Applied Catalysis A, General (v.405, #1-2)
Editorial Board (CO2).
Preparation and performance of Cu-based monoliths for methanol synthesis by Xuyen Kim Phan; Hamidreza Bakhtiary-Davijany; Rune Myrstad; Peter Pfeifer; Hilde J. Venvik; Anders Holmen (1-7).
Display Omitted► CuO/ZnO/Al2O3 coatings on metallic monoliths were prepared by different methods. ► The monoliths with slurry coating show high activity in methanol synthesis. ► Higher activity of the monolith vs. fixed bed attributed to thermal properties.Methanol synthesis from syngas could be carried out in steel monoliths coated with CuO/ZnO/Al2O3 catalysts. The Cu-based coatings were prepared using different techniques: slurry coating of CuO/ZnO/Al2O3 obtained via 2-stage co-precipitation, sol–gel coating of Al2O3 followed by Cu–Zn impregnation, colloid coating of Al2O3 followed by Cu–Zn impregnation, and colloid coating of Al2O3 followed by deposition–precipitation of Cu–Zn. The coated monoliths were characterized (XRD, BET, N2O titration) and studied in the methanol synthesis reaction at 80 bar. Comparison was made to similarly prepared powder catalysts subjected to characterization and laboratory scale fixed bed reactor (FBR) experiments. Monoliths with high activity for the methanol synthesis reaction were obtained with slurry coating of CuO/ZnO/Al2O3, whereas the impregnation and deposition–precipitation methods gave insufficient Cu dispersion. Higher activity of the monolith relative to FBR experiments with the same catalyst was ascribed to the thermal properties of the steel monolith.
Keywords: Monolith; Methanol synthesis reaction; Catalyst coating; Cu;
Evolution of strong acidity and high-alkane-cracking activity in ammonium-treated USY zeolites by Kazu Okumura; Takuya Tomiyama; Nami Morishita; Takashi Sanada; Kazuhiro Kamiguchi; Naonobu Katada; Miki Niwa (8-17).
Display Omitted► Acid properties of USY zeolites treated with an aqueous solution were quantitatively analyzed by IRMS-TPD. ► Treatment of USY zeolites with solutions of ammonium salts led the evolution of strong Brønsted acid (150 kJ mol−1). ► A linear relationship between Brønsted acid strength and apparent activation energy was observed in alkane cracking. ► Acid strength is the primary factor that accounts for change in the intrinsic alkane activation energy among FAU-type zeolites.USY zeolites prepared by steam treatment of NH4-Y zeolites were treated with ammonium nitrate solutions. Treatment with ammonium nitrate solutions resulted in a significant enhancement of the octane-cracking activity of the USY zeolites. We found by infrared spectroscopy/mass spectrometry-temperature programmed desorption (IRMS-TPD) of NH3 that the prepared USY zeolites have acidity strong enough to catalyze alkane cracking. The acid strength (ΔH) values of the enhanced Brønsted OH on the USY are found to be ca. 150 kJ mol−1. A linear correlation between ΔH and the activation energy in alkane cracking was obtained when Y-type zeolites were used for the reaction. The heats of adsorption of octane and hexane were almost constant over various types of FAU zeolites. This means that the higher the strength of the acid site, the smaller the intrinsic activation energy of the alkane cracking. This study clearly indicated that treatment with NH4 + was the key to creating very strong acidity in USY zeolites. Furthermore, the origin of the high catalytic activity of the ammonium-treated USY zeolites was attributed to the evolution of strong acidity rather than changes in the adsorption energies of the alkanes, based on the measurements of acid strength, heat of alkane adsorption, and activation energy.
Keywords: Ultra-stable Y zeolite; IRMS-TPD; Alkane cracking; Ammonium salts;
Gas-phase epoxidation of propylene over nanostructured iron-containing catalysts by Blažej Horváth; Tomáš Soták; Milan Hronec (18-24).
Display Omitted► Effect of potassium chloride on iron incorporation into silica matrix in aim to create an epoxidation catalyst. ► The removal of excess KCl ex-post further improves the yield of propylene oxide. ► A calcium promoter sensitively improves the catalyst's lifetime.The gas-phase epoxidation of propylene using nitrous oxide as an oxidant over nanostructured iron-containing catalysts was studied. Various types of catalytic systems were used, and the effort was aimed at obtaining propylene oxide as the main product of the reaction. Catalysts prepared on various supports with different porosities, various amounts and types of promoters have been tested. The function of potassium chloride and other promoters was investigated with the aim to understand their effect of the iron incorporation into the silica matrix. It has been found that after a partial removal of KCl from the iron-containing catalyst, a maximum of 54% propylene conversion can be obtained. In the presence of calcium promoter, 96% selectivity of propylene oxide formation was reached at 21% conversion of propylene.
Keywords: Epoxidation; Gas phase; Propylene oxide; Nitrous oxide; Nanostructured iron catalysts;
Energy consumption of the electrolytic hydrogen production using Ni–W based activators—Part I by Aleksandar D. Maksic; Snezana M. Miulovic; Vladimir M. Nikolic; Ivana M. Perovic; Milica P. Marceta Kaninski (25-28).
Display Omitted► Investigation on the energy consumption at Ni–W catalyst for the HER. ► Ni–W catalyst electrodeposited in situ under working conditions of the industrial electrolyser. ► Ni–W catalyst reveal lowering of the energy consumption compared to industrial nickel electrodes.The aim of this work is to investigate the energy consumption of alkaline electrolyser with the in situ added ionic activators. Several concentrations of nickel and tungsten based ionic activators were used in the same alkaline electrolyser, and the energy consumption was calculated and compared to conventional electrolyte. The electrolyser operated at several current densities and temperatures, in order to obtain the optimal concentration of the ionic activators. We have obtained lowering of the energy needed to produce certain amounts of hydrogen for about 15% compared to standard electrolyte, just using simplified process of the in situ activation with Ni and W based ionic activators. Alkaline electrolyser operated with the selected concentration of d-metals has shown long term stability under industrial conditions.
Keywords: Alkaline electrolysis; Hydrogen production; Ionic activators; Energy consumption;
Electrochemical characterization of the Ni–W catalyst formed in situ during alkaline electrolytic hydrogen production—Part II by Milica P. Marceta Kaninski; Djordje P. Saponjic; Ivana M. Perovic; Aleksandar D. Maksic; Vladimir M. Nikolic (29-35).
.Display Omitted► Investigation on the electrocatalytic efficiency of Ni–W catalyst for the HER. ► Synergetic effect is observed, with its maximum when applying industrial conditions. ► Ni–W catalyst reveal the Tafel slopes ∼120 mV, j 0 ∼ 10−4 A cm−2. ► The apparent energy of activation of 30 kJ mol−1.Objective of this work was to investigate the electrocatalytic efficiency using quasi-potentiostatic, galvanostatic and impedance spectroscopy techniques of the Ni–W catalysts obtained by in situ electrodeposition in an alkaline, 6 M KOH, electrolyser. Synergetic effect is observed, with its maximum at industrial conditions (high temperature and current density). The Tafel slopes are ∼120 mV and exchange current densities are in the range of 10−4 mA cm−2. Results are presented to show the Tafel slopes, the exchange current densities, the apparent energy of activation and the apparent electrochemical surface of the in situ formed Ni–W catalyst. Obtained results could have significant impact on the industrial process for the alkaline hydrogen production and suggest to good catalytic performance not only from the increase of the real surface area of the electrodes, but also from the true catalytic effect.
Keywords: Electrolysis; Hydrogen; Catalysis; Ionic activators; EIS; Tafel analysis;
Pre-esterification of FFA in plant oil transesterified into biodiesel with the help of solid acid catalysis of sulfonated cation-exchange resin by Masato Kouzu; Atsuko Nakagaito; Jyu-suke Hidaka (36-44).
Display Omitted► Esterification of oleic acid with methanol was carried out at 333 K in the presence of sulfonated cation-exchange resin. ► The macro-reticular type was superior in the internal mass transfer, while the gelular type was more catalytically active. ► Liquid–liquid interfaces formed between oil and methanol phases were advantageous to the acid-catalyzed esterification.One of the ways for the economically reasonable biodiesel production is to use the low quality plant oil as the cost advantageous feedstock. However, a large amount of free fatty acids (FFA) contained in the low quality plant oil causes the various problems: slowdown of the base-catalyzed transesterification, loss of the produced biodiesel and so on. Therefore, much interest has been taken in esterifying FFA into their methyl esters preliminarily with the help of solid acid catalysis of sulfonated cation-exchange resin. In the present research work, the resin catalysts of two types differing in textile structure of the matrix were employed for esterification of oleic acid with methanol at 333 K. For both the gelular resin and the macro-reticular one, the original bead shape provided the lower conversion ratio than the powder form prepared by grinding. The difference in the conversion ratio between the original bead shape and the powder form was larger for the gelular resin than for the macro-reticular one. On the other hand, the gelular resin was more active in catalyzing the esterification than the macro-reticular one. Also, for the purpose of examining the influence of the liquid–liquid interfaces formed between oil and methanol phases, soybean oil and methyloleate were used as a vehicle for the source oil of oleic acid. Additionally, a relation between the reusability of the resin catalyst and the by-production of water was investigated from a data collected by repeating the esterifying batches with reusing the resin catalyst.
Keywords: Biodiesel; Free fatty acids; Esterification; Sulfonated cation-exchange resin; Solid acid catalyst;
Fischer–Tropsch synthesis over Co/montmorillonite—Insights into the role of interlayer exchangeable cations by Guang-Wei Wang; Qing-Qing Hao; Zhao-Tie Liu; Zhong-Wen Liu (45-54).
Display Omitted► Acidic sites and rich pores are created after exchanging Na-montmorillonite with NH4 +, Co2+, or Al3+. ► High selectivity of liquid FT hydrocarbons over Co-supported Na-montmorillonite exchanged with Al3+, Co2+, or NH4 +. ► The content of Na+ is a key factor to control the CO conversion over Co/montmorillonite catalyst.To develop an efficient catalyst for controlling the product distribution of the Fischer–Tropsch (FT) synthesis, the natural Na-type montmorillonite (Na-MMT) was modified by ion-exchanging the interlayer Na+ with selected cations, NH4 +, Co2+, and Al3+. The degree of the interlayer Na+ replaced by the selected cations was regulated by changing the ion-exchange conditions. A 20 wt.% Co/MMT catalyst was prepared by the incipient impregnation method. The materials were characterized by XRD, SEM/EDS, N2 adsorption–desorption at low temperature, H2-TPR, and NH3-TPD techniques, and the results indicate that the MMT interlayer structure was well reserved for all the ion-exchanged MMTs. Moreover, acidic sites, rich micropores and open mesopores were created after exchanging the Na-MMT with NH4 +, Co2+, or Al3+. The Co-supported catalysts were investigated for the FT synthesis in a fixed-bed reactor under the conditions of 1.0 MPa, 235 °C, H2/CO = 2, and W/F = 5.02 g h mol−1. The results show that the Co/Na-MMT is an inefficient catalyst for the FT synthesis. In contrast, the Co/ion-exchanged MMT showed sharply increased CO conversion. The CO conversion was dependent on the ion-exchange conditions used, however. Moreover, the product selectivity over Co/MMT, i.e., 40–47% C4–C12 hydrocarbons and 13–20% C21 + hydrocarbons, significantly deviates from the Anderson–Schulz–Flory distribution in the FT synthesis over the typical Co/SiO2 catalyst. Based on the catalysts characterization, the difference of the FT activity as a result of interlayer cation can be explained as the different reduction behavior of the catalysts. Due to the cracking of the long-chain FT hydrocarbons, a narrow product distribution over the Co/MMT catalyst was observed, which correlates well with the NH3-TPD results.
Keywords: Fischer–Tropsch; Cobalt; Montmorillonite; Ion exchange; Liquid fuel;
Alternative carbon based acid catalyst for selective esterification of glycerol to acetylglycerols by Julián A. Sánchez; Diana L. Hernández; Jorge A. Moreno; Fanor Mondragón; Jhon J. Fernández (55-60).
Display Omitted► Selective esterification of glycerol over carbon-based acid catalysts. ► High conversion with 50% triacetin selectivity was obtained over a sulfonated carbon. ► Carbonization and sulfonation methods were optimized. ► Characterization of active sites and structure–activity correlations are reported.Carbon-based acid catalysts with porous structure were prepared by sulfonation of carbonized sucrose. The catalysts have an amorphous porous structure with a good acid capacity and high thermal stability. The catalytic activity was evaluated by the esterification of glycerol with acetic acid. The sulfonated carbon catalysts showed that glycerol was completely transformed into a mixture of glycerol esters including a high selectivity of about 50% to triacetylglycerol (TAG).
Keywords: Catalytic esterification; Glycerol; Triacetylglycerol; Sulfonated carbon catalyst; Carbon-based acid catalyst;
Quasi-homogeneous catalytic activities of hydrocarbon dispersible HZSM-5 nanocrystals grafted with different alkyl groups by Shiguo Bao; Guozhu Liu; Li Wang; Xiangwen Zhang (61-68).
.Display Omitted► Improving hydrocarbon dispersion of HZSM-5 nanocrystals by regulating grafted alkyl groups. ► Grafting alkyl groups influences the acidity of zeolite. ► Quasi-homogeneous catalytic activity is higher with C6-alkyl groups.HZSM-5 nanocrystals grafted with different alkyl groups (ethyl, butyl, hexyl, dodecyl, and hexadecyl groups) were prepared to study their stable dispersion in the hydrocarbons as well as the quasi-homogeneous catalytic activities. The physical properties of the prepared zeolites were characterized by solid-state nuclear magnetic resonance, X-ray diffraction, N2 adsorption–desorption, fourier transform infrared spectra of pyridine adsorbed, and dynamic light scattering. The results showed that the ZSM-5 crystal structure were kept without obvious change after grafting alkyl groups, but that their stable dispersions in the hydrocarbon significantly improved with increasing chain length of grafted alkyl groups by reducing aggregate size of HZSM-5 nanocrystals. Quasi-homogeneous catalytic cracking of n-dodecane at 427 °C showed that the cracking rates with hydrocarbon dispersible HZSM-5 nanocrystals improved by more than 2 times compared with thermal cracking, wherein the zeolites grafted hexyl group had the best catalytic activity in good agreement with its larger acid amount.
Keywords: Hydrocarbon dispersible HZSM-5 nanocrystals; Quasi-homogeneous catalytic cracking; n-Dodecane; Grafting;
Influence of the thermal treatment on the physicochemical properties and photocatalytic degradation of 4-chlorophenol in aqueous solutions with tungstophosphoric acid-modified mesoporous titania by Mirta Blanco; Luis Pizzio (69-78).
Display Omitted► Mesoporous TPA-modified titania samples were prepared using urea as template agent. ► S BET decreased with the increase of TPA content and the thermal treatment temperature. ► The presence of dispersed TPA retarded the phase transition of anatase to rutile. ► The band gap values slightly decreased with the increment of TPA content. ► TPA–TiO2 calcined at 500 °C and 600 °C present the highest k ap for 4-CP photodegradation.Materials based on titania directly modified with tungstophosphoric acid were prepared using titanium isopropoxide as titania precursor and urea as a low-cost pore-forming agent. The obtained mesoporous solids presented an average pore diameter higher than 3.1 nm. The specific surface area decreased when the TPA amount and the calcination temperature increased. All the modified solids only showed the anatase structure of titania by X-ray diffraction, while for the unmodified sample this structure was transformed into the rutile phase from 600 °C on. The crystallite size increased with the calcination temperature, though the TPA-modified samples presented lower values when the TPA amount was increased. The 31P nuclear magnetic resonance studies showed that the Keggin structure of the tungstophosphate anion was partially transformed when it was thermally treated up to 600 °C, though structure disruption took place at higher temperature. The band gap values estimated from the UV–vis-diffuse reflectance spectra did not show important variation, though they slightly decreased with the TPA content. The 4-chlorophenol degradation was studied in liquid phase, with an air flow continuously bubbled. The degradation behavior of the catalysts as a function of time depended on the TPA amount and the thermal treatment temperature, the samples containing 30% TPA calcined at 500–600 °C and 20% TPA calcined at 600 °C being more effective. The apparent reaction constant, estimated assuming a pseudo-first-order kinetics, followed the same trend. The catalysts can be reused at least three times without an important decrease in the degradation and mineralization degrees.
Keywords: Mesoporous titania; Tungstophosphoric acid; 4-Chlorophenol; Photocatalytic degradation;
Application of cerium oxide electrospun fibers in the catalytic combustion of methane by Geordana Cornejo Pontelli; Raquel Pereira Reolon; Annelise Kopp Alves; Felipe Amorim Berutti; Carlos Pérez Bergmann (79-83).
Display Omitted► CeO2 and copper doped CeO2 nanostructured electrospun fibers apply as catalysts. ► Catalysts applied in the methane combustion at different temperatures. ► The catalyst decreases the methane combustion ignition temperature to below 873 K. ► High conversion and NO/NO x reduction was observed using the electrospun nanostructured catalysts.CeO2 and Cu/CeO2 catalysts were prepared using electrospinning technique for methane oxidation in air. Cerium nitrate or cerium acetylacetonate and different amounts of copper acetate were used as precursors to obtain nanostructured fibers after heat treatment. The influence of the amount of copper in ceria fibers and its influence on the catalysts characteristics and catalytic activity were determined. The catalysts were characterized by means of SEM, SSA and TPR techniques for the methane oxidation using synthetic air, following the consumption of C x H y and O2 and the production of NO/NO x , CO2, CO and residual C x H y .
Keywords: Cerium oxide; Electrospinning; Catalytic combustion;
Effect of supercritical water gasification treatment on Ni/La2O3-Al2O3-based catalysts by Muhammad B.I. Chowdhury; Mohammad M. Hossain; Paul A. Charpentier (84-92).
.Display Omitted► Nanostructured La doped Ni-Al2O3 catalysts were synthesized and treated to SCWG using glucose. ► Physico-chemical characterization showed La was found to reduce graphite coke formation, enhancing H2 formation. ► La was found to adsorb CO2, enhancing the water gas shift reaction and H2 formation. ► La was found to reduce methanation reactions promoting H2 production. ► A novel reaction mechanism is proposed to facilitate an understanding of SCWG.Demand for low cost and high activity catalysts for use in biomass gasification is gaining significant attention. This study investigated the effect of supercritical water gasification (SCWG) on Ni-based Al2O3 catalysts doped with La2O3 in order to gain a better understanding of the catalyst's role. The investigated micron and nano sized catalysts were characterized both before and after SCWG treatment by temperature programmed reduction (TPR) and oxidation (TPO) for determining metal–support interactions and stability. Temperature programmed desorption (CO2-TPD) was measured for CO2 adsorption to the catalyst surface. Pulse chemisorption was conducted to measure the dispersion and crystalline size of the nickel particles while XRD, TGA and Raman analysis were carried out to examine the crystalline phase and coke deposition.The results showed that exposure to SCWG severely affected the physical and chemical structure of the Ni/Al2O3 catalysts leading to agglomeration of active metals, particularly for nanostructured catalysts. Adding La2O3 to the Ni/Al2O3 catalysts retarded coke formation, especially graphitic type coke by forming lanthanum oxycarbonate species.
Keywords: Biomass gasification, Catalyst characterization, Nickel lanthanum, Supercritical water;
Methanolysis of sunflower oil catalyzed by acidic Ta2O5 supported on SBA-15 by I. Jiménez-Morales; J. Santamaría-González; P. Maireles-Torres; A. Jiménez-López (93-100).
Display Omitted► Acid solids were prepared by impregnation of a SBA-15 silica with Ta2O5. ► The catalysts are active in the methanolysis of sunflower oil at 200 °C. ► No leaching of tantalum is detected and catalysts can be reutilized. ► These acid catalysts catalyze the FFAs esterification of and oil transesterification.Tantalum penta-ethoxide has been used as precursor for the preparation, after calcination at 575 °C, of a series of catalysts based on tantalum oxy-hydrate supported on SBA-15 silica. The Ta2O5 loading ranges between 5 and 25 wt%, and all of them exhibit acid properties, as determined by NH3-TPD. These catalysts have been assayed in the methanolysis of sunflower oil at 200 °C, being the catalyst with a 15 wt% of Ta2O5 the most active, giving 92.5% of biodiesel yield with solely 6.7% of catalyst with respect to the oil weight. Moreover, no leaching of tantalum was detected in the liquid medium, and these catalysts are able to simultaneously produce the esterification of free fatty acids (FFAs) and the transesterification of triglycerides, even in the presence of 9% of FFAs. The catalytic activity is well maintained in the presence of 5 wt% of water and after three cycles without any treatment.
Keywords: Tantalum oxide; SBA-15; Transesterification; Sunflower oil;
Role of Cr and V on the stability of potassium-promoted iron oxides used as catalysts in ethylbenzene dehydrogenation by Zheng Li; Brent H. Shanks (101-107).
Display Omitted► K-promoted iron oxide stability impacted by gas phase species. ► Cr stabilizes K–Fe2O3 against reduction. ► V destabilizes K–Fe2O3 oxide via interaction with the K. ► Phase change behavior of K–Fe2O3 correlates with reaction performance.Potassium-promoted iron oxides are the most widely used catalysts for catalytic dehydrogenation of ethylbenzene to styrene. Besides potassium, other minor promoters are also added into the catalyst for different purposes, either enhancing catalyst stability or activity/selectivity. Chromium (Cr) and vanadium (V) are two historically used promoters. Cr is widely accepted to be a structure stabilizer and V can increase the selectivity to styrene but with detrimental effect on stability and activity of the catalysts. Since the effects of these two promoters are known and opposite, the effects of Cr and V on the solid state phase behavior of K-promoted iron oxide were investigated. Gas environments consisting of H2, CO2, ethylbenzene and steam were used to explore the interaction between the gas composition and the phase behavior of the doped iron oxides. The experiments were performed in a thermogravimetric analyzer under various gas environments and X-ray powder diffraction was used to quantitatively characterize the phase changes. The Cr and V promoted K–promoted iron oxide had very different responses to the different gas phase environments, but in the presence of steam and ethylbenzene Cr stabilized the iron oxide against reduction whereas V destabilized the iron oxide. These data support the idea that the promoters influence K-promoted iron oxide stability under low steam-to-ethylbenzene operation via modifying the phase behavior of the iron oxide.
Keywords: Iron oxide catalysts; Potassium-promoted iron oxide ethylbenzene dehydrogenation; Mixed metal oxide materials;
The role of promoters for Ni catalysts in low temperature (membrane) steam methane reforming by D.A.J. Michel Ligthart; Johannis A.Z. Pieterse; Emiel J.M. Hensen (108-119).
Display Omitted► B, Rh and La promoters influence particle size and reducibility of Ni. ► Surface atom based activity of Ni correlates to Ni dispersion. ► Boron improves stability of Ni due to formation of nickel boride active phase.In the search for active and stable Ni-based catalysts for steam methane reforming in membrane reactors, the effect of three different promoters La, B and Rh was compared. Promoted and unpromoted Ni catalysts were characterized by TEM, TPR and X-ray absorption spectroscopy. The average Ni particle size is between 4 and 10 nm. Promoters affected both dispersion and reducibility of Ni. Smaller particles were found to be more difficult to reduce than larger ones. The use of B resulted in very small Ni particles. The degree of Ni reduction strongly increased by use of La and Rh promoters, whereas B strongly impeded Ni reduction. The initial intrinsic rate per surface metal atom was found to increase linearly with the Ni metal dispersion, suggesting that the rate is controlled by dissociative methane adsorption over low-coordinated surface atoms. The data indicate that Rh and La act as structural promoters to the activity. Catalysts modified by B show a much higher activity of the Ni surface atoms. Catalyst stability was investigated by using feed compositions representing the inlet of the membrane reactor and the hydrogen lean reformate towards its outlet. Stability increases in the order La < Rh < B. Deactivation of the catalysts is caused by insufficient removal of carbon species from the surface of Ni particles and the formation of stable, graphitic carbon deposits, most likely covering the surface of metal. This is substantially suppressed when the Ni particles are small. B is an excellent structural promoter to obtain small Ni particles, Rh stabilizes metallic Ni and La aids in the removal of some of the carbon deposits more effectively by gasification.
Keywords: Steam reforming; Membranes; Nickel; Promoters; Deactivation; Coke;
Photocatalytic degradation of 2,4-dichlorophenoxyacetic acid in a fluidized bed photoreactor with composite template-free TiO2 photocatalyst by Adrián A. Vega; Gustavo E. Imoberdorf; Madjid Mohseni (120-128).
Display Omitted► Stable composite TiO2 spheres were developed for use in fluidized bed photoreactors. ► Efficacy of the TiO2 photocatalytic spheres was evaluated through well controlled experiments. ► Effect of concentration and UV fluence rate on contaminant degradation was studied. ► Performance of the TiO2 spheres were compared against that of TiO2 Degussa P-25. ► The photocatalyst showed high efficiency, stability, and high resistance to attrition.The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) was degraded in a photocatalytic fluidized bed reactor with template-free TiO2 photocatalytic spheres in the presence of UV irradiation at 254 nm. The photocatalyst was prepared by binding together pre-calcined commercial TiO2 particles (Degussa P-25) in an aqueous sol of TiO2 nanoparticles (composite sol–gel) by the assistance of a polymeric matrix. The photocatalytic spheres had a considerable degree of consistency in their size and shape. X-ray diffraction (XRD), scanning electron microscopy (SEM), and BET specific surface area were used to characterize the photocatalyst. The effects of the initial contaminant concentration, its adsorption on photocatalyst surface, and the fluence rate on the herbicide degradation were studied. 2,4-D showed significant adsorption on the composite TiO2 spheres. Depending on the initial concentration of 2,4-D, between 50% and 70% was adsorbed on TiO2 spheres. In all the cases, adsorption equilibrium was reached within 75 min of contact in the fluidized bed reactor with the UV lamps off. After the UV lamps were turned on, 2,4-D was completely degraded within 45 min of irradiation with a fluence rate of 4.16 mW cm−2. Experimental results were fitted with a simplified kinetic model that takes into account the initial concentration of 2,4-D and the fluence rate. A comparison of photocatalytic degradation of 2,4-D with commercial particulate TiO2 (Degussa P-25) showed that the composite spheres have a photocatalytic activity 26% higher than that obtained with Degussa P-25. The TiO2 spheres were mechanically robust and demonstrated a high attrition resistance with only 0.014% of TiO2 released from the spheres due to attrition after 3 h of continuous operation.
Keywords: Composite TiO2 spheres; Photocatalyst; Fluidized bed reactor; 2,4-D; Fluence rate;
Metathesis hydrogenation of natural rubber latex by Suwadee Kongparakul; Flora T.T. Ng; Garry L. Rempel (129-136).
Display Omitted► More than 97% hydrogenation was achieved. ► Olefin conversion plot exhibited an S-curve characteristic. ► Proposes the catalytic cycle for hydrogenation of metathesized natural rubber. ► Superior thermal stability hydrogenated product.Metathesis hydrogenation of deproteinized natural rubber (NR) latex was studied using 2nd generation Grubbs catalyst. More than 97% hydrogenation was achieved under mild conditions and without organic solvent addition other than that used to dissolve the catalyst. The olefin conversion plot exhibited an S-curve characteristic which indicated the effect of competition between the metathesis reaction and the hydrogenation reaction. Molecular weight of NR dramatically changed along the reaction time in the first region due to the metathesis reaction and then slightly changed in the second region where the hydrogenation consumption plot obeyed a first-order kinetic model. The kinetic behavior of the hydrogenation region increased with an increase in catalyst concentration and hydrogen pressure. The results showed an inverse behavior with an increase in rubber concentration. The apparent activation energy over the temperature range of 80–96 °C for the hydrogenation of metathesized natural rubber was found to be approximately 169 kJ/mol.
Keywords: Metathesis; Hydrogenation; Natural rubber; Grubbs's catalyst; Catalytic mechanism;
Catalytic isomerization of allyl alcohols to carbonyl compounds using poisoned Pd nanoparticles by Elham Sadeghmoghaddam; Khalil Gaïeb; Young-Seok Shon (137-141).
Isomerization over hydrogenation of allyl alcohols using poisoned Pd nanoparticles.Display Omitted► Sodium S-alkylthiosulfate (Bunte salts) generates less densely packed alkanethiolate monolayers on Pd nanoparticle surface. ► Pd nanoparticles poisoned by alkanethiolate catalyze selective isomerization over hydrogenation of allyl alcohols. ► Both kinetic and thermodynamic effects control the catalytic reactions of substituted allyl alcohols.This article shows that Pd nanoparticles (NPs) poisoned by alkanethiolate monolayers can catalyze the isomerization of allyl alcohols to the corresponding carbonyl compounds in a relatively high efficiency and with a high selectivity. Pd nanoparticles are produced by the borohydride reduction of K2PdCl4 in toluene/H2O using sodium S-dodecylthiosulfate as a source for the alkanethiolate ligands. Both kinetic and thermodynamic effects control the catalytic reactions of various substituted allyl alcohols. In general, less substituted allyl alcohols including prop-2-en-1-ol and pent-1-en-3-ol are isomerized to the corresponding aldehyde or ketone more efficiently. More substituted allyl alcohols such as but-2-en-1-ol and 3-methylbut-2-en-1-ol do not undergo isomerization under the same condition. However, the presence of reactive, less substituted allyl alcohols is found to promote the isomerization of poorly reactive, more substituted allyl alcohols.
Keywords: Pd nanoparticle; Isomerization; Allyl alcohols; Thiol poisoning; Bunte salts;
Mesostructured Ni-doped ceria as an efficient catalyst for styrene synthesis by oxidative dehydrogenation of ethylbenzene by Jie Xu; Bing Xue; Yong-Mei Liu; Yong-Xin Li; Yong Cao; Kang-Nian Fan (142-148).
Display Omitted► Mesostructured doped ceria materials with high surface area over 130 cm3 g−1 as catalysts. ► Catalysts for oxidative dehydrogenation of ethylbenzene to styrene. ► High styren yield of 55% and long-term stability were achieved on the Ce0.90Ni0.10O catalyst at 450 °C.Mesostructured doped Ce1−x M x O catalysts (M = Al, Sn, Zr, Mn, and Ni) with large surface area prepared via template-assisted precipitation method have been tested for the oxidative dehydrogenation (ODH) of ethylbenzene (EB) to styrene. Several techniques including N2 desorption–adsorption, X-ray diffraction, H2-temperature programmed reduction (H2-TPR), total oxygen storage capacity (OSC), and X-ray photoelectron spectroscopy (XPS) were applied to characterize the physicochemical properties of the as-synthesized materials. Of the Ce1−x M x O catalysts tested, the CeNiO composite containing 10 mol% Ni demonstrates the highest ST yield of 55% with long-term stability for ODH of EB under 450 °C. By analysis of H2-TPR and total OSC characterization profiles, the superior performance of Ce0.90Ni0.10O catalyst can be attributed to the dramatic improvement in oxygen mobility and storage capacity of the ceria materials, resulting from the introduction of Ni species into ceria cubic structure and hence a further shrinkage of ceria lattice. A catalytic mechanism via a simple surface redox cycle has been tentatively proposed based on the XPS results.
Keywords: Ceria; Nickel; Oxidative dehydrogenation (ODH); Ethylbenzene; Styrene;
Analysis of catalyst deactivation during steam reforming of jet fuel on Ni-(PdRh)/γ-Al2O3 catalyst by Satish L. Lakhapatri; Martin A. Abraham (149-159).
Display Omitted► Mechanism of catalyst deactivation during steam reforming of Jet A was investigated. ► Decline in H2 yield with time coincided with reduced conversion of thiophene to H2S. ► Sulfur was preferentially adsorbed onto Ni, while no detectable sulfur was seen on Rh. ► Only surface adsorption of sulfur was seen and no bulk sulfur was detected. ► Polymeric/aromatic type carbon was deposited on the catalyst surface.Catalyst deactivation during steam reforming of transportation fuels, primarily due to sulfur poisoning and carbon deposition, is a major hurdle in the commercialization of fuel cell technologies. In an attempt to better understand the phenomena, a previously formulated multi-component (Ni, Pd, Rh) catalyst supported on γ-Al2O3 was studied under steam reforming of Jet A spiked with thiophene to achieve a total sulfur content of 1000 ppm by weight. Analysis of fresh catalysts showed the presence of two groups of active metal particles, primarily distinguished by their size and composition; small particles (1–5 nm) largely comprised of Rh and large particles (10–20 nm) that were predominantly Ni, with or without the presence of Pd. Analysis of used catalysts showed sintering of crystallites containing Ni but no identifiable growth in Rh crystallites. When complete conversion of sulfur compounds to hydrogen sulfide was observed, catalyst deactivation was minimized. However, when the conversion of sulfur compounds was low, significant catalyst deactivation was noted. In the presence of sulfur, increased amounts of cracking products were observed, suggesting that sulfur primarily affected the active sites responsible for steam reforming. Sulfur was preferentially adsorbed on the surface of Ni crystallites. It has been postulated that sulfur adsorption on Ni sites causes the initial deactivation of the catalyst which suppresses carbon gasification on the active sites, leading to the accumulation of carbon deposits over time.
Keywords: Steam reforming; Sulfur poisoning; Carbon deposition; Catalyst deactivation; Ni/Al2O3; STEM; Fuel cells; Transportation fuels;
Trimodal pore catalyst preparation method by growth of zeolite inside macroporous matrices of silica by Xuejun Zhang; Kai Tao; Takashi Kubota; Takeshi Shimamura; Tokimasa Kawabata; Kenji Matsuda; Susumu Ikeno; Noritatsu Tsubaki (160-165).
Display Omitted► A catalyst support with trimodal pore structure was prepared. ► The supports possess intrinsic micro, meso and macroporosity. ► The trimodal catalyst catalyzed the methanation reaction of CO. ► The trimodal catalyst exhibited high activity and stability. ► The trimodal pore structure favored metallic Co surface area and dispersion.In this paper, a novel catalyst support with trimodal pore structure was hydrothermally synthesized by building up nano-particles of titanium silicalite-1 inside the macroporous system of silica gel using the tetrapropylammonium hydroxide (TPAOH) as template, titanium (IV) tetrabutoxide monomer (TBOT) as titanium source and the silica gel with macropores as in situ silicon source as well as matrices. The prepared support exhibited intrinsic pore of TS-1, intercrystalline mesopores and residual macropores of silica gel. When loaded with Co, the trimodal catalyst was employed to catalyze the methanation of carbon monoxide, showing higher CO conversion and CH4 selectivity than the bimodal and unimodal catalysts due to the favored metallic Co surface area and dispersion.
Keywords: Trimodal pore catalyst; Zeolite; Macroporous silica; Methanation; CO;
Catalytic oxidation of ethane with oxygen using fluidised nanoparticle NiO catalyst by Syed Shatir A. Syed-Hassan; Chun-Zhu Li (166-174).
Display Omitted► Fluidised NiO nanoparticles are used to catalyse the reaction between C2H6 and O2. ► NiO nanoparticles behave differently from sub-millimetre-sized NiO/SiO2 catalyst. ► C2H5 radicals desorb from NiO nanoparticles for further gas-phase reactions.In a typical industrial catalyst, a small amount of catalytically active species is finely dispersed inside a large amount of porous support material. The reactor volume is mainly occupied by the catalyst support, not by the catalytic species itself. The use of fluidised nanoparticles as catalyst without the need of a support may result in drastic reduction in catalytic reactor volume for major savings in capital and operating costs. Here we report for the first time the use of fluidised NiO nanoparticles to catalyse ethane–oxygen reaction at temperatures of 240–420 °C. Our data indicate that the fluidised NiO nanoparticles exhibit very different characteristics from the traditional porous catalyst. The lack of a rigid porous structure in the fluidised NiO nanoparticle catalyst allows ethyl radicals to desorb from the catalyst surface into the gas phase to initiate further gas-phase radical chain reactions. Therefore, the ethane–oxygen reaction catalysed by the fluidised NiO nanoparticles shows some typical behaviour of gas-phase reactions. In contrast, the rigid porous structure in the NiO/SiO2 catalyst does not allow the radicals to desorb from catalyst surface into the bulk gas phase.
Keywords: Fluidised nanoparticle catalyst; Radical desorption; Light hydrocarbon conversion; Catalytic oxidation; Ethane; Nickel oxide;