (Be) on the polymerization of ethylene by the MgCl2/ethyl benzoate/p-cresol/AlEt3/TiCl4 catalyst was studied by activation with AlEt3 alone without the use of methyl-p-toluate. The initially formed active site concentration, [Ti], is about doubled in the absence of Be; at 50°C about 93% of the total titanium became catalytic. The same increment of [Ti] was observed without Be. The rate constants of propagation are not appreciably affected by Be; the values are the same at 50° with and without Be. At other temperatures the kp values are somewhat smaller without Be. One major effect was the very large k values for chain transfer with aluminum alkyls in the absence of Be as compared to those with Be. This can be attributed to the greater monomeric AlEt3 concentration in the former, but in much smaller amounts in the presence of Be due to complexation. The rate constants of chain transfer with hydrogen are not much affected by Be. However, the termination rate constants are generally much smaller when Lewis base is not present. 相似文献
13.
James C. W. Chien Youliang Hu 《Journal of polymer science. Part A, Polymer chemistry》1987,25(10):2847-2870
A systematic study has been made on the functions of external Lewis base (Be, methyl-p-toluate, MPT) and internal Lewis base (Bi, ethyl benzoate, EB) for the CW-catalyst system MgCI2/EB/PC/AlEt3/TiCl4–AlEt3/MPT (PC, p-cresol). Bi is a nonstereoselective modifier. It increases the active site concentrations and rate constants of propagation, kp, of both the isospecific and nonspecific sites, and thus the productivities of the stereoregular and irregular polypropylenes by five- to tenfold. It seems that Bi complexes with the MgCl2 support to lower the electronegativity of the surface Mg atoms. It also acts to lower the rate constant of chain transfer to aluminum alkyl, k, by two- to fourfold. The action of Be is highly stereospecific. The isotacticity index of polypropylene is ? 95% in the presence of Be but ? 68% without it. Addition of Be decreases nonspecific [Ti*]a by about (11 ± 2)-fold; there is only about a twofold reduction of the isospecific [Ti*]i. It decreases kp,a about three times but has no effect on kp,i, so that the latter is (21 ± 4) times the former. Be decreases k for transfer with aluminum alkyl much more than it does to k; but it does not affect the rates of chain transfer with monomer and by β-hydride elimination or the rate of catalyst deactivation. The number of active sites without Be is [Ti*]i = 15% and [Ti*]a = 55% for a total of 70%. In the presence of Be they are both about 6%. Optimum performance in propylene polymerizations requires both Bi and Be in the case of the CW-catalyst. 相似文献
14.
Il Kim Hong Ki Choi Jae Ha Kim Seong Ihl Woo 《Journal of polymer science. Part A, Polymer chemistry》1994,32(5):971-977
The kinetics of propylene polymerization catalyzed over a superactive and stereospecific catalyst for the initial build-up period was investigated in slurry-phase. The catalyst was prepared from Mg(OEt)2/benzoyl chloride/TiCl4 co-activated with AlEt3 in the absence or presence of external donor. Despite a very fast activation of the prepared catalyst the acceleration stage of polymerization could be identified by the precise estimation of polymerization kinetics for a very short period of time after the commencement of polymerization (ca. 2 min). The initial polymerization rate, (dRp/dt)0 extrapolated to the beginning of the polymerization was second order with respect to monomer concentration. The dependence of initial polymerization rate on the concentration of AlEt3 could be represented by Langmuir adsorption mechanism. The initial rate was maximum at about Al/Ti ratio of 20. The activation energy for the initiation reaction was estimated to be 14.3 kcal/mol for a short-time polymerization. The addition of a small amount of p-ethoxy ethyl benzoate (PEEB) as an external donor increased the percentage of isotactic polymer, which was obtained after 120 s of polymerization, to 98% and the initial polymerization rate decreased sharply as [PEEB]/[AlEt3] increased. © 1994 John Wiley & Sons, Inc. 相似文献
15.
N. N. Chumachenko G. D. Bukatov S. A. Sergeev V. A. Zakharov 《Kinetics and Catalysis》2011,52(2):234-241
The oxidation state of titanium and the coordination state of Ti3+ ions in TiCl4/D1/MgCl2 (D1 is a phthalate) supported titanium-magnesium catalysts (TMCs) after the interaction with an AlEt3/D2 cocatalyst (D2 is propyltrimethoxysilane or dicyclopentyldimethoxysilane) were studied by chemical analysis and EPR spectroscopy. Different
oxidation state distributions of titanium ions were observed in the activated catalyst and mother liquor: Ti3+ and Ti2+ ions were predominant in the activated catalyst and mother liquor, respectively. The effects of interaction conditions (reaction
temperature and time and Al/Ti and D2/Ti molar ratios) of TMCs with the cocatalyst on the state of titanium in activated samples were studied. The interaction
of TMCs with the cocatalyst decreased the titanium content and caused the appearance of aluminum in the activated sample,
which was most clearly pronounced at a temperature of 25°C and occurred within the first 10 min of treatment. An increase
in the temperature to 70°C and an increase in the interaction time to 60 min only slightly affected the concentrations of
titanium and aluminum. The presence of D2 as a cocatalyst constituent facilitated the removal of titanium compounds and restricted the adsorption of aluminum compounds
on the catalyst surface. The main fraction of titanium consisted of Ti3+ ions (62–89%), and the rest was Ti4+ ions (22–35%) under mild interaction conditions (25°C; Si/Ti = 25) or Ti4+ (0–21%) and Ti2+ (9–21%) ions under more severe conditions (50 or 70°C; Si/Ti from 0 to 5). According to EPR-spectroscopic data, at D2/Ti from 1 to 5, Ti3+ ions mainly occurred as associates, whereas they occurred as isolated ions at D2/Ti = 25. The initial and activated catalysts were similar in activity in the reaction of propylene polymerization, and titanium
compounds, which were removed from the catalyst upon interaction with AlEt3/D2, were inactive in this process. 相似文献
16.
M. A. Schen F. E. Karasz James C. W. Chien 《Journal of polymer science. Part A, Polymer chemistry》1983,21(9):2787-2812
The kinetics of acetylene polymerization initiated by Ti(OBu)4/4AlEt3 catalyst was studied by radioquenching with C*O to count the number of active sites [C] and by CH3OT* to determine the total metal polymer bonds [MPB] and M?n of the polymer. The amount of quenching agent and time of reaction required and the kinetic isotope effect for CH3OT* were determined. The effects of Al/Ti ratio, catalyst aging, catalyst concentration, temperature, and monomer pressure on the polymerization were investigated. Detailed kinetic data on the variation of rate of polymerization, Rp, [C] [MPB], and M?n with time were obtained at 298 and 195°K. The results required the assumption that the catalytic species C, is initially active and within less than 30 min all are converted by bimolecular kinetics to a far less active species. Analysis of the data yielded rate constants of propagation and termination and their energies of activation. Estimates of chain transfer efficiency were obtained. The mechanisms for the propagation, termination, and transfer processes were discussed. By drawing on our earlier EPR results we propose probable structures for the catalytically active species. 相似文献
17.
Ruicheng Ran 《Journal of polymer science. Part A, Polymer chemistry》1993,31(6):1561-1569
A polymer-supported Ziegler–Natta catalyst, polystyrene-TiCl4AlEt2Cl (PS–TiCl4AlEt2Cl), was synthesized by reaction of polystyrene–TiCl4 complex (PS–TiCl4) with AlEt2Cl. This catalyst showed the same, or lightly greater catalytic activity to the unsupported Ziegler–Natta catalyst for polymerization of isoprene. It also has much greater storability, and can be reused and regenerated. Its overall catalytic yield for isoprene polymerization is ca. 20 kg polyisoprene/gTi. The polymerization rate depends on catalyst titanium concentration, mole ratio of Al/Ti, monomer concentration, and temperature. The kinetic equation of this polymerization is: Rp = k[M]0.30[Ti]0.41[Al]1.28, and the apparent activation energy ΔEact = 14.5 kJ/Mol, and the frequency factor Ap = 33 L/(mol s). The mechanism of the isoprene polymerization catalyzed by the polymer-supported catalyst is also described. © 1993 John Wiley & Sons, Inc. 相似文献
18.
Takeo Saegusa Hirosuke Imai Shu-Ichi Matsumoto 《Journal of polymer science. Part A, Polymer chemistry》1968,6(3):459-465
Kinetic studies were carried out on the polymerization of tetrahydrofuran with catalyst systems of aluminum alkyl–epichlorohydrin. As aluminium alkyl species AlEt3, AlEt3–H2O (1:0.1 to 1:1.0), and “oxyaluminum ethyl” were employed. The polymerizations with these catalysts are characterized by a mechanism of stepwise addition without chain transfer or termination, which is expressed by the kinetic relation Rp = Kp[P*] ([M]–[M]e), where [M] and [M]e are the instantaneous and equilibrium concentrations of monomer and [P*] is the concentration of propagating species calculated from the amount and molecular weight of the product polymer. The determination of the rate constant kp for these catalysts has shown that the polymerization rate varied considerably with the change of aluminum alkyl species, i.e., with the water-to-aluminum ratio, but the propagation rate constant itself varied very little. The variation of polymerization rate was, therefore, attributed primarily to the differences in concentration of the propagating species, i.e. the efficiency of the catalyst in forming propagating species. The catalyst efficiency was closely related to the acid strength of the aluminum alkyl species, which was estimated from the magnitude of shift of the xanthone carbonyl band in the infrared spectrum of its coordination complex with aluminum alkyl. The maximal catalyst efficiency was attained at about [H2O]/[AlEt3] = 0.75. 相似文献
19.
James C. W. Chien Jiun-Chen Wu 《Journal of polymer science. Part A, Polymer chemistry》1982,20(9):2445-2460
The reactions between AlEt3 and the modifiers, promoters, and coactivators of a typical magnesium-chloride-supported, high-activity propylene polymerization catalyst were studied. Infrared, MS analysis of the gas evolved, and GC–MS of the hydrolysis products for the reaction between AlEt3 and p-cresol showed rapid and quantitative reactions with p-cresol either in the support or solution. The reaction products from AlEt3 and esters were hydrolyzed, acidified, and dehydrated. The resulting carbonyl and olefinic compounds were identified by GC–MS. Proton and carbon nuclear magnetic resonance (NMR) techniques were also used to study these reactions. The expected intermediates were found in the PMR and CMR spectra. The mechanisms of reactions were proposed. The results of this study showed that when AlEt3 and esters are used as coactivators reaction products that can significantly influence the performance of the catalyst are formed. 相似文献
20.
Irradiations of Ni/TiO2 catalyst by UV in hydrogen at 77 K produced not only Ni+ ions on the catalyst surface, but also Ni3+ and Ti3+ species in bulk or near the interface between nickel and titania. These photo-generated species were detected and characterized by low temperature electron paramagnetic resonance (EPR) spectroscopy. Relative spin concentrations of the photogenerated paramagnetic species (Nin+ and Ti3+) varied with the nickel content in titania. A high nickel content in the sample resulted in a high peak intensity ratio of Nin+ to Ti3+. It was found that the photoinduced self-redox reaction of Ni2+ ions to form Ni+ and Ni3+ ions has a priority over the photoreduction of Ti4+ to Ti3+ ions. The characteristic EPR spectrum of the Ni3+ (3d7) ions with g1 = 2.268, g2 = 2.237, and g3 = 2.045 indicates that the Ni3+ ions are most likely located in the substitutional sites of TiO2, possibly near the surface rutile phase. The Ni+ species (3d9) with g4 = 2.130 and g1 = 2.063 are on the surface of TiO2. Both Ni+ and Ni3+ ions are quite stable in hydrogen. The Ni3+ ions seem to be responsible for anchoring the nickel ions onto titania and stablizing the Ni+ species on the surface. The Ni+ ions are thus free from oxygen poisoning and still show a high activity toward olefin oligomerization. 相似文献