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Applied Catalysis A, General (v.281, #1-2)
Metal foam supported Pt catalysts for the selective oxidation of CO in hydrogen by Amornmart Sirijaruphan; James G. Goodwin Jr.; Richard W. Rice; Dongguang Wei; Kenneth R. Butcher; George W. Roberts; James J. Spivey (pp. 1-9).
Pt has been found to be an active catalyst for the selective oxidation of CO in H2 for fuel cell applications. Washcoated metal foam structures supporting such a catalyst offer interesting possibilities for commercial application due to low pressure drop, excellent flow characteristics through the foam, and excellent heat transfer properties. This study reports on the effects of using γ-Al2O3-washcoated metal foams (FeCrAlY) as structural supports for 5wt.% Pt catalysts. Foam-based catalysts with different number of pores per inch (30–50) were prepared, characterized, investigated for their activities and surface kinetic parameters for the selective oxidation of CO in H2, and compared with a powdered γ-Al2O3-supported Pt catalyst of the same composition. The presence of Fe impurities in the washcoat, probably from the metal foam structure, was found to have a significant impact on the properties of the foam-based catalysts. The foam-based Pt catalysts exhibited reaction properties similar to those of Fe-promoted Pt/γ-Al2O3. Compared to the unpromoted powdered Pt catalyst, the metal foam supported Pt catalysts gave lower H2 and CO chemisorption, higher CO2 selectivity in selective oxidation, and higher pseudo-first-order rate constants based on isotopic tracing—all of which are characteristics of Fe promotion of Pt. Isotopic tracing results show that the number of active sites contributing to the reaction was the same for both types of catalysts. Although site blockage was the main cause for the initial deactivation of the powdered Pt catalyst, both a decrease in intrinsic activity and site blockage were the cause of a similar initial deactivation for the foam-based Pt catalysts. There was also a shift downward in the activity distribution determined by ITKA during the initial deactivation of the foam-based catalysts. These latter two effects are similar to what is seen when Pt/γ-Al2O3 is promoted with Fe. The results indicate that active Pt catalysts for the selective oxidation of CO in H2 can be prepared using washcoated metal foam structures.
Keywords: Selective CO oxidation; Metal foam supports; Pt catalyst; Isotopic tracing; SSITKA
Effect of metal foam supports on the selective oxidation of CO on Fe-promoted Pt/γ-Al2O3 by Amornmart Sirijaruphan; James G. Goodwin Jr.; Richard W. Rice; Dongguang Wei; Kenneth R. Butcher; George W. Roberts; James J. Spivey (pp. 11-18).
Fe promotion is known to significantly increase the activity of Pt catalysts for the selective oxidation of CO in H2 for fuel cell applications. Use of metal foams as catalyst structural supports in catalytic reactors can improve reactor characteristics by lowering the pressure drop and increasing heat transfer. In a previous study on metal foam-supported Pt catalysts, it was shown that Cr and Fe impurities from the metal foam were present in significant quantities in the washcoat, improving the catalytic properties of the catalysts. This study addressed the effect that these Cr and Fe impurities may have on metal foam supported PtFe (5wt.% Pt, 0.5wt.% Fe based on the loading of alumina washcoat) catalysts. Foam-based PtFe catalysts with different numbers of pores-per-inch (30–50) and percentage relative metal densities were characterized, investigated for their activities and surface kinetic parameters for the selective oxidation of CO in H2, and compared with a powdered γ-Al2O3-supported PtFe catalyst (also 5wt.% Pt and 0.5wt.% Fe) and foam-based Pt catalysts. The foam-based PtFe catalysts exhibited reaction properties similar to those of the powdered PtFe/γ-Al2O3 catalyst. The intrinsic site activities of all foam-based PtFe catalysts determined using isotopic transient kinetic analysis (ITKA) were approximately the same and seemed to be characteristic of Fe-promoted Pt/γ-Al2O3. Thus, the presence of Cr and Fe impurities in the washcoat from the metal foam does not seem to have a major impact on reaction on Fe-promoted Pt even though it appears to significantly affect both H2 and CO chemisorption at 37°C. This was not the case for the comparison previously of foam-based and powdered Pt/γ-Al2O3 catalysts. These foam-based PtFe catalysts exhibited only a slight change with time-on-stream of CO oxidation rate and % CO2 selectivity and did not show the rapid initial deactivation to steady state, typically seen for both γ-Al2O3-supported Pt and PtFe catalysts. This initial stable activity and selectivity is preferable for commercial use.
Keywords: CO oxidation; Selective oxidation of CO; Metal foam supports; PtFe; Isotopic transient kinetic analysis; SSITKA; Surface kinetics
Autothermal reforming of methane over Pt/ZrO2/Al2O3 catalysts by Mariana M.V.M. Souza; Martin Schmal (pp. 19-24).
Autothermal reforming of methane, combining steam reforming and partial oxidation was carried out with Pt/Al2O3, Pt/ZrO2 and Pt/ZrO2/Al2O3 catalysts, in the temperature range of 400–900°C. The Pt/ZrO2/Al2O3 catalyst was found to be the most active and stable at 800°C due to the higher resistance to coke formation. The reaction occurs in two simultaneous stages: total combustion of methane and reforming of the unconverted methane with steam and CO2, with the O2 conversion of 100% starting from 450°C. The addition of O2 to the feed increases methane conversion and the catalyst stability, decreasing the H2 and CO yields due to the enhancement of methane combustion. By manipulating the O2/CH4 ratio of the feed it is possible to achieve the H2/CO ratio that is optimal to the GTL processes.
Keywords: Methane; Steam reforming; Partial oxidation; Autothermal reforming; Pt/ZrO; 2; /Al; 2; O; 3; catalysts
Effect of the preparation of Re/γ-Al2O3 catalysts on the HDS and HDN of gas oil by J. Ojeda; N. Escalona; J.L.G. Fierro; A. López Agudo; F.J. Gil-Llambías (pp. 25-30).
The effects of Re content and catalyst preparation on the surface structure of two series of Re/γ-Al2O3 catalysts, prepared by one-step (Re( x)-I) and successive-step impregnation (Re( x)-II) methods, and their catalytic behaviour in the HDS and HDN of gas oil were studied. Characterization data by XRD, Raman spectroscopy and XPS revealed that the structure of Re on Re( x)-I and Re( x)-II catalysts in their oxidic state was very similar; Re in oxided state was present as two slightly different isolated ReO4− monomeric species coordinated to the alumina surface in all the range of Re content studied, but the Re coverage was slightly lower on Re( x)-I than on Re( x)-II catalysts. Upon sulfidation, the dispersion of Re decreased significantly and left to be monomolecularly dispersed above 0.5Reat.nm−2, especially for the Re( x)-I catalysts, causing therefore that the HDS and HDN activities of the two catalyst series reached maximum values at a Re content of about 0.5at.nm−2 and then decreased. The higher activity for both HDS and HDN reactions observed for the Re( x)-II catalysts are consistent with their higher dispersion of the Re sulfided phase. Both Re( x)-I and Re( x)-II catalysts showed exceptionally high HDN/HDS selectivity values, which were slightly higher for the Re( x)-II catalysts due to their slightly higher concentration of acid sites in the oxidic state.
Keywords: Hydrodesulfurization (HDS); Hydrodenitrogenation (HDN); Supported Re catalysts; Re sulphide
Strontium as an efficient promoter for supported palladium hydrogenation catalysts by Unnikrishnan R. Pillai; Endalkachew Sahle-Demessie (pp. 31-38).
The effect of strontium promotion is studied for a series of supported palladium catalysts such as Pd/zeolite-β, Pd/Al2O3, Pd/SiO2, Pd/hydrotalcite and Pd/MgO. Strontium is found to be an effective promoter for enhancing the metal area, percentage dispersion of the metal and therefore the hydrogenation activity of the different supported palladium catalysts with varying acid/base properties. The effect of addition of Sr and Pd onto the support by simultaneous and sequential impregnation methods is studied besides the effect of Sr/Pd ratio. It is revealed that when sequential addition of Sr and Pd by impregnation is advantageous for alumina, silica, magnesia and hydrotalcite supported palladium catalysts, simultaneous impregnation of Sr and Pd is found to be more effective for zeolite-β supported catalyst. This may be attributed to the microporous nature of the zeolite support that could cause the migration of Sr to its micropores thereby making them non-available for the promotional effect if added first. Addition of strontium is also found to enhance the basicity of the supported palladium catalysts. TPR studies suggest a change in the metal environment upon Sr-promotion indicating an electronic effect responsible for the improvement in the hydrogen adsorption capacity and hydrogenation activity. The promotional effect of Sr on the supported palladium catalysts is explained to be both electronic and physical in nature.
Keywords: Supported palladium catalysts; Strontium promotion; Sequential and simultaneous impregnation; Phenol hydrogenation
Direct synthesis, characterization and catalytic performance of novel Ti-SBA-1 cubic mesoporous molecular sieves by Dong Ji; Rui Zhao; Gaomeng Lv; Guang Qian; Liang Yan; Jishuan Suo (pp. 39-45).
The 3d-cubic Pm3n Ti-incorporated SBA-1 mesoporous molecular sieves were directly synthesized under strongly acidic conditions and characterized by various techniques. XRD showed that the synthesized mesoporous materials had a well-ordered cubic structure. N2 adsorption/desorption measurements confirmed that the resultant samples had large mesopores (ca. 20Å) and high surface areas (>1000m2g−1). UV–vis and FT-IR results revealed that incorporated titanium species existed in a highly dispersed state and had tetrahedral coordination. SEM is used to determine the particle size and particle morphology of the synthesized materials. A catalytic test using epoxidation of styrene as a probe reaction proved that the framework Ti in the Ti-SBA-1 possessed relatively high activity and selectivity.
Keywords: Ti-SBA-1; Mesoporous molecular sieves; Synthesis; Characterization; Catalytic performance
Arenesulfonic acid functionalized mesoporous silica as a novel acid catalyst for the liquid phase Beckmann rearrangement of cyclohexanone oxime to É›-caprolactam by Xueguang Wang; Chin-Chang Chen; Shih-Yuan Chen; Yun Mou; Soofin Cheng (pp. 47-54).
Beckmann rearrangement of cyclohexanone oxime to ɛ-caprolactam was performed in liquid phase for the first time on arenesulfonic acid-functionalized SBA-15 (SBA-ar-SO3H) mesoporous silica with different loadings of the acid. The catalysts were prepared via co-condensation of 2-(4-chlorosulfonylphenyl)ethyltrimethoxysilane (CSPTMS) and tetraethyl orthosilicate (TEOS) in the presence of Pluronic 123 (EO20PO70EO20) and characterized by XRD, N2 adsorption–desorption, TGA, EA and acid–base titration method. The oxime conversion and selectivity to ɛ-caprolactam were found to increase with the loading of arene-SO3H groups. The influences of solvent and reaction temperature on the rearrangement of oxime in the liquid phase were examined. The oxime rearrangement and hydrolysis were proposed to be catalyzed on different active sites ofSO3H and SiOH, respectively. The catalytic activity of SBA-ar-SO3H was also compared with the activities of other solid acid catalysts such as propylenesulfonic acid-functionalized SBA-15, H-ZSM-5, H-mordernite, Al-MCM-41 and Al-SBA-15. The results revealed that SBA-ar-SO3H has higher catalytic activity and lactam selectivity.
Keywords: Beckmann rearrangement; Cyclohexanone oxime; É›; -Caprolactam; SBA-15; Arenesulfonic acid
Zeolite/sintered metal fibers composites as effective structured catalysts by Igor Yuranov; Albert Renken; Lioubov Kiwi-Minsker (pp. 55-60).
The catalytic filters of sintered metal fibers (SMF) coated by thin MFI-type zeolite (silicalite-1, ZSM-5) films have been synthesized and tested in the reactor with structured catalytic bed. The catalysts show multifunctional behavior, combining catalysis with heat exchange, mixing, and particulates removal. The reactors based on the zeolite/SMF composite elements have a three-level structure: (i) a micro-scale due to oriented submicron zeolite crystals; (ii) a meso-scale due to homogeneous porosity of metal fiber filters; (iii) a macro-scale due to the design characteristics of the catalyst packing. The catalytic bed of the FeZSM-5/SMFFecralloy was efficient and the one-step benzene hydroxylation to phenol with N2O at temperatures as low as 270°C without loosing N2O via decomposition to nitrogen and oxygen (selectivity close to 100%). The catalyst was effective in the N2O decomposition at temperatures 400–500°C.
Keywords: Structured catalysts; Multifunctional reactor; Zeolite coating; Sintered metal fibers
Partial oxidation of CH4 and C3H8 over hexaaluminate-type oxides by Ryuji Kikuchi; Yasuyuki Iwasa; Tatsuya Takeguchi; Koichi Eguchi (pp. 61-67).
Hexaaluminate catalysts based on BaM xAl12− xO19−α (M=Ru, Pd, Pt, Ni; x=0.25, 0.5, 1.0, 1.5) were prepared via the alkoxide method and investigated for partial oxidation of CH4 and C3H8. Ru- and Ni-hexaaluminate catalysts showed excellent activities for CH4 and C3H8 partial oxidation under a high space velocity of 120,000lkg−1h−1. Pd-hexaaluminate catalyst displayed catalytic activity comparable to the Ru catalyst only in a low temperature range, whereas Pt-hexaaluminate catalyst showed quite low activity for CH4 partial oxidation over the whole temperature range investigated. The catalytic activity of BaRuAl11O19− α depended weakly on the calcination temperature. We studied the dependence on the composition of BaRu xAl12− xO19− α. CH4 conversion was almost constant over the samples with x=0.25, 0.5, and 1.0, but the activity was significantly deteriorated in the case of x=1.5. On the other hand, the activity over the Pd catalysts increased consistently with the x-value and decreased in keeping with the calcination temperature. In the case of the Pd-hexaaluminate catalysts, the amount of carbon monoxide adsorbed on the exposed Pd decreased monotonically as the calcination temperature increased, indicating that most of the Pd species was not incorporated in the hexaaluminate lattice and that sintering of Pd resulted in deterioration of the catalytic activity. The Ru/Al ratio determined by EPMA for the Ru-substituted hexaaluminate catalyst was unchanged between the as-calcined and used catalysts, whereas the ratio of a Ru-supported hexaaluminate catalyst decreased significantly. These results indicate that the strong interaction between Ru and the base oxide in the Ru-substituted hexaaluminate could suppress evaporation of Ru during CH4 partial oxidation reaction.
Keywords: Partial oxidation; Methane; Propane; Hexaaluminate; Ni catalysts; Precious metal
Steam reforming of methanol over Cu/CeO2/ZrO2 catalysts by Hisayuki Oguchi; Toshiya Nishiguchi; Tomoaki Matsumoto; Hiroyoshi Kanai; Kazunori Utani; Yasuyuki Matsumura; Seiichiro Imamura (pp. 69-73).
Steam reforming of methanol was carried out over CuO/CeO2-based catalysts. The optimum amount of CuO in CuO/CeO2 was 80wt.%. The addition of ZrO2 had an accelerating effect; the best weight ratio of CuO/CeO2/ZrO2 was 8/1/1. Although CuO/CeO2 gradually lost its activity during the reaction, no deactivation was observed for CuO/ZrO2 or CuO/CeO2/ZrO2 during the reaction for 5h. X-ray diffraction analysis revealed that copper was present in the form of Cu2O during the reaction when combined with ZrO2, mainly as Cu metal with CeO2, and as a mixture of Cu metal plus trace amount of Cu2O with CeO2/ZrO2. TPR and XANES analyses also showed that all of Cu species were stabilized as Cu2O in the presence of ZrO2. The synergistic effect of ZrO2 was discussed.
Keywords: Steam reforming of methanol; H; 2; production; CuO/CeO; 2; /ZrO; 2
A combined thermodynamic/experimental study for the optimisation of hydrogen production by catalytic reforming of isooctane by L. Villegas; N. Guilhaume; H. Provendier; C. Daniel; F. Masset; C. Mirodatos (pp. 75-83).
The reforming of isooctane in the presence of both steam and oxygen (autothermal reforming, ATR) has been investigated over a Pt/ceria–zirconia catalyst. The aim of this study was to determine the gas feed composition corresponding to an optimum hydrogen production, by using thermodynamic calculations as well as experimental data. Thermodynamic calculations based on energy and component balances show that the ATR of isooctane should be the most efficient with an O/C ratio close to 1 and an H2O/C ratio around 2. The experimental study corroborates the calculations: at constant H2O introduction, increasing the O/C ratio in the feed improves isooctane conversion, but at the expense of the H2+CO selectivity. The optimum O/C ratio is obtained between 0.75 and 1. The steam-to-carbon ratio also has an important impact on hydrogen production, in this case not related to a strong improvement in the conversion of isooctane, but rather to the displacement of the WGS equilibrium. Under optimised feed gas composition and high space velocity (150000h−1), the reaction reaches the thermodynamic equilibrium at 730°C. The good stability of the catalytic activity under reaction conditions suggests that, although a sintering of both support and platinum was evidenced in the used catalyst, this modification probably takes place rapidly at the first exposure to high temperature and steam. There is no evidence for carbon poisoning of the catalyst when used under optimised feed composition.
Keywords: Hydrogen; Fuel cell; Catalytic reforming; Isooctane; Gasoline; Pt/Ce; 0.67; Zr; 0.33; O; 2
Catalytic activity of micro/mesoporous composites in toluene alkylation with propylene by Pavla Prokešová; Naděžda Žilková; Svetlana Mintova; Thomas Bein; Jiřà Čejka (pp. 85-91).
The gas phase alkylation of toluene with propylene was used to investigate the catalytic activity of pure zeolite Beta, pure mesoporous molecular sieve Al-MCM-41 and micro/mesoporous composites. The influence of the structural features and the concentration of acid sites of these catalysts on the toluene conversion and the selectivity to isopropyltoluenes (cymenes) was studied. Various characterization techniques, i.e., DLS, SEM, XRD, FT-IR, NMR, and nitrogen sorption measurements were applied for complete characterization of the catalysts. In addition, the concentrations of Brönsted and Lewis acid sites were determined based on the amount of adsorbed d3-acetonitrile using FT-IR spectroscopy. The catalytic activity in toluene alkylation with propylene was increased in the order: Al-MCM-41
Keywords: Micro/mesoporous composite; Nanocrystalline zeolite Beta; Toluene alkylation
Influence of gold and manganese as promoters on surface and catalytic performance of Fe2O3/Al2O3 system by Nagi R.E. Radwan; E.A. El-Sharkawy; A.M. Youssef (pp. 93-106).
The physicochemical, surface and catalytic properties of pure and doped Fe2O3/Al2O3 solid catalysts with Au and Mn2O3 calcined at 300, 500 and 700°C were investigated. The dopant concentration of Au was varied between 0.4 and 1.6mol%, while Mn2O3 concentration was varied between 1.0 and 8.0mol%. The techniques employed were DTA, XRD, TPR, EDX, nitrogen adsorption at −196°C, CO oxidation by O2 at 225–275°C and H2O2 decomposition in aqueous solution at 30–50°C.The results obtained revealed that the doping of Fe2O3/Al2O3 solids with different amounts of Au and Mn2O3 changed the degree of crystallinity of Al2O3 and Fe2O3 phases. The doping process led to a progressive increase in the specific surface area of the treated solid catalysts to an extent proportional to the amount of Au and Mn2O3 added. This process led also to a progressive increase in the catalytic activities of the investigated solid catalysts towards CO oxidation by O2 and H2O2 decomposition. The doping of solid catalysts with Au calcined at 300, 500 and 700°C exhibited catalytic activity in CO oxidation by O2 higher than those measured for solid catalysts doped with Mn2O3 calcined at the same temperatures. Opposite results have been observed in case of H2O2 decomposition. These findings indicate that the active sites taking part in CO oxidation by O2 are different from those involved in H2O2 decomposition.
Keywords: Fe; 2; O; 3; Al; 2; O; 3; Au; Mn; 2; O; 3; TPR; EDX; CO oxidation; H; 2; O; 2; decomposition
Catalytic ketonization over oxide catalysts by M. GliÅ„ski; W. SzymaÅ„ski; D. Å?omot (pp. 107-113).
The 20 wt.% MOx/Al2O3 catalysts, where M = Mn, Ce or Zr have been studied in ketonization of alkyl esters of heptanoic acid. A series of esters with the general formula C6H13COOR, where R = Me, Et, n-Pr, i-Pr, n-Bu, i-Bu, s-Bu and t-Bu, was used as substrates. At high conversions, manganese catalyst showed the highest selectivity. For heptanoates with primary and secondary alkyl groups the maximum yield of 7-tridecanone was observed in the 673–698 K temperature range. In the case of n-alkyl heptanoates the value of maximum yield increased with the elongation of the n-alkyl chain. The highest reactivity was observed for t-butyl heptanoate. In the presence of manganese catalyst, its quantitative conversion and the theoretical yield of 7-tridecanone were observed already at temperatures above 548 and 573 K, respectively. On the basis of XRD and TPR measurements of freshly prepared manganese catalyst, it was concluded that its active phase containsβ-MnO2 which is almost quantitatively reduced to MnO during contact with ethyl or t-butyl heptanoates. TPD measurements of ethyl and t-butyl heptanoates revealed dominant CO2 desorption peak for both esters and lesser peaks for octan-2-one, heptanal, 1-heptanol and 7-tridecanone, and the substrates. Ethene, diethyl ether and ethanol, and 2-methylpropene were found to be desorbates for ethyl and t-butyl ester, respectively.
Keywords: Ketonization; Alkyl heptanoates; 7-Tridecanone; Manganese; Cerium and zirconium oxide catalysts
Spatially resolved mass spectrometry as a fast semi-quantitative tool for testing heterogeneous catalyst libraries under reducing stagnant-point flow conditions by Kathrin Eckhard; Oliver Schlüter; Volker Hagen; Barbara Wehner; Thomas Erichsen; Wolfgang Schuhmann; Martin Muhler (pp. 115-120).
A calibrated quadrupole mass spectrometer (QMS) is combined with a home-made positioning unit deriving from scanning electrochemical microscopy (SECM) to sequentially address 25 catalysts, which are placed in wells. Highly reproducible catalytic data are obtained under stagnant-point flow conditions by means of coupled gas feed and QMS capillaries. The reaction array can be heated and is fully sealed from the atmosphere by a covering glass lid. Additionally, the reaction chamber is flushed with argon making it possible to study the structure-insensitive hydrogenation of ethene over SiO2-supported palladium catalysts unimpaired by oxygen poisoning. Since the derived semi-quantitative degree of conversion is proportional to the Pd metal area under fixed reaction conditions, spatially resolved mass spectrometry provides a novel method for rapidly estimating the metal surface areas of a Pd catalyst library.
Keywords: Spatially resolved mass spectrometry; Palladium; Ethene hydrogenation; High throughput experimentation; Primary screening; Semi-quantitative Pd area determination
Catalytic hydrotreating of heavy gasoil FCC feed on alumina–titania-supported NiMo catalysts by Víctor Santes; Javier Herbert; Maria Teresa Cortez; René Zárate; Leonardo Díaz; Prakash Narayana Swamy; Mimoun Aouine; Michel Vrinat (pp. 121-128).
A series of NiMo/γ-Al2O3–TiO2 catalysts were prepared and tested in the hydrotreating of heavy gasoil FCC feed in a pilot plant fixed-bed reactor. Three different methods were applied to obtain the alumina–titania mixed oxides: impregnation of titanium butoxide over a γ-Al2O3 support, co-precipitation of a mixture of aluminum sulfate, sodium aluminate and titanium sulfate, and a sol–gel method using alkoxides as precursors; the titanium content was kept constant (5wt.%). Additionally, a γ-Al2O3 support was also prepared as a reference. All supports were characterized by XRD, FT-IR pyridine and HRTEM. Catalysts were prepared by spraying at incipient wetness with the appropriate Ni–Mo solution. Catalytic activity results (HDS, HDM and HDA) showed marked influence of the preparation method. This behaviour is explained in terms of the differences in titania dispersion and acidity of the support.
Keywords: Al; 2; O; 3; –TiO; 2; Acidity; XPS; HRTEM; Hydrotreating
Supercritical fluids and phase behavior in heterogeneous gas–liquid catalytic reactions by S. Pereda; S.B. Bottini; E.A. Brignole (pp. 129-137).
Gas–liquid catalyzed reactions carried out in a supercritical medium take advantage of the high reaction rates and improved selectivities that can be achieved by having reactants and products in a homogeneous phase. In this work, the phase behavior of several supercritical reactions are analyzed and the selection of adequate solvents is discussed. The reactions studied include the hydrogenation of terpenic compounds and unsaturated aldehydes, and the hydroformylation of hydrocarbons to produce aldehydes. Recent experimental results from the literature on the kinetics and selectivities of these reactions are discussed on the basis of the phase equilibrium scenario under the reaction conditions.
Keywords: Supercritical reaction media; Hydrogenation; Terpenes; Unsaturated aldehydes; Hydroformylation; 1-Hexene; Phase equilibria
Ethanol auto-thermal reforming on rhodium catalysts and initial steps simulation on single crystals under UHV conditions by E. Vesselli; G. Comelli; R. Rosei; S. Freni; F. Frusteri; S. Cavallaro (pp. 139-147).
By means of ultra high vacuum temperature programmed desorption experiments, we studied the influence of oxygen on the decomposition of ethanol over rhodium(111) and (100) single crystal surfaces. Oxygen at low surface coverage (between 0.1 and 0.25 ML) promotes ethanol decomposition and the formation of carbon dioxide, while carbon monoxide production is not significantly affected, with respect to the reaction on clean samples. Oxygen coverage above 0.25 ML hinders hydrogen formation due to the prevalent oxidising action, which leads to water formation. These results are in line with data we obtained for ethanol decomposition over a 5% Rh/Al2O3 catalyst under typical reforming working conditions (i.e. T=923K and P=1bar), thus indicating that an oxidising environment is required in order to avoid carbon poisoning and to promote C2-containing molecules decomposition. On the contrary, excess of oxygen leads to a strong reduction of hydrogen concentration in the reaction products.
Keywords: PACS; 82.45.Jn; 82.65.+r; 68.43.−h; 68.43.VxHydrogen; Ethanol; Rhodium; Reforming
Titanium oxide nanotubes as supports of nano-sized gold catalysts for low temperature water-gas shift reaction by V. Idakiev; Z.-Y. Yuan; T. Tabakova; B.-L. Su (pp. 149-155).
Titanium oxide nanotubes (TNTs) have been synthesized via the reaction of TiO2 crystalline powders of either anatase or rutile phase and NaOH aqueous solution. Their application as an active supports of gold particles prepared by deposition–precipitation (DP) method is investigated. The TNT supports and the gold catalysts were characterized by a range of methods including powder X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption analysis and temperature programmed reduction (TPR). The catalytic activity of gold-supported titania nanotubes (Au/TNTs) was evaluated for the first time in water-gas shift reaction (WGSR) at wide temperature range (140–300°C) and has been compared with Au/surfactant-templated-mesoporous-titania and Au/Al2O3 catalysts under the same operating conditions. We try to establish a correlation between the catalytic performance of Au/TNTs and the nature of the support.
Keywords: Titanium oxide nanotubes; Gold catalysts; Water-gas shift reaction
Epoxidation of alkenes in the presence of molybdenum–squarate complexes as novel catalysts by Mariana G. Topuzova; Stefan V. Kotov; Tsonko M. Kolev (pp. 157-166).
Several molybdenum-containing organic complexes based on 3,4-dihydroxy-3-cyclobutene-1,2-dione (squaric acid) have been synthesized and characterized by infrared (IR) spectroscopy, thermogravimetric (TGA) and elemental analyses. The resulting molybdenum complexes were introduced as catalysts in the epoxidation of cyclohexene, 1-octene, 2,4,4-trimethyl-1-pentene, 1,5-cyclooctadiene and 1,5,9-cyclododecatriene with t-butylhydroperoxide (TBHP). The catalytic activities of these complexes for the various alkenes employed as reactants were compared and their versatility as catalysts for the epoxidation reaction was estimated. Thus the most appropriate molybdenum-containing complex was selected, for which the catalytic activity and selectivity were comparable to those of the commercially available molybdenyl acetylacetonate (MoO2(acac)2).
Keywords: Squaric acid; Molybdenum-containing complexes; Catalysts; Epoxidation
Catalytic formation of acetic anhydride over tungstophosphoric acid modified SBA-15 mesoporous materials by Nong-Yue He; Chang-Soo Woo; Hyeon-Gook Kim; Ho-In Lee (pp. 167-178).
Tungstophosphoric acid H3PW12O40 (TPA) was impregnated on mesoporous materials SBA-15 with pore sizes 91.9 and 63.9Å at different loadings. TPA-containing SBA-15 samples were synthesized with various TPA contents. The samples were characterized by means of XRD, FTIR, TEM, ICP, and N2 adsorption. For the impregnated samples, TPA species was finely dispersed. TPA IR spectrum was not detected for loading up to 1:5 (TPA:SBA-15, w:w) and became obvious with the increase in loading. The XRD diffraction peaks of HPA were not found for samples with loading up to 1:4 and were very weak for the samples with loading 2:3, while the TPA XRD diffraction peaks of physical mixtures of TPA and mesoporous (1:10, w:w) were very strong. The chemically high-dispersed TPA species thus favored the selectivity of acetic anhydride catalytically condensed from acetic acid at 823K. The bigger the pore size, the better the selectivity. For the directly synthesized TPA-containing samples, the chemically bound TPA species remained after hot water extraction at 373K for 3h. The selectivity of acetic anhydride was further increased to 96% over the TPA-containing sample with 6.37wt.% of chemically bound TPA species, regardless of the smaller pore size (30.4Å) compared to those of the TPA-impregnated samples, but the activity was decreased at low TPA content (≤3.37wt.%). Generally, results revealed that the finely dispersed and chemically bound TPA species and pore size were responsible for the enhanced selectivity in our systems, bigger pore size favored both the activity and selectivity over samples with TPA loading ≤5wt.%, while the pure bulk TPA showed no selectivity for acetic anhydride under investigation.
Keywords: Tungstophosphoric acid; Mesoporous material; Acetic anhydride; Impregnation; Direct synthesis
Mechanistic effects resulting from the cesium-doping of a NiMoO4 catalyst in n-butane oxidative dehydrogenation by Luis M. Madeira; Manuel F. Portela (pp. 179-189).
In this paper, the catalytic n-butane oxydehydrogenation was studied over two catalysts: undoped and Cs-doped α-NiMoO4. The effects of both reaction temperature and contact time on the catalytic performances were evaluated, providing a further insight about the reaction network. It is shown that 1-butene and 2-butenes isomers are primary products, being butadiene formed through a consecutive dehydrogenation step via any n-butene. Carbon oxides are also secondary products, resulting from the deep oxidation of any hydrocarbon species, but direct oxidation of butane must also be considered, particularly to CO2. The effects of cesium-doping are an increase in the butenes production with a simultaneous inhibition of the deep oxidation to CO x species, practically not affecting the butenes to butadiene dehydrogenation step.
Keywords: Butane; Oxydehydrogenation; Mechanism; Nickel molybdate; Cesium promoter
Study of alkaline-doping agents on the performance of reconstructed Mg–Al hydrotalcites in aldol condensations by S. Abelló; F. Medina; D. Tichit; J. Pérez-Ramírez; X. Rodríguez; J.E. Sueiras; P. Salagre; Y. Cesteros (pp. 191-198).
The influence of alkaline-doping agents (Na, Li, K) on the catalytic activity of gas-phase rehydrated hydrotalcites has been investigated for the aldol condensation of citral and acetone to pseudoionone. Various amounts of alkalines were added (0.5–4.9wt.%) either deliberately by impregnation or retained in the washing step during the preparation of the hydrotalcite by co-precipitation. The samples were characterised by ICP-OES, XRD, SEM and CO2-TPD. The alkaline-free rehydrated hydrotalcite (<0.05wt.% Na), which requires large amounts of water during the washing step (10l per 20g of solid), displayed very poor catalytic activity. Activity improved when the content of alkaline metals in the solid was increased. These metals act as strong basic centers in the aldol condensation. The catalytic performance of the samples correlates with their strength and number of basic sites. Thorough washing is vital during the synthesis of hydrotalcite-like materials in order to remove all alkalines and properly attribute their catalytic performance to basic hydroxyl groups in the interlayer space. Alkaline-promoted hydrotalcites show an important leaching of the alkaline to the reaction medium upon consecutive runs.
Keywords: Aldol condensation; Alkaline; Promoter; Hydrotalcite; Rehydration
Dispersion and surface states of copper catalysts by temperature-programmed-reduction of oxidized surfaces (s-TPR) by Antonella Gervasini; Simona Bennici (pp. 199-205).
Surface and sub-surface oxidation of dispersed copper phase by N2O adsorptive decomposition at controlled temperature followed by H2 temperature-programmed-reduction of the Cu2O surface layers formed (s-TPR) was performed on siliceous supported catalysts (ca. 6wt.% Cu). The combined analysis permitted to measure the copper dispersion and to identify different surface copper species. Copper dispersion parameters were calculated from the H2-uptakes in the back-titration of the oxygen atoms fixed on the Cu particles by the s-TPR analysis. S-shaped curves were obtained plotting the H2-uptakes versus N2O oxidation temperature, the change of slope could indicate the beginning of copper deep oxidation, ca. 70°C, that continued up to bulk oxidation at higher temperatures. Extrapolation of the H2-uptake to “zero-temperature� allowed calculating the “true� copper dispersion (DCu*) and related parameters. In addition, s-TPR provided qualitative and quantitative reduction profiles of the copper surface species. Besides Cu2O, formed by N2O oxidation of Cu(0) particles, copper species strongly interacting with support were clearly individuated as a function of the support nature.
Keywords: Cu catalysts; Cu dispersion; Cu surface species; N; 2; O oxidation; Temperature-programmed-reduction
Highly active and selective AlSBA-15 catalysts for the vapor phase tert-butylation of phenol by A. Vinu; Biju M. Devassy; S.B. Halligudi; Winfried Böhlmann; Martin Hartmann (pp. 207-213).
Hexagonally ordered mesoporous AlSBA-15 catalysts having nSi/ nAl ratios from 7 to 215 have been synthesized hydrothermally using a cheap non-ionic block copolymer as the structure-directing agent. The obtained materials were analyzed by XRD and nitrogen adsorption to determine the structural order and the textural properties. It has been observed by27Al MAS NMR spectroscopy that aluminum atoms are exclusively in tetrahedral coordination for all samples except AlSBA-15(7), where octahedral aluminum has been detected to some extent. Temperature-programmed desorption of pyridine showed that AlSBA-15(45) has a higher number of strong acid sites as compared to other mesoporous materials such as FeMCM-41, AlMCM-41 and FeAlMCM-41. The catalyst AlSBA-15(45) showed superior performance in the acid-catalyzed tertiary butylation of phenol employing tert-butanol as the alkylation agent. A high phenol conversion of 86.3% is observed for this catalyst at a reaction temperature of 150°C. Over AlSBA-15(45), the 4-TBP yield amounts to 40.5% and the 2,4-DTBP yield corresponds to 37.9%.
Keywords: SBA-15; Aluminum incorporation; AlSBA-15; Butylation of phenol; Acidity
Hydrogenative regeneration of a Pt/La-Y zeolite catalyst deactivated in the isobutane/ n-butene alkylation by Raoul Klingmann; Rouven Josl; Yvonne Traa; Roger Gläser; Jens Weitkamp (pp. 215-223).
The formation of carbonaceous deposits during the alkylation of isobutane with 1-butene was investigated on a La-Y zeolite catalyst loaded with 0.4wt.% of platinum in a continuous-flow stirred tank reactor at 75°C in the liquid phase. By combined elemental analysis and UV–vis spectroscopy, the amount and the nature of the coke deposits were found to change significantly with time-on-stream. Olefins formed by cracking of isododecyl- or higher carbocations are supposed to be important precursors of the carbonaceous deposits, as they form unsaturated carbocations blocking the acid sites. The hydrogenative regeneration of coked alkylation catalysts was studied in the gas phase. Under suitable regeneration conditions, e.g. at a hydrogen pressure of 15bar and a temperature of 300°C, the alkylation activity can be fully restored.
Keywords: Alkylation; Isobutane/butene alkylation; Deactivation; Hydrogenative regeneration; Coke characterization; Hydrocracking; UV–vis spectroscopy; Alkenyl cations
Low-pressure hydrogenolysis of glycerol to propylene glycol by Mohanprasad A. Dasari; Pim-Pahn Kiatsimkul; Willam R. Sutterlin; Galen J. Suppes (pp. 225-231).
Hydrogenolysis of glycerol to propylene glycol was performed using nickel, palladium, platinum, copper, and copper-chromite catalysts. The effects of temperature, hydrogen pressure, initial water content, choice of catalyst, catalyst reduction temperature, and the amount of catalyst were evaluated. At temperatures above 200°C and hydrogen pressure of 200psi, the selectivity to propylene glycol decreased due to excessive hydrogenolysis of the propylene glycol. At 200psi and 200°C the pressures and temperaures were significantly lower than those reported in the literature while maintaining high selectivities and good conversions. The yield of propylene glycol increased with decreasing water content. A new reaction pathway for converting glycerol to propylene glycol via an intermediate was validated by isolating the acetol intermediate.
Keywords: Hydrogenolysis; Glycerol; Propylene glycol; Copper-chromite; Acetol
La–Ce–Ni–O monolithic perovskite catalysts potential for gasoline autothermal reforming system by Aidu Qi; Shudong Wang; Guizhi Fu; Changjun Ni; Diyong Wu (pp. 233-246).
Hydrogen generation from gasoline is essentially one of the critical technologies for the commercialization of small-scale fuel cells auxiliary/backup power systems, so catalysts suitable for autothermal reforming (ATR) of gasoline are desperately needed. La0.8Ce0.2NiO3 with a crystal structure of perovskite was developed both in pellet and on cordierite substrate by citrate method. Autothermal reforming of gasoline or its surrogates, n-octane with or without thiophene additive, was carried out on either bulk perovskite pellet or monolithic perovskite catalyst. During the 220-h long-term test, the pellet catalyst exhibited high thermal stability and activity with hydrogen yield approaching to the theoretical maximum value and only minor amount of CH4 slipping through. It possessed fairly good sulfur tolerance, almost immune to 5ppmw sulfur although could still be seriously poisoned when subjected to high concentration of sulfur or gasoline. The monolithic perovskite catalysts were developed by screening slurries, binders as well as substrates with or without pre-washcoating CeZrO2. The monolithic La0.8Ce0.2NiO3 formed in situ on the raw cordierite monolith could be an effective catalyst for ATR of gasoline, exhibiting superior performance to the catalyst of 0.3wt.%Rh/CeO2–ZrO2/cordierite at a temperature range 650–800°C. On whatever the pellet or monolithic catalysts, the active sites were presumably the in situ reduced Ni0 which were well dispersed and stabilized by the perovskite crystal structure. The good performances of La0.8Ce0.2NiO3, better thermal stability and immunity to carbon foul and sulfur poison than LaNiO3 could be ascribed to the increased oxygen mobility with the presence of sesquioxide of cerium.
Keywords: Perovskite; Monolithic catalyst; Hydrogen; Gasoline; Autothermal reforming; Distributed power system; Fuel cells
Catalytic performance in citral hydrogenation and characterization of PtSn catalysts supported on activated carbon felt and powder by Irene M.J. Vilella; Sergio R. de Miguel; Concepción Salinas-Martínez de Lecea; Ángel Linares-Solano; Osvaldo A. Scelza (pp. 247-258).
The liquid phase citral hydrogenation carried out at 70°C and atmospheric pressure over Pt and PtSn catalysts supported on both activated carbon powder (C) and felt (ACf), was investigated. It was found that the addition of Sn to the Pt catalysts increases the reaction rate of the citral hydrogenation, this influence being more important for carbon-based catalysts. Besides, the Sn addition sharply enhances the selectivity to double unsaturated alcohols (nerol and geraniol) for both catalyst series. The secondary products were the unsaturated aldehyde (citronellal), the single-unsaturated alcohol (citronellol) and the cyclization products (isopulegol and menthol). The performance of these catalysts in the citral hydrogenation was related with the characteristics of the metallic phase, which were determined by test reactions of the metallic phase (cyclohexane dehydrogenation and cyclopentane hydrogenolysis), H2 chemisorption, TPR and XPS in order to postulate the models of the metallic surface. In this sense, a fraction of ionic Sn (detected by XPS) would be deposited near Pt aggregates, thus enhancing the polarization of the carbonyl group of the citral molecule, and leading to an increase in the selectivity to nerol and geraniol. This effect appears to be different depending on the support type.
Keywords: Supported PtSn catalysts; Citral hydrogenation; Characterization of the metallic phase; Activated carbon powder; Activated carbon felt
Synthesis of higher alcohols from syngas over Cu-Co2O3/ZnO, Al2O3 catalyst by Vahid Mahdavi; M.H. Peyrovi; M. Islami; J. Yegane Mehr (pp. 259-265).
Cu-Co2O3/ZnO, Al2O3 catalysts prepared by co-precipitation were studied by temperature-programmed reduction (TPR) and chemisorption of nitrous oxide (N2O). Catalytic activity for synthesis of C1–C6 alcohols was determined in a fixed bed flow reactor system. Changes in activity and selectivity were obtained with respect to changes of percentage composition of Co-Cu catalyst, temperature (270–355°C), ratio of H2/CO (0.5–2), pressure (40–70atm), feeding flow with GHSV (2260–5060h−1). In optimum condition, the selectivity for alcohol ( SA) and heavier alcohols (SC2OH+) were more that 80% and 50%, respectively. The distribution of alcohol products obeys Schulz-Flory distribution. The chain growth probability factor of higher alcohols was independent of conversion.
Keywords: Higher alcohol synthesis; Copper/cobalt catalyst; Syngas
Heterogenization of chiral molybdenum(VI) dioxo complexes on mesoporous materials and their application in catalysis by Ayyamperumal Sakthivel; Jin Zhao; Gabriele Raudaschl-Sieber; Marianne Hanzlik; Anthony S.T. Chiang; Fritz E. Kühn (pp. 267-273).
Optically active molybdenum(VI) dioxo complexes bearing hydrosalen derivatives as ligands were synthesized, grafted on the surface of MCM-41 and MCM-48 and examined as catalysts for asymmetric epoxidation. In case of cis-β-methylstyrene and trans-β-methylstyrene moderate enantiomeric excesses of up to 31% can be reached when the reaction is carried out at room temperature. The catalysts can also be applied for non-chiral oxidation reactions.
Keywords: Catalysis; Chirality; Mesoporous materials; Molybdenum; Epoxidation
CO oxidation over palladium- and sodium-promoted tin dioxide: catalyst characterization and temperature-programmed studies by Burcu Mirkelamoglu; Gurkan Karakas (pp. 275-284).
One weight percentage PdO/SnO2 and 0.1wt.% Na–1wt.% PdO/SnO2 catalysts have been synthesized through a sol–gel route and these catalysts have been characterized by XRD, BET, SEM and temperature-programmed adsorption and desorption techniques with regard to their activity for the CO oxidation reaction. CO adsorption and CO–O2 co-adsorption followed by O2 TPD have been carried out to observe the role of sodium promotion on the catalytic activity. The catalytic activity of PdO/SnO2 catalysts is suppressed by blockage of CO active sites by O2 on co-adsorbed catalysts. Sodium-promoted catalysts possess increased affinity to oxygen and thus, exhibit superior activity upon CO–O2 co-adsorption, but these catalysts have been observed to perform poorly upon consecutive adsorption of CO and O2. The effect has been ascribed to enhanced interaction of sodium-promoted surfaces with CO hindering oxygen adsorption on CO precovered surface.
Keywords: Alkali promotion; Carbon monoxide oxidation; Tin dioxide; Temperature-programmed characterization
TS-1 oxidation of aniline to azoxybenzene in a microstructured reactor by Yu Shan Susanna Wan; King Lun Yeung; Asterios Gavriilidis (pp. 285-293).
A multichannel membrane microreactor for continuous selective oxidation of aniline by hydrogen peroxide on TS-1 nanoparticles was successfully demonstrated. The high surface area to volume ratio that can be attained in the microreactor (3000m2/m3) facilitates the selective removal of water by-product, which reduces the effect of catalyst deactivation during the reaction. An improvement in the product yield and selectivity towards azoxybenzene was also observed. Azobenzene was obtained as by-product and its formation was attributed to homogeneous reaction of nitrosobenzene with aniline. Increasing temperature was beneficial for both yield and selectivity, but beyond 340K, microreactor operation was ineffective due to bubble formation and hydrogen peroxide decomposition.
Keywords: Aniline; Azoxybenzene; Microreactor; Micromembrane; Zeolite