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Applied Catalysis B, Environmental (v.97, #1-2)
Recent achievements in direct ethylene glycol fuel cells (DEGFC) by Alexey Serov; Chan Kwak (pp. 1-12).
In the present review recent achievements in the development of new type of liquid fed fuel cell, specifically ethylene glycol (EG) operated in acid and alkaline media were summarized. The mechanism of EG electrooxidation in acid media on the platinum surface as well as on different platinum alloys is described. The development in the preparation of new effective electrocatalysts both for ethylene glycol oxidation and oxygen reduction in the presence of EG is discussed. Methods for improving the performance of direct ethylene glycol fuel cells (DEGFC), e.g., MEAs fabrication, operation conditions, etc. are shown.
Keywords: Ethylene glycol; Fuel cell; Anode; Catalyst
Modeling of NO x adsorption–desorption–reduction cycles on a ruthenium loaded Na–Y zeolite by M. Labaki; M. Issa; S. Smeekens; S. Heylen; C.E.A. Kirschhock; K. Villani; M. Jeguirim; D. Habermacher; J.F. Brilhac; J.A. Martens (pp. 13-20).
Adsorption of NO from a gas stream containing oxygen and water and desorption and reduction using a rich gas mixture were investigated in the temperature range 230–315°C on Na–Y zeolite loaded with 3wt.% ruthenium. The NO x storage capacity was found little dependent on temperature and water content of the gas. The adsorption–desorption–reduction process was modeled using a one-dimensional fixed-bed model and assuming co-adsorption of NO and NO2 molecules on Na–Y zeolite, ruthenium catalyzed NO into NO2 oxidation by molecular oxygen during adsorption and ruthenium catalyzed NO x reduction by hydrogen during desorption. Kinetic constants were estimated through data fitting. An acceptable agreement between experimental and calculated values was obtained. NO x adsorption and desorption kinetics on Na–Y zeolite with and without ruthenium were substantially different revealing that ruthenium besides catalyzing NO x oxidation and reduction had a drastic influence on the NO x adsorption sites of Na–Y zeolite.
Keywords: Ru/Na–Y; NO; x; storage and reduction; N; 2; O; 3; Kinetic modeling
Limiting mechanisms in catalytic steam reforming of dimethyl ether by Kajornsak Faungnawakij; Naohiro Shimoda; Nawin Viriya-empikul; Ryuji Kikuchi; Koichi Eguchi (pp. 21-27).
The limiting mechanisms in dimethyl ether steam reforming (DME SR) are experimentally investigated over the nanocomposite catalysts of Cu spinel and alumina. The dominant reactions involved in DME SR are proved to be DME hydrolysis to methanol over acidic sites of alumina and subsequent methanol steam reforming to H2 and CO2 over Cu sites, followed by reverse-water gas shift reaction. The contribution of other side reactions is also clearly evaluated. DME hydrolysis is limited by the equilibrium, and the hydrolysis rate was much slower than the methanol SR rate, and thus was a rate-determining step in DME SR. The deactivation of Cu spinel was significantly faster than that of alumina, and would determine the lifetime of the composite catalysts. With varied superficial velocities up to 5.2cms−1 (25°C, 1atm), the evidence of mass transfer-limiting mechanism and reaction-limiting mechanism was observed in the low flow rate and the high flow rate regions, respectively.
Keywords: Limiting mechanism; Steam reforming; Dimethyl ether; Deactivation; Hydrogen fuel cell
Preferential oxidation of carbon monoxide on Co/CeO2 nanoparticles by Matthew P. Woods; Preshit Gawade; Bing Tan; Umit S. Ozkan (pp. 28-35).
A highly active CoO x/CeO2 nanoparticle catalyst with high surface area (78m2/g) has been prepared and tested in the preferential oxidation of carbon monoxide (PROX) in the presence of hydrogen. Three distinct temperature regions of catalyst activity are observed corresponding to CO oxidation, H2 oxidation and methanation. The catalyst achieves near 100% CO conversion under a wide range of reaction conditions demonstrating peak activity near 175°C. The catalyst is stable with time-on-stream at the temperature of highest CO conversion. The presence of H2 decreases the CO oxidation rate, possibly due to competitive adsorption between H2 and CO. CO oxidation and H2 oxidation activation energies were 52 and 74kJ/mol, respectively. Raman spectroscopy and X-ray diffraction experiments have demonstrated that the cobalt takes the form of Co3O4 and no CoO was detected under any experimental conditions.
Keywords: PROX; CO oxidation; H; 2; combustion; Cobalt; Ceria; CeO; 2; Cobalt oxide; Co/CeO; 2; Co; 3; O; 4
Effect of manganese and calcium ions on the photoinduced water oxidation with photosynthesis organ grana from green plant by Yutaka Amao; Koichi Takai; Ami Ohashi (pp. 36-40).
To develop the visible light-induced hydrogen and oxygen production based on the water photolysis, 2,6-dichloroindophenol (DCIP) reduction based on the photoinduced water oxidation with oxygen evolved centre (OEC) of PSII in photosynthesis organ, grana from spinach was studied. It noted that manganese–calcium (4Mn–Ca) cluster consisted of four manganese and one calcium ions in OEC, and the role and effect of manganese (III) and calcium ions on the DCIP reduction were investigated. By addition of manganese (III) acetate up to 80μmoldm−3, the concentration of the reduced DCIP with irradiation was increased compared with the system in the absence of manganese (III) acetate. The activity of DCIP reduction in the presence of 80μmoldm−3 manganese (III) acetate was 4.7 times higher than that in the absence of manganese (III) acetate. This result shows that the DCIP photoreduction with grana was promoted by addition of manganese (III) ion. In contrast, the activity of DCIP reduction in the presence of 120μmoldm−3 manganese (III) acetate was 1.5 times higher than that in the absence of manganese (III) acetate, indicating that photoreduction of DCIP activity of grana was inhibited under higher concentration of manganese (III) ion or acetate anion. By addition of 80μmoldm−3 calcium chloride, on the other hand, 5.9μmoldm−3of reduced DCIP was produced and the reduction ratio of the reduced DCIP to DCIP was 8.6% after 240min irradiation. The activity of DCIP reduction in the presence of 80μmoldm−3 calcium chloride was almost the same in the absence of calcium chloride. This result shows the no effect on the DCIP photoreduction based on the water oxidation with grana by addition of calcium ion.
Keywords: Artificial photosynthesis; Manganese–calcium cluster; Water oxidation; Photosystem II
The effect of Ni on the structure and catalytic behavior of model Pd/Ce0.67Zr0.33O2 three-way catalyst before and after aging by Guangfeng Li; Bo Zhao; Qiuyan Wang; Renxian Zhou (pp. 41-48).
Ce0.67Zr0.33O2 (CZ) doped by nickel oxide with different content and the corresponding Pd-only three-way catalysts before and after aging has been prepared and characterized. The investigations show that CZ doped with nickel oxide obviously results in more active fresh catalysts with enhanced textural properties, but suffers from a net loss of activity after aging. The introduction of Ni promotes the reducibility of samples, causing the enhancement of oxygen storage capacity (OSC) of fresh samples. CZNi(3%) exhibits better textural and structural properties because of the formation of more homogeneous Ce–Zr–Ni–O ternary solid solution, which promotes the interaction between Ce–Zr and Ni. However, the thermal aging leads to a loss of surface area and a significant decrease of the reducibility and OSC, except for CZNi(3%). Only Pd/CZNi(3%) represents better catalytic activity after aging. It reveals that the catalytic behavior of these bimetallic systems is strongly affected by the nature of support.
Keywords: Ce; 0.67; Zr; 0.33; O; 2; Pd; Ni; Aging; Three-way catalyst
Novel mesoporous zirconia-based catalysts for WGS reaction by Joanna Goscianska; Maria Ziolek; Emma Gibson; Marco Daturi (pp. 49-56).
Newly synthesized mesoporous zirconia-based catalysts were investigated for the WGS reaction, using niobium oxide as a promoter and platinum as the active metal. Their performances for hydrogen production were correlated to the surface properties. Niobium addition gives rise to different effects: the 0.3 loading considerably enhances the catalytic performances of the catalyst for all temperatures, for both hydrogen production and selectivity (with respect to the CO to CO2 oxidation). On the contrary, when a Nb monolayer is produced on the zirconia surface, the activity is highly reduced with respect to the Pt/ZrO2 sample. In particular, the acid–base behaviour of the surface was linked to the zirconia–niobia interaction and its consequence on the metal–support interaction. A description of the surface was attempted and a reaction pathway through formate species formation and decomposition proposed.
Keywords: Pt/niobia–zirconia; Acidity; WGS; Formate intermediate; Operando; –FT-IR/MS
Metal–support interactions in Pt/Al2O3 and Pd/Al2O3 catalysts for CO oxidation by A.S. Ivanova; E.M. Slavinskaya; R.V. Gulyaev; V.I. Zaikovskii; О.А. Stonkus; I.G. Danilova; L.M. Plyasova; I.A. Polukhina; A.I. Boronin (pp. 57-71).
Platinum and palladium catalysts supported on γ-Al2O3 were studied by XRD, UV–vis DRS, HRTEM, TPR-H2, XPS together with measurements of their catalytic properties. The properties of the catalysts denoted as Pt(Pd)/Al2O3( X)- Y ( X— the calcination temperature of support,°C; Y— the calcination temperature of catalyst,°C) were studied as a function of the temperatures used for calcination of the support and/or the catalyst in oxygen or in a reaction mixture of CO+O2. It was found that the deposition of Pt or Pd on γ-Al2O3 did not alter the structure of the support. Two types of the Pt and Pd particles were typically present on the γ-Al2O3 surface: individual particles with dimensions of 1.5–3nm and agglomerates about 100nm in size. In the catalysts calcined at relatively low temperatures (Pt/Al2O3(550)-450), platinum was present in the form of metal clusters. However, in the Pd/Al2O3(550)-450 catalyst, the palladium particles were almost completely decorated with a thin layer of an aluminate phase. These structures are not reduced in hydrogen in the temperature range of −15 to 450°C, and are stable to treatment in a reaction mixture of CO+O2. Pd deposition on the γ-Al2O3-800 support was found to result in stabilization of the active component in two main forms, Pdo and PdO, with varying degrees of interaction due to the decoration effect. Calcination at the low temperature of 550°C led to the formation of a so-called “core–shell structure”, where a palladium metal core is covered with a thin shell of an aluminate phase. Depending on the calcination temperature of the catalyst in the range of 450–1000°C, the morphological form of the active component was converted from the “core-shell” state to a state consisting of two phases, Pdo and PdO, with a gradual decrease of the Pdo/PdO ratio, weakening the interaction with the support and the growth of palladium particles. Under the action of the reaction mixture, the Pd/Al2O3(800)-(450,600,800,1000) catalysts underwent changes in the Pdo/PdO ratio, which regulates the light-off temperature. After catalyst calcination at the highest temperature used in this study, 1200°C, the palladium particles became much larger due to the loss of the palladium interaction with the support. Only the metal phase of palladium was observed in these catalysts, and their catalytic activity decreases substantially.
Keywords: Supported catalysts; Alumina; Palladium; Platinum; CO oxidation; SMSI; HRTEM; XPS; TPR-H; 2; Catalysis
Preparation and characterization of bimetallic Rh-Ni/Y2O3-Al2O3 for hydrogen production by raw bioethanol steam reforming: influence of the addition of nickel on the catalyst performances and stability by Anthony Le Valant; Nicolas Bion; Fabien Can; Daniel Duprez; Florence Epron (pp. 72-81).
The influence of the addition of Ni on the catalytic behaviour of a Rh/Y2O3-Al2O3 catalyst (Rh/Y-Al) was evaluated in the ethanol steam reforming reaction in the presence of methyl-2-propan-1-ol as impurity. Physical-chemical properties of modified materials were determined by H2 chemisorption, XRD, BET, TPR, IR spectroscopy and TPO. It was established that the catalytic behaviour of the Rh/Y-Al base catalyst is widely improved by the addition of Ni. Nickel incorporation leads to the formation of both dispersed nickel phase and nickel aluminate species. Basic properties of the support were not modified by the addition of Ni but it was concluded to a rearrangement of acid sites. NiAl2O4 phase leads to an increase of the Lewis acid sites (LAS) of weak strength, generating a decrease of the production of coke and higher catalyst stability. It has been shown that the incorporation of Ni on the Rh/Y-Al catalyst increases the rhodium accessibility and stabilizes the rhodium particles size. Finally, the higher performances of RhNi/Y-Al catalyst were correlated to an increase in the methane steam reforming activity.
Keywords: Rhodium; Nickel; Ethanol steam reforming; Rare earth elements; Yttrium; Hydrogen production; Impurity; Methyl-2-propan-1-ol; Infrared study; Bimetallic catalysts
Kinetics of oxidative degradation/mineralization pathways of the phenylurea herbicides diuron, monuron and fenuron in water during application of the electro-Fenton process by Mehmet A. Oturan; Mohamed C. Edelahi; Nihal Oturan; Kacem El kacemi; Jean-Jacques Aaron (pp. 82-89).
The electrochemical advanced oxidation method “electro-Fenton process” has been applied to three phenylurea herbicides, namely diuron, monuron and fenuron. The reactivity of these phenylurea herbicides toward hydroxyl radicals has been found to depend on the number of chlorine substituents of the aromatic cycle. The degradation reaction rate constants ranged from 4.8×109 to 12×109M−1s−1, and increased in the following order: diuron (2 Cl)
Keywords: Electro-Fenton process; Phenylurea herbicides; Hydroxyl radicals; Mineralization pathways; Wastewater treatment
The impact of urea on the performance of metal exchanged zeolites for the selective catalytic reduction of NO x by Maik Eichelbaum; Robert J. Farrauto; Marco J. Castaldi (pp. 90-97).
Urea-SCR over metal exchanged zeolites is one of the leading catalytic technologies to abate NO x emissions in diesel exhaust. Ideally, urea injected into the diesel exhaust upstream of the SCR catalyst decomposes only to the gaseous products CO2 and NH3, where the latter gas can react with NO x emissions to form harmless N2 and H2O. However, solid by-products can be formed as well, and if deposited on the catalyst harm the long-term catalytic performance. In order to identify the impact of various urea decomposition products on the catalytic activity, we studied the pyrolysis and hydrolysis of neat urea and of urea over different zeolites (H-Y, Cu-Y, H-Beta, Na-Beta, and Fe-Beta). The experiments were run in dry and steam-containing N2 between 20 and 750° C by using simultaneous thermogravimetric analysis (TGA), differential thermoanalysis (DTA), and online GC/MS evolved gas analysis. Solid intermediate products at different decomposition temperatures were identified by means of ATR-FTIR and luminescence spectroscopy. As for neat urea, CO2, NH3 and HNCO could be detected as major gaseous products. At 270° C significant amounts of cyanuric acid and ammelide and at 500° C of melem and melon were identified as solid intermediates. Above 625°C, all solid residues decomposed to cyanogen and isocyanic acid. Furthermore, it could be shown clearly that the investigated zeolites significantly accelerate the pyrolysis of urea and cyanuric acid, and the hydrolysis of HNCO, by shifting the decomposition processes to lower temperatures and by inhibiting the formation of solid by-products. In addition, the presence of steam in the feed gas can prevent even further the formation of solid residues and the high temperature adsorption of gaseous products.
Keywords: Fe-Beta; FTIR; Metal-exchanged zeolites; NO; x; reduction; SCR; Thermogravimetry; Urea decomposition
The impact of urea on the performance of metal-exchanged zeolites for the selective catalytic reduction of NO x—Part II. Catalytic, FTIR, and NMR studies by Maik Eichelbaum; Ansgar B. Siemer; Robert J. Farrauto; Marco J. Castaldi (pp. 98-107).
The selective catalytic reduction (SCR) with urea over metal-exchanged zeolites is one of the most promising contenders for the reduction of NO x emissions in diesel exhaust. However, one major concern – a possible deactivation of the catalyst by urea deposits – has not been investigated sufficiently as yet. The formation of urea deposits on the catalyst after long-term operation was simulated by impregnating Fe–beta zeolite powder with 32.5wt.% aqueous urea solution followed by hydrothermal aging at temperatures between 250 and 750°C. The SCR activity was measured after each hydrothermal aging step. It could be shown that Fe–beta can be reversibly deactivated by urea deposits such as cyanuric acid and ammelide (as identified by ATR-FTIR) if the impregnated catalyst was hydrothermally aged at temperatures not higher than 250°C. Upon steaming at 500°C a complete regeneration of the SCR activity as well as a total decomposition of urea deposits left on the catalyst was observed. In addition, MAS27Al and29Si NMR experiments clearly show that no detrimental changes of the Si/Al zeolite framework were induced by urea-impregnation followed by steaming at 750°C compared to the dealumination observed for hydrothermal aging alone. Thus, the urea-induced deactivation is fully reversible since no permanent structural changes in the zeolite could be identified.
Keywords: Catalyst deactivation; Fe–beta; FTIR; Metal-exchanged zeolites; NMR; NO; x; reduction; SCR; Urea
Sn-doped Ni/YSZ anode catalysts with enhanced carbon deposition resistance for an intermediate temperature SOFC by Hyuk Kan; Hyunjoo Lee (pp. 108-114).
Solid oxide fuel cells (SOFCs), capable of operating in an intermediate temperature range with a high power density, are fabricated using Sn-doped Ni/YSZ as an anode catalyst with a functional layer between the anode and electrolyte. The cell shows a high power density of 0.41Wcm−2 at 650°C when operated using humidified methane fuel. A comparison of this cell with a single cell prepared without Sn shows that the long-term stability is greatly improved; the Sn-doped Ni/YSZ cell operates for 137h, whereas the Ni/YSZ cell ceases operation within 27h. A minimal level of Sn-doping yields the best cell performance; higher levels of Sn-doping results in occupation of most catalytic active sites, causing poorer performance. In the case that carbon deposited on the Sn-doped Ni/YSZ surface during operation is removed, the long-term stability of the cell is further improved, and the cell operates stably for 300h without degradation. The quantity and distribution of Sn on the anode surface remains nearly unchanged over the course of operation.
Keywords: Solid oxide fuel cell; Methane; Tin; Carbon resistance; Ni/YSZ
Development of a visible-light-responsive rutile rod by site-selective modification of iron(III) ion on {111} exposed crystal faces by Naoya Murakami; Asami Ono; Misa Nakamura; Toshiki Tsubota; Teruhisa Ohno (pp. 115-119).
{111} exposed crystal faces of shape-controlled rutile titanium(IV) oxide (TiO2) were site-selectively modified with trivalent iron(III) (Fe3+) ions by utilizing adsorption property of iron(III)/iron(II) (Fe3+/Fe2+) ions. The rutile TiO2 with site-selective modification of Fe3+ ions showed high photocatalytic activity under visible-light irradiation as a result of separation of redox sites, i.e., oxidation and reduction proceed over Fe3+ ions on {111} faces and the bare TiO2 surface on {110} faces, respectively. Double-beam photoacoustic spectroscopic analyses suggest that the high activity of TiO2 with site-selective modification of Fe3+ ions is attributed to not efficient electron injection from Fe3+ ions but efficient reduction by injected electrons on {110} faces.
Keywords: Visible-light-responsive photocatalyst; Shape-controlled rutile titanium(IV) oxide; Site-selective modification of metal ion
Catalytic combustion of ethyl acetate and nano-structural changes of ruthenium catalysts supported on tin oxide by Naoto Kamiuchi; Tomohiro Mitsui; Hiroki Muroyama; Toshiaki Matsui; Ryuji Kikuchi; Koichi Eguchi (pp. 120-126).
Correlation between the catalytic activity and the nano-structure of ruthenium catalyst supported on tin oxide was investigated. As-calcined Ru/SnO2 catalyst exhibited high catalytic activity for ethyl acetate combustion despite its low surface area of ca. 5.0m2g−1. The catalytic activity was degraded by the reduction treatment at 400°C, whereas it was partially restored by the subsequent reoxidation treatment at 400°C. To elucidate the variation in the catalytic activity, the ruthenium catalysts heat-treated under reductive or oxidative condition were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). In the as-calcined catalyst, it was revealed that the fine particles with the small contact angles were well-dispersed on the surface of tin oxide support. In the deactivated catalyst treated at 400°C under a reductive atmosphere, the large particles of intermetallic compounds with the core–shell structure were clearly observed. On the other hand, upon the reoxidation treatment at 400°C the particles with the core–shell structure disappeared accompanied with the appearance of the nano-sized particles. Accordingly, it was clarified that the catalytic activity was strongly influenced by the structural changes of active sites such as sintering and redispersion.
Keywords: Ruthenium; Tin oxide; Catalyst; Catalytic combustion; Ethyl acetate; Chemical interaction; TEM
Catalytic wet air oxidation of phenol with air and micellar molybdovanadophosphoric polyoxometalates under room condition by Shun Zhao; Xiaohong Wang; Mingxin Huo (pp. 127-134).
Micellar molybdovanadophosphoric polyoxometalate (POM) catalysts [(C nH2 n+1)N(CH3)3]3+ xPV xMo12− xO40 ( x=1, 2, 3; n=8, 12, 14, 16, 18) were prepared and used for catalytic wet air oxidation (CWAO) of phenol. X-ray photoelectron spectrum (XPS), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) were used to characterize the resulting samples. The best catalytic activity was obtained over (C16TA)6PV3Mo9O40, which showed 95.3% degradation efficiency, 98.5% COD removal and 93.0% TOC reduction with air under room condition toward complete degradation product CO2 within 90min. The leaching test showed that the POM micellar catalysts have an excellent stability and can be used as heterogeneous catalysts for about six times.
Keywords: Catalytic wet air oxidation; Polyoxometalate; Micellar catalysis; Degradation of phenol
Effects of electrolyte on the electrocatalytic activities of RuO2/Ti and Sb–SnO2/Ti anodes for water treatment by Soonhyun Kim; Sung Kyu Choi; Bok Young Yoon; Sang Kyoo Lim; Hyunwoong Park (pp. 135-141).
The study of high efficiency electrochemical water treatment systems is of great importance in contributing to a sustainable water supply. In this study, we prepared RuO2/Ti and Sb–SnO2/Ti electrodes and investigated their electrocatalytic activities for the oxidation of water and three model substrates (methylene blue, acid orange 7, and 4-chlorophenol) in two supporting electrolytes: NaCl vs. Na2SO4. Irrespective of the electrolyte, the particulate RuO2/Ti anode was found to oxidize water at ca. 0.8V lower potential ranges with significantly higher currents than the cracked-mud type of Sb–SnO2/Ti, indicating that the latter is more suitable for substrate oxidation. In the system of Sb–SnO2/Ti anode–stainless steel cathode couple, the degradation rates of all the substrates were highly enhanced in NaCl, whereas their complete oxidation (i.e., CO2 evolution) occurred more markedly in Na2SO4. Additional detailed experimental results indicated that the relative superiority of Sb–SnO2/Ti over RuO2/Ti for treating the model substrates depended greatly on the employed supporting electrolytes, and that the superiority particularly vanished when NaCl was used as the electrolyte. Using this electrolyte, active chlorine species-mediated indirect reactions seemed to occur at both anodes, while in the Na2SO4 electrolyte, the surface-specific reaction occurred. Finally, surface analysis and diverse electrochemical experiments were performed to compare both anodes in a more quantitative way and to investigate the effect of the electrolytes on the electrocatalytic activities of the anodes.
Keywords: RuO; 2; /Ti; Sb–SnO; 2; /Ti; NaCl; Na; 2; SO; 4; Water treatment
Mesoporous supported cobalt catalysts for enhanced hydrogen production during cellulose decomposition by Ming Zhao; Nicholas H. Florin; Andrew T. Harris (pp. 142-150).
Two groups of cobalt (Co) catalysts, supported on SBA-15 and MCM-41, respectively, were prepared by incipient wetness impregnation and tested for their influence on the thermal decomposition of acetyl cellulose. γ-Al2O3 supported Co catalysts were investigated as a comparison. A thermogravimetric analyser coupled with a mass spectrometer (TG-MS) was used to examine the influence of catalyst loading, support material and the presence of additional water vapour on H2 production and selectivity. Normalization of the raw MS data enabled semi-quantitative analysis of the product gas distribution, which facilitated reliable comparison between different experimental conditions. Catalysts were characterized by physisorption, chemisorption, TGA, XRD, SEM and TEM. SBA-15 and MCM-41 supported catalysts significantly elevated the yield and selectivity of H2, under dry Ar and with the injection of additional water vapour, when compared with the γ-Al2O3 support. 15wt.%Co/SBA-15 and 10wt.%Co/MCM-41 were identified as the most active catalysts from the two groups with indicative yields of 202 and 303mlH2/g cellulose, respectively. The 10wt.%Co/MCM-41 catalyst gave with the highest H2 selectivity reaching 21.7% of the dry product gas.
Keywords: Hydrogen; H; 2; production; Cellulose; Mesoporous; Supported Co catalyst; TG-MS
The remarkable effect of vanadium doping on the adsorption and catalytic activity of magnetite in the decolorization of methylene blue by Xiaoliang Liang; Sanyuan Zhu; Yuanhong Zhong; Jianxi Zhu; Peng Yuan; Hongping He; Jing Zhang (pp. 151-159).
In this study, a series of vanadium doped magnetites (Fe3− xV xO4, 0≤ x≤0.34) was synthesized by a precipitation–oxidation route and show good adsorption and catalytic activities. Powder X-ray diffraction (PXRD) and Mössbauer spectra analysis of Fe3− xV xO4 confirm the formation of magnetite, while Fourier transform infrared spectroscopy (FTIR), Mössbauer spectroscopy and X-ray absorption fine structure (XAFS) spectra indicate vanadium preferentially occupies the octahedral site. The valency of vanadium in magnetite is mainly +3, as inferred from FTIR and XAFS. Thermal analysis (TG–DSC) shows that the incorporation of vanadium in magnetite structure leads to an increase of superficial hydroxyl groups and a decrease in temperature of phase transformation maghemite–hematite. Vanadium incorporation can promote the adsorption of methylene blue (MB) on Fe3− xV xO4 and degradation of the dye with high degree of decolorization. The improvement of adsorption activity may be related to the increase of superficial hydroxyl. The high catalytic activity is related to the improvement of adsorption activity, the intensification of H2O2 decomposition by vanadium on the magnetite surface to produceOH and the improvement of electron transfer by vanadium to produce a more efficient regeneration of the Fenton active specie Fe2+.
Keywords: Vanadium doped magnetite; Synthesization; Characterization; Adsorption; Degradation
The integration of ozonation catalyzed with MgO nanocrystals and the biodegradation for the removal of phenol from saline wastewater by Gholamreza Moussavi; Ali khavanin; Rahime Alizadeh (pp. 160-167).
Efficient treatment of saline wastewaters, particularly those containing inhibitory and toxic compounds, has been a challenge in recent years. This study proposed and investigated an efficient option for treating such streams. An MgO nanocrystal mesoporous powder was prepared from natural magnesite, and its potential to serve as a catalyst for degradation and chemical oxygen demand (COD) removal of phenol from saline wastewater was evaluated. The influence of several parameters including pH, dose of MgO nanocrystals, and NaCl concentration was investigated on the catalytic ozonation process (COP) of phenol in saline wastewater. The concentration of NaCl had no adverse influences on the phenol degradation. The results indicated that 96% of the phenol and 70% of the COD were removed in the COP (initial phenol concentration was 1100mg/L and initial COD was 2500mg/L) under optimum experimental conditions of pH 7 and a 4g/L catalyst dose after an 80min reaction time. A synergistic influence of about 39% was observed for phenol degradation in the COP. The effluent from the COP obtained from the aforementioned conditions was efficiently post-treated in a batch biological reactor, such that after 10h of aeration, the COD was reduced to around 20mg/L. In contrast, it took 50h for reduction of COD to below 100mg/L when adding raw phenol wastewater into the bioreactor. Therefore, the prepared powder was found to be an efficient and promising catalyst for ozonation, and coupling the developed COP with a biological process might be an attractive treatment option for saline wastewaters containing high concentrations of toxic compounds.
Keywords: Saline wastewater; Phenol; Advanced oxidation process; Catalytic ozonation; Biological process
Photocatalysis with nanostructured zinc oxide thin films: The relationship between morphology and photocatalytic activity under oxygen limited and oxygen rich conditions and evidence for a Mars Van Krevelen mechanism by Arshid M. Ali; Emma A.C. Emanuelsson; Darrell A. Patterson (pp. 168-181).
The aim of this study was to evaluate the effectiveness of using a range of innovative nanostructured high surface area zinc oxide (ZnO) thin films as photocatalysts, and thereafter to systematically relate initial and reacted surface morphology and irradiated surface area to photocatalytic activity under both limited and rich oxygen conditions.The thin films were produced using an innovative combination of magnetron sputtered surfaces and hydrothermal solution deposition that allows the morphology, porosity and thickness to be controlled by varying the composition and processing conditions. Methylene Blue (MB) was chosen as the model compound and the reaction was performed with ultra violet light (UV) at 254nm. The thin film morphology and surface area before and after reaction was determined by scanning electron microscopy (SEM). The photocatalytic activity (measured as the rate and extent of MB degradation) was determined for seven different ZnO nanostructured thin films: three different ZnO hydrothermal solution depositions on bare glass slides (S1-CG, S2-CG and S3-CG films), the same three ZnO hydrothermal solution depositions but on glass slides coated with a magnetron sputtered ZnO film (S1-MS, S2-MS and S3-MS films), and glass slides coated with just a magnetron sputtered ZnO film (MS films).A clear relationship between surface morphology (and the related thin film preparation method) and photocatalytic activity was observed for ZnO thin film supported catalysts: the tallest, most aligned structure had the highest photocatalytic activity, whilst the smallest, least aligned structure had the lowest photocatalytic activity. Thus, MB degradation rate was the fastest for the 1μm thick ZnO thin film with a uniform arrayed structure from the S2-MS deposition technique. The degradation rates of the ZnO thin films were comparable to commercially available ZnO powder on a surface area basis. Photocatalytic degradation of MB under oxygen rich conditions increased for all other films except one film (S1-CG). This was most effective for thin film structure S2-MS, whose reaction rate was increased by 15%. Adding oxygen made the films more stable: in oxygen limited conditions, SEM and atomic absorption spectroscopy indicated zinc leaching had occurred. However, with additional oxygen the zinc leaching was minimised under the same reaction conditions. It is thought that this additional oxygen is either minimising the release of or replacing lost ZnO lattice oxygens, indicating that this ZnO photocatalytic oxidation could be occurring via a Mars Van Krevelen type redox mechanism.
Keywords: Zinc oxide; Nanostructured thin film; Photocatalyst; Methylene Blue; Magnetron sputtered; Mars Van Krevelen
Effective visible light-active boron and carbon modified TiO2 photocatalyst for degradation of organic pollutant by Yongmei Wu; Mingyang Xing; Jinlong Zhang; Feng Chen (pp. 182-189).
A visible light-active TiO2 photocatalyst modified by boron and carbon was synthesized by sol–gel followed solvothermal process. The resulting photocatalyst was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV–vis absorption spectroscopy, and electron paramagnetic resonance (EPR). It was found that the boron and carbon modified TiO2 showed obvious absorption in the range 400–500nm. XPS results suggested boron species entered into interstitial site of TiO2 matrix and formed the B–O–Ti bond, while carbon species were in the form of carbonates species. EPR results showed the existence of oxygen vacancy in carbon and boron modified TiO2. This may result in the sensitivity of the as-synthesized photocatalyst to visible light. The resulting boron and carbon modified TiO2 exhibited significantly higher photocatalytic activity than carbon modified TiO2 and undoped anatase TiO2 on the degradation of Acid Orange 7 (AO7) in aqueous solution under visible light irradiation. The presence of carbon originating from organic precursor has great influence on the surface properties of B-doped TiO2.
Keywords: C and B modification; Titanium dioxide; Visible light photocatalytic activity; Photocatalyst
Degradation of VOC gases in liquid phase by photocatalysis at the bubble interface by Kazuhiko Sekiguchi; Wakana Morinaga; Kazuhiko Sakamoto; Hajime Tamura; Fumio Yasui; Mohammad Mehrjouei; Siegfried Müller; Detlev Möller (pp. 190-197).
Photocatalytic reactions in the gas phase have a number of disadvantages including the adverse effects of relative humidity, the emission of decomposition intermediates at the reactor exit and the deactivation of the photocatalyst surface by decomposition intermediates. In this study, these disadvantages can be overcome using a novel photocatalytic reaction system. Volatile organic compound (VOC) gases were decomposed at the bubble interface in a TiO2 suspension by using TiO2 photocatalysis in the heterogeneous liquid-bubble (LB) phase since the intermediates dissolve into water and then are continuously decomposed regardless of humidity. Toluene, p-xylene, styrene and formaldehyde were chosen as model VOC gases to investigate photocatalytic reactivity in the LB phase. The removal ratio of VOC gases in the LB phase was equal to or greater than that in the gas phase, although the reactivity in the LB phase depended on the reaction rate of OH radicals and the hydrophobicity of the VOC gases. The reaction in the LB phase also depended on the wavelength and intensity of UV light. Specifically, the removal and mineralization ratios were improved by using shorter wavelengths of UV irradiation. Finally, as a trial experiment, we applied the microbubble technique to this system. When VOC gases were introduced into the system as microbubbles, VOC gas was effectively removed and high removal ratios were obtained regardless of the wavelength and intensity UV light.
Keywords: Volatile organic compound; Titanium dioxide; Photocatalysis; Heterogeneous liquid-bubble phase; Microbubble
High photocatalytic activity of ZnO and ZnO:Al nanostructured films deposited by spray pyrolysis by Monserrat Bizarro (pp. 198-203).
Zinc oxide and aluminum doped zinc oxide films were produced using the spray pyrolysis technique. The substrate temperature and the solution flow rate were varied to optimize the surface morphology of the films. Different concentrations of aluminum were added to the precursor solution in Al/Zn=0.05, 0.10, 0.25, and 0.50 to study the effect on the photocatalytic activity of ZnO. The films were characterized by profilometry, scanning electron microscopy (SEM), X-ray diffraction (XRD) and the photocatalytic activity was tested by the decomposition of methyl orange dye under UV illumination. The addition of aluminum did not change the ZnO crystalline structure, but changed the surface morphology and increased the photocatalytic activity of ZnO films reducing the time taken to degrade an 80% of the dye from 4 to only 1.25h.
Keywords: Zinc oxide; Photocatalysis; Spray pyrolysis
Study on the co-catalytic effect of titanate nanotubes on Pt-based catalysts in direct alcohol fuel cells by Pu Xiao; Huanqiao Song; Xinping Qiu; Wentao Zhu; Liquan Chen; Ulrich Stimming; Petra Bele (pp. 204-212).
In this paper, titanate nanotubes were synthesized and their co-catalytic effects in direct alcohol fuel cells (DAFC) were studied by physically mixing them with commercial Pt/C catalyst. BET results showed the surface area increased significantly when a big amount of nanotubes were formed. Infrared (IR) spectra and thermal gravity analysis (TGA) showed that less water existed in nanoparticles and nanotubes when the raw materials were calcinated at higher temperature. Electrochemical measurements showed that titanate nanotubes which contained more structural water had a better catalytic performance. Proton conductivity of titanate nanotubes was also considered to be an important factor for enhancing oxidation reactivity and was studied by impedance tests.
Keywords: TiO; 2; Titanate nanotube; Direct ethanol fuel cell; Anode catalyst; Co-catalytic effect
Homogeneous photocatalytic mineralization of acetic acid in an aqueous solution of iron ion by Masachiyo Imanishi; Keiji Hashimoto; Hiroshi Kominami (pp. 213-219).
Homogeneous photocatalytic mineralization (decomposition to carbon dioxide (CO2)) of acetic acid in dilute aqueous solutions of various metal ions was examined at room temperature under irradiation of UV light in the presence of oxygen (O2). Iron ion exhibited a much higher level of activity among the metal ions studied for mineralization of acetic acid. The rate of CO2 formation was proportional to first-order partial pressure of O2 and concentrations of iron ion and acetic acid, whereas the rate was in inverse proportional to first-order proton concentration. The rate equation, r= kPO2 [[FeIII(H2O)6]3+] [AcOH] [H+]−1, in overall photocatalytic mineralization of acetic acid was derived from these results. The mechanism of the photocatalytic mineralization of acetic acid in an aqueous solution of ion was proposed.
Keywords: Photocatalyst; Mineralization; Acetic acid; Iron ion
Highly dispersed Pt nanoparticle catalyst prepared by atomic layer deposition by Jianhua Li; Xinhua Liang; David M. King; Ying-Bing Jiang; Alan W. Weimer (pp. 220-226).
Nanoparticulate platinum has been well dispersed onto large quantities of micron-sized mesoporous silica gel using atomic layer deposition in a fluidized bed reactor (i.e. ALD-FBR). Transmission electron microscopy (TEM) cross-sectional investigations showed that the Pt nanoparticles were homogeneously distributed throughout primary 30–75μm silica gel particles, including the inner surfaces comprising 5–7nm pores. The Pt catalyst loading level was tightly controlled by the number of coating cycles. An extremely low Pt loading with 3.1×10−6mg Pt/cm2 (0.10atom/nm2), 4.8×10−6mg Pt/cm2 (0.15atom/nm2) and 2.9×10−5mg Pt/cm2 (0.91atom/nm2) was prepared with 3, 5 and 10 coating cycles, respectively. The average Pt particle size is approximately 1.2nm for 3 cycles. For 5 and 10 coating cycles, the Pt particle size is measured to be 1.9nm and 2.3nm, respectively. The sample with a 3.1×10−6mg Pt/cm2 loading exhibits the highest metal dispersion of 90%. Thermal stability studies indicated an initial sintering of the Pt particles during the first 4h of heat treatment at 450°C in an air environment. After that, there was no noticeable change of the particle size during the following heat treatment process. Carbon monoxide oxidation demonstrated nearly 100% conversion of CO to CO2 over 20mg of 4.8×10−6mg Pt/cm2 loaded silica gel particles at 180°C for 100sccm flow rate of 1% CO in argon.
Keywords: Silica gel; Mesoporous; Catalyst; Platinum; Atomic layer deposition
Heterogeneous catalytic wet peroxide oxidation of paraquat in the presence of modified activated carbon by Anissa Dhaouadi; Nafaâ Adhoum (pp. 227-235).
The catalytic wet peroxide oxidation (CWPO) method was applied to the degradation of paraquat, a widely used and highly toxic herbicide. The effect of ammonia pre-treatment and iron impregnation on Fenton-driven reaction efficiency was first investigated. Iron amendment and acidic oxygen-surface groups were found to promote the catalytic activity towards paraquat degradation. The effects of three significant operational parameters (hydrogen peroxide concentration, catalyst dosage and temperature) on catalytic performance of the most promising catalyst (AC-Fe) were then investigated. The best degradation yield (71.4% of COD abatement in a 20mgL−1 solution) was obtained with 12.5mmolL−1 H2O2, 1gL−1 catalyst dosage and T=70°C, although ambient temperature could be preferred for application convenience.A nearly complete degradation of paraquat and its intermediates (∼92% of COD removal) was achieved after 12h treatment, when proceeding at ambient temperature via regular sequential additions of the spent amount of H2O2 in the presence of optimal catalyst dosage. A reasonably good stability of the catalyst was demonstrated during consecutive re-use of the same recovered sample, in long-term CWPO runs. Only a slight decrease of catalytic performance (from 92% to 85% of COD removal) was observed after five consecutive cycles, probably due to high stability of the supported iron species.Time evolutions of aromatic intermediates and short-chain carboxylic acids were recorded using HPLC analysis, and clearly indicated that CWPO is capable of effectively degrading the paraquat herbicide.
Keywords: Advanced oxidation process; Activated carbon; Catalytic wet peroxide oxidation; Hydroxyl radical; Mineralization; Paraquat
New insights into the promoting effect of H2O on a model Pt/Ba/Al2O3 NSR catalyst by Jin-Yong Luo; William S. Epling (pp. 236-247).
The effects of H2O on the performance of a model Pt/Ba/Al2O3 catalyst and regeneration of the catalyst surface were investigated, both in the absence and presence of CO2. In the absence of CO2, an unexpected promotional effect of H2O was observed at low temperature. For example, in the presence of H2O, 90% NO X conversion was obtained at 150°C, which is the same as that at 350°C under otherwise identical conditions. The results demonstrate that regeneration, the rate-limiting step at low temperature, occurs through hydrogen spillover to the nitrates, and not through reverse NO X species migration to the Pt sites, and the presence of H2O greatly promotes the hydrogen spillover rate by providing and stabilizing surface hydroxyl groups. The promotional effect of H2O gradually decreases with increasing temperature, and shows no positive effect above 350°C. In the presence of CO2, however, the presence of H2O always results in improved performance in the entire temperature range. Besides enhanced hydrogen spillover, another contribution of H2O when CO2 is present, is to weaken the detrimental effect of CO. CO is formed via the reverse water–gas shift reaction and poisons Pt sites as well as forms barium isocyanates. The H2O decreases the amount of CO formed as well as hydrolyzes the –NCO species.
Keywords: Hydrogen spillover; Isocyanates; Automotive catalysis; NO; X; trap; NO; X; reduction
Hydrogenolysis of glycerol to propanediols over a Pt/ASA catalyst: The role of acid and metal sites on product selectivity and the reaction mechanism by I. Gandarias; P.L. Arias; J. Requies; M.B. Güemez; J.L.G. Fierro (pp. 248-256).
Pt supported on amorphous silico alumina (Pt/ASA) was studied as a catalyst for glycerol hydrogenolysis (dehydration+hydrogenation) to 1,2-propanediol under mild operation conditions (493K and 45bar H2 pressure). Glycerol hydrogenolysis also took place in experiments performed under N2 pressure due to hydrogen available from glycerol aqueous phase reforming. As both acid and metallic sites are involved in this process a study including activity tests and different characterization techniques (TPR and FTIR of adsorbed pyridine, NH3-TPD, XPS and TGA) were applied to this catalytic system (ASA support and Pt/ASA catalyst) in order to get a deeper understanding about their interactions.
Keywords: Glycerol; Hydrogenolysis; Propanediol; Pt/ASA; Hydrogen spillover; Solid acid
SBA-15 type materials as support of catalysts based on ruthenium sulfide for sulfur removal by A. Romero-Pérez; A. Infantes-Molina; E. Rodríguez-Castellón; A. Jiménez-López (pp. 257-268).
In the hydrodesulfuration (HDS) of dibenzothiophene (DBT) performed on catalysts derived from SBA-15-supported ruthenium sulfide systems, the roles of the support and the sulfiding temperature were studied. In this sense, three ruthenium sulfided catalysts supported on SBA-15 type materials have been prepared. The three employed supports were: a pure mesoporous silica SBA-15 (Si-SBA), that doped with zirconium (Zr-SBA) and that doped with aluminium (Al-SBA). The supports, precursor, sulfided and spent catalysts were characterized by X-ray diffraction (XRD), N2 adsorption–desorption isotherms at −196°C, NH3-TPD, XPS analysis and H2-TPRS. The catalytic properties of these materials in the hydrodesulfurization (HDS) of dibenzotiophene (DBT) were tested between 260 and 360°C under a hydrogen pressure of 3.0MPa. The catalytic activity increased when catalysts were sulfided at 500°C because of the formation of a greater amount of RuS2 having pyrite structure. Moreover, catalysts supported on Si-SBA and Zr-SBA turned out to be more active than that supported on Al-SBA due to a higher dispersion of the active phase, with conversions close to 100% at a reaction temperature of 360°C.
Keywords: Mesoporous SBA-15; Ruthenium sulphide; Dibenzothiophene; HDS
CsF and alumina: A mixed homogeneous–heterogeneous catalytic system for the transesterification of sunflower oil with methanol by J. Ni; D. Rooney; F.C. Meunier (pp. 269-275).
The activity and nature (i.e. heterogeneous and/or homogeneous) of catalysts based on CsF supported on α-Al2O3 were investigated for the transesterification of vegetable oil with methanol. The effect of the activation temperature, CsF loading and the reusability in a recirculating reactor were first studied. CsF/α-Al2O3 exhibited the highest activity for a CsF loading of 0.6mmol/g and when activated at 120°C. An important aspect of this study is the effect of CsF leaching into the reaction mixture, which is attributed to the high solubility of CsF in methanol, leading to a complete loss of activity after one run. It was identified that the activity of the catalyst resulted from a synergy between alumina and dissolved CsF, the presence of both compounds being absolutely necessary to observe any conversion. The use of an alumina with a higher surface area resulted in a far greater reaction rate, showing that the concentration of surface site on the oxide (probably surface hydroxyl) was rate-limiting in the case of the experiments using the low surface area α-Al2O3. This work emphasizes that combined homogeneous–heterogeneous catalytic systems made from the blending of the respective catalysts can be used to obtain high conversion of vegetable oil to biodiesel. Despite the homogeneous/heterogeneous dual character, such a catalytic system may prove valuable in developing a simple and cost-effective continuous catalytic process for biodiesel production.
Keywords: Biodiesel; Transesterification; Caesium; Fluoride; Alumina; Catalyst; Leaching
Catalytic wet air oxidation of N,N-dimethylformamide aqueous solutions: Deactivation of TiO2 and ZrO2-supported noble metal catalysts by Nicolas Grosjean; Claude Descorme; Michèle Besson (pp. 276-283).
N,N-dimethylformamide (DMF) is largely used as versatile solvent in various processes. It is thus present in large quantities in many industrial effluents. Oxidation of aqueous solutions of DMF with air was conducted at 180–230°C under 50–70bar total pressure in a batch reactor, in the absence or in the presence of heterogeneous noble metal catalysts (platinum, palladium, and ruthenium) supported on TiO2 or ZrO2. Under the examined reaction conditions, DMF decomposition and oxidation produced dimethylamine (DMA), methylamine (MA), and ammonium as the major N-containing products. Formic acid was also intermediately formed from the scission of the C–N bond. Nitrites and nitrates were only present in very low amounts. The addition of a catalyst accelerated the initial rates of DMF and TOC (total organic carbon) conversions, but the selectivity to N2 was low. The production of DMA and MA was demonstrated to be very much detrimental to the chemical stability of these catalysts. A dramatic leaching of the noble metals occurred because of the complexation with the free lone pair electrons on the nitrogen atom of these amines.
Keywords: Catalytic wet air oxidation; Dimethylformamide (DMF); Dimethylamine; Methylamine; Complexation; Leaching; Supported platinum and ruthenium catalysts
Influence of textural parameters on the catalytic behavior for CO oxidation over ordered mesoporous Co3O4 by Shijiao Sun; Qiuming Gao; Huanlei Wang; Jingkang Zhu; Hongliang Guo (pp. 284-291).
Ordered mesoporous Co3O4 has been synthesized by nanocasting from three-dimensional cubic KIT-6 template. The cobalt precursor is introduced into the silica pores by the “bi-solvent” method. The structure and textural characteristics are investigated by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, nitrogen sorption at 77K. By changing the hydrothermal temperature of the KIT-6 template, two kinds of Co3O4 replicas with different mesostructured symmetries are obtained. Mesoporous Co3O4 oxides prepared from KIT-6 aged at low temperature have uncoupled sub-frameworks while mesoporous Co3O4 oxides prepared from KIT-6 aged at high temperature possess coupled sub-frameworks. CO oxidation is carried out as a model reaction to evaluate the catalytic activity. Co3O4 replicas with uncoupled sub-frameworks which possess higher surface area and more open pore system exhibit better performance than Co3O4 replicas with coupled sub-frameworks. The light-off temperature of CO oxidation reaches as low as 68°C with a space velocity of120,000mLh−1gcat−1 over the uncoupled Co3O4 replica. Calcination temperature of the cobalt precursor only has negligible or slight impact on the catalytic activity.
Keywords: Nanocasting; KIT-6 silica; Mesoporous Co; 3; O; 4; CO oxidation
Evaluation of operating parameters involved in solar photo-Fenton treatment of wastewater: Interdependence of initial pollutant concentration, temperature and iron concentration by A. Zapata; I. Oller; L. Rizzo; S. Hilgert; M.I. Maldonado; J.A. Sánchez-Pérez; S. Malato (pp. 292-298).
A mixture of five commercial pesticides (Vydate®, Metomur®, Couraze®, Ditimur-40® and Scala®) commonly used in intensive agriculture has been selected as an example of highly toxic, non-biodegradable wastewater to be treated by solar Photo-Fenton. The effect of the total concentration of organics as dissolved organic carbon (100–500mg/L), operating temperature (25–50°C), dissolved iron concentration and their relationship to different process efficiency parameters (mineralization rate, hydrogen peroxide consumption and treatment time) were evaluated. Experiments were carried out under sunlight in a pilot plant. It consists of four compound parabolic collectors (CPCs) and a total volume of 75L. From the results of the study it can be concluded that solar plants should be designed for operating at temperatures below 45°C to avoid significant loss of iron. H2O2 should be carefully dosed during the photo-Fenton treatment to avoid its continued excess and inefficient use.
Keywords: Advanced oxidation processes; Hydrogen peroxide; Pesticides; Solar photocatalysis
Selective production of olefins from bioethanol on HZSM-5 zeolite catalysts treated with NaOH by Ana G. Gayubo; Ainhoa Alonso; Beatriz Valle; Andrés. T. Aguayo; Javier Bilbao (pp. 299-306).
The behaviour of a HZSM-5 zeolite (SiO2/Al2O3=30) in several time treatments with 0.2M NaOH solution has been studied for the transformation of bioethanol into hydrocarbons in an isothermal fixed bed reactor and in the 225–425°C range. A short treatment (for 10min) decreases the acid strength of the sites from 135kJ(mol of NH3)−1 to 125kJ(mol of NH3)−1, which is effective for increasing the selectivity of propene and butenes and for attenuating the deactivation by coke. This catalyst allows obtaining a yield of 30wt% of propene+butanes at 400°C with 136(g of catalyst)h(gethanol)−1 and a feed of ethanol/water with 5wt% water. The operation in reaction–regeneration cycles can be carried out continuously without irreversible deactivation of the catalyst, which means not exceeding extreme conditions in the reaction step: 375°C and 400°C for water contents in the feed of 75wt% and 5wt%, respectively. More severe treatments decrease the hydrothermal stability of the zeolite.
Keywords: Biorefinery; Bio-ethanol; HZSM-5 zeolite; Olefins; Deactivation; Hydrothermal stability