Applied Catalysis A, General (v.311, #C)
Editorial Board (CO2).
Fabrication of structured vanadium catalyst for SO2 conversion by Wei Jiang; Bin Liang (1-7).
A novel structured vanadium catalyst (SVC) for the catalytic oxidation of SO2 was designed and synthesized based on a monolith substrate with regular and interconnecting channels. The new catalyst was synthesized by a molding compressing method. Specifically, plastic templates were compressed with a slurry containing active components, and then the templates were removed by thermal treatment, resulting in a monolithic structure with uniquely designed channels. It was discovered that low moisture capacity and high fluidity of the slurry help improve the mechanical strength of SVC. Pre-processing the slurry under optimized conditions can greatly improve the fluidity of the slurry. Both plastic and liquid limits of the slurry could be reduced by about 50% through pre-processing. The mechanical strength of the SVC prepared reached 1.1 MPa. The activity of SVC is comparable to the traditional vanadium catalyst, but its pressure-drop is only 30% of that of a commercial cylindrical catalyst.
Keywords: Structured vanadium catalyst; Pressure-drop; Mechanical strength; Diatomite; Sulfur dioxide;
Catalytic partial oxidation of n-tetradecane in the presence of sulfur or polynuclear aromatics: Effects of support and metal by Dushyant Shekhawat; Todd H. Gardner; David A. Berry; Maria Salazar; Daniel J. Haynes; James J. Spivey (8-16).
Catalytic partial oxidation (CPOX) of liquid fuels is an attractive option for producing a hydrogen-rich gas stream for fuel cell applications. However, the high-sulfur and aromatic content present in these fuels increases the propensity towards deactivation of noble metal-based catalysts used in this reaction. The relationship between catalyst supports and deactivation has been studied here for three catalysts (Rh/Ce0.56Zr0.44O2−x , Pt/Ce0.56Zr0.44O2−x and Pt/Al2O3) in a fixed-bed catalytic reactor using various mixtures of n-tetradecane with 1-methylnaphthalene or dibenzothiophene to simulate logistic fuels. Carbon deposition during CPOX reforming was shown to be directly related to the concentration of unsaturated products formed. Unsaturates (olefins + aromatics), which are known coke precursors, were observed on both platinum catalysts during CPOX of n-tetradecane with no sulfur (particularly from Pt/Al2O3), but not on Rh/Ce0.56Zr0.44O2−x . For the Rh/Ce0.56Zr0.44O2−x , yields of hydrogen and carbon monoxide dropped to a stationary level after the introduction of sulfur-containing feed (1000 ppm sulfur) or aromatic-containing feed (5 wt%), however, the catalyst activity was restored after removing the sulfur or aromatics from the feed. For the platinum catalysts, hydrogen and carbon monoxide yields dropped continuously over time in the presence of sulfur or aromatics in feed. The superior performance of Rh/Ce0.56Zr0.44O2−x can be attributed to the higher oxygen-ion conductivity of the Ce0.56Zr0.44O2−x support as well as the higher activity of rhodium compared to platinum.
Keywords: Fuel reforming; Catalytic partial oxidation; Logistic fuels; Carbon formation; Sulfur resistance; Oxygen-ion conductivity;
Esterification of acetic acid by isoamylic alcohol over catalytic membranes of poly(vinyl alcohol) containing sulfonic acid groups by J.E. Castanheiro; A.M. Ramos; I.M. Fonseca; J. Vital (17-23).
In this study, poly(vinyl alcohol) (PVA) membranes crosslinked with sulfosuccinic acid (SSA) were used for the esterification of acetic acid by isoamylic alcohol. In order to study the effects of the crosslinking degree and, simultaneously, the amount of sulfonic groups, different membranes were prepared with SSA:PVA ratios in the range of 5–40 mol%. Aiming at to eliminate the dependence between the amount of acid sites and the crosslinking degree, were also prepared PVA membranes in which the –SO3H groups were introduced by anchoring 5-sulfosalisilic acid (SA) on the PVA chains.The conversion of isoamylic alcohol increases when the amount of sulfosuccinic acid used in the polymer crosslinking is increased from 5 to 20%. However, when crosslinking degree increases from 20 to 40%, the conversion of isoamylic alcohol increases only slightly, probably due to the increase of molecules mobility restrictions, in the PVA matrix.In the case of the PVA membranes where the –SO3H groups were introduced by esterifying 5-sulfosalisilic acid on the PVA –OH groups, it was observed that membrane activity increases with the polymer crosslinking. It was also observed an increase of the activity of these membranes with the amount of –SO3H groups in the polymeric matrix.Catalytic stability of PVA membranes, prepared with SSA and SA, was evaluated by performing consecutive batch runs with the same membrane being observed, after the third run, a trend to stabilization of catalytic activity.An experiment with a membrane reactor operating under sweep gas pervaporation conditions is described.
Keywords: Isoamylic alcohol; Acetic acid; Sulfonic groups; PVA; Polymeric catalytic membranes;
Syngas production from partial oxidation of methane over Ce1−X Ni X O Y catalysts prepared by complexation–combustion method by Wenjuan Shan; Matthieu Fleys; Francois Lapicque; Dariusz Swierczynski; Alain Kiennemann; Yves Simon; Paul-Marie Marquaire (24-33).
Synthesis gas production from partial oxidation of methane (CH4/O2/Ar = 4/2/94) over Ce1−X Ni X O Y (X = 0.05–0.6) catalysts was investigated between 500 and 900 °C by using a jet stirred reactor. The highest conversion rate of CH4 and O2 was obtained on Ce0.6Ni0.4O Y where the selectivity of hydrogen was close to 80% and the CO selectivity was higher than 90%, although the residence time was very low (δ = 3 s). The desired ratio H2/CO about 2 was obtained at about 700 °C for all catalysts. Moreover, the catalyst exhibited good stability as no reaction activity decrease was observed during 160 h reaction at 650 °C due to the high redox property of the catalyst in the reaction. The structure and property of the catalysts were investigated by XRD, TPR, BET, N2-adsorption, and XPS for the fresh and used samples. The TPR and XPS results suggested that Ce3+/Ce4+ and Ni2+/Ni0 couples coexisted in the reaction by Ni2+ + Ce3+ + □ → Ni0 + Ce4+ due to the strong interaction between the Ni and Ce species in the catalysts. The lattice oxygen actived by Ce3+ with oxygen vacancy is the main active oxygen species for the reaction. Both Ni0 and Ce3+ with oxygen vacancy are the active sites for the reaction. The active site transferred between Ni0 and Ce3+-□ depending on the availability of lattice oxygen in the reaction.
Keywords: Syngas; Partial oxidation of methane and Ce1−X Ni X O Y ;
Synthesis of hydrogen peroxide from carbon monoxide, water and oxygen catalyzed by amorphous NiP(B)/Al2O3 by Zhong-Long Ma; Shao-Kun Jiang; Lun Zhang; Chuan-Qiang Liu (34-42).
Amorphous NiP(B)/Al2O3 catalysts were prepared by a coating method. The factors that influence the preparation of the catalysts, such as plating temperature, the initial pH value of the plating solution, the loadings of NiP and the temperature of heat treatment, were studied in detail. The catalysts were characterized with XRD, SEM and XPS, and were studied in the reaction for the synthesis of hydrogen peroxide from carbon monoxide, water and oxygen. The results showed that the catalysts had amorphous structure with Ni–P–B alloy formed on the surface; that the catalysts had better activity and stability than the catalysts reported previously when the H2O2 production rate reached 0.228 mmol/(g h), which is higher than the maximum rate of 0.1 mmol/(g h) over noble catalysts (5% Pd/CaCO3 and 1% Ru/graphite) and 0.07 mmol/(g h) over Ni–La–B/Al2O3 catalyst; and that the preparation conditions significantly influenced the activities of the catalysts. The higher stability values of the catalysts were attributed to the amorphous Ni–P–B structure.
Keywords: Amorphous alloy; NiP(B)/Al2O3; Carbon monoxide; Oxygen; Hydrogen peroxide;
Polystyrene-bound imidazole as a heterogeneous axial ligand for Mn(salophen)Cl and its use as biomimetic alkene epoxidation and alkane hydroxylation catalyst with sodium periodate by Valiollah Mirkhani; Majid Moghadam; Shahram Tangestaninejad; Bahram Bahramian (43-50).
In the present work, an account of biomimetic oxidation, Mn(III) salophen has been successfully bonded to imidazole modified polystyrene. Polystyrene-bound imidazole, (PSI), is not only a heterogeneous axial base but also is a support for immobilization of Mn(III) salophen. Mn(salophen)Cl-PSI catalyze alkene epoxidation with sodium periodate under agitation with magnetic stirring. Alkyl aromatic and cycloalkanes were oxidized efficiently to their corresponding alcohols and ketones in the presence of this catalyst. This new heterogenized catalyst is of high stability and reusability in the oxidation reactions. This heterogenized system showed the higher selectivity and stability in comparison with the homogeneous system, Mn(salophen)Cl. The catalyst, Mn(salophen)Cl-PSI, has been characterized by FT-IR, UV–vis spectroscopic techniques, SEM, thermal and elemental analysis. The effect of reaction parameters such as solvent and oxidant in the epoxidation of cis-cyclooctene were also investigated.
Keywords: Biomimetic; Epoxidation; Hydroxylation; Polystyrene; Periodate; Schiff base;
Oxidative dehydrogenation of isobutane over activated carbon catalysts by José de Jesús Díaz Velásquez; Luis M. Carballo Suárez; José Luis Figueiredo (51-57).
In past work, we reported on the textural and chemical modifications induced by treating an activated carbon under nitrous oxide, oxygen and hydrogen. In this work, we are reporting on the testing of surface modified activated carbons in the oxidative dehydrogenation of isobutane (ODHI). The results show that the different treatments lead to a given catalytic performance associated with the degree of oxidation. At 648 K, isobutene yields are higher in the initial stages for the activated carbons with the highest amounts of carbonyl/quinone groups on the surface, which are considered the active sites for this reaction, and the isobutene yields are lower for the catalysts with lower concentrations of these groups. As the reaction proceeds, the reactant mixture (isobutene–oxygen and argon as carrier gas) is able to introduce active sites onto the carbon surface to the point where they are stabilized for the case of treatment in H2 and without pretreatment. For the other treatments, N2O and oxygen, the active sites are rearranged and stabilized after a while. It is observed that there is a tendency towards a similar CO/CO2 relationship as measured by TPD, corresponding to a yield of about 7% after 5 h of reaction.
Keywords: Activated carbon; Surface treatment; Catalytic properties; Oxidative dehydrogenation; Functional groups;
Desulfurization of Tier 2 gasoline by divalent copper-exchanged zeolite Y by David L. King; Carlos Faz (58-65).
The desulfurization of Tier 2 gasoline (<30 ppmw S) by divalent copper-exchanged zeolite Y (Cu(II)Y) zeolite was examined. Sulfur removal was found to be greater at 150 °C than at lower temperatures for Cu(II)Y adsorbents containing as the secondary cation either Na+ (CuNaY) or H+ (CuHY). Capacities on the order of 60 ml gasoline/g adsorbent were obtained with both materials before the sulfur concentration in the effluent exceeded 3 ppmw. Overall, the CuHY zeolite showed somewhat better desulfurization performance. It is proposed that acid sites (H+) that are present play a role in the desulfurization process, facilitating chemical reactions involving the sulfur-containing molecules. This leads to the generation of sulfur-bearing compounds having molecular weights and sizes greater than those present in the initial feed. Some of these heavier sulfur species are eluted but many do not elute. The net effect is a desulfurization pathway that is the result of entrapment of sulfur-containing molecules in addition to a desulfurization pathway involving direct interaction between the copper and sulfur atoms.
Keywords: Desulfurization; Copper zeolite Y; Tier 2 gasoline; Divalent copper ion; Thiophene;
Hydrogenation of carbon oxides over promoted Fe-Mn catalysts prepared by the microemulsion methodology by T. Herranz; S. Rojas; F.J. Pérez-Alonso; M. Ojeda; P. Terreros; J.L.G. Fierro (66-75).
The microemulsion technology was used in order to improve the preparation of iron-based catalysts for the CO and CO2 hydrogenation reactions. This technique led to a sample with a higher surface area when compared with a similar solid prepared by conventional precipitation. As a consequence, a higher catalytic activity was obtained.The hydrogenation of carbon oxides was also performed over promoted iron-manganese catalysts. The preparation of these samples by the microemulsion methodology yielded to homogeneous mixed oxides. Manganese-containing catalysts presented a higher activity towards the formation of hydrocarbons, at the same conversion levels, than the iron counterparts.These catalysts were promoted with copper, sodium and potassium. Carbon dioxide conversion was favoured by alkaline addition, especially by potassium, due to the promotion of the water-gas shift reaction. Furthermore, alkaline promotion enhanced selectivity towards long-chain products either in CO2 and CO hydrogenation processes. Addition of copper caused a more facile reducibility of the solids, resulting in a significant increment in both carbon monoxide and carbon dioxide conversion without modifying products selectivity.
Keywords: Iron catalysts; Fischer–Tropsch; Carbon dioxide hydrogenation; K-promoted catalysts; Cu-promoted catalysts; Microemulsion;
A novel Fe catalyst FeCl2·4H2O/hexamethylphosphoric triamide for the ATRP of MMA by Jian Cao; Jin Chen; Keda Zhang; Qi Shen; Yong Zhang (76-78).
A novel catalyst system FeCl2·4H2O/hexamethylphosphoric triamide (HMPA) induced ATRP of MMA in combination with ethyl 2-bromoisobutyrate (EBiB) to give the polymers with controlled molecular weights and narrow molecular weight distributions (MWDs) (Mw/Mn) < 1.20. With the use of benzyl chloride as the initiator, the MWDs were broader. The ratio of FeCl2·4H2O to HMPA has an effect on the catalytic activity. The reason was discussed based on the result obtained by the isolated crystal of FeCl2 (HMPA)2 as the catalyst.
Keywords: Catalyst; ATRP; Radical polymerization; Reaction kinetics;
Water gas shift reaction studies on 2% Pd/AMn1−x Fe x O3 (A = Ba, La, Pr; x = 0.4, 0.6) perovskites by Markus J. Koponen; Tapani Venäläinen; Mika Suvanto; Kauko Kallinen; Toni-J.J. Kinnunen; Matti Härkönen; Tapani A. Pakkanen (79-85).
BaMn0.6Fe0.4O3, BaMn0.4Fe0.6O3, LaMn0.6Fe0.4O3, LaMn0.4Fe0.6O3, PrMn0.6Fe0.4O3, and PrMn0.4Fe0.6O3 perovskites were synthesized via malic acid complexation and impregnated with 2% of palladium by dry-wet method. WGSR measurements were carried out in a stainless steel continuous flow reactor. The A-site metal increased the conversion of H2 and CO2 in the order Ba < La < Pr. Comparison of the B-site metal combinations showed higher conversions for Mn0.4Fe0.6 than Mn0.6Fe0.4. The formation of carbonaceous surface species was observed. In measurements with a gas chromatograph, the oxidation of surface palladium was found to decrease in the order La > Pr > Ba. No correlation was observed between WGSR activity and oxidation of palladium.
Keywords: Perovskite; WGSR; Oxidation of palladium;
Copper-promoted cobalt catalysts for 2,3-dihydrofuran synthesis by L. Leite; V. Stonkus; K. Edolfa; L. Ilieva; L. Plyasova; V. Zaikovskii (86-93).
The conversion of 1,4-butanediol to 2,3-dihydrofuran in the liquid phase has been studied over novel kaolin-supported Co–Cu catalysts, prepared by means of a simple mechanochemical method. The improvement of the catalytic properties and decrease in the optimum reduction temperature of Co–kaolin catalysts, promoted by copper, has been observed. It was established that a Co:Cu ratio 5:1 is optimum for the specific activity and for the yield in the conversion of 1,4-butanediol to 2,3-dihydrofuran. In the present study, the highest 2,3-dihydrofuran yield (81%) was obtained with the ultrasonically treated catalyst and after reduction pretreatment at 320–350 °C. The existence of an optimum reduction temperature for the catalyst pretreatment was established. In agreement with the results, obtained in our previous studies, the high 2,3-dihydrofuran yield is favoured by the coexistance of cobalt both in the metallic and oxidic state. The increased specific activity of copper-containing catalysts could be related to the lowering of the reduction temperature, which leads to a hexagonal metallic cobalt phase formation. The latter is favourable for 2,3-dihydrofuran synthesis. The advantage of mechanochemical preparation of Co–Cu (5:1) catalyst is that the method prevents penetrating of cobalt ions into the support, thus the whole amount of cobalt loaded is available for the catalyst performance. This is one of the probable reasons for higher specific activity of the 2,3-DHF formation over these catalysts.
Keywords: 1,4-Butanediol; Co–Cu–kaolin catalyst; 2,3-Dihydrofuran; Mechanochemistry; Ultrasonication;
Structural features of La1−x Ce x NiO3 mixed oxides and performance for the dry reforming of methane by S.M. Lima; J.M. Assaf; M.A. Peña; J.L.G. Fierro (94-104).
Mixed oxides La1−x Ce x NiO3 (x = 0, 0.05, 0.4 and 0.7) have been prepared by the citrate method and tested, after reduction activation, in the CO2 reforming of methane reaction into synthesis gas. The compounds were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), specific surface area measurements, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), transmission electron microscopy (TEM) and temperature-programmed oxidation (TPO). The LaNiO3 perovskite exhibited activity to methane reforming, but suffered a slow deactivation with time-on-stream. Nevertheless, substitution of the A site metal ion with a tetravalent metal cation (Ce) led to an increase in catalytic activity. Moreover, the insertion of Ce increased the stability of the catalysts with respect to the reforming reaction. The La0.95Ce0.05NiO3 catalyst showed the highest activity, with CO2 conversion of 62% at 1023 K. The XRD and TPR analyses confirmed that at high Ce contents, ceria appears as segregated CeO2 phase and interferes with the rate of perovskite structure formation, so that NiO and La2NiO4 are produced. As a consequence of the low solubility of cerium oxide, its insertion in the perovskite structure is also possible in the low Ce-content regions. This low amount of cerium incorporated is responsible not only for the enhancement of catalytic performance of the perovskite after its activation by reduction, but also for the inhibition of carbon formation.
Keywords: Methane reforming reaction; Perovskite-type oxides; Metal catalysts precursors; Crystal structure; Reduction properties;
Characteristics of vanadia–titania aerogel catalysts for oxidative destruction of 1,2-dichlorobenzene by Jinsoon Choi; Chee Burm Shin; Tae-Jin Park; Dong Jin Suh (105-111).
Vanadia–titania catalysts prepared by a sol–gel method and by supercritical drying showed a very high activity and thermal stability for gas phase oxidation of 1,2-dichlorobenzene (DCB) in the range of 150–600 °C. The selectivity for carbon oxides was kept over 95% unless the reaction temperature was relatively low (<200 °C). The conversion was maintained over 90% at above 350 °C with a residence time of less than 0.05 s and deactivation was not observed during the 48 h of operation at 450 °C.The surface structure of vanadia played a critical role on the catalytic activity, but the structure of crystalline titania was revealed to have exclusive dependency. For the vanadia–titania catalysts with the inherent characteristics of aerogels such as high specific surface area and chemical homogeneity, little bulk vanadia was observed and catalytic activity was maintained or improved due to the formation of surface mono- and poly-vanadates after repeated reactions.
Keywords: Vanadia–titania aerogel; 1,2-Dichlorobenzene; Oxidation; Vanadate;
State-of-the-art in the monolithic catalysts/reactors by Vesna Tomašić; Franjo Jović (112-121).
According to some authors development of monolithic catalysts and/or reactors has been one of major achievements in the field of heterogeneous catalysis and chemical reaction engineering of the recent years. This work is aimed at pointing out the advantages of monolithic catalysts and/or reactors with respect to the conventional ones, with particular focus on the integral approach to the catalyst and reactor design.The paper is divided into several parts. The first part gives basic definitions and classification of monolithic catalysts, including basic features of the monoliths and factors that have proceeded to the development and application of the monolith structures. It is explained that monoliths belong to the class of the catalytic reaction systems, where usual differences between catalysts and reactors, arising from their action level, are diminishing. Second part of paper is devoted to the preparation of monolithic catalysts. Next part deals with their commercial application with particular emphasis on the less known applications, and those which are still under development. The paper concludes with forecast of potential monoliths applications and ends up with the future research priorities and directions.
Keywords: Monolithic catalysts and/or reactors; Properties; Preparation; Application;
Cobalt aluminum silicate complexes prepared by the non-hydrolytic sol–gel route and their catalytic activity in hydrocarbon oxidation by B.L. Caetano; L.A. Rocha; E. Molina; Z.N. Rocha; G. Ricci; P.S. Calefi; O.J. de Lima; C. Mello; E.J. Nassar; K.J. Ciuffi (122-134).
This work describes the optimized conditions for the preparation of cobalt aluminum silicate complexes through a simplified methodology. These materials, designated CoAlSi-NHG, were obtained by a non-hydrolytic sol–gel route involving the condensation of aluminum chloride with diisopropylether in the presence of cobalt chloride, followed by reaction with tetraethoxysilane. The obtained solids were heat-treated at various temperatures, and the resulting materials were characterized by ultraviolet-visible spectroscopy, X-ray diffraction, 29Si and 27Al NMR, transmission electron microscopy, surface area, thermogravimetric analysis, and differential thermal analysis. All the materials consisted of an aluminum silicate matrix, and they all remained amorphous throughout heat treatment up to 750 °C. The onset of crystallization took place at 1000 °C, and the formation of mullite was observed thereafter. All the CoAlSi-NHGs obtained in this work via different heat treatments were used as catalysts in the oxidation of (Z)-cyclooctene, cyclohexane, and n-heptane by iodozylbenzene. The non-hydrolytic sol–gel route led to the obtention of extremely interesting catalytic systems capable of selectively oxidizing various types of reactions. The intermediate species is the oxidizing species oxo-cobalt, which is similar to the active species obtained in the case of enzymes such as cytochrome P-450.
Keywords: Cobalt; Non-hydrolytic route; Selective oxidation;
Role of the oxide support on the performance of Rh catalysts for the autothermal reforming of gasoline and gasoline surrogates to hydrogen by Magali Ferrandon; Theodore Krause (135-145).
Catalysts consisting of 2 wt% Rh deposited on Gd-CeO2, Y-ZrO2, γ-Al2O3, La-Al2O3, and CaAl12O19 were tested for the autothermal reforming (ATR) of isobutane and sulfur-free gasoline. The catalysts were characterized for activity by microreactor tests and temperature-programmed reduction (TPR), and for physical properties by surface area measurements, CO chemisorption, X-ray diffraction (XRD), and extended X-ray absorption fine structure (EXAFS) analyses. The order of activity for ATR of isobutane was Rh/La-Al2O3 > Rh/Y-ZrO2 > Rh/Gd-CeO2 > Rh/γ-Al2O3 > Rh/CaAl12O19, which paralleled the ranking of the catalysts based on the dispersion and reducibility of Rh, with Rh/La-Al2O3 having the highest dispersion and the lowest reduction temperature. After subjecting the catalysts to an accelerated ageing process, the activity for ATR of isobutane was similar for all catalysts except for Rh/Gd-CeO2, which experienced a significant loss in steam reforming activity. Rhodium dispersion measurements confirmed that the ageing process had caused Rh to sinter on all of the supports. A major conclusion from this study is that the primary effect of the support was on the dispersion of Rh.
Keywords: Rh; Ceria; Alumina; Zirconia; Hexaaluminate; Reforming; Isobutane; Gasoline; Deactivation; TPR; EXAFS;
Novel aspects of the physical chemistry of Co/SiO2 Fischer–Tropsch catalyst preparations by I. Puskas; T.H. Fleisch; P.R. Full; J.A. Kaduk; C.L. Marshall; B.L. Meyers (146-154).
Co/SiO2 catalysts were prepared by both impregnation and precipitation techniques and analyzed by IR, TPR, XRD, and BET methods at intermediate stages of their preparation to define the stage and mechanism of cobalt silicate formation. To prove that reducing conditions can lead to cobalt silicate, one part of a catalyst prepared by impregnation of silica with cobalt nitrate was calcined in air at 350 °C, and another part in H2–N2 atmosphere at the same temperature. Infrared spectra revealed the presence of Co–O–Si absorption in the sample exposed to reducing atmosphere. Cobalt silicate formation is postulated to be a reaction between migrating silicic acid and hydrated cobalt hydroxide generated in the reduction process.Precipitation of cobalt nitrate solution at 80–90 °C with potassium hydroxide solution in the presence of Davison 952 silica resulted in amorphous cobalt silicate formation. Precipitation with sodium carbonate solution gave no IR-detectable quantities of cobalt silicate in the presence of Davison 952 silica, but cobalt silicate was detected when Cab-O-Sil HS-5 silica was used. Precipitations of Co and Mg nitrates (∼2:1 Co/Mg ratio) with sodium carbonate gave essentially quantitative yield of amorphous cobalt silicates whether the precipitation occurred in the presence of Davison 952 silica, or the silica was added after the precipitation. Cobalt silicate formation during precipitation either by KOH or Na2CO3 solutions is a heretofore unrecognized facile reaction of hydrated cobalt hydroxide with silicic acid (dissolved silica). The mechanism which can explain Co(OH)2(H2O) x formation during Na2CO3 precipitations is an acid–base reaction between hydrated Co ions and carbonate ions. This reaction also yields carbonic acid, which competes with silicic acid for Co(OH)2(H2O) x in secondary reactions.
Keywords: Fischer–Tropsch; Cobalt; Silica; Cobalt silicate;
Comparison of P-containing γ-Al2O3 supported Ni-Mo bimetallic carbide, nitride and sulfide catalysts for HDN and HDS of gas oils derived from Athabasca bitumen by V. Sundaramurthy; A.K. Dalai; J. Adjaye (155-163).
Phosphorus containing γ-Al2O3 supported bimetallic Ni-Mo carbide, nitride and sulfide catalysts have been synthesized from an oxide precursor containing 12.73 wt.% Mo, 2.54 wt.% Ni and 2.38 wt.% P and characterized by elemental analysis, pulsed CO chemisorption, surface area measurements, X-ray diffraction, temperature-programmed reduction and DRIFT spectroscopy of CO adsorption. DRIFT spectroscopy of adsorbed CO on activated catalysts showed that carbide and nitride catalysts have surface exposed sites of Mo ø+ (0 < ø < 3) and Mo δ+ (0 < δ < 2) sites respectively, and these sites are susceptible to sulfidation with H2S/H2 mixture at 370 °C. The hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) activities of the bimetallic Ni-Mo carbide, nitride and sulfide catalysts were compared against commercial Ni-Mo/Al2O3 catalyst in a trickle bed reactor using light gas oil and heavy gas oil derived from Athabasca bitumen in the temperature range 340–370 and 375–400 °C respectively at 8.8 MPa. The gradual transformation of Ni-Mo carbide and nitride phases into Ni-Mo sulfide phases was observed during precoking period, and the formed Ni-Mo sulfide phases enhanced the HDN and HDS activities of carbide and nitride catalysts. The γ-Al2O3 supported Ni-Mo bimetallic sulfide catalyst was found to be more active for HDN and HDS of light gas oil and heavy gas oil than the corresponding carbide and nitride catalysts on the basis of unit weight.
Keywords: Ni-Mo carbide; Ni-Mo nitride; Sulfided Ni-Mo carbide and nitride; DRIFT of CO adsorption; Hydrodesulfurization; Hydrodenitrogenation; Light gas oil; Heavy gas oil;
CO2 reforming of CH4 over La–Ni based perovskite precursors by Germán Sierra Gallego; Fanor Mondragón; Joël Barrault; Jean-Michel Tatibouët; Catherine Batiot-Dupeyrat (164-171).
LaNiO3 and La2NiO4 type perovskites were prepared by the “self-combustion” method and were used as catalyst precursors for the CO2 reforming of CH4 reaction at 700 °C. The catalysts were tested in reduced and non-reduced form. High CH4 and CO2 conversion were obtained without carbon deposition. This result was explained by the occurrence of the RWGS (reverse water gas shift) reaction. The La2NiO4 perovskite used as precursor presents the smallest nickel particles after the reduction treatment. Consequently the catalytic activity is higher than that obtained with Ni/La2O3 or LaNiO3.When La2NiO4 is used without treatment prior to the reaction high methane and carbon dioxide conversions are reached but a carbon deposition is observed. The perovskite structure is not completely transformed and the presence of metallic nickel particles at the surface of La2NiO4 would be responsible for the carbon deposition. It is assumed that the role of the support is to allow the activation of carbon dioxide, which is favoured over La2O3 whereas it is limited over La2NiO4. Consequently the reaction between the complex C–Ni species (resulting from methane activation at the surface of the nickel particle) and gaseous CO2 is inhibited over Ni/La2NiO4 leading to a carbon accumulation at the surface of the catalyst.As soon as the perovskite structure is completely transformed, after reductive treatment or during the reaction, a high activity is reached and no carbon deposition was further observed, the catalytic performances being optimal when the average nickel particles size is the smallest.
Keywords: Perovskite precursors; La2NiO4; LaNiO3; CO2/CH4 reforming; Coke formation;
Influence of exchange cations on the catalytic conversion of limonene over Serra de Dentro (SD) and SAz-1 clays by C. Catrinescu; C. Fernandes; P. Castilho; C. Breen (172-184).
A bentonite collected at Serra de Dentro (SD), Porto Santo Island, Portugal, and the source clay SAz-1 (Cheto, Arizona) were ion-exchanged with different cations (Al3+, Ni2+, Cr3+ and Na+). Variable temperature diffuse reflectance infrared Fourier transform spectroscopy (VT-DRIFTS) of pyridine treated samples, thermal desorption of cyclohexylamine and real time mass spectrometry of the evolved gases were used to evaluate the acidic properties of the prepared catalysts. The catalytic activity of these ion-exchanged clays was tested in the acid-catalysed conversion of limonene at 150 °C, to yield isomerization products (terpinolene, α-terpinene, γ-terpinene and isoterpinolene), disproportionation products (p-cymene and p-menthenes) and high molecular-weight compounds. The possibility of increasing the selectivity toward p-cymene, over a catalyst with substantial Lewis acid character, was particularly envisaged. Catalysts derived from SD were significantly more active than their SAz-1 counterparts. This was mainly attributed to the greater inherent acidity, to the higher structural iron content (providing dehydrogenation activity) and to the higher nitrogen surface area of the starting SD clays. Within the M n+-SD series, the order of activity decreased as Ni2+ > Al3+ > Cr3+ > Na+. A direct comparison between Al3+-SD (with maximized Brönsted acidity) and Ni2+-SD (with predominant Lewis acid character) provided no support for enhanced p-cymene production over Lewis acid sites.
Keywords: Ion-exchanged clays; Acidity; Catalysis; Limonene; p-Cymene;
Gold on titania: Effect of preparation method in the liquid phase oxidation by Nikolaos Dimitratos; Alberto Villa; Claudia L. Bianchi; Laura Prati; Michiel Makkee (185-192).
The effect of preparation method (deposition-precipitation versus sol immobilisation method) and reduction method (calcination versus chemical reduction) on Au/TiO2 catalysts for the liquid phase oxidation of glycerol has been studied. It was revealed that a different trend existed in terms of activity and distribution of products. The catalytic activity is shown to be dependent not only on the choice of the reduction method but also on the use of protective agent (PVA, THPC) for the stabilization of the gold colloids. In fact, the highest activity was found when a low temperature chemical reduction was employed on a Au/TiO2 sample synthesised by the deposition-precipitation method. The use of a higher pre-treatment temperature or of a protective agent resulted in a lower activity but could be used to direct selectivity in oxidation reactions. The structural data (HRTEM and XPS) along with the catalytic results indicate that the combination of metallic Au0 species with small particle size (2–5 nm) are responsible for the high activity observed in the liquid phase oxidation of glycerol.
Keywords: Catalysis by gold; Liquid phase oxidation; Effect of preparation method;
Hydrocarbons from ethanol using [Fe,Al]ZSM-5 zeolites obtained by direct synthesis by Nádia Regina Camargo Fernandes Machado; Valmir Calsavara; Nelson Guilherme Castelli Astrath; Antonio Medina Neto; Mauro Luciano Baesso (193-198).
The search for new energy sources has impulsed hydrocarbon production from methanol and ethanol over ZSM-5 zeolites. Iron incorporation by different methods has led to a variety of chemical applications. Thus, hydrocarbon production from ethanol was evaluated using a [Fe,Al]ZSM-5 zeolite which was synthesized without nitrogenated templates, using ethanol and crystallization seeds and partially substituting iron for aluminium in the reaction mixture. Characterization was done by X-ray diffraction (XRD), Fourier-transform infra-red spectroscopy (FTIR), temperature programmed reduction (TPR), temperature programmed desorption of ammonia (TPD), nitrogen adsorption, electron paramagnetic resonance (EPR) and photoacoustic spectroscopies. Iron content in the synthesized samples varied from 0.02 to 1.82%. The obtained samples were used for the ethanol transformation, producing hydrocarbons from ethene to aromatics. Maximum production of liquid hydrocarbons was achieved with the zeolite with 0.5% iron. The procedure for obtaining the acid form of the zeolites, involving ammonium exchange and calcinations, has changed the iron species, probably with extraction from the structure, migration and agglomeration.
Keywords: Fe/ZSM-5; Ethanol; Hydrocarbons;
Synthesis and characterization of niobium modified montmorillonite and its use in the acid-catalyzed synthesis of β-hydroxyethers by Jean Marcel R. Gallo; Sergio Teixeira; Ulf Schuchardt (199-203).
Montmorillonite K10 was ion-exchanged with polyhydroxyniobium obtained from niobium pentachloride by hydrolysis. This modified clay was characterized by X-ray diffraction, thermogravimetric analysis, inductively coupled plasma emission (ICP-OES) and nitrogen adsorption/desorption. The obtained material was used in the alcoholysis of epoxidized methyl oleate with methanol, leading to β-hydroxyethers. The reaction with ion-exchanged montmorillonite (Nb-Mont) was four times faster at 60 °C and three times faster under reflux than the one using the original clay. This proves the increase of Brønsted acidity when polyhydroxyniobium is present. The Nb-Mont was also calcined at 300, 500 and 900 °C to obtain the Nb-pillared montmorillonite. However, the activity of the calcined Nb-Mont decreased with increasing calcination temperature. On the other hand, calcined montmorillonite maintained its basal distance, even after treatment at 900 °C.
Keywords: Montmorillonite; Polyhydroxyniobium exchanged; Acid catalyst; Epoxidized methyl oleate; Ring-opening reaction;
LaCo1−x Cu x O3−δ perovskite catalysts for higher alcohol synthesis by N. Tien-Thao; H. Alamdari; M.H. Zahedi-Niaki; S. Kaliaguine (204-212).
Perovskite-type materials LaCoO3, LaCo1−x Cu x O3−δ , and Cu2O/LaCoO3 were synthesized by the mechano-synthesis process known as reactive grinding. Their characterization was performed by BET, X-ray diffraction, SEM, O2-TPD, and H2-TPR. The partial cobalt substitution by copper in perovskite lattice gives rise to a distorted structure of LaCoO3 and influences the thermal stability and redox properties of perovskites. Temperature-programmed reduction (TPR) analysis showed a complete reduction of Co3+, Cu2+ to metallic state in the temperature range of 310–580 °C. A lower cobalt reduction temperature observed for LaCo1−x Cu x O3−δ in comparison to LaCoO3 produces a finely dispersed bimetal on a La2O3 support. Quantitative TPR data showed that cobalt ions in the grain boundaries of the ground perovskites are directly reduced to metals at a relatively low temperature (310–450 °C). The existence of strong cobalt–copper interaction in perovskites could enhance the metallic dispersion of cobalt and prevent copper sintering. The reduced forms of LaCo1−x Cu x O3−δ catalysts were tested as alcohol synthesis catalysts in a fixed bed flow reactor system at 275 °C and space velocity of 4000 h−1 (H2/CO = 2/1). A mixture of C1–C7 alcohols with the chain growth propagation factors of 0.34–0.42 was produced. The alcohol productivity is from 36.5 to 49.6 mg/gcat/h and selectivity towards higher alcohols took values in the range of 40–49.5%. The preliminary catalytic data indicated that copper located outside of the perovskite lattice is solely leading to the production of methanol and methane whereas its location in the octahedral position of the perovskite precursor framework is necessary for higher alcohol synthesis. Therefore, a uniform distribution of the metallic cobalt–copper atoms in the prereduced catalysts is crucial for the conversion of carbon monoxide and hydrogen into higher alcohols.
Keywords: Perovskites; LaCoCuO3; High dispersion; Higher alcohols; Syngas; Co–Cu;
Calendar of Forthcoming Events (213-214).