Applied Catalysis A, General (v.356, #2)
Editorial Board (CO2).
Supported Pd catalysts for the hydrogenation of campholenic aldehyde: Influence of support and preparation method by G. Neri; G. Rizzo; L. De Luca; A. Donato; M.G. Musolino; R. Pietropaolo (113-120).
The selective catalytic reduction of the unsaturated campholenic aldehyde to naturanol was investigated over 2 wt.% Pd supported on different metal oxides (MeO x = SiO2, TiO2, ZnO, Fe2O3, NiO, Co3O4). Results obtained have shown that the activity and products distribution depend both on the nature of the support and the preparation method. Pd/Co3O4 catalyst resulted the most selective, with a yield to the unsaturated alcohol > 85%.The selective catalytic reduction of the unsaturated campholenic aldehyde to the corresponding unsaturated alcohol, naturanol, was investigated over 2 wt.% Pd supported on different metal oxides (MeO x = SiO2, TiO2, ZnO, Fe2O3, NiO, Co3O4). Pd/MeO x catalysts have been prepared by impregnation (series I) and coprecipitation (series CP) and characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and temperature programmed reduction (TPR).Results obtained in the hydrogenation of campholenic aldehyde have shown that the activity and products distribution depend both on the nature of the support and the preparation method. Regarding the catalysts of series I, palladium supported on SiO2 and TiO2 resulted totally unselective towards formation of naturanol, but, when Pd was supported on reducible metal oxides (ZnO, Fe2O3, NiO, and Co3O4), the selectivity to naturanol strongly increases. Higher selectivity values to naturanol have been obtained on catalysts of the CP series. Among these latter, the Pd/Co3O4 catalyst resulted the most selective, with a yield to the unsaturated alcohol > 85%.On the basis of characterization and kinetic data, the role of the support and of the preparation method in the catalytic behaviour of Pd catalysts for the selective reduction of the carbonyl group is discussed.
Keywords: Pd supported catalysts; Naturanol; Selective hydrogenation;
The influence of the preparation method on the structural, acidic and redox properties of V2O5-TiO2/SO4 2− catalysts by H. Zhao; S. Bennici; J. Shen; A. Auroux (121-128).
V2O5-TiO2/SO4 2− catalysts were prepared by different methods and calcined at different temperatures. Co-precipitation was by far the best preparation method. The reaction of isopropanol conversion in air was used to probe the strength of surface acidic sites and redox properties. The surface acidic properties were enhanced and the redox properties weakened upon addition of SO4 2− species.The introduction of sulfates into vanadia-titania catalysts and the influence of the preparation method on the properties of the sulfated samples have been studied. Series of V2O5-TiO2/SO4 2− (VTiS) catalysts were prepared by co-precipitation, sol–gel and mechanical grinding methods and calcined at different temperatures. Their structural properties were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). Co-precipitation was by far the best preparation method in terms of maximizing the surface area and the mesoporosity. Temperature-programmed reduction (TPR) revealed that only the vanadia species were reducible. The results from XRD and FT-IR showed that V2O5 was well dispersed on the surface of TiO2. XPS showed that the surface vanadium oxide was composed of stoichiometric V2O4 and V2O5, as well as V2O3 species especially for the samples prepared by mechanical grinding. Meanwhile, titanium was present in its fully oxidized state in all the VTiS samples, and the sulfur-containing species presented an oxidation state of +6. The reaction of isopropanol (IPA) conversion in air was used to characterize the surface acid/base and redox properties. The higher activity for the IPA conversion over the VTiS catalysts as compared to TiO2 was possibly due to the generation of redox sites upon the addition of V2O5. Moreover, the surface acidic properties were enhanced and the redox properties weakened upon addition of SO4 2− species.
Keywords: V2O5-TiO2/SO4 2−; Co-precipitation; Sol–gel; Mechanical grinding; Structural properties; Redox properties; Isopropanol conversion;
Preparation of Cu/SBA-15 catalysts by different methods for the hydrogenolysis of dimethyl maleate to 1,4-butanediol by Liang-Feng Chen; Ping-Jun Guo; Ling-Jun Zhu; Ming-Hua Qiao; Wei Shen; Hua-Long Xu; Kang-Nian Fan (129-136).
Cu/SBA-15 catalyst prepared by the homogeneous deposition precipitation (HDP) method shows the highest activity and selectivity in gas phase hydrogenolysis of dimethyl maleate to 1,4-butanediol. The effects of the preparation methods on the textural and structural properties of Cu/SBA-15 catalysts have been systematically investigated.Mesoporous siliceous SBA-15-supported Cu catalysts have been prepared by different methods and systematically characterized. The results revealed that the incipient wetness impregnation (IWI) method gives poor dispersion of copper species, whereas much better dispersion is found in catalysts prepared by the deposition precipitation (DP), grafting, and homogeneous deposition precipitation (HDP) methods. The Cu/SBA-15 catalyst prepared by the grafting method is rich in Cu+, while a partial destruction of the hexagonal mesostructure of SBA-15 occurs in the catalyst prepared by the HDP method. In gas phase hydrogenolysis of dimethyl maleate (DMM) to 1,4-butanediol (BDO), the hydrogenolysis activities of the catalysts follow the sequence of the metallic Cu surface areas; the catalyst prepared by the HDP method exhibits the highest activity and selectivity. Irrespective of the much smaller metallic Cu surface area of the catalyst prepared by the grafting method, this catalyst exhibits only slightly lower activity than that prepared by the DP method, suggesting that Cu+ also participates in DMM hydrogenolysis. The reaction conditions are further investigated over the Cu/SBA-15 catalyst prepared by the HDP method, aiming to obtain a high yield of BDO.
Keywords: Cu/SBA-15; Preparation method; DMM; BDO; Hydrogenolysis;
n-Dodecane reforming over monolith-based Ni catalysts: SEM study of axial carbon distribution profile by Xiaoyin Chen; Benjamin D. Gould; Johannes W. Schwank (137-147).
The axial gradient of carbon, which was deposited over monolith-based Ni catalysts during autothermal reforming (ATR), partial oxidation (POX), and steam reforming (SR), was characterized by a combination of temperature-programmed oxidation (TPO), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The amount, location, and type of carbon proved to depend strongly on the type of reforming reaction and the geometry of monolith.The extent and nature of carbon deposition that occurs during catalytic reforming reactions of hydrocarbons depends strongly on the reaction conditions and the surface properties of the catalyst. In conventional packed bed reactors it is difficult to track the spatial distribution of carbon and link it to the location of individual catalyst particles. The present work uses monolith-based nickel catalysts to investigate the axial carbon gradient post n-dodecane reforming. The carbon, which was deposited during autothermal reforming (ATR), partial oxidation (POX), and steam reforming (SR) over Ni/cerium-zirconium oxide (CZO)/monolith and Ni/monolith catalysts, was characterized by a combination of temperature-programmed oxidation (TPO), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The amount, location, and type of carbon deposited strongly depended on the type of reforming reaction. The majority of carbon deposition was concentrated inside cordierite pores of the monolith. In general, the catalysts showed the expected trend of increased filamentous carbon deposition down the length of the monolith, reflecting the axial variation in temperature and oxygen concentration, except for POX over Ni/monolith catalyst where massive coating carbon deposition occurred in the upstream section of the monolith.
Keywords: Dodecane; Reforming; Carbon; Hydrogen; Nickel; Monolith; Ceria; SEM;
Dehydrogenation of ethane to ethylene over a highly efficient Ga2O3/HZSM-5 catalyst in the presence of CO2 by Zhenhao Shen; Jian Liu; Hualong Xu; Yinghong Yue; Weiming Hua; Wei Shen (148-153).
Dehydrogenation of ethane to ethylene over Ga2O3/HZSM-5 catalysts in the presence of CO2 was investigated. High activity and stability were achieved on the Ga2O3/HZSM-5(97) catalyst with a yield of 14% without any observable trend of deactivation in 70 h. The enhancement of the stability with increasing Si/Al ratio of the support is caused by the decrease of the catalyst acidity.Dehydrogenation of ethane to ethylene in the presence of carbon dioxide was investigated over various gallium-based catalysts. Ga2O3/HZSM-5 catalysts show better stability than β-Ga2O3, and the higher Si/Al ratio HZSM-5 supported gallium oxide catalysts are more resistant to deactivation. The Ga2O3/HZSM-5(97) catalyst exhibits both high activity and stability for dehydrogenation of ethane, with an ethane conversion of 15% and ethylene selectivity of 94% without any observable trend of deactivation in 70 h. The results of NH3-TPD and FT-IR spectra of adsorbed pyridine revealed that the enhancement of the catalyst stability with increasing Si/Al ratio of the support is caused by the decrease of the acidity of the catalysts, resulting in the suppression of the side reactions, such as cracking and oligomerization. The promoting effect of CO2 on the dehydrogenation reaction is attributed to the reverse water gas shift reaction. The catalyst stability is also enhanced by the introduction of CO2.
Keywords: Dehydrogenation; Ethane; Ga2O3/HZSM-5; Stability; Carbon dioxide;
Influence of phase composition and particle size of atomised Ni–Al alloy samples on the catalytic performance of Raney-type nickel catalysts by F. Devred; A.H. Gieske; N. Adkins; U. Dahlborg; C.M. Bao; M. Calvo-Dahlborg; J.W. Bakker; B.E. Nieuwenhuys (154-161).
Atomisation process is used to prepare initial Raney Ni–Al alloy and is compared with the classical cast can crush process. The composition of the initial alloy plays an important role in the catalytic performance of the activated catalysts: increasing the volume fraction of the NiAl3 phase in the atomised powder leads to higher activity for citral hydrogenation.Hydrogenation of citral has been investigated over Raney-type nickel catalysts prepared from various Ni–Al atomised alloys. These alloys differ in phase composition; in particular in the NiAl3 concentration. The starting alloys were prepared by gas atomisation or cast and crush process and subsequently activated by a conventional leaching process. The aim was to investigate the influence of the phase composition and the effect of the initial particle size of the alloys on the catalytic performance. It appears that the composition of the initial alloy plays an important role in the catalytic performance of the activated catalysts: catalysts prepared from atomised alloys that contain a higher volume fraction of NiAl3 in comparison to the standard 50–50 wt% (Ni–68.5 at.% Al) alloy exhibit higher activity. X-ray photoelectron spectroscopy (XPS), inductively coupled plasma optical emission spectroscopy (ICP-OES) and BET measurements were used for surface analysis, bulk analysis and determination of the surface area, respectively. It is proposed that the amount of remaining metallic aluminium after activation influences the catalytic properties. As the concentration of aluminium in the activated catalysts is essentially the same at the near surface, the microstructure of the catalyst, with different concentrations of Al in the bulk may be the origin of the differences in catalytic performance. Advantages of the atomisation process over the traditional cast and crush process are demonstrated.
Keywords: Raney-type nickel catalysts; Gas atomisation process; Leaching process; Citral hydrogenation; XPS;
The oxidation of 2-methyl-1-naphthol to menadione with H2O2, catalyzed by Nb-based heterogeneous systems by G. Strukul; F. Somma; N. Ballarini; F. Cavani; A. Frattini; S. Guidetti; D. Morselli (162-166).
This paper examines the reactivity of catalysts based on niobium oxide dispersed in silica, for the oxidation of 2-methyl-1-naphthol to 2-methyl-naphthoquinone (menadione) with aqueous hydrogen peroxide. The catalytic performance is affected by the hydroperoxide concentration, and by the mode of oxidant addition. The reaction scheme is rather complex, including, along with the desired reaction, also parallel and consecutive side processes.This paper examines the reactivity of catalysts based on niobium oxide dispersed in silica, for the oxidation of 2-methyl-1-naphthol to 2-methyl-1,4-naphthoquinone (menadione) with aqueous hydrogen peroxide. The catalytic performance is affected by the hydroperoxide concentration, and by the mode of oxidant addition. The reaction scheme is rather complex, including, along with the desired reaction, also parallel and consecutive side processes. The catalyzed oxidation reaction to yield menadione is always accompanied by radical reactions leading to coupling products. The use of diluted hydrogen peroxide solutions (concentration 3.5 wt.%) favors the formation of these heavy compounds. On the other hand, in the presence of concentrated hydrogen peroxide solution (35 wt.%), the oxidation of the substrate to menadione occurs even without catalyst. High selectivity to menadione (i.e., 93%) is achieved only at the very beginning of the reaction when the substrate is added to the catalyst-containing hydrogen peroxide solution, the oxidant concentration being 35%. Under the latter conditions, the low concentration of substrate disfavors the undesired coupling reactions.
Keywords: 2-Methyl-1-naphthol; 2-Methylnaphthoquinone; Menadione; Niobia-silica; Selective oxidation; Hydrogen peroxide;
Di-, tri- and tetra-valent ion-exchanged NaY zeolite: Active heterogeneous catalysts for hydroxylation of benzene and phenol by Hanna S. Abbo; Salam J.J. Titinchi (167-171).
Ion-exchanged NaY zeolite with various valent cations are tested for hydroxylation of benzene and phenol with H2O2 in 1:1 and 3:1 molar ratios, respectively; the highest conversion of benzene (33%) in green one-step process is achieved using Cu–NaY with 100% selectivity to phenol, while V–NaY shows >36% phenol conversion with 91% selectivity to catechol, whereas TOF exceeds 1000 with Zn–NaY after 6 h reaction time.Ion-exchanged NaY zeolite with various valent cations are tested for hydroxylation of benzene and phenol with H2O2 in 1:1 and 3:1 molar ratios, respectively; the highest conversion of benzene (33%) in green one-step process is achieved using Cu–NaY with 100% selectivity to phenol, while OV–NaY shows >36% phenol conversion with 91% selectivity to catechol, whereas TOF exceeds 1000 with Zn–NaY after 6 h reaction time which is among the highest value reported so far.
Keywords: Ion-exchanged zeolite; Hydroxylation; Phenol; Benzene;
Tungstophosphoric acid supported on polycrystalline TiO2 for the photodegradation of 4-nitrophenol in aqueous solution and propan-2-ol in vapour phase by Daniel Carriazo; Maurizio Addamo; Giuseppe Marcì; Cristina Martín; Leonardo Palmisano; Vicente Rives (172-179).
The preparation of tungstophosphoric acid (up to 30% in weight)-doped TiO2 samples, their characterisation and catalytic activity in photodegradation of 4-nitrophenol in water and photo-oxidation of 2-propanol in vapour phase, is reported. A progressive improvement of the photocatalytic activity is observed in both regimes, when up to 20% tungstophosphoric acid is dispersed over the oxide.The present work reports the preparation of samples based on Millennium PC-500 TiO2 loaded with different amounts of tungstophosphoric acid (up to 30% in weight) and their characterisation by means of different physicochemical techniques: powder X-ray diffraction, N2 adsorption–desorption at −196 °C, transmission electron microscopy, UV–vis and FT-IR spectroscopies and thermogravimetric analyses. The acidity of samples was evaluated by FT-IR using pyridine as probe molecule, and the catalysts activity was tested for the photodegradation of 4-nitrophenol in aqueous solution and for the photo-oxidation of propan-2-ol in vapour phase. The results show a noticeable improvement (8 and 2.5 times faster in the photodegradation rate of 4-nitrophenol and propan-2-ol, respectively), in both regimes for these specific substrates, when tungstophosphoric acid is dispersed over the oxide up to a certain amount (20% in weight). A partial leaching of the polyoxometalate was also detected in solution for samples loaded with the largest amounts on this compound.
Keywords: Photocatalysis; Titania; Polyoxometalate; Surface acidity;
IR study on methanol-to-olefin reaction over zeolites with different pore structures and acidities by Ji Won Park; Gon Seo (180-188).
The IR spectra recorded in situ during the MTO reaction over FAU and CHA zeolite catalysts showed considerable differences in the nature of the alkylaromatic species formed in their pores, indicating the influences of their pore structure and acidity on the reaction path carried out over them.The effects of the pore structure and acidity of zeolites on their product distribution and deactivation rates in the methanol-to-olefin (MTO) reaction were studied according to the different topologies of CHA, LTA, MFI, BEA, MOR and FAU zeolites. The in situ IR study of the MTO reaction over various zeolites with different pore structures and acidities confirmed the considerable effect exerted by these factors on the species of alkylaromatics formed and on the rates of further condensation of alkylaromatics to polycyclic aromatic hydrocarbons (PAHs). The nature and continuing concentration of alkylaromatics formed in the zeolite pores determined their product composition and deactivation rate in the MTO reaction. LTA and FAU zeolites with large cages and high acid site density were deactivated rapidly due to the high concentration of alkylaromatics with large substituents and their rapid condensation to PAHs. However, the small cages of CHA zeolite and the sinusoidal pores of MFI zeolite suppressed the accumulation of large hydrocarbon molecules in their pores and lengthened their catalyst lives, although the composition of the products formed over them clearly differed because of their different pore structures.
Keywords: Methanol-to-olefin; Zeolite; Pore structure; Acidity; IR;
Kinetic modeling of oxidative steam reforming of methanol over Cu/ZnO/CeO2/Al2O3 catalyst by Sanjay Patel; K.K. Pant (189-200).
A kinetic model for oxidative steam reforming of methanol (OSRM) has been developed using Langmuir–Hinshelwood (LH) approach over Cu/ZnO/CeO2/Al2O3 catalyst. The model incorporates the partial oxidation of methanol, steam reforming of methanol and reverse water–gas shift reactions. The appropriate kinetic model for OSRM has been obtained after rigorous parameter estimation and model discrimination among three kinetic models.A kinetic model for oxidative steam reforming of methanol (OSRM) has been developed using Langmuir–Hinshelwood (LH) approach over Cu/ZnO/CeO2/Al2O3 catalyst. The kinetic model incorporates the partial oxidation of methanol, steam reforming of methanol and reverse water–gas shift reactions for the OSRM process. Kinetics study was performed over a wide range of reaction temperatures and contact-times in an integral reactor under the chemical reaction-controlled regime. Three intrinsic Langmuir–Hinshelwood kinetic models were developed based on the two proposed reaction mechanisms. The appropriate kinetic model for OSRM has been obtained after rigorous parameter estimation and model discrimination among all the three kinetic models. Parameters were estimated by non-linear least square regression. The correlations among them were minimized by temperature centering of Arrhenius and van’t Hoff equations. A good agreement was obtained between experimental and model predicted results for the LH kinetic model based on formation of formate from oxymethylene, dissociation of formic acid, and formation of adsorbed CO and surface hydroxyls from formate species as the rate-determining steps for methanol partial oxidation, methanol steam reforming and reverse water–gas shift reactions respectively.
Keywords: Oxidative steam reforming of methanol; Hydrogen; Kinetics; Cu catalyst;
Oxidative dehydrogenation of propane over chromium-loaded calcium-hydroxyapatite by Charifa Boucetta; Mohamed Kacimi; Alain Ensuque; Jean-Yves Piquemal; François Bozon-Verduraz; Mahfoud Ziyad (201-210).
The chromium deposited on the surface of the apatite creates various types of sites on it, especially entities such as Cr3+–O–Ca2+. Those sites are active in the propane ODH. The increase of chromium loading increases the amount of the sites detected by TPR but does not decreases the temperature at which the propane ODH becomes significant.Chromium-loaded hydroxyapatite catalysts Cr(x)/CaHAp (0.1 ≤ x ≤ 3.7 wt.% Cr) were prepared by ion-exchange and characterized by several techniques including FTIR, Raman, XPS, UV–vis-NIR spectroscopies, EPR, DRX and TPR. After calcination in air, several isolated chromium species were identified: (i) surface Cr3+ ions in distorted octahedral symmetry, (ii) bulk octahedral Cr3+ ions, (iii) octahedral Cr5+ ions in low concentration and (iv) Cr6+ ions. Cr6+ ions present as monochromates are predominant only at very low loadings (x ≤ 0.1 wt.% Cr) whereas, at higher Cr amounts (up to 3.7 wt.% Cr), Cr3+ species are preponderant. The majority of Cr3+ ions are located on the apatite surface; they do not form Cr2O3 crystallites but isolated Cr3+–O–Ca2+ or Cr3+–O–Cr3+ entities at the highest Cr amounts.The Cr(x)/CaHAp catalysts were tested in propane oxidative dehydrogenation in the 300–550 °C temperature range. The Cr6+ centres initially present on the catalysts may initiate the cracking of propane because of their acidity and improve the conversion; however, as they are reduced by the reaction mixture, the propane conversion decreases upon running at 550 °C. Cr2+ ions are also formed upon running. Isolated Cr3+ species are believed to be responsible for the propylene formation (propylene yield around 7% at 550 °C). This limitation of performance is ascribed to the decrease of the basicity induced by the fixation of Cr3+ which counterbalances the positive effect of chromium on oxygen reactivity. The proposed mechanism involves the contribution of oxygen vacancies or Cr2+ species.
Keywords: Chromium catalysts; Hydroxyapatite; Propane ODH; TPR; XPS; UV–vis;
Deactivation phenomena of MoO3/SiO2 and TiO2/SiO2 during transesterification between dimethyl carbonate and phenol by Yong Tae Kim; Eun Duck Park (211-215).
The catalytic stability of MoO3/SiO2 and TiO2/SiO2 was examined for transesterification between dimethyl carbonate and phenol. The gradual decrease in the activity was observed over both catalysts due to the strong adsorption of reactants. Some of the Mo species in MoO3/SiO2, leached out during a reaction, appeared to take part in this reaction.The catalytic stability of MoO3/SiO2 and TiO2/SiO2, which have been reported to be active for transesterification between dimethyl carbonate and phenol, was examined in a batch reactor for the same reaction. X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and the temperature programmed oxidation (TPO) were conducted to characterize the catalysts. The gradual decrease in the activity was observed over both catalysts with increasing the number of a batch reaction. The strong adsorption of reactants was observed from the temperature programmed oxidation experiment. The deactivated MoO3/SiO2 can be regenerated after oxidation in air at 823 K. However, the deactivated TiO2/SiO2 can be only partially regenerated even after oxidation in air at 973 K. Some of the Mo species in MoO3/SiO2 were leached out during a reaction. This dissolved homogeneous Mo species appeared to take part in this reaction.
Keywords: Deactivation; Transesterification; Dimethyl carbonate; Methyl phenyl carbonate; MoO3/SiO2; TiO2/SiO2;
Modeling of kinetics and stereoselectivity in liquid-phase α-pinene hydrogenation over Pd/C by Irina L. Simakova; Yulia Solkina; Irina Deliy; Johan Wärnå; Dmitry Yu. Murzin (216-224).
The kinetics and stereoselectivity of α-pinene hydrogenation to two stereoisomers were investigated over 4 wt% Pd/C at 50–90 °C and 2–11 bar of hydrogen pressure using n-octane as a solvent. The rate was temperature, pressure and reactant concentration dependent. Stereoselectivity was independent on conversion, but was sensitive to temperature and hydrogen pressure. Advanced kinetic model described the formation of the products with satisfying accuracy.The hydrogenation of α-pinene was investigated in a batch reactor over 4 wt% palladium on carbon (Pd/C) catalyst in temperature range of 50–90 °C and 2–11 bar of hydrogen pressure using n-octane as a solvent. The reaction network involves hydrogenation of α-pinene to two stereoisomers. The reaction kinetics was established in conditions free from diffusional limitations. The rate was temperature, pressure and reactant concentration dependent. Stereoselectivity was independent on conversion, but was sensitive to temperature and hydrogen pressure. A reaction network and mechanisms were proposed and corresponding kinetic equations were derived. The parameters of the mechanistic kinetic models were determined by using non-linear regression analysis. The kinetic models described the formation of the products with satisfying accuracy.
Keywords: Pinene; Hydrogenation; Kinetics; Modeling; Pd/C;
The effect of thermodynamic properties of zirconia-supported Fe3O4 on water-gas shift activity by Ivan Baldychev; John M. Vohs; Raymond J. Gorte (225-230).
The thermodynamics of the oxidation and reduction of a series of zirconia- and alumina-supported iron-oxide catalysts were measured using coulometric titration and then compared to their activity for the water-gas shift (WGS) reaction. For the supported iron oxide catalysts with weight loadings of 5–30 wt%, the Gibbs free energy for the phase transition between Fe2O3 and Fe3O4 decreased by factor of two compared to that for bulk, unsupported iron oxide. This difference in thermodynamic properties was also found to affect the WGS reaction rates, with the rates on the supported catalysts being an order of magnitude lower than that for bulk iron oxide. We propose that the differences in the thermodynamic properties of the supported and unsupported catalysts are due to lattice strain in the supported iron oxide resulting from interactions at the FeO x -support interface.The thermodynamics of the oxidation and reduction of a series of zirconia- and alumina-supported iron-oxide catalysts were measured using coulometric titration and then compared to their activity for the water-gas shift (WGS) reaction. For the supported iron oxide catalysts with weight loadings of 5–30 wt%, the Gibbs free energy for the phase transition between Fe2O3 and Fe3O4 decreased by factor of two compared to that for bulk, unsupported iron oxide. This difference in thermodynamic properties was also found to affect the WGS reaction rates, with the rates on the supported catalysts being an order of magnitude lower than that for bulk iron oxide. We propose that the differences in the thermodynamic properties of the supported and unsupported catalysts are due to lattice strain in the supported iron oxide resulting from interactions at the FeO x -support interface.
Keywords: Iron oxide; Water-gas shift; Thermodynamic properties;
Citrate or hydrotalcite? by Yingying Zhan; Dalin Li; Kazufumi Nishida; Tetsuya Shishido; Yasunori Oumi; Tsuneji Sano; Katsuomi Takehira (231-242).
Trace amounts of Pt- and Ru-doped Ni/Mg(Al)O catalysts were prepared by a citrate method and tested in the oxidative reforming of C3H8 under daily start-up and shut-down (DSS) operation. The activity and the sustainability of the catalysts were compared with those of the Pt- and Ru-doped Ni/Mg(Al)O catalysts derived from hydrotalcite (HT) precursor. The DSS operation of C3H8 reforming was carried out with O2 gas or O2/H2O mixed gas between 200 °C and 600 °C or 700 °C under air purging conditions. The catalysts underwent steaming treatment with H2/H2O mixed gas at 900 °C for 10 h. This allowed us to test the effect of Ni sintering on the catalyst deactivation. Coking was significantly suppressed on both HT- and citrate-derived Ni catalysts. Although both preparations produced highly dispersed Ni particles on the catalysts, the HT-derived catalysts exhibited more finely dispersed Ni particles, resulting in higher activity values than those of the citrate-derived catalysts. The regenerative activity due to redispersion of sintered Ni particles was enhanced over the HT-derived catalysts compared with the activity over citrate-derived catalysts. Although a clear redispersion of Ni particles was not observed in the oxidative reforming, i.e., in the absence of steam, the size decrease in Ni particles was more significant over the HT-derived catalysts than over the citrate-derived catalysts. The Mg(Al)O periclase structure derived from Mg-Al HT likely plays an important role in the regenerative activity of Pt- and Ru-Ni/Mg(Al)O catalysts. Pt-doping was more effective than Ru for the catalyst sustainability in the oxidative reforming of C3H8.Trace amounts of Pt-doped Ni/Mg(Al)O catalysts derived from hydrotaclite exhibited higher and more sustainable activity than those prepared by the citrate method. Mg(Al)O periclase that originated from Mg-Al HT played an important role in the regenerative activity of the catalysts via reversible reduction-oxidation between Ni0 and Ni2+ on/in Mg(Al)O assisted by hydrogen spillover from Pt.
Keywords: C3H8 reforming; H2 production; Pt or Ru-Ni/Mg(Al)O catalyst; Citrate; Hydrotalcite;
Pillared clays with Al–Fe and Al–Ce–Fe in concentrated medium: Synthesis and catalytic activity by N.R. Sanabria; M.A. Centeno; R. Molina; S. Moreno (243-249).
A new methodology for the modification of clays with the mixed Al–Fe and Al–Ce–Fe systems, which involves the synthesis of solid polymeric precursors and their use as pillaring agents in the modification of clays. The pillared clays using this new methodology show a catalytic activity and selectivity comparable to those of solids synthesized by the conventional method in a dilute medium.This paper proposes a new methodology for the modification of clays with the mixed Al–Fe and Al–Ce–Fe systems, which involves the synthesis of solid polymeric precursors and their use as pillaring agents in the modification of clays. The process of intercalation of clay with Al13, Al13 + Fe and Al13 + Ce + Fe nitrate was performed using ultrasound. The pillaring agents Al13, Al13 + Fe and Al13 + Ce + Fe were characterized by XRF, XRD, SEM and 27Al NMR techniques, and pillared clays were characterized by XRF, XRD and N2 adsorption to 77 K. The catalytic properties of pillared clays were evaluated using catalytic wet peroxide oxidation of phenol in dilute aqueous medium, demonstrating activity comparable to that of solids modified by the conventional method.
Keywords: Polyhydroxocation multimetallic; Al–Fe; Al–Ce–Fe; Pillared clays; CWPO;