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Applied Catalysis A, General (v.379, #1-2)

Contents (pp. iii-ix).

Editorial Board (pp. co2).

In memoriam Jerzy Haber (1930–2010) (pp. 1-2).

The effect of PdZn particle size on reverse-water–gas-shift reaction by V. Lebarbier; R. Dagle; A. Datye; Y. Wang (pp. 3-6).

The effect of PdZn particle size on the activity of Pd/ZnO catalysts for the reverse-water–gas-shift (RWGS) reaction was studied. The results indicated that the turnover frequency increases as the PdZn crystallite size decreases. Interestingly, this relationship is consistent with that previously observed for methanol steam reforming. Thus, RWGS was identified as a likely potential reaction pathway to undesired CO formation in methanol steam reforming on Pd/ZnO catalysts.The effect of PdZn particle size on the catalytic activity of Pd/ZnO catalysts for the reverse-water–gas-shift (RWGS) reaction was studied. The PdZn particle size was varied by adjusting Pd loading and reducing the catalysts at different temperatures. XRD and IR spectroscopy characterization confirmed the absence of metallic Pd on the catalyst surface. Consequently, the effect of PdZn alloy particle size on the RWGS reaction can be unambiguously studied without the complication of reactions catalyzed by metallic Pd. The results indicated that the turnover frequency increases as the PdZn crystallite size decreases. Interestingly, this structure relationship between PdZn particle size and RWGS activity is consistent with that previously observed for the steam reforming of methanol, i.e., higher CO selectivity on smaller PdZn particles. Thus, RWGS has been identified as a likely potential reaction pathway to undesired CO formation in methanol steam reforming on Pd/ZnO catalysts for hydrogen production.

Keywords: PdZn catalyst; PdZn particle size; PdZn alloy; Reverse-water–gas-shift; CO formation

Preparation and characterization of V-Ag-O catalysts for the selective oxidation of toluene by Mingwei Xue; Hui Chen; Huiliang Zhang; Aline Auroux; Jianyi Shen (pp. 7-14).

V-Ag-O complex oxide catalysts with relatively high surface areas of 13–21m²/g could be prepared by the heterogeneous azeotropic distillation (HAD) method, which exhibited much higher activity and selectivity than the counterparts prepared by the co-precipitation (CP) method for the selective oxidation of toluene to benzaldehyde and benzoic acid.V-Ag-O complex oxide catalysts with relatively high surface areas of 13–21m²/g could be prepared by the heterogeneous azeotropic distillation (HAD) method. Specifically, V₂O₅ and AgNO₃ were dissolved in aqueous solution of H₂O₂, followed by evaporation and drying in n-butanol at 353K. Silver vanadates with highly dispersed nano silver particles in the layered structures of VO_x might be formed during the preparation process, which were then turned into Ag_0.68V₂O₅ and metallic silver during the reaction of selective oxidation of toluene at 573K. Characterizations with microcalorimetric adsorption of NH₃, temperature programmed reduction and isopropanol probe reactions showed that the V-Ag-O catalysts exhibited weaker surface acidity but stronger redox ability than the VO_x, and therefore the better performance for the selective oxidation of toluene to benzaldehyde and benzoic acid. In addition, the V-Ag-O catalysts prepared by the HAD method exhibited much higher activity than its counterpart prepared by the co-precipitation for the conversion of isopropanol and the selective oxidation of toluene to benzaldehyde and benzoic acid in air.

Keywords: Heterogeneous azeotropic distillation drying; Silver vanadates; Surface acidity; Surface redox property; Selective oxidation of toluene

High temperature water gas shift catalysts with alumina by Tiberiu Popa; Guoqing Xu; Thomas F. Barton; Morris D. Argyle (pp. 15-23).

Al₂O₃ was added as a component of conventional high temperature iron oxide-based water gas shift catalysts. A series of catalysts were prepared with 5–20wt% Al₂O₃, each with 8wt% Cr₂O₃, 4wt% CuO, and balance Fe₂O₃. Addition of 10–15wt% alumina increased the catalyst activity and thermal stability, with approximately 15wt% alumina addition being optimum.Alumina (Al₂O₃) was added as a component of conventional iron oxide-based high temperature water gas shift (WGS) catalysts. The catalysts contained Fe–Al–Cr–Cu–O and were synthesized by coprecipitation. A series of catalysts were prepared with 5–50wt% Al₂O₃, 8wt% Cr₂O₃, 4wt% CuO, and the balance Fe₂O₃. One catalyst was prepared in which the chromia was replaced by alumina. All of the catalysts were compared to a reference WGS catalyst (88wt% FeO_x, 8wt% Cr₂O₃, and 4wt% CuO) with no alumina. The catalysts were characterized using temperature programmed reduction (TPR), surface area analysis using nitrogen physisorption, and scanning electron microscopy (SEM) with compositional analysis. The catalysts were also tested kinetically under WGS conditions.Addition of 10–15wt% alumina increased the catalyst activity and thermal stability, with approximately 15wt% alumina addition being optimum, as this catalyst produced a reaction rate (normalized per mass) 74% higher than the reference catalyst. The effect of alumina addition was greater than the surface area increase alone, which suggests that alumina alters the activity of the iron oxide domains, likely through an increase in reducibility, as shown by the TPR results. This synergistic effect was only observed when both alumina and chromia were present. Alumina alone (as a replacement for chromia) was not as an effective stabilizer as chromia. Although both the alumina-containing catalyst (without chromia) and the reference with chromia had similar initial surface areas (∼160m²/g), the alumina-containing catalyst retained only 74% as much surface area after reaction. Results from the catalysts with 50wt% alumina suggest that the loss of catalytic activity is also due to the formation of aluminates.

Keywords: Alumina; Thermal stability; HT water gas shift catalyst

Sulfated titania [TiO₂/SO₄²⁻]: A very active solid acid catalyst for the esterification of free fatty acids with ethanol by J.L. Ropero-Vega; A. Aldana-Pérez; R. Gómez; M.E. Niño-Gómez (pp. 24-29).

In depending on the sulfation method, important effects on the acidity, textural properties as well as on the activity for the esterification of fatty acids with ethanol. Conversions up to 82.2% of the oleic acid and selectivity to ester of 100% were reached after 3h of reaction at 80°C in sulfated titania: (▾) titania impregnated with ammonium sulfate; (♦) titania sol–gel sulfated with ammonium sulfate; (▴) titania sol–gel sulfate with sulfuric acid; (●) titania sol–gel; (■) without catalyst.Sulfated titanias were prepared by using ammonium sulfate and sulfuric acid as sulfate precursors. Depending on the sulfation method, important effects on the acidity, textural properties as well as on activity were found. After ammonium sulfate was used, a large amount of SO linked to the titania surface was observed by FTIR spectroscopy. The acidity strength determined with Hammett indicators showed strong acidity in the sulfated samples. The FTIR-pyridine adsorption spectra evidenced the presence of Lewis and Brönsted acid sites in the catalysts sulfated with ammonium sulfate, while in the titania sulfated with sulfuric acid, only Lewis-type sites were observed. The sulfated titanias showed very high activity for the esterification of fatty acids with ethanol in a mixture of oleic acid (79%). Conversions up to 82.2% of the oleic acid and selectivity to ester of 100% were reached after 3h of reaction at 80°C. The results showed that sulfated titanias are promising solid acid catalysts to be used in the esterification of free fatty acids with ethanol.

Keywords: Sulfated titania–Hammett titration; Sulfated titania–pyridine adsorption; 2-Propanol decomposition; Esterification of free fatty acids

Chitosan as a support for heterogeneous Pd catalysts in liquid phase catalysis by Silke E.S. Leonhardt; Achim Stolle; Bernd Ondruschka; Giancarlo Cravotto; Cristina De Leo; Klaus D. Jandt; Thomas F. Keller (pp. 30-37).

Four different chitosan-supported palladium catalysts were prepared. The activity of these catalysts was tested in thermal and microwave-assisted Suzuki reactions in aqueous media, and resulted without phase-transfer catalyst in good yields and selectivities. The study was extended to microwave-assisted Heck and Sonogashira reactions with NaOAc as base in organic solvents.Four different chitosan-supported palladium catalysts were prepared, whereby two of them were modified as Schiff base by reaction with salicylaldehyde and 2-pyridinecarboxaldehyde before complexation with palladium. The remaining differ in their preparation method: co-precipitation or adsorption. The properties of the catalysts were characterized by FTIR, XPS, ICP-MS, and TGA. Comparison of the catalysts activity was assessed in microwave-assisted Suzuki reactions in aqueous media, resulting in good yields and excellent selectivities concerning cross-coupling product. Additionally, the catalysts prove their activity under conductive heating conditions. The study was extended to microwave-assisted Heck and Sonogashira reactions in DMF, confirming the efficiency of chitosan-supported palladium derivatives as catalysts for C–C couplings. Experiments revealed that catalysts prepared by co-precipitation furnished inferior yields concerning the employed C–C coupling reactions. Modification of chitosan with 2-pyridinecarboxaldehyde and subsequent palladium deposition resulted in highly active catalysts affording high product selectivities and yields.

Keywords: Chitosan support; Palladium catalyst; C–C coupling reaction; Catalysis; Microwave

Efficient hydrogenation of carbonyl compounds using low-loaded supported copper nanoparticles under microwave irradiation by Kenta Yoshida; Camino Gonzalez-Arellano; Rafael Luque; Pratibha L. Gai (pp. 38-44).

Highly active and dispersed copper nanoparticles on mesoporous silicas were found to be highly active, selective and reusable in the reduction of substituted aromatic ketones and aldehydes, providing quantitative conversion of starting material within 5–10min reaction at mild reaction conditions with complete selectivity to the alcohols.Highly active and dispersed copper (Cu) nanoparticles on mesoporous silicas have been prepared via microwave irradiation of a solution of copper precursors with a previously synthesized mesoporous hexagonal silica (HMS) support. The protocol allowed differently low-loaded (typically 0.5wt%) Cu materials containing Cu metal and small quantities of metal oxides. Materials were then tested as catalysts in the hydrogenation of carbonyl compounds under microwave irradiation. Cu materials were found to be highly active, selective and reusable in the reduction of substituted aromatic ketones and aldehydes, providing quantitative conversion of starting material within 5–10min reaction at mild reaction conditions with complete selectivity to the alcohols.

Keywords: Metal nanoparticles; Microwave irradiation; Cu; Transfer hydrogenation

Intermolecular condensation of ethylenediamine to 1,4-diazabicyclo(2,2,2)octane over H-ZSM-5 catalysts: Effects of Si/Al ratio and crystal size by Yong Wang; Lifang Guo; Yun Ling; Yueming Liu; Xiaohong Li; Haihong Wu; Peng Wu (pp. 45-53).

H-ZSM-5, which has nanosized crystals (100nm) and a medium Al content corresponding to an Si/Al ratio of 110 catalyzes effectively the intermolecular condensation of EDA to TEDA, giving 99% EDA conversion and 74% selectivity to TEDA.The intermolecular condensation of ethylenediamine (EDA) to 1,4-diazabicyclo [2.2.2] octane (DABCO) or triethylenediamine (TEDA) was conducted over H-ZSM-5 catalysts. The effects of reaction parameters, Al content and crystal size on the EDA condensation over H-ZSM-5 have been investigated. The H-ZSM-5 catalyst with a medium Al content (Si/Al=110) and a small crystal size (ca. 100nm) showed 99% EDA conversion and afforded a TEDA yield as high as 74% under optimized conditions. The mechanism for the H-ZSM-5-catalyzed condensation of EDA has also been considered. The framework Al-related Brønsted acid sites were assumed to contribute to selective intermolecular condensation of EDA to TEDA. The primary intermolecular condensation of EDA to piperazine (PIP) took place mainly inside the micropores of the MFI structure, while the secondary condensation of PIP with EDA to TEDA was favored by the acid sites located near the pore entrance and on the external surfaces of crystals.

Keywords: Ethylenediamine; Triethylenediamine; Piperazine; Condensation; H-ZSM-5

Benzene adsorption on Mo₂C: A theoretical and experimental study by A.S. Rocha; A.B. Rocha; V. Teixeira da Silva (pp. 54-60).

Continuous gas-phase benzene hydrogenation at 363K and atmospheric pressure was studied using bulk molybdenum carbide as a catalyst. It was observed that benzene conversion to cyclohexane was initially 100%, dropping to zero after four hours of reaction. After deactivation the catalyst was submitted to a heating program under helium flow from room temperature (RT) up to 1273K. On-line mass spectrometry showed desorption of benzene and hydrogen suggesting that the deactivation occurred due to strong absorption of benzene on the molybdenum carbide surface. Density Functional Theory (DFT) calculations support this hypothesis showing the adsorption energy of benzene on the molybdenum carbide varies from −377kJmol⁻¹ to −636kJmol⁻¹ depending on the surface and on the crystal phase. Based on the experimental and theoretical results, a reaction scheme is proposed with the following steps: (i) after synthesis, the molybdenum carbide surface is completely covered by chemisorbed hydrogen; (ii) when the reaction begins, benzene molecules react with the chemisorbed hydrogen via an Eley-Riedeal mechanism, producing cyclohexane and vacant sites on the surface; (iii) other benzene molecules strongly and irreversibly adsorb to these vacant sites, poisoning the surface and thus leading to deactivation of the catalyst.Continuous gas-phase benzene hydrogenation at 363K and atmospheric pressure was studied using bulk molybdenum carbide as a catalyst. It was observed that benzene conversion to cyclohexane was initially 100%, dropping to zero after four hours of reaction. From experimental and DFT results the deactivation is attributed to strong benzene chemisorption on the surface of molybdenum carbide.

Keywords: Benzene hydrogenation; Molybdenum carbide; Adsorption; DFT

Zirconium doped MCM-41 supported WO₃ solid acid catalysts for the esterification of oleic acid with methanol by I. Jiménez-Morales; J. Santamaría-González; P. Maireles-Torres; A. Jiménez-López (pp. 61-68).

A series of zirconium doped MCM-41 silica supported WO_x solid acid catalysts were prepared and characterized. XRD and UV–vis spectroscopy have allowed us to establish that at temperatures higher than 700°C occurs the formation of (WO)_x/ZrO₂ nanoparticles on the surface of MCM-41 support, which exhibit acidic properties and are very active in the esterification of oleic acid with methanol at 65°C..A series of zirconium doped MCM-41 silica supported WO_x solid acid catalysts, with WO₃ loading ranging from 5 to 25wt%, has been prepared by impregnation with ammonium metatungstate, and subsequent activation at temperatures between 450 and 800°C. XRD, Raman and UV–vis spectroscopies have allowed us to establish that at temperatures higher than 700°C occurs the formation of (WO)_x/ZrO₂ nanoparticles on the surface of MCM-41 support, which exhibit acidic properties and are active in the esterification of oleic acid with methanol at 65°C. WO₃ loadings of 15–20wt%, after activation at 700°C, lead to the most active catalysts, with conversion values close to 100%. The catalyst with 15wt% WO₃ is stable even when the reaction is carried out at 200°C, reusable at least during four cycles and no leaching of tungsten species in the liquid phase was found.

Keywords: Esterification; Oleic acid; Tungstated zirconia; Mesoporous solids

Improved methanol oxidation activity and stability of well-mixed PtRu catalysts synthesized by electroless plating method with addition of chelate ligands by Taigo Onodera; Shuichi Suzuki; Yoshiyuki Takamori; Hideo Daimon (pp. 69-76).

A new synthetic scheme of PtRu catalyst for methanol oxidation reaction is reported. PtRu catalyst was obtained by using an electroless plating method with chelate ligands. The well-mixed PtRu catalyst synthesized with chelate ligands (PtRu/C WCL) showed higher methanol oxidation reaction activity and stability relative to those of PtRu catalyst synthesized without chelate ligands (PtRu/C WOCL).Change in surface Ru composition and in MOR activity of PtRu catalysts with repeated cycliv voltammetry durability tests: (a) PtRu/C WCL and (b) Pt/Ru/C WOCL.A new synthetic scheme of PtRu catalysts for methanol oxidation reaction is reported. P containing PtRu nanoparticles 2nm in size were synthesized by electroless plating method using phosphinic acid as a reducing agent as well as the source of P. Chelate ligands were added in the synthetic system to decrease the difference of effective reduction potentials between Pt⁴⁺ and Ru³⁺ cations in their chloride precursors. Coordination ability of the chelate ligands with the cations was evaluated using UV–vis spectroscopy. It was found thatdl-tartaric acid has the highest coordination ability with the cations and that the difference decreases from 0.4 to 0.19V with addition ofdl-tartaric acid. Microstructure, bulk and surface compositions of the PtRu catalysts were analyzed by means of XRD, XRF and Cu stripping voltammetry techniques, respectively. Results revealed that Pt and Ru atoms are well mixed and that both bulk and surface compositions are close to Pt₅₀Ru₅₀ in PtRu catalyst synthesized withdl-tartaric acid. The well-mixed PtRu catalyst synthesized withdl-tartaric acid showed higher methanol oxidation reaction activity and stability values relative to those of PtRu catalyst synthesized withoutdl-tartaric acid.

Keywords: Methanol oxidation; PtRu; P; Surface composition; Stability; Chelate ligands; Electroless; Plating method

Aliphatic carbonyl reduction promoted by palladium catalysts under mild conditions by Maria Grazia Musolino; Concetta Busacca; Francesco Mauriello; Rosario Pietropaolo (pp. 77-86).

The hydrogenation of aliphatic aldehydes and ketones promoted by supported palladium catalysts, prepared by co-precipitation, is performed under mild conditions (0.1MPa H₂ and 323K) for the first time. Formation of bimetallic ensembles (Pd/CoO and Pd/ZnO in less extent) or alloys (Pd/NiO) changes the electronic properties of palladium on the surface, increasing the d-orbital energy at the Fermi level and allowing the activation of the CO bond. Accordingly the reactivity of Pd/Fe₂O₃ and Pd/CeO₂ is attributed to a redox interaction of Fe³⁺ or Ce⁴⁺ with the oxygen moiety of the carbonyl bond.The catalytic reduction of aliphatic aldehydes (propanal, pentanal and hexanal) and ketones (pentan-2-one, pentan-3-one and cyclohexanone) to the corresponding alcohols promoted by palladium catalysts, such as Pd/CoO, Pd/NiO, Pd/ZnO, Pd/Fe₂O₃ and Pd/CeO₂, was performed under mild conditions (0.1MPa H₂ and 323K) for the first time.All the catalysts were obtained by the co-precipitation technique and characterized by BET, TPR, XRD, TEM and XPS. The co-precipitation method allows, after reduction, formation of bimetallic ensembles (Pd/CoO and Pd/ZnO in less extent) or alloys (Pd/NiO) thus changing the electronic properties of the palladium on the surface, increasing the d-orbital energy at the Fermi level and permitting the activation of the CO bond also in aliphatic carbonyls. Accordingly the reactivity of Pd/Fe₂O₃ and Pd/CeO₂ towards aliphatic aldehydes is attributed to a redox interaction of Fe³⁺ or Ce⁴⁺ with the oxygen moiety of the carbonyl bond, leading to the π* orbital energy decrease.Analogous reactions, carried out with Pd/CoO and Pd/Fe₂O₃, prepared by impregnation, gave a very slow reduction.Additional catalytic tests were performed with aromatic carbonylic compounds in order to compare their reactivity with that of aliphatic systems: the differences were interpreted taking into account the Δ energy value between π and π* orbitals, much lower in aromatic carbonyls, that favours an easier activation of the aromatic CO bond.

Keywords: Aldehydes; Hydrogenation; Ketones; Supported palladium catalysts; Surface chemistry

The effect of support properties on the activity of Pd/C catalysts in the liquid-phase hydrodechlorination of chlorobenzene by V.I. Simagina; O.V. Netskina; E.S. Tayban; O.V. Komova; E.D. Grayfer; A.V. Ischenko; E.M. Pazhetnov (pp. 87-94).

The activity of palladium catalysts on the basis of carbon materials in the liquid-phase hydrodechlorination of chlorobenzene has been studied. It was shown that the high activity of Pd/AG-2000 can be explained by the presence of oxygen-containing impurities in the initial activated carbon used as the support. These oxygen-containing impurities act as centers to anchor palladium and interact with HCl decreasing its deactivating action.The activity of palladium catalysts prepared using active carbons (AG-2000, MeKS) and Sibunit type carbon in the liquid-phase hydrodechlorination of chlorobenzene has been studied. The use of AG-2000 activated carbon prepared from coal raw material provided the highest initial activity of the catalyst (9.4molC6H5Cl/molPdmin for the catalyst with particle size of 0.08–0.1mm) which not reduced within next 4 cycles. However, this activity cannot be explained only on the basis of support texture characteristics. From results of chemical analysis as well as X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HR TEM) data the high activity of the Pd/AG-2000 catalyst is explainable by the presence on the surface of the initial activated carbon of oxygen-containing compounds of iron, aluminum, silicon, calcium and magnesium. The overall ash content of the activated carbon was 11.9wt.%. It can be assumed that the oxide compounds of iron act as anchoring centers for palladium, and that oxide containing impurities may interact with HCl decreasing deactivation. The experimental data of this work has shown that the main contribution to the Pd/AG-2000 catalyst activity is made by the palladium particles with a size of 3nm and higher which remain stable under the aggressive conditions of the chlorobenzene hydrodechlorination process.

Keywords: Hydrodechlorination; Chlorobenzene; Palladium catalyst; Carbon support; Structure sensitivity; Particle size effect

Co,Ba,K/ZrO₂ coated onto metallic foam (AISI 314) as a structured catalyst for soot combustion: Coating preparation and characterization by E.D. Banús; V.G. Milt; E.E. Miró; M.A. Ulla (pp. 95-104).

The structured catalyst obtained based on Co,Ba,K/ZrO₂ coated onto the AISI 314 foam walls resulted to be stable and active for soot combustion. The sequential process used to produce catalytic coatings: (i) original foam calcination at 900°C (ii) ZrO₂ layer formation and iii) active metal incorporation proved to be efficient.Co,Ba,K/ZrO₂ coating onto the wall surface of an AISI 314 (American Iron and Steel Institute) foam was obtained using a sequential process: (1) original foam calcination, (2) ZrO₂ layer formation and (3) active metal incorporation. After the different processes, the samples were characterized by X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Laser Raman Spectroscopy (LRS), Energy Dispersive X-ray Analysis (EDX) and Scanning Electron Microscope (SEM) and the coating adherence was confirmed by means of an ultrasound test. Their catalytic behavior was evaluated using the soot combustion (Temperature-programmed Oxidation (TPO) and isothermal reactions). The soot particles were added via immersion in a 600-ppm soot suspension in n-hexane. The sequential process used to produce catalytic coatings proved to be efficient. After calcination at 900°C, the wall surface of the original foam was covered with a uniform rich Cr oxide layer. This layer presented an interesting roughness, which favored the anchorage of the ZrO₂ layer, obtained via washcoating. The latter layer was characterized by its mosaic-type morphology, an important fraction of the surface being rich in Zr (ZrO₂ flakes). In this fraction, ZrO₂ prevented the reaction between the active elements (Co, Ba, and K) and Cr₂O₃. The major components in the catalytic coating were Co₃O₄, BaCO₃, KNO₃ and ZrO₂. Each one of these components and the synergy between them generated a good combination for catalysts to be used in the abatement of soot and NO_x in diesel exhausts. The whole catalytic system has an interesting mechanical and thermal stability and the apparent activation energies for soot conversions lower than 0.5 (92kJmol⁻¹) are comparable to the global activation energy reported for the powder Co,Ba,K/ZrO₂ catalyst (82kJmol⁻¹).

Keywords: Structured catalyst; Soot combustion; Metallic foam; Co,Ba,K/ZrO; ₂; coating

Fischer-Tropsch synthesis. Influence of the crystal size of iron active species on the activity and selectivity by L.A. Cano; M.V. Cagnoli; N.A. Fellenz; J.F. Bengoa; N.G. Gallegos; A.M. Alvarez; S.G. Marchetti (pp. 105-110).

In the present work the influence of the crystal size of the iron active phase in the Fischer-Tropsch synthesis (FTS) is evaluated. The catalyst with higher crystal size (Fe/SBA-15) presented higher conversion, higher chain growth and lower CH₄ production. These results confirm that the FTS is a “structure sensitive” reaction in a sizes range within, approximately, 3–10nm.In order to analyze the influence of the crystal size of the active phase in the Fischer-Tropsch synthesis (FTS), two iron catalysts, supported on MCM-41 and SBA-15, were prepared by incipient wetness impregnation and tested in this reaction. The solids were characterized by atomic absorption spectroscopy, N₂ adsorption, X-ray diffraction at low angles and Mössbauer spectroscopy. The activated catalysts showed the same iron species. However, the average crystal size of the active phase is about three times higher in SBA-15 than in MCM-41. Besides, both systems displayed a narrow size distribution. The catalyst with higher crystal size (Fe/SBA-15) presented higher conversion, higher chain growth and lower CH₄ production. These results would indicate that the FTS is a “structure sensitive” reaction in a sizes range within, approximately, 3–10nm.

Keywords: Fischer-Tropsch synthesis; Mesoporous materials; Fe/MCM-41; Fe/SBA-15; Iron catalysts

DFT study on the reaction of NO oxidation on a stepped gold surface by José L.C. Fajín; M. Natália D.S. Cordeiro; José R.B. Gomes (pp. 111-120).

The oxidation of NO to NO₂ by atomic or molecular oxygen on the stepped Au(321) surface has a low energetic cost with GGA/PW91 computed energy barriers of 0.07 and 0.25eV, respectively. These barriers are significantly smaller than the barriers for dissociation of molecular oxygen and for desorption of NO₂, which have values of about 1.0eV.The NO oxidation either with atomic or molecular oxygen on the stepped Au(321) surface was studied by means of DFT calculations (GGA/PW91). A periodic supercell approach was used to model the gold stepped surface and the kinetic profiles of the reactions were determined with the dimer approach. It was found that the co-adsorption of NO and O occurs preferentially with these species interacting with top and hollow sites nearby the steps, respectively. In the case of co-adsorbed NO and O₂ species, the most stable configuration on the surface is a ONOO* intermediate. The NO₂ product adsorbs strongly on the Au(321) surface ( E_ads=−1.10eV) also nearby the step. The reaction of NO oxidation by atomic oxygen has an energy cost of 0.07eV, whereas moderate-low energy barriers of 0.21 and 0.25eV were computed for the reaction with molecular oxygen, via the ONOO* intermediate, following Elay–Rideal (ER) or Langmuir–Hinshelwood (LH) mechanisms, respectively. The reaction route following the ER mechanism is energetically more favorable since it is unnecessary to overcome the very high barriers (∼1eV) needed for NO₂ desorption and for dissociation of molecular oxygen in the cases of NO reaction via LH mechanism and NO oxidation with atomic oxygen, respectively.

Keywords: NO oxidation; Gold; Stepped surface; Density functional theory

Bimetallic Ni-Rh catalysts with low amounts of Rh for the steam and autothermal reforming of n-butane for fuel cell applications by Magali Ferrandon; A. Jeremy Kropf; Theodore Krause (pp. 121-128).

Mono-metallic Ni and Rh catalysts and bimetallic Ni-Rh catalysts supported on La-Al₂O₃, were prepared and evaluated for catalyzing the reforming of n-butane. Extended X-ray absorption fine-structure analysis showed evidence of Ni-Rh alloy during preparation and after 150h of autothermal reforming, which resulted in higher H₂ yields than Ni or Rh alone.Mono-metallic nickel and rhodium catalysts and bimetallic Ni-Rh catalysts supported on La-Al₂O₃, CeZrO₂ and CeMgO_x were prepared and evaluated for catalyzing the steam and autothermal reforming of n-butane. The binary Ni-Rh supported on La-Al₂O₃ catalysts with low weight loading of rhodium exhibited higher H₂ yields than Ni or Rh alone. The Ni-Rh/CeZrO₂ catalyst exhibited higher performance and no coke formation, compared to the same metals on other supports. A NiAl₂O₄ spinel phase was obtained on all Ni and Ni-Rh catalysts supported on La-Al₂O₃. The presence of rhodium stabilized the spinel phase as well as NiO_x species upon reforming while Ni alone was mostly reduced into metallic species. Extended X-ray absorption fine-structure analysis showed evidence of Ni-Rh alloy during preparation and even further after an accelerated aging at 900°C in a H₂/H₂O atmosphere.

Keywords: Rh; Ni; Ceria; Alumina; Reforming; Butane; Coke; TPR; EXAFS; SEM

Effects of nanotubes pore size on the catalytic performances of iron catalysts supported on carbon nanotubes for Fischer–Tropsch synthesis by Reza M. Malek Abbaslou; Jafar Soltan; Ajay K. Dalai (pp. 129-134).

In this report, the effects of pore diameter and structure of iron catalysts supported on carbon nanotubes (CNTs) on the reaction rates and product selectivities of Fischer–Tropsch (FT) reactions are presented. In order to study the effects of pore diameter, two types of CNTs with different average pore sizes (12 and 63nm), however, with similar surface areas were prepared. Deposition of metal particles on the CNT with narrow pore size resulted in more active and selective catalyst due to higher degree of reduction and higher metal dispersion.In this report, the effects of pore diameter and structure of iron catalysts supported on carbon nanotubes (CNTs) on the reaction rates and product selectivities of Fischer–Tropsch (FT) reactions are presented. In order to study the effects of pore diameter, two types of CNTs with different average pore sizes (12 and 63nm), however, with similar surface areas were prepared. The iron catalysts were prepared using incipient wetness impregnation method and characterized by ICP, BET, XRD, TPR, SEM and TEM analyses. According to the TEM images of iron catalysts supported on narrow pore CNTs (Fe/np-CNT) and wide pore CNTs (Fe/wp-CNT), a vast majority (∼80%) of the iron oxide particles were deposited inside the nanotubes’ pores. The TEM and XRD analysis showed that the iron oxide particles on the Fe/wp-CNT (17nm) were larger than those on Fe/np-CNT sample (11nm). Temperature programmed reduction analyses of the catalysts showed that the extent of reduction of the Fe/np-CNT catalyst was 17% higher compared to that of the Fe/wp-CNT catalyst. Finally, catalytic performances of both catalysts were evaluated in a fixed-bed reactor for FT reactions at 2MPa and 275°C. At these conditions, the activity of the np-CNT catalyst (%CO conversion of 30) was 2.5 times that of the wp-CNT catalyst (%CO conversion of 12). In addition, the Fe/wp-CNT was more selective toward lighter hydrocarbons with a methane selectivity of 41% compared to that of the np-CNT catalyst with methane selectivity of 14.5%. Deposition of metal particle on the CNT with narrow pore size resulted in more active and selective catalyst due to higher degree of reduction and higher metal dispersion.

Keywords: Abbreviations; AAO; anodic aluminum oxide; BET; Brunauer, Emmett, and Teller; CNT; carbon nanotubes; CVD; chemical vapor deposition; FTS; Fischer–Tropsch synthesis; ICP; inductively coupled plasma; SEM; scanning election microscopy; Sl; standard litter; TEM; transition electron microscopy; TOS; time on stream; TPR; temperature programmed reduction; WGS; water–gas shift; XRD; X-ray diffraction; Fe/wp-CNT; iron catalysts deposited on wide carbon nanotubes; Fe/np-CNT; iron catalysts deposited on narrow pore carbon nanotubesFischer–Tropsch Synthesis; Iron; Carbon nanotubes; Pore size

Etherification of aldehydes, alcohols and their mixtures on Pd/SiO₂ catalysts by Trung T. Pham; Steven. P. Crossley; Tawan Sooknoi; Lance L. Lobban; Daniel E. Resasco; Richard G. Mallinson (pp. 135-140).

Dialkyl ethers have been selectively produced from etherification of aldehydes and alcohols on supported Pd catalysts. A yield of 79% ether with a selectivity of 90% was observed when feeding 2-methylpentanal with 2-methylpentanol at a molar ratio 1:1 at 125°C. Etherification when only aldehyde or alcohol is fed arises due to aldehyde–alcohol inter-conversion to produce the necessary co-reactant.Dialkyl ethers have been selectively produced from etherification of aldehydes and alcohols on supported Pd catalysts. A yield of 79% ether with a selectivity of 90% was observed when feeding 2-methylpentanal with 2-methylpentanol at a molar ratio 1:1 at 125°C. Cross etherification of n-butanol with 2-methylpentanal shows a much higher rate than that observed when the alcohol or aldehyde is fed alone. This enhanced activity is in line with the catalyst requirement for large ensembles that allow surface alkoxide species next to η² adsorbed aldehydes. Etherification when only aldehyde or alcohol is fed arises predominantly due to aldehyde–alcohol inter-conversion to produce the necessary co-reactant. The ether yield at the same reaction conditions decreases with metal loading in the order 16>10>3wt.% Pd. Increasing reduction temperature also increases ether yield. It is apparent that etherification is highly sensitive to metal particle morphology, consistent with needing ensembles that accommodate the two adjacent adsorption sites.

Keywords: Etherification; Hydrogenation; Decarbonylation; Aldehyde; Alcohol

Catalytic properties of WO_x/SBA-15 for vapor-phase Beckmann rearrangement of cyclohexanone oxime by Ankur Bordoloi; S.B. Halligudi (pp. 141-147).

WO_x/SBA-15 nanocomposite materials with different WO_x loadings were prepared by one step hydrothermal synthesis and used in the vapor-phase Beckmann rearrangement of cyclohexanone oxime to ɛ-caprolactam. The acidities of the catalysts were estimated by ammonia TPD and pyridine FTIR. Under optimized conditions WO_x/SBA-15(20) gave maximum oxime conversion of 79% with 93%, ɛ-caprolactam selectivity.WO_x/SBA-15 nanocomposite materials with different WO_x loadings were prepared by one step hydrothermal synthesis and used in the vapor-phase Beckmann rearrangement of cyclohexanone oxime to ɛ-caprolactam. The catalysts were thoroughly characterized by X-ray diffraction (XRD), sorption analysis, energy dispersive X-ray analysis (EDAX) and Raman spectroscopy. The acidities of the catalysts were estimated by ammonia temperature programmed desorption (NH₃-TPD) and Fourier transform infrared studies of adsorbed pyridine (pyridine-FTIR). The optimum temperature for the Beckmann rearrangement was 350°C. Using WO_x/SBA-15(20) under the vapor-phase reaction conditions [temperature=350°C, WHSV=0.6h⁻¹, oxime concentration=2.5% (w/w) in MeOH] gave 79% cyclohexanone oxime conversion with 93%, ɛ-caprolactam selectivity. The ɛ-caprolactam selectivity was found to be dependent on temperature and space velocity. A correlation has been made between the rearrangement activity and acidity and the structural properties of the catalysts.

Keywords: Beckmann rearrangement; WO; _x; /SBA-15; Vapor-phase reaction; Cyclohexanone oxime; ɛ-Caprolactam

Nano-structural changes of SnO₂-supported palladium catalysts by redox treatments by Naoto Kamiuchi; Hiroki Muroyama; Toshiaki Matsui; Ryuji Kikuchi; Koichi Eguchi (pp. 148-154).

The nano-structures of Pd/SnO₂ catalysts treated under several conditions were carefully investigated. The core-shell and the particle intrusion structures were formed by the reduction in 10% H₂/N₂ at 400°C. After the reoxidation treatment, the core-shell structure disappeared while the particle intrusion structure remained. Furthermore, the decrease in the mean particle diameter was confirmed in the reoxidized catalyst.The structural changes in Pd/SnO₂ catalyst upon redox treatments were studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). In the as-calcined catalyst, the fine particles of palladium species with the amorphous and the well-cyrstallized states were highly dispersed on the surface of SnO₂ support due to the strong chemical interaction. The heat-treatment at 200°C in hydrogen induced the reduction of palladium species and the particle growth, resulting in the formation of the well-crystallized Pd particles. Some peculiar structures, called the core-shell structure and the particle intrusion structure, were formed by the reduction at 400°C. After the reoxidation treatment, the core-shell structure disappeared while the particle intrusion structure remained. Furthermore, the decrease in the mean particle diameter was confirmed in the reoxidized catalyst. The proposed formation mechanism of the unique structures from TEM observation was supported by the combination of XRD and XPS measurements.

Keywords: Palladium; Tin oxide; Catalyst; Structural change; Chemical interaction; TEM

Phase transitions of V-Mo-W mixed oxides during reduction/re-oxidation cycles by Lars Giebeler; Andreas Wirth; Johan A. Martens; Herbert Vogel; Hartmut Fuess (pp. 155-165).

Tungsten-doped vanadium molybdenum oxide catalysts for the selective oxidation of acrolein to acrylic acid prepared from evaporated or spray-dried precursors form different phases. Treatments under reducing and oxidizing mostly acrolein-containing atmospheres between 653 and 773K uncover steps of active phase formation and catalyst deactivation depending on tungsten content and preparation. The results are related to industrial acrylic acid production.V-Mo-W mixed oxides are prepared by a hydrochemical preparation route with a stoichiometry of V₂Mo₈W_xO_y with 0≤ x≤5 via evaporation/crystallization and by spray-drying of ammonium polyoxometallate solutions combined with a subsequent calcination procedure. The phase composition has been examined by electron and X-ray powder diffraction. Significant changes are observed after reduction/re-oxidation and after/during reactions in an air–acrolein atmosphere for all crystalline samples. Samples prepared from spray-dried precursors with tungsten contents x>1 are amorphous/nanocrystalline. Independent of the preparation and reaction procedure, the formation of the thermodynamically metastable, tetragonal Mo₅O₁₄ phase is detected. Deactivation starts at the latest at 723K in air with the formation of thermodynamically stable phases like orthorhombic MoO₃. Smaller particles exhibit higher stability against deactivation or reduction. Reaction networks are established to illustrate the effect of various chemical reactions on crystalline and amorphous/nanocrystalline structures. The temperatures of the industrial processes are interpreted on the basis of the presented results.

Keywords: Vanadium molybdenum oxides; Oxidation catalysis; Acrolein; Acrylic acid; Phase transition; Deactivation; X-ray powder diffraction; Electron diffraction

Transalkylation of diisopropylbenzenes with benzene over hierarchical beta zeolite by Heqin Yang; Zhicheng Liu; Huanxin Gao; Zaiku Xie (pp. 166-171).

The hierarchical beta zeolite has better activity compared with the conventional beta zeolite for the transalkylation of diisopropylbenzene with benzene. By studying the effects of pore structure, crystal size and acidity on catalytic activity, one finds that the better activity of the hierarchical beta zeolite is mainly due to the presence of meso/macropores and nanocrystals.The catalytic performance of the hierarchical beta zeolite prepared via the dry gel conversion method was compared with that of the conventional beta zeolite for transalkylation of diisopropylbenzene with benzene. The results indicate that diisopropylbenzene conversion decreases from 74% to 29% after a reaction time of 32h over the conventional beta zeolite. However, for the hierarchical beta zeolite, diisopropylbenzene conversion still remains above 60% after 32h under the same reaction conditions. In order to learn the factors leading to the difference in catalytic activity, we studied pore structure, crystal size and acidity of the hierarchical beta zeolite and the conventional beta zeolite and we discussed their effects on catalytic activity. The results reveal that the better activity and stability of the hierarchical beta zeolite is mainly due to the presence of meso/macropores and nanocrystals for the liquid transalkylation reaction.

Keywords: Hierachical; Zeolite; Meso/macropores; Transalkylation; Liquid

Role of transalkylation reactions in the conversion of anisole over HZSM-5 by Xinli Zhu; Richard G. Mallinson; Daniel E. Resasco (pp. 172-181).

Anisole (methoxybenzene), a model compound of methoxy group containing phenolics in bio-oil, has been studied with varying space time, reaction temperature, type of carrier gas, water addition, and coke analysis over HZSM-5. Kinetic study reveals that bimolecular transalkylation reactions are the major reactions over HZSM-5, while unimolecular isomerization reactions are the minor ones.Conversion of anisole, a typical component of bio-oil, was studied over an HZSM-5 zeolite at varying space times (W/F), reaction temperatures, type of carrier gas, and concentration of water in the feed. Several bimolecular and unimolecular reactions are proposed to explain the evolution of products observed. The bimolecular reactions include the following transalkylation reactions: (a) anisoles to phenol and methylanisole; (b) phenol and methylanisole to cresols; (c) phenol and anisole to cresol and phenol; (d) methylanisole and cresol to phenol and xylenol. A pseudo first-order kinetic model based on these bimolecular reactions was found to describe well the observed product distribution as a function of W/F. It is observed that shape selectivity effects prevail over electrophilic substitution and thermodynamic equilibrium effects in the formation of methylanisole isomers. However, the opposite is true for the distribution of cresol isomers. The kinetic analysis indicates that the contribution of unimolecular reactions such as isomerization is much lower than that of bimolecular reactions. The carrier gas composition was found to have a moderate effect on catalyst activity. When H₂ was used as a carrier, catalyst stability showed a moderate improvement in comparison to the runs under He. However, a remarkable increase in catalytic activity was observed upon the addition of water in the feed.

Keywords: Anisole; Phenolic compounds; HZSM-5; Methoxy group; Biomass conversion; Bio-oil upgrading

Selective methanation of CO in hydrogen-rich gases involving large amounts of CO₂ over Ru-modified Ni-Al mixed oxide catalysts by Masae Kimura; Toshihiro Miyao; Shingo Komori; Aihua Chen; Kazutoshi Higashiyama; Hisao Yamashita; Masahiro Watanabe (pp. 182-187).

Ru-doped Ni-Al oxide catalysts, prepared by the solution-spray plasma technique, exhibited excellent catalytic activity and selectivity for the methanation of CO in hydrogen-rich gases including 20% CO₂ and water vapor.Selective methanation of CO was investigated in hydrogen-rich gas streams involving 20% CO₂ over a Ru-modified Ni-Al mixed oxide catalyst. The Ni-Al mixed oxide was prepared by the solution-spray plasma technique, by which fine powders of homogeneous mixed oxides can be easily synthesized. By the addition of a small amount of Ru, the catalytic activity and selectivity of the Ni-Al mixed oxide catalyst for CO methanation was improved dramatically. The added Ru enhanced the formation of nano-sized Ni metal particles via reduction of the mixed oxide by spill-over-hydrogen during reduction treatment, even at low temperature. Kinetic measurements revealed that the methanation of CO took place predominantly over the Ni metal sites. Selectivity for the CO methanation was also improved significantly by the addition of Ru due to suppression of CO₂ dissociation over the Ni metal sites.

Keywords: Selective CO methanation; Ru-modified Ni-Al mixed oxide catalyst; Hydrogen production; Solution-spray plasma technique

Enhanced sulfur resistance of bifunctional Pd/HZSM-5 catalyst comprising hierarchical carbon-templated zeolite by A. Martínez; M.A. Arribas; M. Derewinski; A. Burkat-Dulak (pp. 188-197).

Bifunctional Pd/HZSM-5 catalyst comprising a hierarchical zeolite (HZSM-5-BP) does display a superior sulfur resistance during the hydroconversion of n-C₈ in the presence of 100ppm S than an equivalent catalyst based on a conventional zeolite thanks to a limited extent of migration and sintering of Pd⁰ nanoparticles (NPs) when confined within the intracrystalline mesovoids generated upon combustion of the carbon template in the former.A bifunctional hierarchical micro-mesoporous Pd/HZSM-5-BP catalyst (2wt% Pd) has been prepared by impregnating an HZSM-5 sample hydrothermally synthesized in the presence of nearly uniform carbon nanoparticles (Black Pearls 2000) of ca. 12nm in size in order to generate intracrystalline mesovoids (mostly in the 10–20nm range, as ascertained by TEM). An equivalent catalyst (Pd/HZSM-5-ref) comprising an HZSM-5 zeolite having roughly the same Si/Al ratio (26, from ICP-OES), crystallite size and morphology (SEM), and acidity (FTIR-pyridine and NH₃-TPD) but synthesized in the absence of carbon has also been prepared for comparison purposes. TEM, CO chemisorption and XPS results on reduced catalysts (400°C in H₂ flow) revealed that Pd⁰ is better dispersed in the catalyst involving the hierarchical carbon-templated zeolite, for which a large fraction of metal nanoparticles was found to be confined within the intracrystalline mesocavities (TEM). Despite the differences in dispersion, both bifunctional catalysts were found to be well balanced in terms of metal/acid ratio and consequently equally active and selective for the hydroconversion of n-octane (which is able to easily access all the acid sites in the 10-ring channels of ZSM-5) in the absence of sulfur. However, after addition of 100ppm sulfur to the n-octane feed, the hierarchical Pd/HZSM-5-BP catalyst displayed a superior thioresistance leading to a notably higher steady conversion (48% as compared to 21% attained on Pd/HZSM-5-ref). The higher sulfur resistance of the hierarchical catalyst is ascribed to the inhibition of the sulfur-induced migration and sintering of Pd⁰ nanoparticles on the external zeolite surface when confined within the mesovoids, as revealed by TEM after catalysis.

Keywords: Hierarchical carbon-templated ZSM-5 zeolite; Intracrystalline mesovoids; Bifunctional catalyst; Pd dispersion; n; -Octane hydroconversion; Sulfur tolerance

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Applied Catalysis A, General (v.379, #1-2)

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Applied Catalysis A, General (v.379, #1-2)