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γ-Al2O3 and γ-Al2O3 impregnated with phosphorus and/or molybdenum, amorphous AlPO4, and Al2 (MoO4) 3 have been studied by the recently introduced multiple-quantum magic angle spinning (MQMAS) NMR and off-resonance nutation NMR. Average ...
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The morphology of WS2 on sulfided tungsten and nickel–tungsten catalysts supported on alumina and fluorinated alumina, prepared from ammonium metatungstate and ammonium tetrathiotungstate, was investigated by means of high-resolution... more
The morphology of WS2 on sulfided tungsten and nickel–tungsten catalysts supported on alumina and fluorinated alumina, prepared from ammonium metatungstate and ammonium tetrathiotungstate, was investigated by means of high-resolution transmission electron microscopy. The sulfided catalysts prepared from ammonium metatungstate contain mainly single-layered WS2 slabs, while those prepared from ammonium tetrathiotungstate contain more multilayered WS2 slabs. Incorporation of nickel increases the stacking and stabilizes small WS2 crystallites. Fluorination of the alumina support increases the fraction of multilayered WS2 slabs and increases the WS2 slab diameter.
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ABSTRACT The hydrogenation of (S)-proline-modified anthranilic acid was studied on Rh and Ru catalysts. The hydrogenation occurred with a very high diastereoselectivity but a moderate chemoselectivity. In general, the carbon-supported... more
ABSTRACT The hydrogenation of (S)-proline-modified anthranilic acid was studied on Rh and Ru catalysts. The hydrogenation occurred with a very high diastereoselectivity but a moderate chemoselectivity. In general, the carbon-supported catalysts exhibited a higher activity but a lower diastereoselectivity than the alumina-supported catalysts. The use of water as the solvent instead of ethanol resulted in higher activities but lower diastereoselectivities. Rh- and Ru-based homogeneous catalysts gave a comparable selectivity but a lower activity than their heterogeneous counterparts.
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The nitration of toluene and nitrotoluene was studied using solid acid catalysts and nitric acid in acetic anhydride. Increased para selectivity was observed with zeolite H-beta both for the nitration of toluene and nitrotoluene. The... more
The nitration of toluene and nitrotoluene was studied using solid acid catalysts and nitric acid in acetic anhydride. Increased para selectivity was observed with zeolite H-beta both for the nitration of toluene and nitrotoluene. The increased selectivity was related to sites located in the micropores of the zeolite and seems to originate from steric hindrance induced by adsorption.
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The feasibility of reinsertion of non-framework aluminum into the lattice of dealuminated HZSM-5 zeolites upon acid treatment was investigated by powder X-ray diffraction, nitrogen adsorption, elemental analysis, solid-state NMR and... more
The feasibility of reinsertion of non-framework aluminum into the lattice of dealuminated HZSM-5 zeolites upon acid treatment was investigated by powder X-ray diffraction, nitrogen adsorption, elemental analysis, solid-state NMR and Fourier transform infrared (FTIR) spectroscopy. XRD and nitrogen adsorption revealed that no structural degradation of the HZSM-5 zeolite matrix took place during dealumination and acid treatment. FTIR and multinuclear NMR spectroscopy showed that hydrothermal treatment was more effective in dealumination than the mere calcination treatment. In the dealuminated samples, a fraction of the tetrahedral aluminum was present as extra-lattice aluminum. No spectroscopic evidence of reinsertion of aluminum into the framework was observed after acid treatment. On the contrary, in addition to leaching of the octahedral extra-framework aluminum, part of the framework aluminum was extracted as well. A fraction of the tetrahedral aluminum did not belong to the zeolite lattice. Elemental analysis revealed that silicon was present in the mother liquor of the acid treatments. It is proposed that an amorphous phase of silico-aluminate, with aluminum in tetrahedral coordination, is formed as a result of the reaction between this silicon and the aluminum in the extracted solution.
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ABSTRACT Well-dispersed palladium nanoparticles immobilized onto modified silica (SiO2-pr-NH-cyanuric-SH) have been prepared in some facile steps. The catalyst exhibits high catalytic activity in the Heck reaction, and can be easily... more
ABSTRACT Well-dispersed palladium nanoparticles immobilized onto modified silica (SiO2-pr-NH-cyanuric-SH) have been prepared in some facile steps. The catalyst exhibits high catalytic activity in the Heck reaction, and can be easily recovered and reused without significant loss of its activity in several runs.
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The mechanism of the hydrodenitrogenation of the mixed dialkyl- and trialkylamines C1NHC6 and C1N(C6)2 was studied over sulfided NiMo/γ-Al2O3 at 280°C and 3MPa. C1NHC6 reacted by disproportionation to C1N(C6)2 as well as C6N(C1)2 and by... more
The mechanism of the hydrodenitrogenation of the mixed dialkyl- and trialkylamines C1NHC6 and C1N(C6)2 was studied over sulfided NiMo/γ-Al2O3 at 280°C and 3MPa. C1NHC6 reacted by disproportionation to C1N(C6)2 as well as C6N(C1)2 and by substitution by H2S to methylamine and hexanethiol as well as hexylamine and methanethiol. C1N(C6)2 reacted by substitution with H2S to C1NHC6 and C6NHC6 and methane- and hexanethiol. The probability of breaking the C1N bond was only slightly smaller than of breaking the C6N bond in C1N(C6)2. In the reaction of an equimolar mixture of C5NHC5 and C1N(C6)2 both C1N(C5)2 and C6N(C5)2 were formed. The transfer of the methyl group in these reactions cannot be explained by imine and enamine intermediates, only iminium cation intermediates can explain all the products in the hydrodenitrogenation of monoalkyl-, dialkyl- and trialkylamines.