Chinese Journal of Catalysis

One-Step Catalytic Synthesis of Methylene Diphenyl Dicarbamate

LIU Limin;LI Fang;WANG Yanji*;ZHAO Xinqiang

2007, 28 (8): 667-669.

Abstract ( 2174 ) [Full Text(HTML)] ()

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Methylene diphenyl dicarbamate (MDC), an intermediate for the production of methylene diphenyl diisocyanate, was directly synthesized from dimethyl carbonate (DMC), aniline, and formaldehyde solution over the bifunctional H4SiW12O40-ZrO2/SiO2 catalyst. The effects of reaction time, reaction temperature, and H4SiW12O40loading were studied. Suitable reaction conditions are as follows: DMC/aniline/formaldehyde molar ratio is 20/1/0.05, H4SiW12O40loading is 10%, and reaction temperature is controlled by stages (i.e., reaction at 443 K for7 hand then at 373 K for 4.5 h). Under these conditions, the yield of MDC is 24.9%.

Selective Hydrogenation of Acetonitrile over Molybdenum Phosphide Catalysts

YANG Pengfei;JIANG Zongxuan;YING Pinliang;LI Can*

2007, 28 (8): 670-672.

Abstract ( 2002 ) [Full Text(HTML)] ()

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A series of molybdenum phosphide catalysts were prepared at initial Mo/P molar ratios ranging from 0.6 to 2.6. The catalytic activity of the catalysts for the selective hydrogenation of acetonitrile was studied. The catalysts with initial Mo/P ratios>1.0 have high selectivity for ethylamine (80%-90%), and for the catalysts with Mo/P ratios<1.0, the selectivity for diethylamine and triethylamine is more favorable (about 90%). When Mo/P ratio=1.0, the highest conversion of acetonitrile is attained.

Direct Asymmetric Aldol Reactions on Heterogeneous Bifunctional Catalyst

ZHONG Lin;XIAO Jianliang;LI Can*

2007, 28 (8): 673-675.

Abstract ( 2011 ) [Full Text(HTML)] ()

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A heterogeneous bifunctional catalyst was synthesized by incorporating chiral amine and acid groups into silica. This catalyst showed modest reactivity and enantioselectivity (up to 60%ee) for the direct asymmetric aldol reactions. It is suggested that the suitable incorporation between the amine and the acid groups in the bifunctional solid catalyst is crucial for the reactivity and the chiral induction of the reactions.

Preparation and Catalytic Performance of Monolayer-Dispersed Pd/Ni Bimetallic Catalysts for Hydrogenation

WANG Songrui;ZHU Yuexiang*;XIE Youchang;Jingguang G. CHEN

2007, 28 (8): 676-680.

Abstract ( 2363 ) [Full Text(HTML)] ()

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The Pd/Ni bimetallic catalyst was prepared by replacement reactions, characterized byX-raydiffraction, CO chemisorption, and H2 temperature-programmed desorption, and evaluated for the hydrogenation of cyclohexene, styrene, and acetone. The results show that Pd atoms are monolayer-dispersed on the Ni surface in this Pd/Ni catalyst. Consequently, the Pd/Ni catalyst is much more active than Pd/Ni and Pd/γ-Al2O3 with the same Pd loading prepared by the conventional impregnation method.

Effect of SO2-4 on Fischer-Tropsch Synthesis over Iron-Based Catalyst

AN Xia;WU Baoshan*;WAN Haijun;LI Tingzhen;TAO Zhichao;XIANG Hongwei;LI Yongwang

2007, 28 (8): 681-686.

Abstract ( 2140 ) [Full Text(HTML)] ()

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A series of Fe-based catalyst samples with different amounts of SO2-4 for Fischer-Tropsch synthesis (FTS) were prepared by iso-volume impregnation of the FeCuK/SiO2 precursor with NH4HSO4 solution. The catalyst samples were characterized by atomic emission spectroscopy, N2 adsorption,X-rayphotoelectron spectroscopy, temperature-programmed reduction, and Mssbauer effect spectroscopy. The catalytic performance of the catalyst samples for the FTS reaction was measured in a continuous stirred tank slurry reactor under the reaction conditions ofn(H2)/n(CO)=0.67, WHSV=2000h-1, 1.5 MPa, and 250 ℃. The results showed that the addition of SO2-4 promoted the reduction of the catalyst in H2. A low level of SO2-4 slightly influenced the extent of carburization, and the excessive addition of SO2-4 restrained carburization apparently in syngas. The catalyst samples with different SO2-4 amounts displayed different FTS reactivity, but all the samples were stable during 500 h on stream. Moreover, the addition of SO2-4 could suppress the water-gas shift reaction. The low level of SO2-4 suppressed methane selectivity and promoted slightly alkene selectivity.

A Corrected Comprehensive Kinetic Model of Fischer-Tropsch Synthesis

TENG Botao*;CHANG Jie;WAN Haijun;LU Jiqing;ZHENG Shaocheng;LIU Ya;LIU Ying;GUO Xiaohui

2007, 28 (8): 687-695.

Abstract ( 2180 ) [Full Text(HTML)] ()

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A corrected comprehensive Fischer-Tropsch synthesis kinetic model was developed on the basis of the CH2 insertion alkyl mechanism, in which readsorption and secondary reactions of olefins, alcohols, and acids and their non-intrinsic effects (diffusion, physisorption, and solubility) were involved. The values of kinetic parameters estimated by the regression between the corrected kinetic model and the data in the literature are within the ranges reported in the literature. The predicted paraffin, olefin, alcohol, and acid distributions and the corresponding olefin/hydrocarbon, alcohol/hydrocarbon, and acid/hydrocarbon ratios fit well with the experimental data. It further suggests that paraffin, olefin, alcohol, and acid formation reactions over the Fe-Mn catalyst are parallel competitive reactions. The higher constant of alcohol and acid readsorption and secondary reactions than that of olefin indicates that alcohols and acids have more propensity to readsorb over the catalyst surface and have more chances to take part in chain growth reactions and can be hydrogenated to corresponding paraffins. Diffusion effects of olefins and oxygenates with low carbon numbers on product distributions are not the dominant reason for the readsorption and secondary reactions of olefins, alcohols, and acids according to the comparison of their liquid molecular volumes and boiling points with low carbon numbers.

A Density Functional Theoretical Study on the Chemical Adsorption of Oxygen on CuCl(111) Surface

WANG Xia;CHEN Wenkai*;XU Xianglan;LU Chunhai

2007, 28 (8): 696-702.

Abstract ( 2065 ) [Full Text(HTML)] ()

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The adsorption of O2 molecules and O atoms on the CuCl(111) surface was studied using first-principle calculations based on the density functional theory with the generalized gradient approximation developed by Perdew and Wang (PW91). Adsorption models under different coverages of the CuCl(111) surface were considered. The adsorption over various adsorption sites (top-V, hollow-V, bridge-V, Cl-V, top-P, hollow-P, bridge-P, and Cl-P sites) was selected for calculation. The optimized results indicated that the adsorption was very stable when the coverage was set to 0.25 monolayer. The O2 molecule was inclined to adsorb aslant on the CuCl(111) surface, and theO-Ostretching vibrational frequencies were significantly red-shifted. The results of the Mulliken population analysis and the density of states indicated that the charges transferred from Cu to oxygen. The O atom was likely to adsorb at the hollow site of the CuCl(111) surface. The Mulliken population analysis and the density of states were calculated to explain the computed results.

Factors Influencing the Performance of Catalysts in Direct Methanol Fuel Cells

CHEN Weimin;;SUN Gongquan;MAO Qing;YANG Shaohua;SUN Pichang;XIN Qin*

2007, 28 (8): 703-708.

Abstract ( 2344 ) [Full Text(HTML)] ()

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Several factors including temperature, potential, and intermediates that influence the performance of electrocatalysts in direct methanol fuel cells were examined. The results show that the sintering process of Pt catalyst particles was accelerated at high temperatures, and for PtRu catalysts, this process was largely inhibited by ruthenium oxides/hydroxides. The alloying degree of PtRu catalysts was elevated to some extent after the discharge test at a high temperature. The degradation of electrocatalysts was accelerated by high potential. The methanol oxidation reaction was hindered to some extent by intermediates such as formic acid and formaldehyde, especially the latter.

Lumped Kinetic Model for Intermolecular Hydrogen Transfer of Pine Gum over Pd/C Catalyst

WANG Linlin;CHEN Xiaopeng*;SUN Wenjing;XU Xu;CHEN Zufen;TONG Zhangfa

2007, 28 (8): 709-714.

Abstract ( 1991 ) [Full Text(HTML)] ()

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Using a novel experimental apparatus with an improved agitator, a lumped kinetic model for the intermolecular hydrogen transfer reaction of pine gum over a Pd/C catalyst was investigated under nitrogen atmosphere. The component concentrations were acquired by tracking analysis by gas chromatography. The lumped components of the complex reaction systems were defined and the reaction network was proposed. The lumped kinetic model of monoterpene, abietic type resin acid, pimaric acid type resin acid, p-cymene, hydro-monoterpene, dehydro-abietic acid, hydro-abietic type resin acid, and hydro-pimaric acid type resin acid was established based on the structural groups and approximate reaction kinetic theory according to the fundamental principles of the lumped method. The reaction orders of monoterpene and resin acid were1 and2, respectively. The kinetic model parameters were estimated and the activation energy was calculated for various reactions of the lumped kinetic model. The lumping model could characterize the kinetic behavior of the complicated reaction system and predict the reactant-product concentrations at 533 K. The dehydrogenation was the main reaction during the intermolecular hydrogen transfer reaction of pine gum, and the reaction rate of the resin acids was greater than that of monoterpene.

Selective Hydrogenation of1,5-Cyclo-octadiene over Porous Pd/α-Al2O3 Active Membrane

ZHOU Yonghua;YE Hongqi;Reinhard SCHOMACKER

2007, 28 (8): 715-719.

Abstract ( 2376 ) [Full Text(HTML)] ()

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Porous Pd/α-Al2O3 catalytically active membrane was prepared by microemulsion and impregnation techniques. Palladium nanoparticles in the microemulsion and in the pore structure of α-Al2O3 membrane were characterized by transmission electron microscopy, scanning electron microscopy, andX-raydiffraction. The results show that the palladium nanoparticles dispersed in microemulsion are evenly immobilized in the pore structure of the membrane in the form of palladium crystalline particles with several hundred nanometers by impregnation. The catalytic activity and selectivity of porous Pd/α-Al2O3 active membranes were investigated for the hydrogenation of1,5-cyclo-octadiene (COD) in a catalytic membrane contactor and were compared with the Pd-polyacrylic acid (PAA) membrane reactor (MR), slurry reactor, and fixed-bed reactor (FBR). The results show that both reaction rate of COD and selectivity for 1-cyclo-octene in Pd/α-Al2O3 MR are considerably improved compared with Pd-PAA MR and FBR. The effects of Pd/α-Al2O3 MR in facilitating mass transfer and in eliminating diffusion inside the pores are remarkable. This can be attributed to the distribution of palladium in the membrane structure and the high flow rate of reactants in the membrane pores.

Catalytic Performance of PdCl2-CuCl2/Li-Al-O for Synthesis of Diethyl Carbonate from CO and Ethyl Nitrite at Low Pressure

GAO Xiaochen;MA Xinbin*;WANG Shengping;LI Zhenhua

2007, 28 (8): 720-724.

Abstract ( 2420 ) [Full Text(HTML)] ()

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The catalytic performance of the PdCl2-CuCl2/Li-Al-O catalyst, with palladium as the active component and porous lithium alumina spinel (Li-Al-O) as the support, for vapor-phase synthesis of diethyl carbonate (DEC) from CO and ethyl nitrite was studied in a continuous fixed-bed reactor at low pressure. The Li-Al-O spinel support was synthesized by impregnation of γ-Al2O3(2-3 mm) with aqueous LiNO3 solution. Under the mild reaction conditions of 5%CO-20%EtONO-75%N2, GHSV=2500h-1, 0.3 MPa, and 110 ℃, the CO conversion was 40% and the space time yield of DEC was 418 g/(L•h). The perfectly close-packed spinel structure could be obtained because of the lithium ions that entered the vacancy of γ-Al2O3. The Li-Al-O catalyst support had no strong acid sites, and the catalyst had stable palladium chloride, both of which were favorable for the DEC synthesis reaction.

Promotion Effect of Platinum Electrode Modified by Phosphomolybdic Acid on Dimethyl Ether Electrochemical Oxidation

CHEN Jinwei;ZENG Jie;JIANG Chunping;WANG Yaohui;ZHAO Beijun;ZHU Shifu;WANG Ruilin*

2007, 28 (8): 725-729.

Abstract ( 2177 ) [Full Text(HTML)] ()

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A Pt electrode modified by H3PMo12O40(PMo12) was prepared by cyclic voltammetry. The preparation process showed that more PMo12was adsorbed on the surface of the bare Pt electrode when the number of scanning increased at the beginning, but finally the total adsorbed amount reached saturation. The electrooxidation of dimethyl ether (DME) was studied on the surface of the PMo12-modified Pt electrode by cyclic voltammetry. The results showed that the Pt electrode modified by PMo12had higher activity for DME oxidation, and its onset potential had a negative shift of 50 mV. The peak current density was enhanced more than 1.86 times with the negative shift of 35 mV on its peak potential, compared with the unmodified electrode. There was a positive current peak at the reverse scan, which was different from the literature. This might indicate the change of the mechanism for DME oxidation on the modified electrode surface. The peak could response methanol oxidation, and the methanol was more likely the mid-product of DME oxidation at the PMo12-modified Pt electrode. The experimental results also showed that the decrease of scan rate put more PMo12on the surface of the bare Pt electrode, however, the activity for DME oxidation was reduced due to the decrease of the effective sites on the surface of the Pt electrode.

Influence of Ba Precursors on NOx Storage Property of Ba/(Pt/γ-Al2O3) Catalysts

WANG Hui;DUAN Lianyun*;XIE Youchang

2007, 28 (8): 730-736.

Abstract ( 1878 ) [Full Text(HTML)] ()

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NOx storage-reduction catalysts, Ba/(Pt/γ-Al2O3), were prepared by the impregnation method using Ba(NO3)2 and Ba(CH3COO)2 as the barium precursors. Characterization studies of the catalysts were performed by means ofX-raydiffraction,X-rayphotoelectron spectroscopy, temperature-programmed reaction desorption, and differential thermal analysis-thermogravimetry. The results indicate that the dispersion threshold of Ba(NO3)2 is 0.047 g/g (Ba/(Pt/γ-Al2O3) mass ratio), which is only about 1/3 of that ofBa(CH3COO)2. After the calcination treatment, the threshold of barium for the catalyst using Ba(CH3COO)2 as the precursor is larger than that using Ba(NO3)2 as the precursor. As a result, the Ba/(Pt/γ-Al2O3) catalyst prepared from Ba(CH3COO)2 has a higher NOx storage capacity than the catalyst prepared from Ba(NO3)2.

Synthesis and Catalytic Polymerization of Acetylene with Steric Substitute

ZHA Daijun;CHEN Yiwang;*;CHEN Lie;QIN Zhiyong;ZHOU Dan

2007, 28 (8): 737-742.

Abstract ( 2322 ) [Full Text(HTML)] ()

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A novel acetylene derivative, 2-propargyloxy-1,4-dimethyl terephthalate, was synthesized. The monomer acetylene with steric substitute was polymerized using WCl6, WCl6-SnPh4, and [Rh(nbd)Cl]2 as catalyst. The structure and optical properties of polyacetylene were studied by means of nuclear magnetic resonance, infrared spectroscopy, ultraviolet-visible absorption spectroscopy, and photoluminescence spectroscopy. The polymerization using WCl6-SnPh4 as catalyst afforded polyacetylene with only 60% of cis-content due to the steric substitute. The polymerization yield was strongly dependent on reaction temperature and solvent. High yield and high trans-content of polyacetylene were obtained by polymerization using [Rh(nbd)Cl]2 catalyst. The steric effect of bulky substitute led to a narrow conjugation of polyacetylene.

Synthesis of Pyrrolidonium Acidic Ionic Liquids and Their Catalytic Activity for Esterification of Acetic Acid and Butanol

HUANG Baohua*;WANG Yanfei;ZHANG Kun;FANG Yanxiong*;ZHOU Beilei

2007, 28 (8): 743-748.

Abstract ( 2776 ) [Full Text(HTML)] ()

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A series of Brnsted acidic ionic liquids, including 2-pyrrolidonium hydrogen sulfate ([Hnhp]HSO4), 1-methyl-2-pyrrolidonium hydrogen sulfate ([Hnmp]HSO4), 1-methylimidazolium hydrogen sulfate([Hmim]-HSO4), 1-(3-sulfonic acid)propyl-3-methylimidazolium hydrogen sulfate ([C3SO3Hmim]HSO4), and 1-(3-sulfonic acid)propyl-2-pyrrolidonium hydrogen sulfate ([C3SO3Hnhp]HSO4), were synthesized and characterized. The catalytic activity of the acidic ionic liquids for the esterification of acetic acid with n-butanol was measured. Under the optimized conditions ofn(n-BuOH)∶n(MeCO2H)∶n([C3SO3Hnhp]HSO4)=1.2∶1∶0.005, 120 ℃, and1 h,the yield ofn-butylacetate could be greater than 99%. The reaction system exhibited good biphasic behavior when the reaction was completed. There was no appreciable decrease in the yield ofn-butylacetate after the esterification was repeated 8 times. The miscibility of the five acidic ionic liquids with the related components of the reaction was investigated, and their biphasic effects on ester yields were examined. The structure-reactivity and Brnsted acidity-catalytic activity relationships were also studied. The acidity and miscibility of the acidic ionic liquids are the important factors relevant to the catalytic activity for the esterification reaction. The activity of the acidic ionic liquids is in good agreement with their acidity order.

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