The TpTiCl2(OR) (where Tp = hydrotris(pyrazolyl)borate; R = Me, Et, i-Pr, n-Bu) and TpTiCl3 complexes activated with very low concentration of MAO (≥200 Al/Ti) showed very high activity in the ethylene polymerization. The substitution of one chlorine ligand in the TpTiCl3 for one alkoxyl ligand increases the catalytic activity up to 76 times and 3.4 times respect to Cp2ZrCl2 at the same reaction conditions. The TpTiCl2(OR) precatalysts activity decreases in the following order: TpTiCl2(OEt) > TpTiCl2(On-Bu) ≈ TpTiCl2(Oi-Pr) ≫ TpTiCl2(OMe) > TpTiCl3. The alkyl chain size of the alkoxyl ligands strongly affects the catalytic activity and the molecular weights of the polymers, prevailing the steric effect over the electronic effect. The resulting polymers can be classified as ultra-high molecular weight polyethylenes with basically linear structure.

Reported here are the in situ FT-IR and 13C-NMR spectroscopic studies of the complex cis-[Ir(CO)2(py)2](PF6 ) (py = pyridine) dissolved in 80% aqueous pyridine used as a precursor in the homogeneous catalysis of the water gas shift reaction (WGSR, CO + H2O AE CO2 + H2). These spectroscopy studies reveal the presence of aminocarbonyliridium complexes with linear and bridging carbonyls groups as reaction intermediates. The WGSR catalysis by Ir4(CO)12 complex dissolved in 80% of aqueous 4-picoline or pyridine under 1.9 atm of CO at 100 C and the FT-IR and 1H-NMR in situ studies of the pyridine promoted disproportionation of Ir4(CO)12, are also described

This paper is focused on establishing the grafting products of diethylmaleate onto ethylene-alpha-olefin copolymers of varying comonomer contents. Several commercial ethylene/alpha-olefin copolymers ranging in comonomer contents from 0.35 to 3.70 mol% were used, as well as a hydrogenated polybutadiene (HPB) with a 1,2 unit content of 13.9 mol%. The polymers were functionalized with DEM in solution. The experimental techniques employed to verify the grafting and to ascertain the exact positioning of the insertion with respect to the branching points were: Fourier transform infra red spectroscopy (FTIR), carbon 13 nuclear magnetic resonance (C-13 NMR) and Distortionless enhancement polarization transfer NMR (C-13 NMR-DEPT). Thermal fractionation was performed by Differential Scanning Calorimetry (DSC) employing the successive self-nucleation and annealing technique (SSA).The results obtained show that the DEM insertion onto polyethylene chains occurs in secondary carbons of the main chain regardless of the copolymer branch type and content. The reasons for this behavior may be related to a statistical factor being involved in the peroxide radical attack since there is an excess of secondary carbons as compared to tertiary ones per PE chain. Also, steric effects produced by the size of the DEM molecules are probably involved in the DEM insertion step. Our C-13 NMR-DEPT results suggest that DEM not only avoids the tertiary carbons where the branches are located but also, in polyethylenes with less than 4 mol% branch content, it prefers to insert in the secondary carbons that are at least 5 carbon atoms away from the branch point. In those cases where unsaturations are present in PE chain ends, FTIR shows that they can also be depleted by DEM grafting. However, in the HPB case where no unsaturations are present and the branching content is very high, the insertion still occurs only in the secondary carbons of the main chain. The thermal fractionation performed by SSA corroborated the aforementioned results since the fractions with the longest linear chains were always the first to be depleted by the grafting reactions. (C) 2002 Elsevier Science Ltd. All rights reserved.

The catalytic transformations of n-butane were performed over a Pt-promoted Ga-substituted silicoaluminophosphate molecular sieve (Pt/GaAPSO-11), over a Pt-promoted Ga-supported silicoaluminophosphate molecular sieve, and over a Pt-promoted SAPO-11 solid. The results showed similar yields for the formation of isobutane+isobutene, lower yields for the formation of C1–C3 hydrocarbons, for the Ga containing samples, particularly for the Pt/Ga/SAPO-11 catalyst. The latter also showed higher yields for the formation of dehydrogenated products. Different techniques were used to characterize the metallic and acid functions. The possible formation of a Pt-Ga alloy and/or the formation of discrete Pt particles decorated by metallic Ga, are invoked to explain the higher dehydrogenation and lower hydrogenolysis activity shown by the Pt/Ga/SAPO-11 sample.

Homogeneous catalysts for the water gas shift reaction prepared from Rh2(μ-Pz)2(COD)2 (Pz = pyrazolate ion and COD = 1,5-cyclooctadiene) in aqueous organic solvent media (pyridine, 4-picoline or 2-ethoxyethanol) and Rh2(μ-Pz)2(CO)2(TPPMS)2 (TPPMS = meta-sulfonatophenyl-diphenyldiphosphine) in acidic aqueous media under mild conditions are described. In situ FT-IR, 1H and 13C NMR spectroscopic studies of the Rh2(μ-Pz)2(COD)2 catalytic system reveal the presence of hydrido-Rh complexes with linear and bridging carbonyls. These complexes also catalyze the reduction of nitrobenzene to aniline.

A series of highly crystalline silicoaluminophosphates having the AFI topology (SAPO-5) were synthesized with silicon content varying from 0 (AlPO4-5) to 0.11 molar fraction. As the silicon content increases, the total acidity per gram of solid, as determined by temperature programmed desorption of ammonia (NH3-TPD), also increases. However, the number of total acid sites per Si atom decreases by about 20% when passing from the lowest to the highest Si-containing SAPO. The previous finding is in line with the higher SM2+SM3 Si-substitution character of the latter, as determined by the 29Si MAS NMR technique. Brönsted sites retaining pyridine above 623K (medium+strong acidity) increase progressively with the Si content; however, only the solid with the lowest Si-loading showed Lewis sites of high acid strength. The highest specific activity observed for the latter sample during both the m-xylene and the α-pinene transformation can then be explained by the occurrence of a Lewis–Brönsted synergism. The specific rate of α-pinene transformation over SAPO-5 lay between that for dealuminated mordenite and that for dealuminated Y-zeolite. Camphene and limonene were the main products of the α-pinene transformation amounting up to 80% of the α-pinene converted, with a camphene/(camphene+limonene) ratio of 0.50, at conversion levels between 48 and 55%. Undesirable heavy compounds (HRTP) were less than 1%.

Three different molecular sieves were synthesised and characterized using31P and27Al magic angle spinning nuclear magnetic resonance (31P and27Al MAS NMR) spectroscopy and acidity measurement techniques. The synthesized solids were: a silicoaluminophosphate (SAPO-11) sample, a chromium-substituted silicoaluminophosphate (CrAPSO-11) sample and a chromium-supported SAPO-11 (Cr/SAPO-11) sample. Significant differences were observed between the CrAPSO-11 MAS NMR spectra and the spectra for the other two solids. The differences can be understood in terms of a different chemical environment for the Al(III) and P(V) ions in the molecular sieve framework, as a result of a different type of interaction, probably with substituted chromium ions in the framework. The acidity measurements were in agreement with the MAS NMR spectroscopy results, providing further evidence for the incorporation of chromium ions into the molecular sieve framework.

The skeletal isomerization of 1‐butene was performed over a series of silicoaluminophosphate molecular sieves with AEL structure (SAPO‐11). The results were compared with those obtained over an aluminophosphate molecular sieve (AlPO 4 ‐11). The three SAPO‐11 samples, with different acidic properties, were synthesized by either varying the chemical composition of the synthesis gel or by varying the preparation time of the aforementioned gel. The catalytic results indicate that irrespective of how the acidity of the SAPO‐11 samples is changed (viz., independently of the method elected to modify the acidic properties of the samples), a close parallelism between the selectivity towards the skeletal isomerization and the number of (moderate + strong) Brønsted acid sites (sites retaining pyridine above 623 K) was observed for the SAPO‐11 solids. These results, definitively, indicate the participation of these acid sites in the skeletal isomerization process.

Surface and chemical characterization were performed on a manganese-substituted silicoaluminophosphate molecular sieve (MnAPSO-11), and on a manganese-supported silicoaluminophosphate molecular sieve (Mn/SAPO-11). For comparison purposes, the characterization process was also carried out over the parent SAPO-11 molecular sieve. Different characterization techniques were used: XPS, redox cycles, P-31 MAS NMR, and acidity measurements. The transformations of n-butane were carried out over the corresponding platinum promoted solids (Pt/MnAPSO-11, Pt/Mn/SAPO-11 and Pt/SAPO-11). Platinum dispersion was measured by H-2 chemisorption. XPS results indicated that manganese was better dispersed on the MnAPSO-11 solid than on the supported Mn/SAPO-11 catalyst. Redox cycles showed a strong difference between the H-2 (or O-2) consumed by each solid. The Mn/SAPO-11 consumed nearly three times as much H-2 (or O-2) per Mn atom as the MnAPSO-11 solid. P-31 MAS NMR results showed an increase in the intensity of the side bands, probably due to an anisotropic paramagnetic shift caused by a stronger dipolar interaction between the P-31 and the paramagnetic Mn(II) ions on the MnAPSO-11 sample, when compared with the Mn/SAPO-11 solid. These results suggest a better dispersion of the manganese species on the MnAPSO-11 solid, which would facilitate the above mentioned P-31-Mn(II) interaction, in agreement with the XPS results. Acidity was measured by pyridine chemisorption at different temperatures. A larger number of (moderate + strong) Bronsted acid sites was found for the MnAPSO-11 solid compared with the SAPO-11 and Mn/SAPO-11 samples. The addition of platinum decreased the acidity. The Pt dispersions were 83%, 68% and 54% for the Pt/SAPO-11, Pt/Mn/SAPO-11 and Pt/MnAPSO-11 solids, respectively. The catalytic results indicate higher yields for the production of isobutane and isobutene over the Pt/MnAPSO-11. A severe decrease in the yield of formation of hydrocarbons with less than four carbon atoms (undesirable side reaction) was also observed for the Pt/MnAPSO-11 system compared with the Pt/SAPO-11 and Pt/Mn/SAPO-11 systems. An ensemble effect is suggested as responsible for the differences observed in the yield of formation of hydrocarbons with less than four carbon atoms. The higher yield and selectivity observed for the formation of isobutane (iso-C4) and isobutene (iso-C4=) hydrocarbons over the Pt/MnAPSO-11 solid, was accounted for in terms of the largest number of (moderate + strong) Bronsted acid sites found on this solid. The catalytic and characterization results suggest the incorporation of manganese into the molecular sieve structure for the substituted MnAPSO-11 solid. (C) 1999 Elsevier Science B.V. All rights reserved.

Dealuminated mordenite (MOR) and faujasite (FAU) zeolites, and a 13% alumina amorphous aluminosilicate were tested as catalysts for the liquid-phase transformation of cr-pinene at 120 degrees C in a batch reactor. Limonene and camphene were the main products observed over zeolites. Mordenites gave the maximum yield (68%) of limonene and camphene with a selectivity of camphene/(limonene+camphene) greater than 0.54. Wider pore diameters and larger pore volumes gave higher yields of undesired products, probably sesquiterpenes and other heavy compounds. The amorphous aluminosilicate selectivity to camphene+limonene was the poorest (18%) and gave the highest yield of undesired products (48%). The specific transformation rate of cl-pinene passes through a maximum at 0.4 Al-IV per 1000 Angstrom(3) Of unit cell, corresponding to 1 Al-IV/MOR unit cell or 6 Al-IV/FAU unit cell. (C) 1998 Elsevier Science B.V. All rights reserved.

We report the C-13 NMR chemical shifts of some active quinolones against Plasmodium falciparum, namely 3-amino-9-phenyl-1H-pyrazolo [3,4-b]quinolones and 2,4-diamino-10-phenylpyrimido[4,5-b]quinolones. They were characterized and assigned on the basis of C-13-H-1 (short and long-range) correlated spectre. (C) 1998 John Wiley & Sons, Ltd.

Two proanthocyanidin-containing preparations were isolated from the pulp of ripe Coffea canephora coffee cherries. The preparations were partially purified by Sephadex LH-20 column chromatography and characterised by means of infrared and C-13 NMR spectroscopy, and reactions with several functional group-specific reagents, These proanthocyanidin-rich extracts from coffee pulp, obtained also from coffee leaves, inhibit the germination in vitro of Hemileia vastatrix race 2 uredospores. Greater proanthocyanidin content was associated with greater potency, and the leaves of Coffea arabica, a coffee species susceptible to rust, contained less proanthocyanidins than the leaves of C canephora a, a rust-resistant coffee. (C) 1995 SCI.

The catalytic transformations of n-butane were performed over a platinum-promoted manganese-substituted aluminophosphate molecular sieve (Pt/MnAPO-11), and over a Pt promoted manganese-supported aluminophosphate molecular sieve (Pt/Mn/ALPO(4)-11). For comparison purposes, the reactions were also carried out over a Pt-supported AlPO4-11 molecular sieve (Pt/AlPO4-11). X-ray diffraction (XRD) was used to determine the crystallographic structure of the unpromoted and Pt-promoted samples. Phosphorous 31-magic angle spinning-nuclear magnetic resonance (P-31 MAS NMR) spectroscopy was used to study the possible P-31-Mn(II) dipolar interaction. Bronsted and Lewis acidity were measured by pyridine chemisorption at different temperatures. Pt dispersions were determined by hydrogen chemisorption. CO chemisorption followed by IR spectroscopy was used to corroborate the dispersion measurements and to evaluate possible changes in the electronic density of the Pt phase. The catalytic results indicate higher yields (and selectivities) for the production of isobutane and isobutene over the Pt/MnAPO-11, compared with those observed over the Pt/Mn/ALPO(4)-11 and Pt/AlPO4-11 samples. Also, a severe decrease in the yield, in the selectivity and in the turnover frequency (TOF), for the formation of hydrocarbons with less than four carbon atoms, was observed for the Pt/MnAPO-11 system when compared with the Pt/Mn/AlPO4-11 and Pt/AlPO4-11 solids. A larger number of (moderate + strong) Bronsted acid sites was found for the MnAPO-11 solid compared to the Mn/AlPO4-11 and AlPO4-11 samples. For the last two solids, no Bronsted acidity was detected after evacuation of the catalyst at 623 K. P-31 MAS NMR results showed an increase in the intensity of the side bands, probably due to an anisotropic paramagnetic shift caused by a stronger dipolar interaction between the 31P and the paramagnetic Mn(II) ions on the MnAPO-11 sample, when compared with the Mn/AlPO4-11 solid. These results suggest a better dispersion of the manganese species on the MnAPO-11 solid, which would facilitate the above mentioned 31P-Mn(II) interaction. The addition of platinum decreased the Lewis and Bronsted acidity for all the catalysts studied. The Pt dispersions were 68%, 59%, 49% for the Pt/AlPO4-11, for the Pt/Mn/AlPO4-11 and for the Pt/MnAPO-11 solids, respectively. The constant value obtained for the IR CO-Pt stretching frequency (Pt/AlPO4-11 and Pt/MnAPO-11 samples) (ca 2067 cm(-1)), as well as the drop in the Pt dispersion observed for the manganese containing solids, suggest an ensemble effect as responsible for the differences observed in the yield, selectivity, and TOF of formation of hydrocarbons with <C4. The higher yield and selectivity observed for the formation of iso-C4 and iso-C4= hydrocarbons over the Pt/MnAPO-11 solid, were accounted for in terms of the largest number of (moderate + strong) Bronsted acid sites found on this solid. The catalytic and characterization results suggest the incorporation of manganese into the molecular sieve structure, for the Pt/MnAPO-11 sample. (C) 1998 Academic Press.

A series of substituted AlPO4 molecular sieves with the AEL topology were prepared and characterized by different techniques, to evaluate the amount and nature of the additional elements and their effect on the acidity and catalytic properties of the resulting solids. It was found that a one-to-one interaction between Lewis (L) and Brønsted (B) sites occurs after calcination of the substituted materials, leading to an enhanced acidity and causing, as a result, an increase in the selectivity towards isobutene during the transformation of 1-butene. Substitution models are discussed in order to rationalise the origin and nature of such B-L synergism.

Ga-71 MAS n.m.r. analysis and the catalytic behavior during the transformation of l-butene and n-butane strongly suggest the incorporation of Ga into the AIPO(4)-11 (AEL) framework during the synthesis of GaAPSO-11. A unique clear signal at around +120 ppm is proposed to be associated with the presence of tetrahedral Ga in the AEL framework of the unmodified GaAPSO-11. Migration of structural Ga atoms to the silicon domain of the AEL framework seems to occur as a result of a mild hydrothermal treatment, giving rise to an additional signal at +156 ppm, previously associated with tetrahedral gallium in gallosilicates with the MFI topology. The fact that GaAPO-11 and GaAPSO-11 behaved in a way similar to their counterparts AIPO(4)-11 and SAPO-11 during the skeletal isomerization of n-butenes reinforces the idea of an isomorphous substitution of Al(III) by Ga(III) in the AEL framework. The transformation of n-butane was shown to be a valuable test for detecting the presence of small amounts of hydro-dehydrogenating extraframework gallium species (EFGS) in Ga-supported SAPO-11 (Ga/SAPO-11). The fact that the sample of GaAPSO-11 was completely inactive for Eh is transformation leads us to believe that the incorporation of gallium into the tetrahedral positions of the AEL framework was almost complete. (C) Elsevier Science Inc. 1997.

The catalytic transformations of 1-butene were performed over a chromium-substituted silicoaluminophosphate molecular sieve (CrAPSO-11), over a Cr-supported SAPO-11 molecular sieve (Cr/SAPO-11), and over two SAPO-11 samples. For times-on-stream under 2.5 h, the CrAPSO-11 catalyst showed a higher skeletal isomerization efficiency (SIE) than the two prepared SAPO-11 samples and the supported chromium system. After 2.5 h a drastic decrease in the SIE occurred (for the CrAPSO-11 sample) with a concomitant increase in the formation of butadiene and 2-butenes. The formation of butadiene was considerably hindered over the supported system compared to that of the CrAPSO-11 sample. The cracking reactions as well as the formation of C5+ hydrocarbons were also suppressed over the supported system. The catalysts were recently characterized by XPS and redox cycles (12) and presently studied by XRD, DRS, and NO chemisorption followed by IR spectroscopy and acidity measurements performed with pyridine chemisorption. A larger amount of Cr(VI) was found by DRS and XPS (∼70%) for the oxidic CrAPSO-11 (O2, 773 K), compared to the supported system. For the latter, Cr(III) was the main species present. The NO chemisorption experiments showed the presence of high chromium oxidation states on the oxidic CrAPSO-11. After reduction (H2, 773 K), the distribution of oxidation states of chromium (XPS and NO chemisorption experiments) for the reduced CrAPSO-11 solid, was different ∼40% Cr(VI) and ∼60% Cr(III) compared to the oxidic sample. Cr(VI) showed a higher stability towards reduction in the CrAPSO-11 catalyst when compared to chromium supported on conventional supports. The distribution of oxidation states of chromium was very similar for the oxidic and the reduced Cr/SAPO-11 catalyst. The oxidic CrAPSO-11 catalyst showed an increase in the number of medium+strong acid sites compared to the other catalysts. The reduction process, however, decreased the Brønsted strong acid sites by a factor of two. A concomitant decrease was observed for the medium+strong Lewis acid sites, upon reduction. These results suggest that a partially unsaturated Cr(VI) in the vecinity of P–OH groups may act as strong Lewis sites, generating Brønsted acidity by Brønsted–Lewis interaction, as suggested in the literature. The supported sample showed a decrease of medium+strong Brønsted acid sites compared to the CrAPSO-11 solid. In this case, however, the reduction process did not cause major changes in the acidity distribution. The characterization as well as the catalytic data support and reinforce the model presented by Chen and Sheldon (J. Catal.153, 1 (1995)) for the related CrAPO-5 system. The results suggest the incorporation of chromium into the molecular sieve framework for the CrAPSO-11 catalyst.

The catalytic transformations of 1-butene were performed over a zinc-substituted silicoaluminophosphate molecular sieve (ZnAPSO-11), over a Zn-supported SAPO-11 molecular sieve (Zn/SAPO-11) and over the unpromoted SAPO-11 solid. The ZnAPSO-11 catalyst showed the highest selectivity towards skeletal isomerization as well as the highest skeletal isomerization efficiency (SIE). In addition, the largest number of acid sites, particularly strong acid sites, were observed with temperature-programmed desorption of ammonia (NH3-TPD) over the ZnAPSO-11 catalyst. The acid strength over the latter was also the highest. The agreement between the catalytic and the acidity results obtained in the present work can be explained in terms of the model of Gielgens et al. In this model, the substitution of Al(III) ions by Zn(II) ions leads to partially unsaturated Zn(II) ions in the vicinity of structural P-OH groups. The Brønsted acidity of the latter may be enhanced by Brønsted-Lewis interaction, thus rendering catalysts with stronger acidity necessary for the skeletal isomerization. The lower molar fraction of Al(III) cations found in the ZnAPSO-11 solid, compared to the SAPO-11 sample, strongly supports the above. The results for the Zn-supported system were extremely different. Significant decreases in the strong acidity as well as in the skeletal isomerization selectivity, compared to the ZnAPSO-11 catalyst, were observed. These differences reinforce the idea of incorporation of Zn(II) into the silicoaluminate framework for the ZnAPSO-11 solid.

XRD-pure SAPO-31 and SAPO-11 molecular sieves were obtained from the same synthesis gel, free of seeding, with a relatively low DPA/P2O5 ratio (0.3) after 40 and 120 h of crystallization, respectively, at 353 K. The phase transformation sequence was closely followed by XRD. The initial formation of the dense phases berlinite (B) and cristobalite (C) in the starting gel at a defined proportion seems to play an important role in directing the synthesis toward the desired molecular sieves. Structural factors were invoked to explain differences in the selectivity toward isobutene, observed for samples of SAPO-31 and SAPO-11 with similar acidity characteristics, during the transformation of 1-butene at 743 K and WHSV of 1.8 h(-1). (C) Elsevier Science Inc. 1997.

A chromium-substituted silicoaluminophosphate molecular sieve (CrAPSO-11) and a Cr-supported SAPO-11 molecular sieve (Cr/SAPO-11) were studied by XPS and reduction–oxidation (redox) cycles. The distribution of oxidation states as well as the average oxidation state for chromium were determined for both preparations. The XPS results showed that two chromium 2p doublets (Cr(VI) and Cr(III)) were necessary to curve fit the experimen-tal data. Comparison of curve-fitting results for the two oxidic samples (O2, 773 K) revealed a significantly higher percentage of Cr(III) species in the Cr/SAPO-11 catalyst. The difference between the two samples remained following reduction (H2, 773 K). For the CrAPSO-11 sample, Cr(VI) showed a higher stability towards reduction, compared to chromium supported on conventional supports. This result suggests the incorporation of Cr(VI) into the silicoaluminophosphate framework, as mentioned in the literature. For the Cr/SAPO-11 solid, Cr(III) was extremely stable towards oxidation at 773 K. Due to the redox characteristics and the XPS results, the formation of chromia species on this catalyst is suggested.