Applied Catalysis A, General (v.284, #1-2)
EDITORIAL BOARD (iii).
CONTENTS LIST (v-vi).
Support effects in catalytic wet oxidation of H2S to sulfur on supported iron oxide catalysts by Eun-Ku Lee; Kwang-Deog Jung; Oh-Shim Joo; Yong-Gun Shul (1-4).
Iron oxide catalysts supported on MgO, Al2O3, SiO2 and ZrO2 were prepared by an impregnation method. They were characterized by BET surface analysis, X-ray diffraction (XRD), temperature-programmed reduction (TPR) and Mössbauer spectroscopy. Fe/MgO catalyst shows the highest H2S removal capacity in wet oxidation at room temperature. Both the XRD and the TPR analyses of the catalysts indicate that H2S removal capacity correlates with the dispersion of iron oxide on supports. Mössbauer spectroscopy shows that four kinds of Fe3+ species are present in the supported iron oxide catalysts: two highly dispersed species, Fe3+ oxide clusters, and α-Fe2O3 particles. Two highly dispersed species, Fe3+ cation and MgFe2O4, are present in Fe/MgO. Fe3+ oxide clusters and α-Fe2O3 crystals are evident in both Fe/SiO2 and Fe/ZrO2. α-Fe2O3 crystals are only observed in Fe/Al2O3.
Keywords: Iron oxide catalyst; Fe/MgO; Mössbauer spectroscopy; H2S removal capacity;
Microfabricated high-temperature reactor for catalytic partial oxidation of methane by Osnat Younes-Metzler; Jakob Svagin; Søren Jensen; Claus Hviid Christensen; Ole Hansen; Ulrich Quaade (5-10).
A new setup using microfabricated silicon reactors for studying high-temperature partial oxidation reactions is described in this paper. Methane oxidation is chosen as a test reaction. The system is completely safe to operate due to the small size and the temperature is easy to control even for the highly exothermic reaction. The activation energy obtained for full oxidation of methane on Pd/Al2O3 catalyst is similar to the values reported in the literature for the case of oxidized Pd particles. The simplicity of depositing the catalyst, bonding and mounting the microreactor, gives a fast, safe, and easy way for reliable catalyst screening in studying partial oxidation reactions.
Keywords: Methane; Partial oxidation; Microreactor; Microfabrication; High temperature; Catalysis; Catalyst; Pd catalysts;
The effect of sol–gel promoters on the characteristics of mixed V–Nb oxides and their catalytic properties in propane oxidative dehydrogenation by M. Sarzi-Amadè; S. Morselli; P. Moggi; A. Maione; P. Ruiz; M. Devillers (11-20).
Hydrolytic sol–gel procedures are implemented for the preparation of mixed Nb–V oxide systems, the main objective being the development of potential catalysts for the oxidative dehydrogenation (ODH) of propane. The effects of various Nb precursors (alkoxide or chloride), different acid promoters and/or complexing agents (HCl, HNO3, oxalic acid and citric acid) and the influence of the Nb/V ratio on the hydrolytic sol–gel preparation are investigated. Several 1:1 Nb/V systems are prepared. It is found that the addition of citric acid as complexing agent stabilises the solution of Nb and V precursors after the addition of water, favouring the direct formation of a gel. A homogeneous and well-interdispersed 1:1 Nb–V system is obtained by this method. In all the other cases, precipitation of a yellow solid occurs, leading after calcination to heterogeneous systems, in which the presence of segregated V2O5 is detected.The hydrolytic preparation of systems with higher amount of Nb, 9:1 Nb/V and 4.5:1 Nb/V, does not require the addition of a complexing agent like citric acid. Sols containing higher amounts of Nb precursor are stable and turn rapidly into gels. In both 9:1 Nb/V and 4.5:1 Nb/V samples, there is no evidence of crystalline phases containing vanadium. Only the presence of crystalline Nb2O5 is detected by XRD. The effects of sol–gel additives and niobium amount on the morphological and catalytic properties are investigated. The 4.5:1 Nb/V sample shows both higher activity and selectivity to propene than the 1:1 Nb/V samples. The 9:1 Nb/V sample is found to behave similarly to pure Nb2O5, showing rather poor activity and higher selectivities to propene at increasing propane conversion.
Keywords: Niobium–vanadium mixed oxide; Sol–gel methods; Oxidative dehydrogenation of propane;
The effect of a higher operating temperature on the Fischer–Tropsch/HZSM-5 bifunctional process by F. Gideon Botes (21-29).
The combination of an iron-based Fischer–Tropsch catalyst and an HZSM-5 co-catalyst was studied in a Berty micro reactor at two temperatures, namely 330 and 350 °C. The higher operating temperature adversely affected the performance of the iron catalyst, as it caused a shift in the Fischer–Tropsch product spectrum towards lighter hydrocarbons at the expense of the desired product (gasoline). The synthesis performance of the HZSM-5 co-catalysts over the course of the bifunctional process experiments, the distribution of the xylene isomers during these runs, and subsequent thermogravimetrical analysis of the spent zeolite samples were all largely in agreement with respect to the amount and location of the coke formed on the different zeolitic co-catalysts during synthesis. It was found that the increased synthesis temperature had little effect on the performance of an HZSM-5 zeolite with a high aluminium content, but substantially improved the performance and useful lifetime of an HZSM-5 zeolite with a low aluminium content.
Keywords: Fischer–Tropsch; Iron catalyst; HZSM-5; Bifunctional process; Gasoline (high octane); Coking behaviour; Temperature;
Reverse water-gas shift reaction: steady state isotope switching study of the reverse water-gas shift reaction using in situ DRIFTS and a Pt/ceria catalyst by Gary Jacobs; Burtron H. Davis (31-38).
A previous investigation using steady state isotope switching in combination with DRIFTS demonstrated that surface formates exchange rapidly in a low temperature shift feed for the forward reaction. Transient decomposition of the pseudo-stable formate indicated that water autocatalyzes the forward shift reaction. In the present study, and including water in the RWGS feed (H2 and CO2), surface formates were found to exchange more rapidly during RWGS over Pt/ceria than when a dry feed was used. An earlier claim suggested that Pt―CO and carbonate were intermediates, as they exchange rapidly during RWGS. However, in the present study of 12CO2 to 13CO2 switching, Pt―CO and carbonate exchange rapidly even in the absence of reaction. Furthermore, the formate exchange rate during RWGS in the absence of added water proceeds at a much slower rate, indicating that conclusions on the mechanism of forward shift cannot be inferred on the basis of dry RWGS results.
Keywords: Pt; Ceria; Water-gas shift; Reverse water-gas shift; Isotope exchange; Formate; Carbonate;
Correlating NH3-TPD and 1H MAS NMR measurements of zeolite acidity: proposal of an acidity scale by R. Ramos Pinto; P. Borges; M.A.N.D.A. Lemos; F. Lemos; J.C. Védrine; E.G. Derouane; F. Ramôa Ribeiro (39-46).
The acidities (number and strength of the Brønsted acidic sites) of two zeolite samples, H-MFI and H-BEA, were measured by ammonia temperature-programmed desorption (ATPD) and proton nuclear magnetic resonance (1H MAS NMR). Deconvolutions of the ATPD and 1H MAS NMR spectra lead to acid sites distributions (number and strength) that are nearly similar. Acid sites of increasing acid strength are characterized by higher desorption temperatures and higher 1H NMR chemical shifts. A linear relationship was found between the activation energy for ammonia desorption and the 1H NMR chemical shift. The acid strength distributions determined by ATPD and 1H MAS NMR have been quantitatively correlated.
Keywords: Zeolites; Acidity; TPD; 1H MAS NMR; Acid site distribution; Acidity correlation;
Metathesis of 1-hexene over rhenium oxide supported on ordered mesoporous aluminas: comparison with Re2O7/γ-Al2O3 by J. Aguado; J.M. Escola; M.C. Castro; B. Paredes (47-57).
Self-metathesis of 1-hexene was carried out at 40 °C over Re2O7 supported on two micelle templated aluminas (sol–gel mesoporous alumina (SGAL) and MSU), prepared with cationic and neutral surfactant, respectively, and a reference Re2O7/γ-Al2O3 catalyst with the same rhenium oxide content (∼9 wt%). Both mesostructured catalysts (Re2O7/MSU and Re2O7/SGAL) showed similar activity and far higher than that of the reference Re2O7/γ-Al2O3 catalyst, with a selectivity towards the self-metathesis products above 99%. Among the tested solvents, dodecane yielded the highest conversion likely because of its low polarity and better product removal. Similar TOF values were obtained for Re2O7/SGAL catalysts with mesopore diameter within the 5.0–12.0 nm range. In relation with the rhenium content, an optimum in TOF values was detected for rhenium oxide loadings within 6–10 wt%. The increase in activation temperature within 550–700 °C led towards a greater rise in activity over Re2O7/SGAL catalysts than over Re2O7/γ-Al2O3. DRIFT chemisorbed pyridine spectra disclosed only Lewis acid sites over the activated catalysts and in higher amounts over both mesostructured catalysts. 31P MAS NMR spectra of chemisorbed triethylphosphine oxide (TEPO) indicated the presence of three kind of acid sites (δ ∼58, 68 and 80 ppm), with a higher content of strong Lewis acid sites (80 ppm) over both mesostructured catalysts. The remarkable performance of both ordered mesoporous catalysts was ascribed to the presence of these strong Lewis acid sites, likely stemming from the interaction of linked rhenium species with the weak Lewis acid sites of the support.
Keywords: Metathesis; 1-Hexene; γ-Al2O3; MSU; Rhenium oxide; Sol–gel mesoporous alumina;
2-Ethylanthraquinone hydrogenation on Pd/Al2O3 by A. Drelinkiewicz; R. Laitinen; R. Kangas; J. Pursiainen (59-67).
The effect of water and NaOH was studied on the hydrogenation of 2-ethylanthraquinone (eAQ) over alumina supported 2% Pd/Al2O3-A and 1.2% Pd/Al2O3-B catalysts. The hydrogenation was performed in a fixed-bed reactor by circulating the eAQ solution (the concentration of eAQ was 60 g/dm3) at 50 °C and 5 bar hydrogen pressure. The egg-shell catalysts were prepared by the precipitation of palladium hydroxide onto the support A (activated alumina, preimpregnated with NaH2PO4) or support B (alumina containing 10% SiO2, and preimpregnated with Na2SiO3). Prior to the hydrogenation, the catalysts were dried and pre-treated with water vapour or NaOH solution. The effect of water and NaOH on the amount of active quinones (eAQ and 2-ethyl-5,6,7,8-tetrahydroanthraquinone, H4eAQ) and in particular the role of such reagents in the consumption of aromatic hydroquinone eAQH2, the primary product of the quinone system of eAQ reduction was examined. The saturation of the phenyl rings in eAQH2 produces H4eAQH2, which is a reactive compound and the hydrogenolysis of the C−O bond in the tautomerized eAQH2 leads to other degradation products. Water and NaOH influence the hydrogenation of C＝O and the hydrogenolysis of C−O bond but have no effect on the hydrogenation of the aromatic rings. The increase in activity in the former C＝O to C−OH reduction did not depend of alumina A and B as well as the type of reagent (NaH2PO4 or Na2SiO3) introduced to alumina during the catalyst preparation. These reagents however, influenced the course of degradation processes. Water when introduced to the catalyst exhibited unprofitable effect on maintenance the activity of catalyst during the hydrogenation run. Such an unprofitable role is related to influence of water on the course of reactions yielding degradation products.
Keywords: 2-Ethylanthraquinone; Hydrogenation; Palladium catalyst;
Influence of the sulfate content on the activity of Pt containing sulfated zirconia by K. Föttinger; K. Zorn; H. Vinek (69-75).
Sulfated zirconias (SZ) with different sulfur content were prepared by controlled impregnation of zirconium hydroxide with corresponding amounts of 1N H2SO4. After drying the samples were impregnated with 2.5 wt% Pt. All samples exhibited pure tetragonal structure except one with the lowest sulfur content where small amounts of the monoclinic ZrO2 phase were detected. Temperature-programmed desorption of ammonia and pyridine adsorption followed by IR measurements were carried out in order to determine the nature of acid sites. It was found that the concentration of Brønsted acid sites depends on the concentration of surface sulfates. On samples with more than half of a monolayer sulfates Brønsted acid sites were detected. On SZ with 46% of a monolayer sulfates and on a sample, which was inactive after regeneration in an inert atmosphere only Lewis acid sites were observed.The n-heptane conversion was studied at 473 K and atmospheric pressure. SZ catalysts were only active when Brønsted acid sites were present on the surface. The activity increased with increasing sulfate content whereas the isomerization selectivity decreased.
Keywords: Pt; Sulfated zirconia; Brønsted and Lewis acid sites; n-Heptane;
Rh-ions and Rh-complexes intercalated in γ-titanium or γ-zirconium hydrogen phosphate as highly efficient catalysts for arene hydrogenation by Potenzo Giannoccaro; Michele Gargano; Antonello Fanizzi; Carla Ferragina; Michele Aresta (77-83).
Monocyclic arenes (C6H5X, X = H, CH3, OH, OCH3, Cl) are efficiently hydrogenated to their corresponding aliphatic hydrocarbons under relatively mild condition (T = 393 K, pH2 = 1–4 MPa) using rhodium(III) (Rh(III)) ions or Rh(III) N,N′-complexes (N,N′ = 2,2′-bipyridyl, 1,10-phenanthroline) intercalated into γ-titanium or zirconium hydrogen phosphate, (γ-M(PO4)(H2PO4); M = Ti, Zr), acting as ionic exchange supports. The hydrogenation rate depends on the catalyst, the substrate and their molar ratio, the temperature and the hydrogen pressure.Zirconium materials charged with naked Rh-ions, γ-Zr(PO4)2H x Rh y , or with Rh-complexes, γ-Zr(PO4)2H x (Rh-L) y (L = 2,2′-bipyridyl; 1,10-phenanthroline), proved to be more active than the titanium analogous compounds γ-Ti(PO4)2H x Rh y and γ-Ti(PO4)2H x (Rh-L) y . For both series of materials the M(PO4)2H x Rh y catalysts, (M = Ti, Zr), are more active than the corresponding M(PO4)2H x (Rh-L) y system.For the most active catalysts, γ-Zr(PO4)2H x Rh y and γ-Zr(PO4)2H x (Rh-L) y , the influence of the hydrogen pressure on the turnover frequency (TOF) and the stability over recycling was studied in the benzene hydrogenation. The activity increases with the pressure and at 4 MPa of H2, a TOF of 4019 h−1, expressed as mol of benzene hydrogenated per mol of Rh per hour, was found, using a Rh/benzene molar ratio of 1/8045. The catalysts remained stable for six runs in the case of benzene hydrogenation, while with toluene, a loss of activity was observed after the third cycle. The high activity and stability of Rh-zirconium materials used for benzene hydrogenation is also evidentiated by the fact that, under a hydrogen pressure of 2 MPa with a molar ratio Rh/benzene of 1/30171, 975.3 mmol of benzene were hydrogenated in 11 h, corresponding to a turnover number (TON) of 43538 mol of benzene hydrogenated per mol of Rh.Monocyclic arenes are efficiently hydrogenated to their corresponding aliphatic hydrocarbons under relatively mild condition (T = 393 K, pH2 = 1–4 MPa) using Rh(III) ions or Rh(III) N,N′-complexes (N,N′ = 2,2′-bipyridyl, 1,10-phenanthroline) intercalated into γ-titanium or zirconium hydrogen phosphate. ▪
Keywords: Heterogeneous catalysis; Arene hydrogenation; Zirconium and titanium hydrogen phosphate; Inorganic supports; Rhodium supported catalysts;
Dehydrocyclization of n-heptane over a PtBa/Kl catalyst: reaction mechanism by Adolfo Arcoya; Xosé L. Seoane; Javier M. Grau (85-95).
The dehydrocyclization of n-heptane to toluene over a 1 wt.% PtBa/KL catalyst was studied in a fixed bed tubular reactor, at 723 K, 100 kPa and space–time in the range of 1.8–117.0 g h mol−1. The catalyst was prepared by incipient wetness impregnation of a KL zeolite, previously alkalized with BaO, using an aqueous solution of tetraammineplatinum(II) hydroxide as platinum precursor. The solid was successively calcined in an oxygen stream and reduced in flowing hydrogen, at 773 K. Reaction is highly selective towards toluene (>60%) at conversion levels even close to 100%, with benzene, heptenes, methylcyclohexane and ethylcyclopentane as major byproducts. From the product distribution and the dehydrocyclization results of the reaction products performed in separate experiments, a macroscopic mechanism is proposed. Essentially, n-heptane is adsorbed and transformed on the catalyst surface through an alkene-like intermediate (σC7 ＝ ), following five possible parallel interconnected paths, involving hydrogenolysis, isomerization, dehydrogenation and cyclization reactions. Formation of toluene as a primary product is explained by a “rake scheme” in which the σC7 ＝ intermediate is successively transformed, following two possible routes: (a) C1–C6 ring closure and subsequent further dehydrogenation; (b) successive dehydrogenation to heptatriene and then cyclization to toluene. These transformations occur in the adsorbed phase and on the same active site, in such a way that only a small fraction of the total adsorbed intermediates formed appear in the gas phase. The rest are not desorbed due to their high reactivity.
Keywords: Pt/KL catalysts; n-Heptane dehydrocyclization mechanism; Toluene; Methylcyclohexane; Ethylcyclopentane;
Selective hydrogenation of citral over amorphous NiB and CoB nano-catalysts by Yin-Zu Chen; Biing-Jye Liaw; Shu-Jen Chiang (97-104).
Alloy catalysts of P-1NiB and P-1CoB were prepared by reduction of their acetate salts with NaBH4 in aqueous solution. Alloy catalysts of P-2WNiB and P-2WCoB were similarly prepared in ethanolic solution. The NiB and CoB catalysts prepared by this method were characterized as nano-scale (10–20 nm) particles with amorphous structure. These nano-scale alloy catalysts were used for the selective hydrogenation of citral to citronellal, nerol/geraniol and citronellol, which are important perfumery products. These catalysts are compared with the popular commercial catalysts: Raney nickel and Raney cobalt. The NiB and CoB catalysts were generally much more active and selective than Raney nickel or Raney cobalt. The distribution of products depended on the catalysts, the solvent used to prepare the catalysts and the solvent employed as the reaction medium. Over P-1NiB, the conjugated C＝C bond was preferentially reduced and citronellal was the main product in a reaction medium of cyclohexane, while citronellol was the major one in an ethanol medium. P-2WNiB was much more active than P-1NiB, but citronellol was further reduced to form the completely saturated product 3,7-dimethyloctanol. Over CoB catalysts, the conjugated C＝O bond was preferentially reduced to form nerol/geraniol and then consecutively reduced to citronellol; no observable 3,7-dimethyloctanol was formed. A yield of citronellal over 85% was obtained over P-1 and P-2WNiB in cyclohexane, and a 100% yield of citronellol was obtained over P-1 and P-2WCoB in ethanol. Only a 65% yield of nerol/geraniol was obtained over CoB catalysts.
Keywords: Amorphous alloy catalyst; Citral hydrogenation; CoB; NiB; Nano-catalysts;
Structure and Fischer–Tropsch performance of iron–manganese catalyst incorporated with SiO2 by Yong Yang; Hong-Wei Xiang; Lei Tian; Hong Wang; Cheng-Hua Zhang; Zhi-Chao Tao; Yuan-Yuan Xu; Bing Zhong; Yong-Wang Li (105-122).
A systematic study has been carried out to investigate the impacts of SiO2 content, incorporation manner of SiO2 and drying process on the physico-chemical and catalytic performances of a precipitated iron–manganese catalyst for Fischer–Tropsch synthesis (FTS) in a fixed bed reactor (H2/CO = 2.0, T = 265 °C, P = 2.5 MPa and GHSV = 1000 h−1). Characterization technologies of N2 physisorption, X-ray diffraction (XRD), Mössbauer effect spectroscopy (MES), temperature-programmed reduction (TPR) and scanning electron microscopy (SEM) were used to study the textural properties, bulk phase composition, reduction behavior and morphologies of the catalysts, and the SiO2 framework in the catalysts. The results of characterization showed that the incorporation of SiO2 leads to the increase in surface area. The catalyst with incorporated with precipitated SiO2 has the highest surface area and exhibits a stronger interaction between iron and SiO2 matrix than the interaction with binder SiO2. The strong Fe–SiO2 interaction restrains the reduction in H2 and the carburization in syngas of the catalysts. The addition of both binder and precipitated SiO2 greatly influences the activity and selectivity of FTS, and obviously improves its stability. For the FTS reaction tests, it was found that the catalyst activity is decreased with the increase of the amount of SiO2 incorporated. For the catalysts incorporated with the same levels of SiO2, the spray-dried catalyst has lower activity than the normal dried one. In addition, the catalyst incorporated with precipitated SiO2 has higher activity than that with binder SiO2. The FTS stability of the catalysts is improved with the incorporation of SiO2. The selectivity to gaseous hydrocarbons (C1–C4) and olefins decreases with the increase of SiO2 content. The spray-dried catalysts incorporated with either precipitated SiO2 or binder SiO2 produce more gaseous hydrocarbons and fewer olefins, while the normal-dried process and the addition of binder SiO2 cause a great increase in selectivity to light hydrocarbons. The selectivity to oxygenates in product decreases with the increase of SiO2 content in the catalyst. For the catalysts incorporated with binder SiO2, the spray-dried catalyst (SPUW) produces more oxygenates than the normal dried catalyst (FMSC), whereas the spray-dried catalyst incorporated with precipitated SiO2 (FSCP) produces the least oxygenates among all catalysts.
Keywords: Fischer–Tropsch synthesis; Iron–manganese catalyst; SiO2 support; Mössbauer spectroscopy; Hydrocarbon product distribution;
H2 reduction of hydrogen molybdenum bronze to porous molybdenum oxide and its catalytic properties for the conversions of pentane and propan-2-ol by Hirotoshi Sakagami; Yoko Asano; Nobuo Takahashi; Takeshi Matsuda (123-130).
The effects of H2 reduction on the physical and catalytic properties of one type of hydrogen molybdenum bronze, H1.55MoO3, were studied. H2 reduction enlarged the surface areas of H1.55MoO3 and Pt/MoO3, but not the surface area of MoO3. H1.55MoO3 became an active catalyst for pentane isomerization and for propan-2-ol dehydration after H2 reduction. The catalytic activities of H2-reduced H1.55MoO3 were comparable to those of H2-reduced Pt/MoO3, and were much higher than those of H2-reduced MoO3. In reduction of H1.55MoO3 and Pt/MoO3, molybdenum oxyhydride, MoO x H y , was formed after the decomposition of the hydrogen molybdenum bronze phase. By contrast, MoO3 was reduced to MoO2 without the formation of hydrogen bronze. We propose from these results that H2 reduction of hydrogen molybdenum bronze will generate the MoO x H y phase that can act as the active phase for the conversions of pentane and propan-2-ol.
Keywords: Hydrogen molybdenum bronze; H2 reduction; Surface area; Isomerization; Dehydration;
Visible-light sensitization of TiO2 photocatalysts by wet-method N doping by Shinri Sato; Ryuhei Nakamura; Shinji Abe (131-137).
Titanium dioxide powders prepared by a wet method, i.e., the hydrolysis of titanium tetra-isopropoxide or titanium tetrachloride with an aqueous ammonia solution, followed by calcination at temperatures above 330 °C, exhibit photocatalytic activity in the visible-light region owing to N doping. The maximum absorption of visible light by the N-doped TiO2 was about 50% at around 440 nm. Thermal analysis revealed that N doping occurs upon the oxidation of ammonia included in titanium hydroxide with lattice oxygen in TiO2. XPS analysis showed that the N doped in TiO2 is less than 1.3 at.% and is not bound directly to Ti. The oxidation state of doped N was found close to that of NO. Quantum yield for the CO photooxidation on the N-doped TiO2 in the visible region was less than that in UV region. These results show that the N doping by the wet method is similar to impurity doping such as metal ion doping.
Keywords: Photocatalysts; Visible-light sensitization; N-doped TiO2; Wet-method N doping;
Basic properties of molybdenum and tungsten nitride catalysts by Randolph C.V. McGee; Shyamal K. Bej; Levi T. Thompson (139-146).
The basic and related properties of high surface area Mo2N and W2N catalysts were characterized using CO2-temperature programmed desorption (TPD), the decomposition and dehydration of 2-methyl-3-butyn-2-ol (MBOH), and changes in the reaction rates on the addition of CO2, a base site poison. The Mo2N and W2N catalysts were prepared using the temperature programmed reaction method and had surface areas of 135 and 45 m2/g, respectively. The CO2-TPD and MBOH decomposition rates to acetone and acetylene indicated significant densities of base sites. The CO2 poisoning study implicated the involvement of weak sites in MBOH decomposition. The density of base sites and the rate of acetone formation were functions of the reduction temperature. Results for the nitride catalysts were compared to those for MgO and ZnO, known base catalysts. Base sites on the nitrides were of similar strength and density as those on the ZnO catalyst, but were weaker and less dense than those on MgO. Estimated turnover frequencies for the Mo2N and W2N catalysts were (6.0 ± 1.0) × 10−3 and (1.8 ± 0.4) × 10−3 s−1, respectively at 180 °C, and were slightly lower than those for the MgO and ZnO catalysts.
Keywords: Molybdenum nitride; Tungsten nitride; Base catalysis; MBOH decomposition; CO2-TPD; Poisoning studies;
The nitrobenzene activation step in the carbonylation reaction using PdCl2/Fe/I2/Py catalytic system by Jadwiga Skupińska; Monika Karpińska; Maria Ołówek (147-154).
The effect of PdCl2 concentration and of carbon monoxide pressure on the rate of nitrobenzene carbonylation reaction in the presence of PdCl2/Fe/I2/Py (Py = pyridine) catalytic system was studied. The reaction was shown to be of the first order with respect to palladium chloride and nitrobenzene concentrations as well as to carbon monoxide pressure. The effects of substituents in the aromatic ring on the rates of the nitrobenzene carbonylation, aniline carbonylation with nitrobenzene as an oxidant and the nitrobenzene reduction were also investigated. The first deoxygenation of nitrobenzene by carbon monoxide was shown to be the rate limiting step in the carbonylation reaction. The electron transfer from carbon monoxide to nitrobenzene molecule initiates the reaction.
Keywords: Nitrobenzene carbonylation; Palladium catalysts; Urethanes;
Resin catalyzed alcoholysis of epoxidized fatty esters: Effect of the alcohol and the resin structures by Luis A. Rios; Patrick P. Weckes; Hans Schuster; Wolfgang F. Hoelderich (155-161).
The effects of different alcohol molecular configurations and resin structures were analyzed on the acid-resin catalyzed addition of alcohols to epoxidized fatty esters. Emphasis was placed on the addition of α- and β-branched alcohols. Regarding the catalysts, the effect of the acid strength as well as that of the diffusion constraints on the reaction rate and products distributions, was determined. Reaction rate increases with the acid strength but the selectivity shows the opposite trend when highly branched alcohols are added. Epoxide ring-opening rate decreases by increasing the number of branches and size of the alcohol. Branches in α position introduce a higher steric hindrance than branches in β position. Low resin crosslinkage and/or high external surface area are necessary conditions to activate the epoxide when polystyrene-based resins are used as catalysts. The obtained by-products were the ketone, from epoxide rearrangement reaction, and trans-esterified products, when reaction times were relatively long.
Keywords: Oils; Epoxides; Alcoholysis; Hydroxy-ether; Resins;
Reconstruction of platinum–rhodium catalysts during oxidation of ammonia by Lenka Hannevold; Ola Nilsen; Arne Kjekshus; Helmer Fjellvåg (163-176).
The oxidation of ammonia to nitrogen monoxide is catalyzed by platinum–rhodium alloys. During the first few hours of operation the originally smooth surfaces on Pt–Rh catalysts with Rh contents of 0–13 and 100 wt.% are heavily reconstructed. The process starts on the grain boundaries, but soon spreads to cover the entire surface with “cauliflower”-like excrescences. Only slight reconstructions on the grain boundaries are observed for Pt/20 wt.% Rh and Pt/30 wt.% Rh catalysts. The present paper describes studies of oxidation of ammonia along Pt–Rh catalyst wires, including mass spectrometric surveys of the gaseous species formed. Scanning electron microscopy, electron microprobe, and X-ray powder diffraction characterizations were made of the catalyst wires before and after reaction. The amount and appearance of the reconstructions depend strongly on the Rh content of the catalyst. Marked concentration gradients in platinum-to-rhodium content are observed between wires and “cauliflowers” as well as within the “cauliflowers”. A qualitative account for the formation of the “cauliflowers” and related features is advanced using concepts from chemical vapor-transport reactions. PtO2 and/or RhO2 act as transporting molecules and the processes are driven by local temperature gradients between hotspots and colder regions on the catalyst surface. The ultimate net effect of the involved atomic transfer processes is to establish an approximately equiatomic (Pt50Rh50) composition at all catalyst surfaces.
Keywords: Platinum–rhodium catalyst reconstruction; Ammonia oxidation; Catalytic etching; “Cauliflower”-shaped excrescences;
Effect of α-Fe2O3 surface coating on reconstruction of platinum–rhodium catalysts during oxidation of ammonia by Lenka Hannevold; Ola Nilsen; Arne Kjekshus; Helmer Fjellvåg (177-184).
Surface coating of α-Fe2O3 has been shown to affect the reconstruction of platinum–rhodium catalysts during oxidation of ammonia at 900 °C and atmospheric pressure. Surfaces of wire-formed Pt–Rh specimens with 0–30 and 100 wt.% Rh were coated with thin layers of α-Fe2O3, deposited by thermal decomposition of iron(III) nitrate or by atomic layer chemical vapor deposition. Scanning electron microscopy, electron microprobe analysis, and powder X-ray diffraction were used to examine the catalyst wires before and after use in ammonia oxidation. The reconstruction on Pt–Pt/10 wt.% Rh and Rh catalysts with α-Fe2O3-coated surfaces involves “cauliflower”-like excrescences similar to those observed on corresponding materials without coatings. The reconstructions on α-Fe2O3-coated catalysts of Pt/20 wt.% Rh and Pt/30 wt.% Rh carry the same characteristics. However, for these alloys the reconstruction process becomes much faster and the resulting patterns more extensive than for corresponding materials without α-Fe2O3 coating. The boundary zones between the α-Fe2O3 cover and the liberated Pt–Rh surfaces appear to stand out as spots (hotspots in the thermal sense) with enhanced catalytic activity. A certain decrease in activity and selectivity with time is observed for all tested specimens. This is attributed to gradual degradation of α-Fe2O3 to more inactive Fe3O4. The progressing degradation of α-Fe2O3 to Fe3O4 shows that the temperature in the hotspots must exceed some 1400 °C or that reducing conditions prevail locally at the surface.
Keywords: Platinum–rhodium catalyst reconstruction; Platinum–rhodium catalyst with α-Fe2O3 coating; Ammonia oxidation; Catalytic etching; “Cauliflower”-shaped excrescences;
Surface reconstruction on noble-metal catalysts during oxidation of ammonia by Lenka Hannevold; Ola Nilsen; Arne Kjekshus; Helmer Fjellvåg (185-192).
Surface reconstructions on Pd, Pd/5 wt.% Ni, Ag, Ir, Pt/10 wt.% Ir, Pt/20 wt.% Ir, and Au wire-shaped specimens have been studied after ammonia oxidation at 900 °C and atmospheric pressure. The tested specimens were examined by powder X-ray diffraction, electron microprobe analysis, and scanning electron microscopy. Extensive surface reconstructions, with numerous pits, well developed facets, and “cauliflower”-like excrescences were, except for Au, observed on all tested specimens. Neglecting Au, the tested catalyst materials were active for oxidation of NH3 to NO, however, the selectivity and effective lifetime of these catalysts are strongly composition dependent. Au did not catalyze ammonia oxidation and its surface reconstructions are negligible. Solid oxides of NiO, PdO and IrO2 were identified on the surfaces of Pd–Ni, Pd, and Ir specimens, respectively. The results are discussed in relation to findings for Pt–Rh alloy catalysts, for which surface reconstruction is attributed to chemical-vapor-transport reactions driven by local temperature gradients between hotspots and colder regions on the catalyst surface.
Keywords: Catalyst reconstruction; Palladium; Palladium−nickel; Silver; Iridium; Platinum−iridium; Gold; Ammonia oxidation; “Cauliflower”-like excrescences; Catalytic etching;
Synthesis of titania–silica mixed oxide mesoporous materials, characterization and photocatalytic properties by Xin Zhang; Feng Zhang; Kwong-Yu Chan (193-198).
Titania–silica mixed metal oxide materials with a mesostructure have been prepared by a novel method in which hydrolysis and condensation of titanium tetraisopropoxide (TTIP) and tetraethoxysilane (TEOS) were controlled by the pH change of acidic solution using cetyltrimethylammonium bromide (CTAB) as the structure-directing agent. The prepared materials were characterized by TEM, XRD, XPS, FT-IR and nitrogen sorption. The resulting materials showed a short-range ordered mesoporous structure with the nanoparticles (8 nm) of TiO2 dispersed uniformly on SiO2 supports. These TiO2–SiO2 mesoporous materials were also found to have a higher photocatalytic activity than that of commercial pure TiO2 nanoparticles at the same titanium loading for the degradation of methyl orange.
Keywords: Titania–silica mixed oxides; Mesostructure; Photocatalysts; Methyl orange;
CO oxidation over gold nanocatalyst confined in mesoporous silica by Yu-Shan Chi; Hong-Ping Lin; Chung-Yuan Mou (199-206).
Au nanoparticles embedded within mesoporous silica particles have been prepared and used as catalysts for CO oxidation. The silane APTS (H2N(CH2)3-Si(OMe)3) was used to surface-functionalize mesoporous silica in a direct method. The functionalized mesoporous silica was used to absorb the gold precursor AuCl4 − and gold nanoparticles were formed inside the nanochannels after chemical reduction. The catalysts were activated by calcinations, followed with hydrogen reduction at 600 °C. MCM-41, MCM-48 and SBA-15 were used as the supports to prepare Au nanoparticles, resulting in different particle sizes of Au. The catalysts are active in the oxidation of carbon monoxide, reaching activity values as high as 7.0 × 10−3 mmol g cat − 1 s−1 at 353 K. The conversion of CO increases with decreasing size of gold nanoparticles.
Keywords: Gold; Nanotechnology; Heterogeneous catalysis; Oxidation; Mesoporous silica;
Modeling of side reactions of isobutane alkylation with butenes catalyzed by trifluoromethane sulfonic acid by A.S. Berenblyum; E.A. Katsman; R.A. Berenblyum; S.I. Hommeltoft (207-214).
The 2,2,4-trimethylpentane (2,2,4-TMP) decomposition kinetics in the presence of trifluoromethane sulfonic acid (TfOH) and acid soluble oil (ASO) was studied at the temperatures of 15–35 °C in a wide concentration range. 2,2,4-TMP partially undergoes isomerization during the reaction. The adequate kinetic model is designed for isooctane sum decomposition including light ends, heavy ends, and ASO formations. In this model heavy ends are the intermediate in ASO formation. Light ends’ evolving accompanies both heavy ends and ASO formations. Rate equations are first order in catalyst concentration and its Hammett proton activity controlled by ASO content. In particular the heavy ends formation rate is first order in isooctanes concentration, slowed down by light ends and auto-accelerated by heavy ends. The ASO formation rate is 0.6 orders in heavy ends’ concentration, slowed down by light ends, and accelerated by isooctanes and heavy ends. The reaction mechanism explaining all these phenomena is proposed and discussed in connection with practice of commercial isobutane alkylation with olefins.
Keywords: Trimethylpentane; Degradation; Alkylation; Acid soluble oil; Hammett acidity function; Trifluoromethane sulfonic acid;
Synthesis and characterization of Al-, Bi-, and Fe-incorporated mesoporous titanosilicate (MPTS) materials and their hydrophilic properties by Misook Kang; Mi-Hae Lee (215-222).
Mesoporous titanosilicates (MPTS) including Al, Bi, and Fe ions of three positive oxidation states (Metal3+) were prepared using a common hydrothermal method. The XRD result indicated that these metals (10.0 wt.% per titania amount) are stably incorporated in a titanosilicate framework. The mesopore sizes were distributed in the range of 1.0–6.0 nm in TEM images, and the surface areas obtained were above 300 m2/g in all metal-incorporated MPTSs. The dehydrated amount decreased in the order of Al- > Bi- > Fe- > non-metal MPTS, and the activation energy needed for H2O desorption from the surface of photocatalyst decreased in the order of Al- > Fe- > Bi- > non-metal MPTS. The XPS result showed that the special peak for Ti2p in metal-MPTSs shifted to stronger binding energy than in non-metal MPTS. The O1s (Ti–O, Ti–OH) peaks for metal-MPTSs also shifted to stronger binding energy than those for non-metal MPTS. In particular, the shift to the larger binding energy for the second peak (Ti–OH) was remarkable in Al-MPTS. In H2-TPR, Ti3+ could be more easily transferred into Ti0, which affected the photoreaction, over Al- and Fe-MPTSs compared with non-metal MPTS. The photoluminescence intensity from the contribution of emitted electron decreased in the order: non-metal, Al-, Fe-, and finally Bi-MPTSs. Consequently, these findings indicate that the super-hydrophilicity of Al-MPTS was the best, and that the contact angle for water droplets was below 3° under 120 min UV-radiation.
Keywords: Mesoporous titanosilicate; (Al, Bi, Fe)-MPTS; Super-hydrophilicity; XPS; H2-TPR;
A highly stable and selective Pt-modified mordenite catalyst for the skeletal isomerization of n-butane by José Ignacio Villegas; Narendra Kumar; Teemu Heikkilä; Agáta Smiešková; Pavol Hudec; Tapio Salmi; Dmitry Yu. Murzin (223-230).
The aim of this work is to investigate the skeletal isomerization of n-butane to isobutane over Pt-modified mordenite zeolite catalysts and proton form mordenite with different SiO2/Al2O3 ratios. The 2-wt% Pt-H-MOR-20 and 2-wt% Pt-H-MOR-12.8 catalysts were synthesized by impregnation method, while H-MOR-12.8 and H-MOR-20 were obtained by calcinations of their ammonium-form counterparts.The influence of reaction temperature, carrier gas and dilution of the feed stream on the conversion of n-butane and yield of isobutane during time-on-stream has been studied. The Pt-modified mordenite catalysts have been characterized using XRD, scanning electron microscopy (SEM), nitrogen adsorption, CO chemisorption and FTIR of adsorbed pyridine.Pt-H-MOR-12.8 exhibited the highest yield and selectivity to isobutane and it was the most stable towards catalyst deactivation. Typically, an excess of propane with respect to pentanes was formed and the selectivity to pentanes remained constant for the different Pt-H-MOR and conditions tested. Selectivity to propane was inversely dependent on the H2 concentration in the feed and the SiO2/Al2O3 ratio.
Keywords: Skeletal isomerization; n-Butane; Isobutane; Mordenite; Platinum; Stability; Acidity;
Resistance to sulfidation and catalytic performance of titanium–tin solid solutions in SO2 + CO and NO + SO2 + CO reactions by Zhaoliang Zhang; Haoran Geng; Lisheng Zheng; Bin Du (231-237).
The resistance of TiO2–SnO2 solid solutions with different ratios to the sulfidation in the reduction of sulfur dioxide (SO2) and/or nitric oxide (NO) by carbon monoxide (CO) has been studied by temperature-programmed sulfiding (TPS), X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The catalytic performance has been related to these resistance results. A surface chemisorbed sulfur species which can be written as SnS2 is found rather than bulk tin sulfides in the solid solution catalysts after reactions. The resistance of TiO2–SnO2 solid solutions is rationalized by the formation of solid solutions (not mechanical mixtures) of TiO2 and SnO2, by the excellent stability of TiO2 in sulfur-containing gases, and by the bigger relative electronegativity of Sn than Ti. This leads to an extended electronic effect together with the lower stability of tin sulfides than titanium sulfides. The Ti0.88Sn0.12O2 catalyst can be sulfided neither by the SO2 + CO reaction nor by TPS of H2S. As the tin amount increased, TiO2–SnO2 solid solutions might separate into two microscopic agglomeration groups: one is rich in Ti4+ which cannot be sulfided like TiO2, the other is rich in Sn4+ which can be easily sulfided like pure SnO2. The higher tin content means that more Sn4+-rich agglomerate is available, which would suggest that: (1) the solid solution is more oxidative; and (2) the solid solution is more prone to be sulfided. Under the two interactions, the highest SO2 and NO conversions were obtained at a balanced composition of a weight ratio of 1:1 of TiO2 and SnO2 for the SO2 + CO and NO + SO2 + CO reactions. SO2 in the flue gas is a great promoter to the latter reaction.
Keywords: Tin dioxide; Titania; Solid solution; Sulfidation; SO2; NO; CO; Catalytic performance;
Preparation and catalysis of polymer-stabilized NiB catalysts on hydrogenation of carbonyl and olefinic groups by Biing-Jye Liaw; Shu-Jen Chiang; Cheng-Hsuan Tsai; Yin-Zu Chen (239-246).
PVP-stabilized NiB catalysts were prepared using the chemical reduction method with NaBH4, dissolving the water-soluble polymer of polyvinylpyrrolidone (PVP) in the precursor salt solution as a protective reagent. The PVP-NiB catalysts were characterized and examined for their catalysis on the hydrogenation of furfural, crotonaldehyde and citral. PVP polymer could adsorb on the nano-particles of NiB via a weak coordination bonding and stabilize it; a molecular weight of PVP of about 10,000 was suitable, and the optimal quantity of PVP (PVP/Ni) in the salt solution for preparing catalysts was around 20. The PVP-NiB samples were characterized by XRD as an amorphous structure and by TEM with a particle size distribution in the range of 3–5 nm. On catalysis, the PVP-NiB catalyst was significantly more active and slightly more selective than NiB for hydrogenating furfural to furfuryl alcohol and crotonaldehyde to butyraldehyde. A good yield of citronellal, about 90%, could be obtained by reducing citral in cyclohexane at a low reaction temperature of 50 °C over the PVP-NiB catalyst.
Keywords: Chemical reduction; Nano-particle; Polymer-stabilized catalyst; PVP-NiB; Hydrogenation; Furfural; Crotonaldehyde; Citral;
Bimodal porous Pd–silica for liquid-phase hydrogenation by Satoshi Sato; Ryoji Takahashi; Toshiaki Sodesawa; Masashi Koubata (247-251).
Palladium catalysts loaded on bimodal porous silica were examined in the liquid-phase hydrogenation of 2-butenal at 0 °C and a hydrogen pressure of 1.1 MPa. The sizes of mesopores and macropores of the silica support are controllable in the range of 4–23 nm and 0.5–25 μm, respectively. The macropores provide effective paths of mass transfer, and the mesopores present effective surfaces for dispersion of metals. The catalytic activity of Pd–silica with bimodal porous structure depends on the size of mesopores and macropores as well as on the particle size of the support silica. The most active Pd–silica catalyst, with mesopores of 12 nm and macropores of 2 μm, shows much higher activity than does a commercial palladium carbon catalyst without macropores. The results indicate that the diffusion process inside the catalyst particles dominantly determines the reaction rate in the hydrogenation.
Keywords: Hydrogenation; Pd; Bimodal porous silica; Macropore; Mesopore; Diffusivity;
Characterization of Pd–CeO2/α-alumina catalyst for synthesis of dimethyl oxalate by Xiu-Ge Zhao; Qian Lin; Wen-De Xiao (253-257).
Effect of adding CeO2 to Pd/α-Al2O3 as a catalyst promoter was investigated by X-ray diffraction, H2 chemisorption, and X-ray photoelectron spectroscopy methods. The addition of 0.8% CeO2 (wt%) greatly increased palladium dispersion on the α-Al2O3 support and decreased the particle size of palladium. Meanwhile, the addition of CeO2, increased the surface concentration of Pd. The in situ FTIR spectroscopy study indicated that CO was adsorbed on 1% Pd–0.8% CeO2/α-Al2O3 in the forms of linear species (band at 2089 cm−1) and bridged species (bands at 1967 and 1908 cm−1), and that the latter form was more stable. Methyl nitrite was very active and methoxylate could be observed from the IR spectra after methyl nitrite passed through the catalyst. Catalytic effects were evaluated in a micro-fixed-bed reactor at atmosphere pressure by using vapor-phase catalytic coupling reaction of carbon monoxide to (COOCH3)2 (dimethyl oxalate) as a model reaction.
Keywords: Dimethyl nitrite; Dimethyl oxalate; Pd; α-Al2O3; CeO2;