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Applied Catalysis A, General (v.290, #1-2)
Direct synthesis of phenol from benzene on iron-impregnated activated carbon catalysts by Jung-Sik Choi; Tae-Hwan Kim; Ko-Yeon Choo; Jae-Suk Sung; M.B. Saidutta; Si-Ok Ryu; Sun-Dal Song; B. Ramachandra; Young-Woo Rhee (pp. 1-8).
The direct conversion of benzene to phenol by hydroxylation with hydrogen peroxide was carried out over catalysts containing iron impregnated on activated carbon. Iron was impregnated on various surface modified activated carbons. The catalyst that was made by treating activated carbon with nitric acid, that was treated thermally in the presence of nitrogen at 600°C and impregnated with 5wt.% iron, gave a phenol yield of 20%. It was found that the synergistic interactions of surface groups and the impregnated iron have enhanced the performance of these catalysts.
Factors limiting selectivity in C3 and C4 amm(oxidation) reactions by A. Costine; B.K. Hodnett (pp. 9-16).
An extensive data-mining study of C3 and C4 selective oxidation and ammoxidation reactions occurring in the gas phase over solid catalysts has been conducted. The reactions include the amm(oxidation) of propane, propene, isobutane and isobutene to produce α,β-unsaturated mononitriles and unsaturated carboxylic acids. Selectivity–conversion plots were generated for each reaction from the patent and scientific literature. For each reaction there is a clear upper limit in terms of selectivity–conversion beyond which experimental studies have not advanced. The results show that for some reactions, such as the oxidation of isobutane to methacrylic acid, high product selectivities are never realised due to the production of by-products via parallel oxidation of reaction intermediates, and more importantly, via consecutive oxidation of the unstable product. However, for the reactions of propane amm(oxidation) to produce acrylonitrile and acrylic acid the situation appears to be different. For these reactions, the central problem resides in the inability of conventional catalysts to suppress the propensity of the propene intermediate to desorb and oxidise further to oxides of carbon, rather than the loss in acrylic acid or acrylonitrile selectivity via consecutive oxidation.
Edge dispersion of supported MoS2 and WS2 catalysts as evaluated by using Co(CO)3NO as a probe molecule by Takeshi Kubota; Kenji Sato; Akira Kato; Usman; Takeshi Ebihara; Takashi Fujikawa; Yasuhiro Araki; Katsuaki Ishida; Yasuaki Okamoto (pp. 17-24).
SiO2- and Al2O3-supported MoS2 and WS2 catalysts were prepared to exploit the evaluation technique of the edge dispersion of MoS2 and WS2 particles. A chemical vapor deposition (CVD) technique using Co(CO)3NO as a probe molecule was used for the evaluation. Results were compared with those from conventional techniques such as NO adsorption and TEM. A proportional correlation was obtained between the amount of NO adsorption and the amount of Co atoms accommodated by the CVD technique on WS2/SiO2 and WS2/Al2O3 catalysts, demonstrating a selective location of the Co atoms on the edges of WS2 particles, as previously established for MoS2 catalysts. A comparison of the amounts of NO adsorption and Co accommodation on MoS2 and WS2 catalysts suggested a 70% higher density of sulfur vacancy on MoS2 particles than on WS2 particles regardless of the support. The Co atoms on the edges of MoS2 and WS2 particles showed the identical NO adsorption property. We propose that Co(CO)3NO can be used as a probe molecule to evaluate and directly compare the edge dispersions of MoS2 and WS2 catalysts. The dispersion of MoS2 particles was about two times higher than that of WS2 particles with the SiO2-supported catalysts. With the Al2O3-supported catalysts, MoS2 and WS2 particles were dispersed to a similar extent but much more highly dispersed than the counterparts in the SiO2-supported catalysts. The evaluation of the edge dispersion of MoS2 and WS2 particles by means of TEM may pose problems when SiO2- and Al2O3-supported catalysts are compared. The edges of unpromoted MoS2 particles exhibited a significantly higher intrinsic activity for the HDS of thiophene than those of WS2 particles.
Photodegradation catalyst screening by combinatorial methodology by Qi Xiu Dai; Hai Yuan Xiao; Wen Sheng Li; Yan Qing Na; Xiao Ping Zhou (pp. 25-35).
In this work, a combinatorial methodology was developed for photodegradation catalyst screening. A fluorescence imaging detection system was designed for high throughput analysis, 1,6-hexamethylenediamine was used as the probe molecule for catalyst testing. The photodegradation activity of catalysts was evaluated by 1,6-hexamethylenediamine consumption during the photodegradation reaction. The methodology could provide reliable results. We found that pure TiO2, ZrO2, Nb2O5, MoO3, and WO3 did not show much activity for 1,6-hexamethylenediamine photodegradation under visible light. TiO2 catalysts doped with different metal ions were tested. When TiO2 was doped with Ta2O5, Nb2O5, V2O5, MoO3, or WO3, higher activity for photodegradation was observed. The doping of La3+, Ba2+, and Br− to TiO2 did not improve the catalytic activities. When doping TiO2 with Mn2+, Cl−, Al3+, Cu2+, Fe3+, Na+, Mg2+, Li+, F−, Co2+, or K+, catalytic activity was lower than that of pure TiO2. After elaborate catalysts screening, we discovered new catalysts, such as 50–70% TiO2/0–20% WO3/20–40% VO2.5 and 20–30% TiO2/30–50% MoO3/40–60% VO2.5 as well as 30% WO3/20% ZrO2/50% NbO2.5 (synthesized from ZrCl4, NbCl5, and (NH4)5H5[H2(WO4)6]·H2O in ethanol solution or suspension) and 60–70% WO3/Nb2O5 (synthesized from WCl6 and NbCl5 in ethanol solution). We observed that the catalytic activity is sensitive to preparation methods and catalyst specific surface areas. When P123 (HO(CH2CH2O)20(CH2CH(CH3)O)70(CH2CH2O)20H, designated EO20PO70EO20) was used as template to synthesize mesoporous materials, the mesoporous catalysts showed higher activity than regular catalytic materials.
High combustion activity of methane induced by reforming gas over Ni/Al2O3 catalysts by Baitao Li; Ritsuko Watanabe; Kenji Maruyama; Mohammad Nurunnabi; Kimio Kunimori; Keiichi Tomishige (pp. 36-45).
During the reactions related to oxidative steam reforming and combustion of methane over α-alumina-supported Ni catalysts, the temperature profiles of the catalyst bed were studied using an infrared (IR) thermograph. IR thermographical images revealed an interesting result: that the temperature at the catalyst bed inlet is much higher under CH4/H2O/O2/Ar=20/10/20/50 than under CH4/H2O/O2/Ar=10/0/20/70; the former temperature is comparable to that over noble metal catalysts such as Pt and Pd. Based on the temperature-programmed reduction and oxidation measurements over fresh and used catalysts, the metallic Ni is recognized at the catalyst bed inlet under CH4/H2O/O2/Ar=20/10/20/50, although it is mainly oxidized to NiAl2O4 under CH4/H2O/O2/Ar=10/0/20/70. This result indicates that the addition of reforming gas (CH4/H2O=10/10) to the combustion gas (CH4/O2=10/20) can stabilize Ni species in the metallic state even under the presence of oxygen in the gas phase. This would account for its extremely high combustion activity.
Keywords: Methane; Oxidative steam reforming; Combustion; Hot spot; Thermography; Temperature-programmed reduction; Temperature-programmed oxidation
Synthesis and characterization of alumina-supported Mn(II), Co(II), Ni(II) and Cu(II) complexes of bis(salicylaldiminato)hydrazone as catalysts for oxidation of cyclohexene with tert-buthylhydroperoxide by Masoud Salavati-Niasari; Ahmad Amiri (pp. 46-53).
Complexes of type [M(SAH)(OH2)], where M is Mn(II),Co(II),Ni(II) and Cu(II), and SAH is the Schiff-base formed by condensation of salicylaldehyde (2equiv.) and hydrazine (1equiv.), bis(salicylaldiminato)hydrazone, or “2-({(z)-2-[(E)-1-(2-hydroxyphenyl)methylidene]hydrazono}methyl)phenol� have been prepared and characterized by elemental analysis, IR, UV–vis spectroscopy, conductometric, small area X-ray photoelectron spectroscopy and magnetic measurements. Elemental analysis suggests the stoichiometry to be 1:1 (metal:ligand). The results indicate that the Schiff-base ligand coordinates through one azomethine nitrogen and two phenolic oxygen to the metal ions. Conductance measurements suggest the non-electrolytic nature of the complexes. The atomic concentration of the complexes showed the ratio of M:N:O=1:2:3, that indicates that a water molecule was in the complex. Alumina-supported complexes “[M(SAH)OH2]-Al2O3� catalyze the oxidation of cyclohexene with tert-butylhydroperoxide (TBHP). The major products of the reaction were 2-cyclohexene-1-ol, 2-cyclohexene-1-one and 2-cyclohexene-1-( tert-butylperoxy). The influence of solvent on the oxidation reaction has been studied. [M(SAH)OH2]-Al2O3 shows significantly higher catalytic activity than other alumina-supported complexes. These catalysts can also be reused in the oxidation of cyclohexene several times. The new materials “[M(SAH)OH2]-Al2O3� were characterized by several techniques: chemical analysis and spectroscopic methods (FT-IR, UV–vis, XRD, DRS).
Simultaneous characterization of acidic and basic properties of solid catalysts by a new TPD method and their correlation to reaction rates by Teruoki Tago; Yoshihito Okubo; Shin R. Mukai; Tsunehiro Tanaka; Takao Masuda (pp. 54-64).
We propose a new TPD method for simultaneously characterizing the acidic and basic properties of solid catalysts by utilizing the co-adsorption of NH3 and CO2 on catalysts. First CO2 was adsorbed on the catalyst sample; then NH3 was adsorbed on it. Another adsorption sequence of NH3 and CO2, and CO2 and NH3 single adsorptions were also conducted. The TPD measurements were carried out by heating the catalyst sample from 373 to 773K at a heating rate of 2.5Kmin−1 in a helium stream under a total pressure of 1.3kPa. In solid acid catalysts, there is little difference in the NH3-TPD spectra between single and co-adsorption systems. This results from the absence of any induction effect between the acid and base sites, because the number of base sites in the solid acid catalyst is very small. In contrast, in a solid acid–base catalyst of alumina, a remarkable difference in the NH3-TPD spectra was observed between single adsorption and co-adsorption systems. The difference in the TPD spectra between single and co-adsorption systems was ascribed to a strong induction effect appearing on the acid and base sites, which was proved by an in situ IR measurement. The validity of the TPD method was examined by correlating the number of the strong acid sites to catalytic activities of dehydrolysis of ethanol over solid acid and solid acid–base catalysts. In solid acid–base catalysts, the number of strong acid sites was calculated from the activation energy distribution for the desorption of NH3 in a co-adsorption system because of the strong induction effect. A proportional relationship between the intrinsic reaction rate constant, which is based on the concentration of ethanol within the catalyst, and the number of strong acid sites could be obtained, regardless of the catalysts or their types or pore structure.
Keywords: Temperature-programmed desorption; Acidic and basic properties; Solid acid and base catalyst; Ethanol dehydrolysis; Ammonia and carbon dioxide
Kinetics for benzoylation of sodium 4-acetylphenoxide via third-liquid phase in the phase-transfer catalysis by Chin-Chen Huang; Hung-Ming Yang (pp. 65-72).
In this research, the kinetics for synthesizing 4-acetylphenyl benzoate (R*COOR) from benzoylation of sodium 4-acetylphenoxide via third-liquid phase-transfer catalysis was investigated. The reaction rate was observed to be strongly dependent on agitation speeds in the third-phase catalytic reaction. By forming the third-liquid phase, the observed reaction can be greatly enhanced to give a product yield of 100% in a duration of 3min at 20°C and 200rpm. If a third-liquid phase was not formed in the liquid–liquid system, the reaction rate is very slow and the product yield is only 2% in 3min at 20°C. The reaction conducted in third-liquid phase-transfer catalytic system is faster than that in LLPTC system by 25–28 times. The amount of catalytic intermediate (QOR) in the third-liquid phase was about 50% of the catalyst initially added and kept about 30% of it remained after 1min, and only small amounts of a catalytic intermediate residing in the organic phase were observed during the reaction using methyl t-butyl ether as the solvent. The concentration of catalytic intermediate slightly decreased with increasing reaction time, while the molar ratio of QOR to benzyl tri- n-butylammonium cation in the third-liquid phase remained almost constant after 1min and increased with increasing agitation speeds. The experimental results were well described by the pseudo-first-order kinetics. The present work shows an effective method to synthesize 4-acetylphenyl benzoate.
Keywords: Benzoylation; Kinetics; Third-liquid; Phase-transfer catalysis; 4-Acetylphenyl benzoate
EXAFS study on the sulfidation behavior of Pd, Pt and Pd–Pt catalysts supported on amorphous silica and high-silica USY zeolite by Takashi Matsui; Masaru Harada; Kyoko K. Bando; Makoto Toba; Yuji Yoshimura (pp. 73-80).
The sulfur tolerance of monometallic Pd, Pt and bimetallic Pd–Pt catalysts supported on slightly acidic ultra-stable Y (USY) zeolite (SiO2/Al2O3=390) and on non-acidic silica, having mesopores with a pore diameter of 3 or 10nm, were investigated using the CO adsorption method and the extended X-ray adsorption fine structure (EXAFS) method. Well-dispersed noble metal particles supported on USY zeolite and silica with an average pore diameter of 3nm showed high surface sulfur tolerance and high catalytic hydrogenation activity, although bulk phase sulfidation simultaneously occurred. The synergistic effects of sulfur tolerance were significant in the bimetallic Pd–Pt particles supported on USY zeolite and silica with an average pore diameter of 3nm. On the other hand, on silica with an average pore diameter of 10nm, the surface sulfur tolerance of low dispersed noble metals was the lowest, although its bulk phase sulfur tolerance was the highest. The Pd K-edge and Pt LIII-edge EXAFS spectra indicated a strong interaction between the well-dispersed noble metal particles and the supports of the USY zeolite and silica with an average pore diameter of 3nm. This distorted structure may increase the sulfur tolerance of noble metals, though some surface and bulk phase sulfidation simultaneously occurred.
Keywords: Pd; Pt; Pd–Pt; Noble metal catalyst; USY zeolite; Silica; Mesopore; SULFUR tolerance; EXAFS
Studies on nickel-based catalysts for carbon dioxide reforming of methane by Li Xiancai; Wu Min; Lai Zhihua; He Fei (pp. 81-86).
The catalytic activity and coke resistance of La2O3 promoted nickel-based catalysts are investigated in a fixed-bed flow reactor. The contents of carbon deposited on catalysts were measured by a carbon combustion method. Catalysts were characterized by CO–TPD, CO2–TPD, TPR, XPS and XRD techniques, and the results were correlated with the coke resistance of the catalysts. It is found that the catalytic activity, resistance to carbon deposition and the stability of the catalysts can be greatly improved with the addition of a rare earth oxide. It is found that BaTiO3 is an ideal support. Thus 5.0wt.% Ni–0.75wt.% La–BaTiO3 catalyst shows great resistance to coke formation and higher thermal stability as well as higher catalytic activity, than the catalysts 5.0wt.% Ni/La–BaTiO3 (Ba/La=1/0.002) and 5.0wt.% Ni–1.5wt.% La/BaTiO3.
Keywords: BaTiO; 3; Promoter; Nickel-based catalyst; Reforming; Carbon deposition
Characterizations and activities of the nano-sized Ni/Al2O3 and Ni/La–Al2O3 catalysts for NH3 decomposition by Jian Zhang; Hengyong Xu; Xianglan Jin; Qingjie Ge; Wenzhao Li (pp. 87-96).
A series of nano-sized Ni/Al2O3 and Ni/La–Al2O3 catalysts that possess high activities for NH3 decomposition have been successfully synthesized by a coprecipitation method. The catalytic performance was investigated under the atmospheric conditions and a significant enhancement in the activity after the introduction of La was observed. Aiming to study the influence of La promoter on the physicochemical properties, we characterized the catalysts by N2 adsorption/desorption, XRD, H2-TPR, chemisorption and TEM techniques. Physisorption results suggested a high specific surface area and XRD spectra showed that nickel particles are in a highly dispersed state. A combination of XRD, TEM and chemisorption showed that Ni0 particles with the average size lower than 5.0nm are always obtained even though the Ni loading ranged widely from 4 to 63%. Compared with the Ni/Al2O3 catalysts, the Ni/La–Al2O3 ones with an appropriate amount of promoter enjoy a more open mesoporous structure and higher dispersion of Ni. Reduction kinetic studies of prepared catalysts were investigated by temperature-programmed reduction (TPR) method and the fact that La additive partially destroyed the metastable Ni–Al mixed oxide phase was detailed.
Keywords: Ammonia decomposition; Nano-sized nickel catalyst; Lanthanum promotion; Reduction kinetics; Hydrogen production
Isomerization of n-hexane over mono- and bimetallic Pd–Pt catalysts supported on ZrO2–Al2O3–WO x prepared by sol–gel by A. Barrera; J.A. Montoya; M. Viniegra; J. Navarrete; G. Espinosa; A. Vargas; P. del Angel; G. Pérez (pp. 97-109).
The catalytic performance of mono- and bimetallic Pd (0.6, 1.0wt.%)–Pt (0.3wt.%) catalysts supported on ZrO2 (70, 85wt.%)–Al2O3 (15, 0wt.%)–WO x (15wt.%) prepared by sol–gel was studied in the hydroisomerization of n-hexane. The catalysts were characterized by N2 physisorption, XRD, TPR, XPS, Raman, NMR, and FT-IR of adsorbed pyridine. The preparation of ZrW and ZrAlW mixed oxides by sol–gel favored the high dispersion of WO x and the stabilization of zirconia in the tetragonal phase. The Al incorporation avoided the formation of monoclinic-WO3 bulk phase. The catalysts increased their SBET for about 15% promoted by Al2O3 addition. Various oxidation states of WO x species coexist on the surface of the catalysts after calcination. The structure of the highly dispersed surface WO x species is constituted mainly of isolated monotungstate and two-dimensional mono-oxotungstate species in tetrahedral coordination. The activity of Pd/ZrW catalysts in the hydroisomerization of n-hexane is promoted both with the addition of Al to the ZrW mixed oxide and the addition of Pt to Pd/ZrAlW catalysts. The improvement in the activity of Pd/ZrAlW catalysts is ascribed to a moderated acid strength and acidity, which can be correlated to the coexistence of W6+ and reduced-state WO x species (either W4+ or W0). The addition of Pt to the Pd/ZrAlW catalyst does not modify significantly its acidic character. Selectivity results showed that the catalyst produced 2MP, 3MP and the high octane 2,3-dimethylbutane (2,3-DMB) and 2,2-dimethylbutane (2,2-DMB) isomers.
Keywords: Bimetallic Pd–Pt catalysts; ZrO; 2; –Al; 2; O; 3; –WO; 3; ternary oxide; Sol–gel method; Structure; Reducibility; XPS; Raman; NMR; Acidity; Isomerization of; n; -hexane
Studies of Cu-ZSM-5 by X-ray absorption spectroscopy and its application for the oxidation of benzene to phenol by air by Norma B. Castagnola; A. Jeremy Kropf; Christopher L. Marshall (pp. 110-122).
The oxidation of benzene to phenol has been successfully carried out in air over Cu-ZSM-5 at moderate temperatures. Several parameters such as Cu loading, calcination temperature and co-exchanged metal ions influence the nature of the catalyst. At low Cu loadings, the catalyst is more selective to phenol while at high Cu loadings CO2 is the major product. In situ H2-TPR XAFS studies reveal that at low Cu loadings, Cu exists as isolated pentacoordinated ions, with 4 equatorial oxygens at 1.94Å and a more distant axial oxygen at 2.34Å. At higher loadings, monomeric as well as dimeric Cu species exist, with a Cu–Cu distance of 2.92Å. This suggests that the isolated Cu sites are the active sites responsible for phenol formation. When the catalyst was calcined at 450°C, the activity peaked in the first hour and then slowly deactivated, but when the calcination temperature was increased to 850°C, the activity slowly increased until it reached a plateau. Analysis of the XANES region during in situ H2-TPR shows that at lower calcination temperatures two reduction peaks are present, corresponding to Cu2+→Cu+ and Cu+→Cu0. At high calcination temperatures, only a small fraction of the Cu undergoes the two-step reduction and most of the Cu remains in the +2 state. Slow deactivation of the catalyst calcined at 450°C is due to migration of the Cu ions to inaccessible sites in the zeolite; at high calcination temperatures the Cu is tightly bound to the framework and is unable to migrate. EXAFS analysis of the sample calcined at 850°C reveals two Cu–Si(Al) scattering paths at 2.83Å. Doping the catalyst with other metals, in particular Ag and Pd, further improves the activity and selectivity of the reaction. The addition of water to the reaction increases the selectivity of the reaction by displacing the product from the active site.
Keywords: Phenol; Cu-ZSM-5; X-ray absorption spectroscopy
The effect of ceria content on the performance of Pt/CeO2/Al2O3 catalysts in the partial oxidation of methane by A.C.S.F. Santos; S. Damyanova; G.N.R. Teixeira; L.V. Mattos; F.B. Noronha; F.B. Passos; J.M.C. Bueno (pp. 123-132).
The effect of CeO2 loading (1–20wt.%) on the properties and catalytic behaviors of CeO2–Al2O3-supported Pt catalysts on the partial oxidation of methane was studied. The catalysts were characterized by SBET, X-ray diffraction (XRD), temperature-programmed reduction (TPR) and oxygen storage capacity (OSC). XRD and TPR results showed that the pretreatment temperature of the support influences on the amount of CeO2 with fluorite structure. The pretreatment temperature of the support and CeO2 loading influenced the morphology of Pt. OSC analysis showed a significant increase in the oxygen storage capacity per weight of CeO2 for samples with high CeO2 loading (12 and 20wt.%). TPR analyses showed that the addition of Pt promotes the reduction of CeO2. This effect was more significant for the catalysts with high CeO2 loading (≥12wt.%). The dispersion of Pt, measured by the rate of cyclohexane dehydrogenation, increases with increasing of the pretreatment temperature of the support. It was shown that the kind of the support is very important for obtaining of catalysts resistant to carbon formation. The catalysts with high CeO2 loading (≥12wt.%) showed the highest catalytic activity and stability in the reaction of partial oxidation of methane due to a higher Pt–CeO2 interface.
Effects of kinds of ionic liquid catalysts on alkylations of 1-and 2-methylnaphthalene with alkenes by Zhongkui Zhao; Weihong Qiao; Xiuna Wang; Guiru Wang; Zongshi Li; Lübo Cheng (pp. 133-137).
Alkylations of 1-and 2-methylnaphthalene with long-chain alkenes in different alkyl-containing amine ionic liquids were investigated at room temperature. The effects of both anions and cations of ionic liquids on the alkylations were studied in detail. Results show that the anions determine, to a large extent, the physical and chemical properties of ionic liquids, but organic cations mainly influence physical properties, and have only a little impact on the catalytic performance. High conversion of alkylating agent and excellent selectivity for the desired products were obtained. The products and unreacted reactants were easily isolated from catalysis systems by extraction with cyclohexane. Thanks to the less expensive reagents and the easier synthesis process, methyl and ethylamine chloroaluminate ionic liquids could become novel practical catalysts for long-chain alkylation of methylnaphthalene with alkenes.
Keywords: Alkylation; 1-and 2-Methylnaphthalene; Long-chain alkenes; Ionic liquids
Production of hydrogen via partial oxidation of methanol over Au/TiO2 catalysts by Feg-Wen Chang; Hsin-Yin Yu; L. Selva Roselin; Hsien-Chang Yang (pp. 138-147).
Selective production of hydrogen by partial oxidation of methanol (CH3OH+(1/2)O2→2H2+CO2) over Au/TiO2 catalysts, prepared by a deposition–precipitation method, was studied. The catalysts were characterized by XRD, TEM, and XPS analyses. TEM observations show that the Au/TiO2 catalysts exhibit hemispherical gold particles, which are strongly attached to the metal oxide support at their flat planes. The size of the gold particles decreases from 3.5 to 1.9nm during preparation of the catalysts with the rise in pH from 6 to 9 and increases from 2.9 to 4.3nm with the rise in calcination temperature up to 673K. XPS analyses demonstrate that in uncalcined catalysts gold existed in three different states: i.e., metallic gold (Au0), non-metallic gold (Au δ+) and Au2O3, and in catalysts calcined at 573K only in metallic state. The catalytic activity is strongly dependent on the gold particle size. The catalyst precipitated at pH 8 and uncalcined catalysts show the highest activity for hydrogen generation. The partial pressure of oxygen plays an important role in determining the product distribution. There is no carbon monoxide detected when the O2/CH3OH molar ratio in the feed is 0.3. Both hydrogen selectivity and methanol conversion increase with increasing the reaction temperature. The reaction pathway is suggested to consist of consecutive methanol combustion, partial oxidation and steam reforming.
Vanadium-containing ordered mesoporous silicas: Synthesis, characterization and catalytic activity in the hydroxylation of biphenyl by Jino George; S. Shylesh; A.P. Singh (pp. 148-158).
A series of vanadium-containing ordered mesoporous MCM-41 materials (V-OMS) have been synthesized by direct hydrothermal (V-MCM-41) and grafting (V/MCM-41) methods using hexadecyl trimethyl ammonium bromide (HDTMABr) as the structure-directing agent. The physico-chemical properties of the vanadium-containing materials were characterized in detail by ICP-OES, XRD, FT-IR, N2 adsorption–desorption, DRUV-VIS, TPR, XPS and SEM techniques. The redox performances of the vanadium-modified mesoporous materials were tested in the hydroxylation of biphenyl using aqueous H2O2 (30wt.%) as oxidant. For a better exploitation of the catalytic activity, the reaction parameters are optimized in terms of temperature, solvent, oxidant, etc. A comparison between the catalytic activity values of the vanadium-containing mesoporous materials prepared by the two routes shows that vanadium-substituted (V-MCM-41) materials had increased activity and improved selectivity for mono hydroxyl products in the hydroxylation reaction of biphenyl compared to the V/MCM-41 catalysts. The heterogenity of the catalysts was verified by a series of leaching studies. Both the catalysts enhance the leaching of active vanadia species during the reaction; among them, V/MCM-41 shows the least heterogenity.
Keywords: Mesoporous molecular sieves; MCM-41; Vanadium; Biphenyl; Heterogenity
Surface and bulk investigation of ZSM5 and Al-MCM-41 using synchrotron XPS, XANES, and hexane cracking by P.A. Jalil; M.S. Kariapper; M. Faiz; N. Tabet; N.M. Hamdan; J. Diaz; Z. Hussain (pp. 159-165).
We present a comparative study of ZSM5 and Al-MCM-41 catalysts using spectroscopic and chemical techniques. The analysis of conventional and synchrotron XPS spectra of these catalysts reveals the presence of a topmost surface-related Si peak in addition to the bulk peak. XANES results suggest structural modification upon heating Al-MCM-41 at 500°C. Depth-resolved XPS data show Al depletion from the surface of Al-MCM-41 in contrast to surface enrichment of Al in ZSM5. These surface modifications could be one of the reasons for the weak acidity of Al-MCM-41 in chemical reactions such as hexane cracking at different temperatures.
Keywords: ZSM5; Al-MCM-41; XANES
K-, CeO2-, and Mn-promoted Ni/Al2O3 catalysts for stable CO2 reforming of methane by A. Nandini; K.K. Pant; S.C. Dhingra (pp. 166-174).
Reforming of methane with carbon dioxide into syngas over Ni/γ-Al2O3 catalysts modified by potassium, MnO and CeO2 was studied. The catalysts were prepared by impregnation technique and were characterized by N2 adsorption/desorption isotherm, BET surface area, pore volume, and BJH pore size distribution measurements, and by X-ray diffraction and scanning electron microscopy. The performance of these catalysts was evaluated by conducting the reforming reaction in a fixed bed reactor. The coke content of the catalysts was determined by oxidation conducted in a thermo-gravimetric analyzer. Incorporation of potassium and CeO2 (or MnO) onto the catalyst significantly reduced the coke formation without significantly affecting the methane conversion and hydrogen yield. The stability and the lower amount of coking on promoted catalysts were attributed to partial coverage of the surface of nickel by patches of promoters and to their increased CO2 adsorption, forming a surface reactive carbonate species. Addition of CeO2 or MnO reduced the particle size of nickel, thus increasing Ni dispersion. For Ni–K/CeO2–Al2O3 catalysts, the improved stability was further attributed to the oxidative properties of CeO2. Results of the investigation suggest that stable Ni/Al2O3 catalysts for the carbon dioxide reforming of methane can be prepared by addition of both potassium and CeO2 (or MnO) as promoters.
Hydration of 3-cyanopyridine to nicotinamide over MnO2 catalyst by Subhash Chandra Roy; P. Dutta; L.N. Nandy; S.K. Roy; P. Samuel; S. Muthukumaru Pillai; V.K. Kaushik; M. Ravindranathan (pp. 175-180).
A simple and an eco-friendly process for the hydration of 3-cyanopyridine to nicotinamide in the presence of manganese dioxide catalyst has been described. The reaction is conducted at moderate temperature with the reaction times of 5–8h using an aqueous solution of 3-cyanopyridine. The effect of various reaction parameters on the yield of nicotinamide was studied. In most instances, nearly quantitative yields of amides are obtained without any by-products. The IR and ESCA findings of the catalysts are correlated with the catalytic activity.
Keywords: Catalytic hydration; Nicotinamide; Manganese dioxide catalyst; 3-Cyanopyridine; ESCA; Catalyst recycle
Well-defined group IV supported catalysts: An efficient way to increase activities in the deperoxidation of cyclohexyl hydroperoxide with environmentally systems by Romain Petroff Saint-Arroman; Jean-Marie Basset; F. Lefebvre; Blaise Didillon (pp. 181-190).
Silica-supported (SiO)3MOR (M=Ti, Zr, Hf; R=H, tBu) organometallic complexes of group 4, uniform in composition and in distribution, were synthesized via a molecular engineering approach of the construction of active sites. These catalysts were fully characterized by various methods including solid-state NMR, infrared spectroscopy and microanalysis. In the goal to develop environmentally friendly processes,these solids were used as catalysts for the deperoxidation of cyclohexyl hydroperoxide, an important step in the synthesis of adipic acid, a precursor of nylon 6-6.The best metal is titanium and its performances are far above those of calcined supported titanium catalysts previously reported in the patent litterature. The influence on the catalytic activity of the nature of the coordination sphere and more specifically the number of covalent bonds between titanium and the silica support were studied. The catalysis is mainly heterogeneous as shown by various experiments. A non-negligible amount of titanium is leached during the first stages of the reaction but after some recycles the reaction rate remains constant allowing to suggest that this catalyst should be a good candidate for heterogeneous deperoxidation of cyclohexyl hydroperoxide.
Catalytic cracking of 1-butene to propene and ethene on MCM-22 zeolite by Xiangxue Zhu; Shenglin Liu; Yueqin Song; Sujuan Xie; Longya Xu (pp. 191-199).
Catalytic cracking of butene to propene and ethene was investigated over HMCM-22 zeolite. The performance of HMCM-22 zeolite was markedly influenced by time-on-stream (TOS) and reaction conditions. A rapid deactivation during the first 1h reaction, followed by a quasi-plateau in activity, was observed in the process along with significant changes in product distributions, which can be attributed to the fast coking process occurring in the large supercages of MCM-22.Properly selected reaction conditions can suppress the secondary reactions and enhance the production of propene and ethene. According to the product distribution under different butene conversion, we propose a simple reaction pathway for forming the propene, ethene and by-products from butene cracking.HMCM-22 exhibited similar product distribution with the mostly used high silica ZSM-5 zeolite under the same conversion levels. High selectivities of propene and ethene were obtained, indicating that the 10-member ring of MCM-22 zeolite played the dominant role after 1h of TOS. However, MCM-22 exhibited lower activity and stability than that on high silica ZSM-5 zeolite with longer time-on-stream.
Keywords: Butene; Catalytic cracking; Propene; Ethene; HMCM-22 zeolite
Methane steam reforming over Ni/Ce–ZrO2 catalyst: Influences of Ce–ZrO2 support on reactivity, resistance toward carbon formation, and intrinsic reaction kinetics by N. Laosiripojana; S. Assabumrungrat (pp. 200-211).
Ni/Ce–ZrO2 showed good methane steam reforming performance in term of stability toward the deactivation by carbon deposition. It was first observed that the catalyst with Ce/Zr ratio of 3/1 showed the best activity among Ni/Ce–ZrO2 samples with the Ce/Zr ratios of 1/0, 1/1, 1/3, and 3/1. Temperature-programmed oxidation (TPO) experiments indicated the excellent resistance toward carbon formation for this catalyst, compared to conventional Ni/Al2O3; the requirement of inlet H2O/CH4 to operate without the formation of carbon species is much lower. These benefits are related to the high oxygen storage capacity (OSC) of Ce–ZrO2. During the steam reforming process, in addition to the reactions on Ni surface (*), the redox reactions between the gaseous components present in the system and the lattice oxygen (O x) on Ce–ZrO2 surface also take place. Among these reactions, the redox reactions between the high carbon formation potential compounds (CH4, CH x-* n and CO) and the lattice oxygen (O x) can prevent the formation of carbon species from the methane decomposition and Boudard reactions, even at low inlet H2O/CH4 ratio (1.0/1.0).Regarding the intrinsic kinetic studies in the present work, the reaction order in methane over Ni/Ce–ZrO2 was observed to be approximately 1.0 in all conditions. The dependence of steam on the rate was non-monotonic, whereas addition of oxygen as an autothermal reforming promoted the rate but reduced CO and H2 production selectivities. The addition of a small amount of hydrogen increased the conversion of methane, however, this positive effect became less pronounced and the methane conversion was eventually inhibited when high hydrogen concentration was added. Ni/Ce–ZrO2 showed significantly stronger negative impact of hydrogen than Ni/Al2O3. The redox mechanism on ceria proposed by Otsuka et al. [K. Otsuka, T. Ushiyama, I. Yamanaka, Chem. Lett. (1993) 1517; K. Otsuka, M. Hatano, A. Morikawa, J. Catal. 79 (1983) 493; K. Otsuka, M. Hatano, A. Morikawa, Inorg. Chim. Acta 109 (1985) 193] can explain this high inhibition.
Reaction and oxygen permeation studies in Sm0.4Ba0.6Fe0.8Co0.2O3− δ membrane reactor for partial oxidation of methane to syngas by Masayuki Ikeguchi; Tomohiro Mimura; Yasushi Sekine; Eiichi Kikuchi; Masahiko Matsukata (pp. 212-220).
A disk-type Sm0.4Ba0.6Co0.2Fe0.8O3− δ perovskite-type mixed-conducting membrane was applied to a membrane reactor for the partial oxidation of methane to syngas (CO+H2). The reaction was carried out using Rh (1wt%)/MgO catalyst by feeding CH4 diluted with Ar. While CH4 conversion increased and CO selectivity slightly decreased with increasing temperature, a high level of CH4 conversion (90%) and a high selectivity to CO (98%) were observed at 1173K. The oxygen flux was increased under the conditions for the catalytic partial oxidation of CH4 compared with that measured when Ar was fed to the permeation side. We investigated the reaction pathways in the membrane reactor using different membrane reactor configurations and different kinds of gas. In the membrane reactor without the catalyst, the oxygen flux was not improved even when CH4 was fed to the permeation side, whereas the oxygen flux was enhanced when CO or H2 was fed. It is implied that the oxidation of CO and H2 with the surface oxygen on the permeation side improves the oxygen flux through the membrane, and that CO2 and H2O react with CH4 by reforming reactions to form syngas.
Infrared and ultraviolet–visible spectroscopic studies of silica, [(Cp)2ZrCl2] and trimethylaluminum interactions by Fábio Gomes Costa; Elias Andrade Braga; Soraia Teixeira Brandão; Alexandre de Freitas Espeleta; Zênis Novais da Rocha; Lílian Maria Tosta Simplício; Emerson Andrade Sales (pp. 221-226).
Infrared and UV–vis studies of metallocene immobilization on silica are reported here. The results have indicated changes in the Zr coordination sphere of metallocene depending on the immobilization route used. The reaction of [(Cp)2ZrCl2] with silica formed [(Cp)2ZrCl]+[SiO]− species. The same metallocene, reacting with TMA modified silica, formed monomethylated and dimethylated species by the substitution of chloro for methyl ligands, stabilized on the surface by interaction with “MAO-like� species (methylaluminoxane, MAO). These monomethylated and dimethylated cationic zirconium species are the active centers for the polymerization reaction. Different order of TMA addition in the silica modification step generated surface species of a similar nature, differing in their relative quantities. The highest amount of these active species was obtained when the support was added to the TMA solution rather than adding the TMA solution to the silica support. This was the most significant parameter affecting catalytic activity in ethylene polymerization.