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Chinese Journal of Catalysis
2006, Vol. 27, No. 11
Online: 25 November 2006

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A CoOx/CeO2 Catalyst for Low-Temperature CO Oxidation SHAO Jianjun1,2, ZHANG Ping1, TANG Xingfu2, ZHANG Baocai2, LIU Junlong2, XU Yide2, SHEN Wenjie2 2006, 27 (11):  937-939.  Abstract ( 1821 )   [Full Text(HTML)] () PDF (253KB) ( 755 )   A CoOx/CeO2 catalyst was prepared by the co-precipitation-oxidation method, and its catalytic performance for CO oxidation was investigated under humid and dry conditions ,respectively. The CoOx/CeO2 catalyst exhibited excellent activity and good resistance to water vapor poisoning. Remarkably, 99% CO conversion could be achieved at 196 K for more than 400 min under dry condition, and when the reaction was carried out at 298 K, the conversion of CO was maintained at 94% after 2400 min. Even when 3.1% of water was added, the conversion of CO was still kept at 79% after 2400 min on-stream at 383 K.

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A Novel Porous Mullite Fiber Ceramics as a Support for La0.8Sr0.2CoO3-δ Perovskite Catalysts DUAN Bilin1, ZENG Lingke1, LIU Ping'an1, SHUI Anze1, WANG Xiaohua2 2006, 27 (11):  940-942.  Abstract ( 1844 )   [Full Text(HTML)] () PDF (349KB) ( 720 )   An air extrusion molding method for the preparation of mullite fiber ceramics with high porosity and high temperature stability was developed at a calcination temperature of 1250 ℃. The porous mullite ceramics showed a uniform pore size distribution and a porosity of 96.22%. The porous ceramics was used as the support for perovskite catalysts based on La0.8Sr0.2CoO3-δ, and the catalyst showed excellent activity and stability in the catalytic combustion of NO and CO. Pd doping enhanced the catalyst activity.

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Selective Oxidation of Styrene Catalyzed by Pd/Carboxyl-Appended Ionic Liquids LI Xuehui*, GENG Weiguo, WANG Furong, WANG Lefu 2006, 27 (11):  943-945.  Abstract ( 2006 )   [Full Text(HTML)] () PDF (156KB) ( 843 )   A new catalytic system, PdCl2/TSILs, for catalytic oxidation of styrene to acetophenone with hydrogen peroxide was designed through the combination of PdCl2 and task-specific ionic liquids (TSILs) of N-carboxyl-appended imidazolium cations with various anions. The PdCl2/TSILs catalytic system displayed excellent catalytic properties for the target reaction. The yield and selectivity of acetophenone depended critically on the TSILs structure with different combinations of carboxylic groups and counter-anions. The catalytic activity of PdCl2/TSILs was enhanced with the increase in the number of the carboxylic groups and the asymmetry degree of the cations. The activity of PdCl2/TSILs with the same cation also increased with the assorted anion sequence of PF-6

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Asymmetric Diels-Alder Reactions on Supported Bis(Oxazoline) Catalysts WANG Hong1, LIU Jian1, LIU Peng1, YANG Qihua1, XIAO Jianliang2, LI Can1* 2006, 27 (11):  946-948.  Abstract ( 1848 )   [Full Text(HTML)] () PDF (189KB) ( 688 )   Periodic mesoporous ethane-silicas functionalized with sulfonic acid, cesium salts of 12-tungstophosphoric acid, activated silica, and SBA-15 have been used as solid supports for the immobilization of the bis(oxazoline) copper (Ⅱ) catalyst via non-covalent interactions. These heterogeneous catalysts have been evaluated for the Diels-Alder reaction between 3-((E)-2-butenoyl)-1,3-oxazolin-2-one and cyclopentadiene. The performance of the catalyst relies on the nature of both the support and the anion on the surface of the support. The small number of the silanol groups on the support leads to poor enantioselectivity when SBA-15 is used.

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Synthesis of Mesoporous Titanium Dioxide without Using Organic Templates SHEN Jun, TIAN Congxue, ZHANG Zhao* 2006, 27 (11):  949-951.  Abstract ( 2044 )   [Full Text(HTML)] () PDF (234KB) ( 1143 )   Thermally stable mesoporous anatase TiO2 was prepared in the absence of organic templates via two-step hydrolysis of industrial titanyl sulfate solution to form mesoporous metatitanic acid followed by calcination at 500 ℃ for 2 h. The mesoporous TiO2 obtained has a surface area of 202.2 m2/g and an average pore diameter of 2.8 nm. TiO2 contains SO2-4 and shows superacid properties. The mesoporous material was characterized by various methods and the mechanism of formation of the mesoporous structure was discussed. Sulfuric acid adsorbed on pore walls of the mesoporous metatitanic acid is bonded to the free hydroxyl groups on the pore walls, which acts as a structural directing agent and pore structure support.

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Electrocatalytic Properties of TiN-Based IrO2-Ta2O5 Coating Electrodes for Hydrogen Evolution Reaction XU Haibo1,2*, JIANG Junfeng1, WANG Tingyong2, WANG Jia1,3, XU Likun2 2006, 27 (11):  952-956.  Abstract ( 1902 )   [Full Text(HTML)] () PDF (486KB) ( 891 )   The IrO2-Ta2O5 coating electrodes were prepared by thermal decomposition and supported on TiN films synthesized by multi-arc ion plating. The electrocatalytic properties of coating cathodes for hydrogen evolution reaction (HER) were investigated by cyclic polarization combined with scanning electron microscope, energy dispersive X-ray spectroscopy, and X-ray diffraction. The results showed that there existed TiN substrates on the electrodes and the electrode calcined at 420 ℃ exhibited the best electrocatalytic activity for HER. Electrode potential for hydrogen evolution on coating electrodes was -0.26 V (vs SCE). The Tafel slope was -0.04 V in the low overpotential region of HER. The structure of oxide electrodes was changed by a multitude of hydrogen atoms adsorbed on the electrode surface in the high overpotential region of HER, which restrained the cathodic reduction reaction of oxygen. These results suggest primarily that it is feasible using TiN as support for the IrO2-Ta2O5 coating cathode.

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Effect of Pretreatment Conditions on Initial Catalytic Activity of Silver Screen Catalyst for the Catalytic Decomposition of Highly Concentrated Hydrogen Peroxide ZHOU Zhijiang1,2, WANG Xiaodong1*, SHAN Jihong1, CONG Yu1, YANG Xiaofeng1,2, ZHANG Tao1* 2006, 27 (11):  957-960.  Abstract ( 2069 )   [Full Text(HTML)] () PDF (328KB) ( 1098 )   The silver screen catalyst used for the catalytic decomposition of highly concentrated hydrogen peroxide was plated on the nickel base. Pretreatment with hydrogen peroxide was employed to promote the initial catalytic activity of the catalyst. The results indicated that the initial activity and the start-up performance of the catalyst were greatly improved by the pretreatment with 90% of hydrogen peroxide. The scanning electron microscopy and X-ray photoelectron spectroscopy results showed that a lot of fissures and active species of Ag2O appeared on the silver screen surface after the pretreatment. These probably are the main reasons for the improvement of the catalyst activity.

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Synthesis, Characterization and Catalytic Performance of Titanium-Grafted Mesoporous Ti-HMS Molecular Sieve YU Weihua, ZHOU Chunhui, NI Zheming, ZHANG Bo, GE Zhonghua 2006, 27 (11):  961-966.  Abstract ( 1884 )   [Full Text(HTML)] () PDF (530KB) ( 897 )   A series of Ti-HMS samples with different Ti amounts were prepared by a grafting method using organometallic titanocene dichloride as the Ti source and HMS as the support. The template of HMS was removed by calcination at 600 ℃ or by ethanol-extraction followed by calcination at 400 ℃. The Ti-HMS samples were characterized by thermogravimetric and differential thermal analysis, powder X-ray diffraction, N2 adsorption-desorption isotherm, diffuse reflectance UV-visible spectroscopy, and Fourier transform infrared spectroscopy. The catalytic performance of the Ti-HMS samples for oxidation of 4-tert-butyltoluene with aqueous H2O2 was tested under the mild conditions. Pretreatment of HMS by ethanol-extraction followed by low temperature calcination made OH groups available for grafting. The isolated framework Ti(Ⅳ) decreased with the increase in Ti loading. The four-coordinated Ti state displayed catalytic activity for oxidation of 4-tert-butyltoluene. Non-framework Ti species were responsible for low catalytic activity. A conversion of 4-tert-butyltoluene up to 9.3% and a complete selectivity for 4-tert-butylbenzaldehyde were achieved.

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Effect of Heat Treatment on the Electrocatalytic Activity of Electrodeposited Ni-W-P Alloy for Hydrogen Evolution Reaction ZHANG Weiguo*, LIU Yang, LI He, YAO Suwei 2006, 27 (11):  967-970.  Abstract ( 1718 )   [Full Text(HTML)] () PDF (318KB) ( 820 )   Ni-W-P alloy deposits were prepared by electrodeposition and heat treatment at different temperatures. Cathodic polarization curves and electrochemical impedance spectroscopy were used to study the influence of heat treatment on the electrocatalytic activity of the electrodeposited Ni-W-P alloy for the hydrogen evolution reaction (HER). The results demonstrated that, after heat treatment at 200 ℃, Ni-W-P alloy electrodes exhibited the highest electrocatalytic activity for HER and the overpotential was lowered by 110 mV at 8.0 mA/cm2 compared with the Ni-W-P alloy without heat treatment. The electrochemical reaction resistance for HER of the Ni-W-P alloy heat-treated at 200 ℃ was 17.1 Ω•cm2 and its exchange current density was 4.0 times higher than that of the Ni-W-P alloy without heat treatment. The increase in electrocatalytic activity of Ni-W-P alloys can be attributed to the increase in the real surface area and the decrease in the apparent energy of activation. The surface morphology and microstructure of the Ni-W-P alloy electrode were characterized by differential scanning calorimetry, X-ray diffraction, and scanning electron microscopy. The average grain size of Ni-W-P alloy annealed at 200 ℃ increased from 1.1 to 2.8 nm and its structure changed from amorphous to nano-crystalline.

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Electrocatalytic Reduction of Oxygen at Pyrolytic Graphite Electrode Modified with Novel Copper(Ⅱ) Complex WANG Mingyan1*, XU Xingyou1, GAO Jian1, JIA Nengqin2 2006, 27 (11):  971-975.  Abstract ( 1866 )   [Full Text(HTML)] () PDF (319KB) ( 993 )   A novel five-coordinated copper(Ⅱ) complex (Cu［L(ImH)］(ClO4)2), which was self-assembled with imidazole, Cu2+ center, and 2-［bis(2-aminoethyl)amino］ethanol (L), was synthesized. The ligand L bearing an O atom at the hydroxyethyl arm with proper flexibility provided enough variability to adapt the different configuration requirement of Cu2+/Cu+ in the redox process. The pyrolytic graphite (PG) electrode modified with the Cu［L(ImH)］(ClO4)2 complex was constructed. The electrochemical behavior and electrocatalytic activity of the Cu［L(ImH)］/PG electrode for oxygen reduction were studied by cyclic voltammetry and chronoamperometry. The Cu［L(ImH)］/PG electrode exhibited high electrocatalytic activity and stability for oxygen reduction. The reduction current increased with the increase in scan rate, and the plot of Ip to v1/2 was linear. According to the results of potential step chronoamperometry, the electrocatalytic mechanism of oxygen reduction at the modified electrode might be similar to the ECE (E: electrode reaction, C: chemical reaction) process, the number of electron transfer in the reduction process was about 4, and the oxygen was finally reduced to H2O at the modified electrode.

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Co/CeO2 Catalysts for Steam Reforming of Ethanol WANG Hong, LIU Pengxiang, LIU Yuan*, QIN Yongning 2006, 27 (11):  976-982.  Abstract ( 1806 )   [Full Text(HTML)] () PDF (849KB) ( 884 )   The Co/CeO2 catalysts were prepared by the co-precipitation method and used for H2 production from steam reforming of ethanol. The effects of the Co3O4 content and calcination temperature on the catalyst performance were investigated. The Co/CeO2 catalyst with a Co3O4 content of 10% calcined at 650 ℃ exhibited high ethanol conversion and H2 selectivity under the reaction conditions of 350-600 ℃, water∶ethanol∶N2 molar ratio of 3∶1∶16, and space velocity of 40 L/(g•h). Over this catalyst, ethanol conversion and H2 selectivity kept close to 100% and 65%, respectively, during the stability test at 500 ℃ for 40 h. The catalysts were characterized by N2 adsorption using the BET method and X-ray diffraction. There are three kinds of cobalt in the catalyst, that is, highly dispersed cobalt oxide, bulk Co3O4, and cobalt ions in ceria lattice. It is supposed that the metallic cobalt from the reduction of highly dispersed cobalt oxide is the key active component of the Co/CeO2 catalyst.

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Allylic Oxidation of Cyclohexene Catalyzed by Vanadium Pentoxide CHEN Yuan, YIN Dulin*, ZHONG Wenzhou, MAO Liqiu, WANG Jihui 2006, 27 (11):  983-986.  Abstract ( 1764 )   [Full Text(HTML)] () PDF (217KB) ( 1228 )   Oxidation of cyclohexene catalyzed by vanadium pentoxide was carried out under mild conditions with aqueous hydrogen peroxide as the oxidant. The effects of the solvent type, solvent amount, catalyst amount, and reaction temperature on the reaction were investigated. The allylic oxidation of cyclohexene was the dominate reaction, and cyclohexene-2-one was obtained as the major product. The solvent type significantly affects the catalyst activity and the selectivity for cyclohexene-2-one. Particularly acetone is an optimal choice for improving the conversion of cyclohexene. Under the conditions of V(acetone)∶V(cyclohexene)=4, m(V2O5)∶m(cyclohexene)=1∶40, n(H2O2)∶n(cyclohexene)=3, 20 ℃, and 24 h, the conversion of cyclohexene reached up to 60% and the selectivity for cyclohexene-2-one was 85%. It is proposed that the oxidation of cyclohexene catalyzed by vanadium pentoxide involves a reversible V5+/V4+ species redox cycle using acetone as the oxygen transfer agent.

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Methanol Steam Reforming over CuZnAl Catalysts Derived from Hydrotalcite Precursor Ⅱ. Effect of Catalyst Composition TANG Ying, LIU Ye, LU Yong*, ZHU Ping, HE Mingyuan 2006, 27 (11):  987-992.  Abstract ( 1878 )   [Full Text(HTML)] () PDF (449KB) ( 691 )   A series of catalysts with various Cu/Zn/Al mass ratios were prepared by decomposition of CuZnAl hydrotalcite precursors at 600 ℃ and used for steam reforming of methanol. The effect of the Cu/Zn/Al mass ratio on the catalyst performance for steam reforming of methanol was investigated at 250 ℃ and WHSV of 3.28 h-1 with a H2O/CH3OH molar ratio of 1.3. Cu/Zn/Al ratio of 36.7/13.4/(17-28) was preferred for achieving good activity. The Cu content barely affected the phase composition of the catalysts and the reduction temperature of the CuO phase. However, the catalysts with much lower or higher Cu content showed low activity because of the less active sites or the unsuitable Cu/Zn ratios. Both higher and lower Zn content led to the phase transformation of the catalysts and therefore the catalysts were less active. Higher Al content facilitated the dispersion of CuO and increased the specific surface area of the catalysts, thereby promoting the activity. In addition, the Cu/Zn/Al ratio hardly affected the gas product composition.

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Mechanistic Study of Selective Catalytic Reduction of NOx with C2H5OH and CH3OCH3 over Ag/Al2O3 by in Situ DRIFTS WU Qiang, YU Yunbo, HE Hong* 2006, 27 (11):  993-998.  Abstract ( 2078 )   [Full Text(HTML)] () PDF (560KB) ( 779 )   Although C2H5OH and CH3OCH3 are isomeric compounds, C2H5OH is extremely efficient for NOx reduction while it is not the case for CH3OCH3. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to study the reaction mechanism. The enolic species derived from partial oxidation of C2H5OH over Ag/Al2O3 plays a crucial role in the -NCO species formation during the selective catalytic reduction (SCR) of NOx by C2H5OH. The high reactivity of the enolic species results in high surface concentration of -NCO species and high efficiency of NOx reduction when using C2H5OH as a reductant. In the case of CH3OCH3, the formate species as a main intermediate has lower activity for the formation of -NCO species, which results in the relatively low efficiency during the SCR of NOx.

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Approaches and Nature of Improving Rh-Based Catalyst Performance for CO Hydrogenation to C2-Oxygenates CHEN Weimiao, DING Yunjie*, JIANG Dahao, JIAO Guiping, ZHU Hejun, PAN Zhendong, LUO Hongyuan 2006, 27 (11):  999-1004.  Abstract ( 1764 )   [Full Text(HTML)] () PDF (296KB) ( 788 )   Thermodynamic analysis results revealed that the formation of C2-oxygenates from syngas is much more unfavorable than the formation of hydrocarbons. Therefore, the crucial and effective method to promote the C2-oxygenate synthesis is to develop high selective catalysts. According to the mechanism of C2-oxygenate formation, the natures and the approaches to improve the catalytic performance of the Rh-based catalyst for CO hydrogenation to C2-oxygenates were the improvement and the balance in CO dissociation and insertion activity, the proper hydrogenation activity, and the optimal Rh size on the catalyst surface. The impregnation and reduction conditions were optimized to suppress correctly the catalytic activity of the Rh-Mn-Li-Fe/SiO2 catalyst for CO hydrogenation. Consequently, CO insertion competed favorably with hydrogenation, resulting in a maximum selectivity (91.6% in mass fraction) for C2-oxygenates with a high yield and a much low methane selectivity (6.3% in mass fraction).

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Preparation of Phosphorus-Modified HZSM-5 Zeolite and Its Application in the One-Step Synthesis of Dimethyl Ether from Syngas MAO Dongsen1,2*, ZHANG Bin2, YANG Weimin2, CHEN Qingling2, LU Guanzhong1 2006, 27 (11):  1005-1011.  Abstract ( 1868 )   [Full Text(HTML)] () PDF (402KB) ( 864 )   A series of HZSM-5 zeolite samples modified with various contents of phosphorus were prepared by impregnation with an aqueous solution of phosphoric acid and characterized by N2-adsorption, X-ray diffraction, 27Al magic angle spinning nuclear magnetic resonance spectroscopy, temperature-programmed desorption of NH3, and pyridine adsorption Fourier-transform infrared reflectance spectroscopy. The one-step synthesis of dimethyl ether (DME) from syngas was carried out over the admixed catalysts of the industrial methanol synthesis catalyst (Cu-ZnO-Al2O3) and the prepared HZSM-5 zeolites under pressurized fixed-bed continuous flow conditions. The modification of HZSM-5 with a suitable amount of phosphorus (10%P2O5) significantly enhanced the selectivity for DME from 49.7% to higher than 63%, while the selectivity for the undesired by products of hydrocarbons and CO2 decreased from 3% and 43.3% to less than 0.1% and 33%, respectively. The decrease in the formation of hydrocarbons and CO2 can be attributed to the significant decline in the number of strong acid sites induced by the phosphorus modification. However, when the phosphorus content was too high (15%P2O5), both the conversion of CO and the selectivity for DME decreased remarkably because the produced methanol could not be efficiently converted to DME on account of the significant decline in the number of acid sites and surface area resulted from the phosphorus modification.

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Effect of Precipitants on Structure and Catalytic Activity of Au/Fe2O3 Catalysts for the Water-Gas Shift Reaction HUA Jinming1,2, ZHENG Qi2*, WEI Kemei2, LIN Xingyi2 2006, 27 (11):  1012-1018.  Abstract ( 2021 )   [Full Text(HTML)] () PDF (507KB) ( 833 )   Au/Fe2O3 catalysts were prepared by the coprecipitation method using seven precipitants, K2CO3, Na2CO3, NH4OH, (NH4)2CO3, NaOH, KOH, and urea. These catalysts were used for the low temperature water-gas shift reaction and characterized by N2 adsorption-desorption, X-ray fluorescence spectroscopy, X-ray diffraction, H2 temperature-programmed reduction, and CO temperature-programmed desorption to explore the cause resulting in their significant difference of catalytic activity. The catalysts prepared using K2CO3 or Na2CO3 as the precipitant exhibited higher activity and better stability above 200 ℃. The samples precipitated with NH4OH or (NH4)2CO3 showed moderate activity maximizing at 200 ℃. The samples prepared using the rest three precipitants presented almost no activity below 300 ℃, attaining only 35% of CO conversion above 350 ℃. The type of precipitant exerted significant effect on the coprecipitation of gold and iron ions, and the crystallization behavior of the resulting precipitates during the subsequent calcination step, which further influenced the gold loading, the dispersion of gold particles, and the reduction and CO adsorption-desorption properties of the iron oxide support. The high catalytic activity of Au/Fe2O3 catalysts at low temperature can be attributed to the synergism between higher dispersion of gold particles and easier reduction property of the iron oxide support. The increase in gold loading and dispersion of gold particles and the decrease in the iron oxide crystallites are favorable for improving the catalytic activity of the Au/Fe2O3 catalysts.

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Co-Mo-K Sulfide-Based Catalyst Promoted by Multi-walled Carbon Nanotubes for Higher Alcohol Synthesis from Syngas MA Xiaoming, LIN Guodong, ZHANG Hongbin* 2006, 27 (11):  1019-1027.  Abstract ( 1877 )   [Full Text(HTML)] () PDF (698KB) ( 925 )   Using home-made multi-walled carbon nanotubes (CNT) as the promoter, sulfurized Co-Mo-K catalysts (denoted as CoiMojKk-x%CNT) were prepared by the co-precipitation method. Their catalytic performance for higher alcohol synthesis from syngas was evaluated and compared with that of the CNT-free counterpart (CoiMojKk). Appropriate incorporation of a minor amount of CNT into CoiMojKk led to a significant increase in CO conversion and selectivity for the higher alcohols. Under the reaction conditions of 5.0 MPa, 623 K, V(H2)∶V(CO)∶V(N2)=60∶30∶10, and GHSV=3600 ml/(g•h), the observed space-time-yield of total (C1-4) alcohols reached 241.5 mg/(g•h) with CO conversion of 21.6% over the Co1Mo1K0.3-10%CNT catalyst, which was 1.84 times that over Co1Mo1K0.3. Ethanol became the dominant product of the CO hydrogenation under the conditions mentioned above. The water-gas-shift (WGS) side reaction was inhibited to a greater extent over the CNT-promoted catalyst. The results of catalyst characterization indicated that the addition of a minor amount of CNT into the Co1Mo1K0.3 catalyst did not cause an obvious change in the apparent activation energy for the conversion of CO but led to an increase in the molar percentage of catalytically active Mo-species (Mo4+) in the total Mo amount at the surface of the functioning catalyst. Based on the temperature-programmed desorption results, it could be inferred that, under the conditions of the higher alcohol synthesis, there existed a considerably larger amount of reversibly adsorbed H-species on the CNT-promoted catalyst, which would generate a surface micro-environment with high stationary-state concentration of the adsorbed H-species on the catalyst and thus increase the rate of a series of surface hydrogenation reactions. In addition, high stationary-state concentration of adsorbed H-species on the surface of catalyst would effectively inhibit the WGS side reaction. These factors contribute considerably to the increase in the main product yield.

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Synthesis of Mesoporous Ti-P-Al Material with High Thermal Stability by Post-Synthetic Treatment LIU Ziyu1,2, WEI Yingxu1, QI Yue1, LIU Zhongmin1* 2006, 27 (11):  1028-1032.  Abstract ( 1935 )   [Full Text(HTML)] () PDF (320KB) ( 749 )   Mesostructured TiO2 was prepared hydrothermally using cetyltrimethylammonium bromide (CTAB) as the structure directing agent, and the mesoporous Ti-P-Al material with high thermal stability was subsequently synthesized by a two-step post-synthetic treatment. The sample was characterized by powder X-ray diffraction, transmission electron microscopy, and N2 adsorption. It was found that the composition of the starting gel system greatly affected the mesostructure of TiO2 materials greatly. With the gel composition of Ti(SO4)2∶CTAB∶H2O=1∶0.54∶430 and after being treated at 363 K for 10-20 min, an ordered TiO2 mesostructure was obtained, which presented better long-range order after being treated with 0.25 mol/L phosphoric acid solution. Further treatment with AlCl3 solution resulted in a mesoporous Ti-P-Al material with high thermal stability, which had a high BET specific surface area of 382 m2/g and a pore size of 3.13 nm after calcination at 873 K.

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Preparation of Solid Acid SO2-4/SiO2-TiO2 and Its Catalytic Activity for Esterification ZHANG Qi1,2, CHANG Jie1, WANG Tiejun1*, XU Ying1 2006, 27 (11):  1033-1038.  Abstract ( 2325 )   [Full Text(HTML)] () PDF (512KB) ( 1239 )   Solid acid catalysts SO2-4/SiO2-TiO2 with different SiO2/TiO2 ratios and calcined at different temperatures were prepared by mechanical mixing and impregnation methods. The catalysts were used for esterification of ethanol and acetic acid. SO2-4/40%SiO2-TiO2 prepared by mechanical mixing and calcination at 400 ℃ exhibited the highest activity, and the acetic acid conversion was nearly 100% in partial reflux rectifying esterification and up to 84% in total reflux esterification, which was close to the chemical equilibrium composition. X-ray diffraction patterns indicated that SiO2 inhibited the excessive formation of titanium oxide sulfate. The combination of tetragonal crystal anatase TiO2, orthorhombic crystal titanium oxide sulfate, and cubic crystal titanium with high surface area SiO2 ensured the high activity of the catalysts. Infrared spectra showed that the addition of SiO2 helped the formation of Ti-O-Si linkage which enhanced the strong bonding of SO2-4 with the catalyst surface. The sulfate species bonded were in bidentately chelating and covalent sulfate structures. Thermogravimetric-differential scanning calorimetry proved that SO2-4 was hardly removed with the addition of SiO2 and the temperature for transformation of anatase to rutile was lowered.

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Synthesis of MgAPO-11 Molecular Sieves and the Catalytic Performance of Pt/MgAPO-11 for n-Dodecane Hydroisomerization YANG Xiaomei1,2, XU Zhusheng1, MA Huaijun1,2, XU Yunpeng1, TIAN Zhijian1*, LIN Liwu1,3 2006, 27 (11):  1039-1044.  Abstract ( 1818 )   [Full Text(HTML)] () PDF (391KB) ( 772 )   A series of MgAPO-11 molecular sieves have been synthesized by varying the crystallization time, the P/Al molar ratio, and the Mg source. X-ray diffraction, X-ray fluorescence spectroscopy, and temperature-programmed desorption of NH3 have been employed to characterize the crystalline phase, the Mg content, and the acidity of MgAPO-11, respectively. The results show that the synthesis conditions have an effect on the crystalline phase, the Mg content, the acidity, and thereby the catalytic performance of Pt/MgAPO-11 in the hydroisomerization of n-dodecane. The reaction data reveal that the activity of Pt/MgAPO-11 is dependent on the amount of strong acid sites of MgAPO-11. Short crystallization time, P/Al molar ratio of 1.0, and Mg(NO3)2 as the Mg source favor the increase in the amount of the strong acid sites of MgAPO-11 and hence promote the catalytic activity of Pt/MgAPO-11 for the hydroisomerization of n-dodecane.