Applied Catalysis A, General (v.301, #2)

A study on the catalytic synergy effect between noble metals and cobalt phases in Ce-Al-O supported catalysts by Ming Meng; Yu-qing Zha; Jin-yong Luo; Tian-dou Hu; Ya-ning Xie; Tao Liu; Jing Zhang (145-151).
A series of Co-Pt(Pd, Rh)/Ce-Al-O catalysts were prepared by successive wetness impregnation method. The catalytic activities of the samples for CO oxidation were evaluated in a flow fixed-bed micro-reactor. The techniques of XRD, XPS, EXAFS, H2-TPR and TPO-MS were employed to characterize the catalysts. The results of activity measurement show that for CO oxidation the presence of a small amount of noble metals greatly enhances the activity of Co/Ce-Al-O catalyst, the existence of cerium has increased the activity of the samples because of its capacity for oxygen storage and the interaction between cerium oxide and cobalt phase. The structural characterization results of XRD, XPS and EXAFS indicate that the cobalt in Co-Pt(Pd, Rh)/Ce-Al-O catalysts exists as metallic phase, while in Co/Ce-Al-O catalyst only part of the cobalt has been reduced to zero valence, the rest exists as Co-Al spinel which cannot be reduced at 450 °C by H2. H2-TPR results suggest that the hydrogen spillover may occur during the reduction pretreatment, and therefore increasing the reduction deepness of cobalt phases. The results of TPO-MS show that the oxygen spillover from noble metals to cobalt phase during CO oxidation is very potential. It decreases the activation energy of CO oxidation reaction and results in a prominent increase of the activity. The spilled over species, such as atomic H and O, generated on noble metal sites are mobile on the surface of the catalysts, which makes both of the close and remote cobalt phases involve in reactions at lower temperatures. Additionally, the coordination numbers from EXAFS indicate that the presence of noble metals greatly enhances the dispersion of cobalt phases. The order of this enhancement effect is Pt > Pd > Rh. As a result, the oxygen spillover effect and the enhancement effects on the reduction deepness and the dispersion of cobalt phases should be the main contributions to the catalytic synergy effect between cobalt phases and noble metals.
Keywords: Co-Pt(Pd, Rh)/Ce-Al-O catalysts; CO oxidation; Hydrogen spillover; Oxygen spillover; Catalytic synergy effect; Structural characterization;

Shift of initial mechanism in TiO2-assisted photocatalytic process by Shiying Yang; Liping Lou; Kan Wang; Yingxu Chen (152-157).
There are still open questions concerning the initial steps in photocatalytic mechanisms. In this paper, the effects of TiO2 surface modification on the shift of initial mechanism in UV light photodegradation of three model azo dyes, Orange I (OI), Orange II (OII), and Orange G (OG), are reported. Without modification, the direct hole mechanism plays a major role for all the three dyes; the relative percentage of hole mechanism (p h) is in the order of OI > OII > OG. However, with additives (F or SO4 2−), which change the surface chemistry of the semiconductor, the initial steps shift partly from direct hole oxidation to radical induced mechanism; the reaction sites move from the particle surface to the solution. The shift potential is in the order of OI < OII < OG. Adsorption isotherm experiments show that there is no correlation between the adsorption ability of dyes and the photodegradation mechanism. The reaction mechanism is probably related to the dyes’ affinity with active species.
Keywords: Photocatalysis; Mechanism; Initial steps; Surface modification;

Mechanistic model for the lipase-catalyzed alcoholysis of triacylglycerols by Fernando Camacho; Alfonso Robles; Pedro A. González; Belén Camacho; Luis Esteban; Emilio Molina (158-168).
The enzymatic alcoholysis of triolein and an oil highly rich in polyunsaturated fatty acid with ethanol to obtain 2-monoacylglycerols (2-MG) was studied. Two sn-1,3 specific lipases were used to catalyze this reaction: Lipozyme® IM from Mucor miehei and lipase D from Rhizopus oryzae. The experimental results were acceptably fitted to a mechanistic kinetic model that considers the formation of an acyl–enzyme complex and the isomerization of 2-monoacylglycerols (2-MG) by acyl migration to 1(3)-monoacylglycerols (1(3)-MG). The results of the alcoholysis reaction were both qualitatively and quantitatively dependent on the lipase used. When using Lipozyme IM the process was controlled by the acyl migration of the 2-MG to 1(3)-MG, which finally gave rise to glycerol. In contrast, when using lipase D, no acyl migration occurred and the process was controlled by the formation of 1(3),2-DG and 2-MG. The yields of 2-MG obtained with lipase D (almost 80%) were therefore greater than those obtained using Lipozyme IM in the same experimental conditions. The proposed kinetic model predicted the experimental results of the alcoholysis as a function of the processing intensity (lipase amount × reaction time/reaction volume, m E t/V) irrespective of whether acyl migration took place. It also allowed the kinetic parameters of all the processes involved to be calculated.
Keywords: Immobilised lipase; Kinetic model; 2-Monoacylglycerol; Acyl migration; Alcoholysis;

Selective alkene epoxidation and alkane hydroxylation with sodium periodate catalyzed by cationic Mn(III)-salen supported on Dowex MSC1 by Bahram Bahramian; Valiollah Mirkhani; Majid Moghadam; Shahram Tangestaninejad (169-175).
Efficient alkene epoxidation and alkane hydroxylation with sodium periodate catalyzed by Mn(salen) supported on Dowex MSC1 is reported. ▪Dicationic Mn(III)-salen, containing phosphonium groups at 5,5′-positions of salen ligand, is supported on an ion-exchange resin, Dowex MSC1, via electrostatic interaction. The catalyst, Mn(salen)-Dowex, has been characterized by FTIR, UV–vis spectroscopic techniques, scanning electron micrograph (SEM), thermal and elemental analysis. This heterogenized homogeneous manganese(III)-salen complex can be used as catalyst in the alkene epoxidation with sodium periodate. This catalytic system shows a good activity in the epoxidation of cyclic, aromatic and especially linear alkenes and exhibits a high selectivity in epoxidation of α-pinene and R-(+)-limonene. Alkyl aromatic and cycloalkanes were oxidized efficiently to their corresponding alcohols and ketones in the presence of this catalyst. The stability and reusability of this new heterogenized metallosalen complex was also investigated.
Keywords: Supported catalyst; Manganese salen; Epoxidation; Hydroxylation; Periodate;

The ruthenium(II) 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin carbonyl complex has been covalently attached to a 3-aminoporpyl functionalized silica gel. This supported complex is found to efficiently catalyze the epoxidation of the Δ5-unsaturated steroid derivatives with high conversion, epoxide yield and β-selectivity. High β-selectivity is also observed for the epoxidation of a Δ4-unsaturated steroid though the conversion and derivative are low. This new silica-supported polyhalogenated metalloporphrin catalyst can be easily recovered after reaction and has shown high stability over repeated uses. No catalyst leaching is detected in these reactions.
Keywords: Ruthenium porphyrin; Supported; Unsaturated steroids; β-Selective epoxidation;

Recovery and separation of palladium from spent catalyst by M.A. Barakat; M.H.H. Mahmoud; Y.S. Mahrous (182-186).
An efficient and complete separation of precious metals from the containing secondary materials has a vital economic impact. Palladium loaded on alumina support is usually used as a catalyst in fertilizers industry where the recovery of the metals from the spent catalyst is practically important. Palladium was partially dissolved from the spent catalyst in hot concentrated hydrochloric acid where a large amount of aluminum is also dissolved. The main objective of this work is to find out the optimum conditions for efficient and clean dissolution of palladium with minimum attack to the alumina carrier. Palladium can form different soluble chloro-complexes which can enhance the dissolution process if an oxidizing agent is added. A small amount of hydrogen peroxide could greatly improve the dissolution of palladium in dilute hydrochloric acid while the alumina support was left nearly unaffected. Complete dissolution of palladium was achieved by leaching with a solution contains 7% HCl and 5% H2O2 at 60 °C for 2 h with a liquid/solid ratio of 10/1. The leach liquor contained 0.04% palladium and 0.5% aluminum and the filtered solids was a pure aluminum rich residue. Palladium could be separated from the leach liquor by reduction with formic acid solution. Heating the solution increased the efficiency of palladium reduction and also produced larger palladium particles those can be easily separated by filtration. Palladium powder of 98% purity was produced with recovery efficiency >99%.
Keywords: Palladium; Spent catalyst; Recovery; Separation;

The enantio-differentiation (ED) ability of rigid cinchona alkaloids, such as α- and β-isocinchonines (α-ICN, β-ICN), was investigated in the asymmetric hydrogenation of ethyl pyruvate (EtPy) in toluene at low modifier (M) concentration ([M]0  = 1.2 × 10−5  M). The isocinchonines showed anomalous kinetic behavior, i.e., lack of rate acceleration (α-ICN), low ee values, monotonic decrease-type ee - conversion dependencies, independence of the ee on modifier concentration and reaction temperature. When α-ICN was co-injected with either cinchonidine (CD) or cinchonine (CN) the ee-conversion dependencies observed in the presence of pure CD or CN were not altered. The new results indicate that in aprotic solvent the ED ability of flexible and rigid cinchona alkaloids, such as CD, CN and α-ICN, β-ICN should have different origin. It is suggested that ED can take place either in the liquid phase (CD, CN, β-ICN) or at the Pt surface (α-ICN). The formation of substrate–modifier complex in the liquid phase furnishes pronounced rate acceleration for cinchonidine (CD), cinchonine (CN) and β-ICN, but high ee values were obtained only for CD and CN. However, interactions taking place at the Pt surface (α-ICN) result in low ee values and no rate acceleration. Results presented in this study show that both α-ICN and β-ICN only partly resemble the properties of CD or CN, the flexible alkaloids. No RA was also observed when other rigid modifiers, such as (−)-sparteine and (+)-dihydrovinpocetine, were used. These modifiers show similar kinetic patterns as α-ICN.
Keywords: Enantioselective hydrogenation; Ethyl pyruvate; Pt/Al2O3; Cinchonidine; Cinchonine; α-Isocinchonine; β-Isocinchonine; Enantio-differentiation;

Catalytic oligomerization of ethylene over Ni-containing dealuminated Y zeolites by Michael Lallemand; Annie Finiels; François Fajula; Vasile Hulea (196-201).
Ni-containing dealuminated Y zeolites with different Si/Al ratios were prepared, characterized and tested in the ethylene oligomerization reaction, performed in slurry semi-batch mode, under very mild conditions. A favourable influence of both pore accessibility and mild acidity of NiY materials on their catalytic properties was observed. With these catalysts, high activities (16–30 g of oligomers/gcat  h) were obtained in the temperature range of 30–70 °C. The reaction was also highly selective, resulting almost exclusively in olefins with an even number of C4–C12 carbon atoms.
Keywords: Nickel; Dealuminated Y zeolites; Ethylene; Oligomerization;

Amorphous superbasic ZrO2-KOH of high-surface-area was prepared by reflux-digestion of ZrO(OH)2 gel in aqueous KOH (0.5 M), followed by calcination at 873 K. Incipient wetness impregnation of the high-surface-area superbasic ZrO2-KOH with Ru acetylacetonate [Ru(acac)3] and RuCl3 (dissolved in ethanol), respectively, leads to nanosized Ru (2–7 nm) catalysts. We found that the Ru catalyst performs better when the Cl-free Ru precursor is adopted. Due to the high surface area and superbasicity of the support material, the Cl-free Ru/ZrO2-KOH catalyst is highly effective for the generation of CO x -free hydrogen from NH3 decomposition. The high dispersion of Ru is related to the high surface area of ZrO2 and to the presence of K+. We deduce that the presence of Cl has direct as well as indirect (by weakening the promotional effect of KOH) effects on the electronic state of Ru nanoparticles. The apparent activation energy of ammonia decomposition on Cl-free Ru supported on the superbasic ZrO2-KOH is higher than that on conventional ZrO2. N2-TPD results disclosed that the superbasicity of the support material favors the combinative desorption of surface N atoms, a step generally regarded as the rate-determining in catalytic cycle of ammonia decomposition.
Keywords: Superbasic zirconia; Nanosized ruthenium catalyst; Ammonia decomposition; Hydrogen manufacture; Solid superbase; Promoter in catalysis;

A facile synthesis of amides by selective hydration of nitriles using modified natural phosphate and hydroxyapatite as new catalysts by F. Bazi; H. El Badaoui; S. Tamani; S. Sokori; A. Solhy; D.J. Macquarrie; S. Sebti (211-214).
The selective hydration of several nitriles has been accomplished using sodium nitrate modified natural phosphate (NP) and hydroxyapatite (HAP). The corresponding amides were obtained efficiently and selectively in good yields. This reaction was carried out under eco-friendly conditions using water in the absence of organic solvents.
Keywords: Heterogeneous catalysis; Hydroxyapatite; Natural phosphate; Selective hydration;

One-pot synthesis of dimethyl carbonate catalyzed by n-Bu4NBr/n-Bu3N from methanol, epoxides, and supercritical CO2 by Jie-Sheng Tian; Jin-Quan Wang; Jian-Yu Chen; Jian-Guo Fan; Fei Cai; Liang-Nian He (215-221).
A homogeneous binary catalyst system, n-Bu4NBr/n-Bu3N, was found to be active for the synthesis of dimethyl carbonate from styrene oxide (SO), methanol, and supercritical CO2. Under the optimized conditions, the dimethyl carbonate yield could reach 84% at SO conversion of 98%. Several parameters were studied, i.e. catalyst precursors, reaction time and temperature, methanol/epoxide feed ratio in moles, and CO2 pressure. The best compromise for the one-pot synthesis was achieved with an equimolar amount of n-Bu4NBr/n-Bu3N. A possible mechanism for the present n-Bu4NBr/n-Bu3N-catalyzed one-pot synthesis of dimethyl carbonate was proposed.
Keywords: Supercritical carbon dioxide; Epoxide; Dimethyl carbonate; Methanol; Binary catalyst system (n-Bu4NBr/n-Bu3N); Homogeneous catalysis;

In this work, three catalysts with different chemical and physical properties were synthesized (one HZSM-5 zeolite and two ordered mesoporous aluminosilicates—MCM-41a and MCM-41b) and tested for the pyrolysis of four samples of commercial polymers (LDPE, PP, PS and EVA copolymer), using a thermobalance under nitrogen atmosphere at a heating rate of 10 °C/min. The catalysts were characterized using X-ray powder diffraction, nitrogen adsorption at 77 K and 27Al and 29Si solid state nuclear magnetic resonance (NMR). The HZSM-5 zeolite showed the lowest activity in the catalytic pyrolysis of the four polymers. The two mesoporous catalysts, with a greater pore size, were the most active materials in the catalytic pyrolysis of the polymers, and the MCM-41b sample, with higher acidity, was the most active. The presence of MCM-41 samples during the pyrolysis of the high impact PS sample permits us to distinguish between different decomposition steps which are probably related to the pyrolysis of PS and polybutadiene domains. This processes separation was not observed in absence of the catalyst. Thus, catalytic pyrolysis of such samples in the presence of MCM-41 and other catalysts could be a promising technique to characterize this type of polymers.
Keywords: Catalytic pyrolysis; ZSM-5; MCM-41; TGA; FT-IR; Polymers;

Isomerization of linear alkenes on Amberlyst 15 by Piotr M. Słomkiewicz (232-240).
The kinetics of the isomerization of 1-butene to cis-2-butene and trans-2-butene, of 1-pentene to cis-2-pentene and trans-2-pentene as well as of 1-hexene to cis-2-hexene and trans-2-hexene on sulfonated copolymer Amberlyst 15 in the gas phase was investigated. The Langmuir–Hinshelwood equations were adjusted to the results of the kinetic experiment using the values of adsorption equilibrium constants of the reactants from the adsorption measurements separately taken. The calculations were done by the Levenberg–Marquardt least-squares method using the Origin Microcal program.
Keywords: Isomerization; 1-Butene; Cis-2-butene; Trans-2-butene; 1-Pentene; Cis-2-pentene; Trans-2-pentene; 1-Hexene; Cis-2-hexane; Trans-2-hexane; Langmuir–Hinshelwood kinetics; Amberlyst 15;

Effect of fluorine and boron modification on the HDS, HDN and HDA activity of hydrotreating catalysts by Lianhui Ding; Zisheng Zhang; Ying Zheng; Zbigniew Ring; Jinwen Chen (241-250).
A series of fluorine- and/or boron-modified catalysts were studied, among which the catalysts simultaneously modified with fluorine and boron were prepared and studied for the first time. The hydrodesulfurization (HDS), hydrodenitrogenation (HDN) and hydrodearomatics (HDA) activities of all the catalysts were evaluated with model compounds, 4,6-DMDBT, pyridine and 1-methylnathphlene. The catalysts were also characterized by FT-IR, BET, X-ray photoelectron spectroscopy (XPS), and thermogravity/differential thermal analysis (TG/DTA) for acid type and acidity, pore structure, metal distribution on the surface of catalysts, existing state of hydrogenation metals, and decomposition of fluorine, boric and hydrogenation metal compounds. The experimental results showed that the catalyst simultaneously modified with borane isoproxyl and ammonium fluoride had the best HDN and HDA activities and good HDS activity, though the lowest acidity among the catalysts. The excellent hydrogenation activity of this catalyst may attribute to its highest dispersed active nickel and its large pore volume and surface area. The catalyst modified with NH4F and H3BO3 showed a similar performance to the catalyst modified with H3BO3 only. The incorporation of boron led to a greater increase in hydrogenation activity than the addition of fluorine which presents a detrimental effect on the HDN reaction.
Keywords: Catalyst; Fluorine; Boron; Modification; Hydrotreating; Activity; Hydrodesulfurization; Hydrodenitrogenation; Hydrodearomatics;

The reduction of nitrotoluenes (o-, m- and p-) using aqueous ammonium sulfide as the reducing agent was carried out in an organic solvent, toluene, under liquid–liquid mode with a phase transfer catalyst (PTC), tetrabutylammonium bromide (TBAB). The selectivity of toluidines was found to be 100%. The reaction rate of m-nitrotoluene was found to be highest among the three nitrotoluenes, followed by p- and o-nitrotoluene. The effects of different parameters, such as speed of agitation, temperature, ammonia concentration, elemental sulfur loading, catalyst concentration, sulfide concentration and concentration of nitrotoluene, on the conversion and reaction rate of nitrotoluene were studied to establish the mechanism of the reaction. The rate of reaction of nitrotoluene was found to be proportional to the concentration of catalyst, to the square of the concentration of sulfide and to the cube of the concentration of nitrotoluene. The apparent activation energy for this kinetically controlled reaction was estimated as 19.43, 21.45 and 25.54 kcal/mol for ONT, PNT and MNT, respectively. A generalized empirical kinetic model was developed to correlate the experimentally obtained conversion versus time data for the three nitrotoluenes.
Keywords: Kinetics; Ammonium sulfide; Nitrotoluene; Zinin reduction; Liquid–liquid phase transfer catalysis;

Perfluorinated resinsulphonic acid (Nafion-H®) was found to be highly efficient, environmentally friendly, recyclable heterogeneous catalyst for the oxidation of sulphides to sulphones, tertiary amines to N-oxides, secondary alcohols to esters/lactones and aldehydes to methyl esters in excellent yields under mild reaction conditions using 30% hydrogen peroxide as an oxidant. Alkyl sulphides in general were found to be more reactive than aryl sulphides. Similarly, aliphatic tertiary amines and pyridines substituted with electron donating groups were found to be more reactive. Among the various secondary alcohols and aldehydes studied, alicyclic alcohols and substituted benzaldehydes were found to be more reactive. Acetonitrile and 1,2-dichloroethane were found to be the most suitable solvents for these transformations.
Keywords: Nafion; Oxidation; Hydrogen peroxide; Perfluorinated resinsulphonic acid; Heterogeneous catalysis;

Effect of H2O presence on the propane decomposition reaction over Pd in a proton conducting membrane reactor by George Karagiannakis; Stergios Zisekas; Christos Kokkofitis; Michael Stoukides (265-271).
The reaction of C3H8 decomposition was studied in a proton conducting cell-reactor in the presence of H2O vapor in the feed gas. The proton conductor was a strontia–ceria–ytterbia perovskite disk of the form: SrCe0.95Yb0.05O3−α. Reaction temperature varied between 873 and 1023 K and a polycrystalline palladium film was used as the working electrode-catalyst. The H2 produced by the reaction was electrochemically transported through the walls of the proton conducting disk to the outer reactor-chamber. Upon increasing the H2O partial pressure from 0.3 to 2.8 kPa, a 4-fold increase on the reaction rate was observed. Upon proton “pumping” to the outer chamber, an up to 90% of the produced hydrogen was electrochemically separated from the reaction mixture.
Keywords: Solid state proton conductor; Propane decomposition; Propane dehydrogenation; Production of hydrogen (electrocatalytic); Pd catalyst;

The effect of a range of preparation variables such as the precipitate ageing time and [Fe]/[Co] molar ratio of precipitation solution on the composition and morphology of iron-cobalt oxide catalysts prepared using a co-precipitation method is described and the optimum preparation conditions were identified with respect to the catalyst activity for the Fisher–Tropsch reaction. The effect of different promoters along with loadings of optimum support and promoter on the activity and selectivity of the 40%Fe/60%Co as an optimum molar ratio are studied and it was found that the catalyst containing 40%Fe/60%Co/15 wt%SiO2/1.5 wt%K which aged for 2 h, is an optimum modified catalyst for the conversion of synthesis gas to ethylene and propylene. The results are interpreted in terms of the structure of the active catalyst. Characterization of both precursors and calcined catalysts were carried out using XRD, SEM, BET specific surface area and thermal analysis methods such as TGA and DSC. It was shown that all the different preparation variables influenced the catalyst precursor structure and morphology.
Keywords: Catalyst characterization; Precipitate ageing; Iron-cobalt oxide; Fischer–Tropsch synthesis; Morphology; Catalyst structure;

To further improve the photooxidation techniques for water and wastewater purification, we successfully prepared a new type of photoelectrode, a TiO2 nanotube electrode, first by a sol–gel method and then by treatment to form the tubular structure in NaOH aqueous solution. The structure, surface morphology and band gap energy of the Ti/TiO2 electrode were examined by X-ray diffraction (XRD), scanning electronic microscopy (SEM) and UV–vis absorption microscopy, respectively. The examination results indicated that anatase TiO2 was dominant in its composition and a significant blue-shift in the spectrum of UV–vis absorption was observed. The photoelectrochemical efficiency of the nanotube-like TiO2/Ti electrode has been determined in terms of photocurrent, degradation and mineralization of PCP. To investigate its potentials in environmental applications, we studied the degradation of pentachlorophenol (PCP) in aqueous solution using photoelectrocatalytic (PEC) processes. The results were compared with those of electrochemical process (EP) and photocatalysis (PC). A significant photoelectrochemical synergetic effect was observed. The kinetic constant of PEC degradation of PCP using TiO2 nanotube electrode was 64.7% higher than that using TiO2 film electrode. The dependences of the rate constants on various parameters in the photoelectrocatalytic process, such as applied potential, electrolyte and pH value were investigated in detail. Degradation efficiency increased with increasing applied bias potential and concentration of Na2SO4. PEC degradation of PCP was more favorable in acidic solution than in alkali solution. There was an optimum pH value in the PEC process.
Keywords: Pentacholorphenol; Photoelectrocatalytic oxidation; Nanotube-like; Ti/TiO2 film electrode;

A novel reactivation technique using non-oxygen gas was developed to regenerate the acid sites on the coked mordenite in the disproportionation of toluene (TDP). Hydrogen reactivation procedure is particularly effective. It was found that the novel technique is applicable as long as the H/C atomic ratio of the coke on mordenite is greater than around 1.0. The H/C ratio of deposited coke was correlated with the structures of polyaromatics. These results indicate that application of the reactivation technique is limited to those coke precursors lighter than alkyl-pyrene structure.
Keywords: Disproportionation; Coking; Zeolite regeneration; Mordenite;