Studies of the roles of Sn or Fe on γ-Al2O3-supported Pt catalysts by CO adsorption microcalorimetry and dehydrogenation reaction of C4 alkanes

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.     

Catalytic synthesis of indole from tetrahydroindole on Pd-and Cr-containing catalysts

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.     

Sol–gel synthesis,characterization and photocatalytic activity of mesoporous TiO<Subscript>2</Subscript>/γ-Al<Subscript>2</Subscript>O<Subscript>3 </Subscript>granules

Mesoporous TiO₂/γ-Al₂O₃ composite granules were prepared by combining sol–gel/oil-drop method, using various titania solution. The product granules can be used as a photocatalyst or adsorbent in moving, fluidized bed reactors. The phase composition and pore structure of the granules can be controlled by calcination temperature and using different titania solution. In the photocatalysis of NH₃ decomposition, TiO₂/γ-Al₂O₃ granules using Degussa P25 powder treated thermally at 450 °C showed the highest catalytic ability. However, TiO₂/γ-Al₂O₃ granules using titania made by hydrothermal method had comparable performance in NH₃ decomposition.     

Structural and spectroscopic characterization of Al2−x Cr x O3 powders obtained by polymeric precursor method

Al₂O₃ and Al_2−x Cr _x O₃ (x = 0.01, 0.02 and 0.04) powders have been synthesized by the polymeric precursors method. A study of the structural evolution of crystalline phases corresponding to the obtained powders was accomplished through X-Ray Diffraction and UV-vis spectroscopy (reflectance spectra and CIEL^*a^*b^* color data). The obtained results allow to identify the γ-Al₂O₃ to α-Al₂O₃ phase transition. The single-phase α-Al₂O₃ powder was obtained after heat treatment at 1050 °C for 2 h. The results show that the green to red color transition and ruby luminescence lines observed for the powders of Al_2−x Cr _x O₃ are related to the γ to α-Al₂O₃ phase transition and the temperature and time range for such transition depends on the chromium content.     

Combined transformations of carbon dioxide and ethanol in the presence of the intermetallic compound TiFe0.95Zr0.03Mo0.02, Pd/SiO2, and Al2O3

The influence of the composition of catalytic systems and the method for H₂ feed into the reaction area on the degree of conversion of CO₂ during its joint transformations with ethanol and on the selectivity of formation of liquid organic products (ethyl acetate, acetaldehyde, and hydrocarbons) was studied atp=15 atm andT=573 K. A noticeable conversion of CO₂ and ethanol into ethyl acetate and acetaldehyde was observed in the presence of only the intermetallic compound, its composition with a palladium-containing catalyst, and the whole ternary catalytic system. The selectivity of the reaction changed when the binary catalytic composition consisting of the intermetallic and γ-Al₂O₃ was used. In this case, the fraction of C₉–C₁₄ alkenes and alkenes with normal and iso structures was mostly formed; its content was as high as 40%. The degree of conversion of CO₂ reached 30–36% and the selectivity to liquid products was 70–80% only when the hydrogen desorbed from the intermetallic was used. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1360–1364, July, 1998.     

Non Aqueous Titration and Catalytic Conversion of Cyclohexanol as a Test of Surface Acidity

Summary. The textural characteristics, including surface area, mean pore diameters, and total pore volume of Cr₂O₃–CuO/Al₂O₃ solid catalysts were determined from the low temperature adsorption of N₂ at 77 K. The structural properties were investigated using XRD. The surface acidity of calcined samples was determined using two comparable methods, including the non-aqueous titration of acidic groups with n-butylamine and dehydration/dehydrogenation activity of cyclohexanol. XRD patterns assigned a crystalline CuO and γ-Al₂O₃ for 723 K calcinations products of lower Cr₂O₃ content. The gradual increase of calcinations temperature promoted the crystallinity of Cr₂O₃ and resulted in solid–solid interaction of CuO and Cr₂O₃ forming CuCr₂O₄. The textural parameters varied with both calcinations temperature and catalyst composition. The surface acid density (DAS) increased with the increase of chromia content up to 0.132 mole% Cr₂O₃, while the rise of calcinations temperature led to a decrease of surface acidity. The dehydration/dehydrogenation of cyclohexanol as well as n-butylamine titration succeeded in characterizing of surface acidity. Present address: Chemistry Department, College of Science, King Faisal University, Al-Hofuf 31982, Saudi Arabia     

Pt LIII-edge XANES and EXAFS studies on γ-Al2O3 supported Pt catalysts

Pt L_III-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.     

Hydrogenation of ethyl acetate over supported rhenium catalysts

Re/Sibunite is a more active and selective catalyst for hydrogenation of ethyl acetate to ethanol under elevated temperatures and hydrogen pressures than Re/θ-Al₂O₃ and Re/γ-Al₂O₃. The activity of the catalyst is increased on replacing NH₄ReO₄ with HReO₄ and treatment of the support with a 13% solution of HNO₃. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1006–1008, May, 1999.     

Hydrogenation of 2-ethylanthraquinone over Pd/Zro2-γ-Al2O3 catalyst

A ZrO₂-γ-Al₂O₃ supported Pd catalyst was prepared and characterized by XRD, XPS, H₂-TPR and TEM techniques. The catalytic activity was evaluated in the liquid-phase hydrogenation of 2-ethylanthraquinone. Comparing with Pd/γ-Al₂O₃, it showed high catalytic activity.     

Dehydrogenation of Isobutane Over V2O5/γ-Al2O3 Catalyst

The effect of the type of the support and the amount of V₂O₅ loading on the activity of V₂O₅/γ-Al₂O₃ catalyst for the dehydrogenation of isobutane have been investigated. Based on the experimental results of TPR, XRD and ESR spectroscopy, it is suggested that there are strong interactions between vanadia and carrier and that the V⁴⁺ species on the surface is the active site of V₂O₅/γ-Al₂O₃ for this reaction. This revised version was published online in June 2006 with corrections to the Cover Date.     

Selection of adsorbents for <Emphasis Type="Italic">in-situ</Emphasis> coupling technology of adsorptive desulfurization and biodesulfurization

In-situ coupling of adsorptive desulfurization and biodesulfurization is a new desulfurization technology for fossil oil. It has the merits of high-selectivity of biodesulfurization and high-rate of adsorptive desulfurization. It is carried out by assembling nano-adsorbents onto surfaces of microbial cells. In this work, In-situ coupling desulfurization technology of widely used desulfurization adsorbents of γ-Al₂O₃, Na-Y molecular sieves, and active carbon with Pseudomonas delafieldii R-8 were studied. Results show that Na-Y molecular sieves restrain the activity of R-8 cells and active carbon cannot desorb the substrate dibenzothiophene (DBT). Thus, they are not applicable to in-situ coupling desulfurization technology. Gamma-Al₂O₃ can adsorb DBT from oil phase quickly, and then desorb it and transfer it to R-8 cells for biodegradation, thus increasing desulfurization rate. It is also found that nano-sized γ-Al₂O₃ increases desulfurization rate more than regular-sized γ-Al₂O₃. Therefore, nano-γ-Al₂O₃ is regarded as the better adsorbent for this in-situ coupling desulfurization technology. Supported by National Basic Research Program of China (Grant No: 2006CB202507) and National High-tech R&D Program (Grant No: 2006AA02Z209)     

Cocatalytic effect of palladium and zinc in the condensation of alcohol carbon backbones into hydrocarbons

The results of the direct conversion of ethanol and its mixture with glycerol into a C₄–C₁₀₊ alkane and olefin fraction in the presence of Pd-, Zn-, and Pd-Zn-containing catalysts, which were prepared by supporting homo- and heterometallic acetate complexes onto the surface of γ-Al₂O₃, are reported. It was found that, in the presence of mono- and bicomponent Pd-ZnO (Pd; ZnO)/γ-Al₂O₃ systems, selectivity in the formation of alkanes, olefins, or their mixtures in the target fraction can be controlled as a result of the cocatalytic effect of active components that are responsible for the catalyst activity in condensation and hydrogenation reactions. The structures of the active components were studied and the genesis of the catalytic systems was characterized using XAFS, XPS, and XRD analysis. It was found that the addition of glycerol considerably increased the yield of the target hydrocarbon fraction.     

Racemization of chiral amino alcohols III: Effect of Mg or Ca addition on the activity and stability of the Co/γ-Al2O3 catalyst

The racemization of R-(-)-2-amino-1-butanol in a reaction using Co/γ-Al₂O₃ catalysts and catalysts modified by Mg or Ca was investigated in this paper. Complete racemization was achieved with a yield of over 83% at using the Mg modified Co/γ-Al₂O₃ catalyst under optimized reaction conditions of 170°C and 2.5 MPa of H₂. The catalysts were thoroughly characterized by XRD, XPS, TPR, SEM and TEM. The addition of Mg and Ca may be advantageous for dispersing and stabilizing the active species of the Co/γ-Al₂O₃ catalyst, protecting from sintering, significantly improving its catalytic activity and stability.     

Effect of Fe-modified α-Al2O3 on the properties of Pd/α-Al2O3 catalysts in selective acetylene hydrogenation

The use of nanocrystalline Fe-modified α-Al₂O₃ prepared by sol–gel and solvothermal method as supports for Pd catalysts resulted in an improved catalyst performance in selective acetylene hydrogenation. Moreover, the amount of coke deposits was reduced due to lower acidity of the Fe-modified α-Al₂O₃ supports.     

Infrared absorption spectra of Er3+-doped Al2O3 nanopowders by the sol-gel method

The Er³⁺-doped Al₂O₃ nanopowders have been prepared by the sol-gel method, using the aluminium isopropoxide [Al(OC₃H₇)₃]-derived γ-AlOOH sols with addition of the erbium nitrate [Er(NO₃)₃·5H₂O]. The five phases of γ-(Al,Er)₂O₃, θ-(Al,Er)₂O₃, α-(Al,Er)₂O₃, ErAlO₃, and Al₁₀Er₆O₂₄ were detected with the 0–20 mol% Er³⁺-doped Al₂O₃ nanopowders at the different sintering temperature of 600–1200°C. The average grain size was increased from about 5 to 62 nm for phase transformation of undoped γ-Al₂O₃→α-Al₂O₃ at the sintering temperature from 600 to 1200°C. At the same sintering temperature, average grain size was decreased with increase of the Er³⁺ doping concentration. Infrared absorption spectra of γ-Al₂O₃ and θ-Al₂O₃ nanopowders showed the two broad bands of 830–870 and 550–600 cm⁻¹, the three broad bands of 830–870, 750–760, and 550–600 cm⁻¹, respectively. The infrared absorption spectra for the α-Al₂O₃ nanopowder showed three characteristic bands, 640, 602, and 453 cm⁻¹. The two characteristic bands of 669 and 418 cm⁻¹ for Er₂O₃ clusters were observed for the Er³⁺-doped Al₂O₃ nanopowders when Er³⁺ doping concentration was increased up to 2 mol%. The 796, 788, 725, 692, 688, 669, 586, 509, 459, and 418 cm⁻¹ are the characteristic bands of Al₁₀Er₆O₂₄ phase.     

TPD study of NH3 adsorption/desorption on the surface of V/Ti, V/Al based catalysts for selective catalytic reduction of NOx by ammonia 1. TPD test of γ-Al2O3, TiO2 (anatase) and alumina-supported vanadia catalysts

The effect of temperature on the adsorption/desorption of ammonia from the air mixture on the surface of γ-Al₂O₃, TiO₂ (anatase) and alumina-supported vanadia catalyst samples has been investigated using temperature-programmed desorption (TPD). When the vanadia loading was increased, the fraction of the acid sites providing the NH₃ adsorption in the high-temperature state decreased. At the same time, the fraction of the medium temperature state significantly increased.     

Effects of the support crystallite size and the reduction temperature on the properties of Pd/α-Al2O3 catalysts in selective acetylene hydrogenation

Pd catalysts supported on the solvothermal-derived nanocrystalline α-Al₂O₃ (45 nm) exhibited superior performances in the selective acetylene hydrogenation than those supported on micron-sized ones (44–149 μm). Reduction at 500°C led to an improvement of the ethylene yield for the Pd/nanocrystalline α-Al₂O₃, but not for the Pd/micron-sized α-Al₂O₃.     

Preparation,characterization and thermal decomposition of phenylenediammonium sulfate salts Part. XVI

Polyaniline/α-Al₂O₃ (PANI/α-Al₂O₃) composites were synthesized by in situ polymerization through ammonium persulfate ((NH₄)₂S₂O₈, APS) oxidized aniline using HCl as dopant. XRD and FTIR were used to characterize the PANI/α-Al₂O₃ composites. The thermal stabilities and glass transition temperature (T _g) of PANI/α-Al₂O₃ composites were tested using thermogravimetric (TG) method and modulated differential scanning calorimetry (MDSC) technique. The results of TG showed that the thermal stability of PANI/α-Al₂O₃ composite increased and then decreased with the increase in α-Al₂O₃ content. The derivative thermogravimetry (DTG) curves showed one step degradation of PANI when the α-Al₂O₃ content was lower than 52.5 mass%, and exhibited two steps degradation when the α-Al₂O₃ content was higher than 63.6 mass%. The MDSC curves showed that the T _g of PANI/α-Al₂O₃ composites increased and then decreased with the augment of α-Al₂O₃ for the interaction between PANI chains and the surface of α-Al₂O₃.     

Calorimetric Characterization of Surface Reactivity of Supported Ga2O3 Catalysts

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.     

“Anhydrolycaconitine”, a new diterpene alkaloid fromAconitum septentrionale K

A new alkaloid, anhydrolycaconitine (C₃₆H₄₆N₂O₉), was isolated from roots ofAconitum septentrionale K. Based on the results of¹H and¹³C NMR and IR spectroscopy and mass spectrometry of the alkaloid and the product of its alkaline hydrolysis and on the data of X-ray diffraction analysis of the hydrolysis product, the structure of 1α, 6β, 14α, 16β-tetramethoxy-7-oxo-18-succinylanthranoyloxy-17-(7→8)abeo-aconane was assigned to anhydrolycaconitine. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1640–1644, September, 2000.