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Applied Catalysis A, General (v.296, #1)
Minimisation of carbon monoxide in a hydrogen stream for fuel cell application by D.L. Trimm (pp. 1-11).
Means of minimising carbon monoxide in a hydrogen stream for fuel cell operation are reviewed. Reduction of carbon monoxide to an acceptable level of 10–50ppm involves high temperature and low temperature water gas shift, followed by selective oxidation of residual carbon monoxide. Methanation of very small amounts of carbon monoxide may be an alternative final step.A new range of promoted iron-chromium catalysts for high temperature water gas shift is shown to proceed via a redox mechanism. Precious metals, copper and gold catalysts, mainly supported on ceria, are efficient for the low temperature reaction: ionic gold, held within an oxide lattice, is shown to be particularly effective, even in the absence of nanostructured gold particles.Selective oxidation is also promoted by gold-based catalysts but precious metal systems are widely used. The additional cost associated with the use of two reactors—to maintain temperature control—drives research into alternative systems.
Keywords: Fuel cell feed; Carbon monoxide minisation; Water gas shift; Selective oxidation
Esterification catalysis using functionalized membranes by T.N. Shah; S.M.C. Ritchie (pp. 12-20).
Novel functionalized microfiltration membranes have been developed for use as a heterogeneous, solid-phase, flowthrough catalytic structure for the esterification reaction between ethanol and acetic acid. Catalytic sites are located on each repeat unit of sulfonated polystyrene chains grafted in the flow pathways of the membrane. Batch studies showed that the activity of the catalytic membrane was comparable to the standard ion-exchange resin (IER) for the same acid capacity. Significant improvement in reaction kinetics was observed in flowthrough studies; a residence time of 20s gave the same conversion as 11h in batch reaction. The activation energy in flowthrough reaction was at least 20% lower than for the conventional IER. Some loss of grafted polystyrene (∼25%) in the reaction permeate was observed during flowthrough experiments, resulting in partial loss of activity. However, an increase in the graft chain length reduced graft loss by 60%, and there was essentially no graft loss when the grafts were covalently bound.
Keywords: Abbreviations; A.A.; acetic acid; CMR; catalytic membrane reactor; IEC; ion-exchange capacity; IER; ion-exchange resin; PES; polyethersulfone; RPES; raw polyethersulfoneMicrofiltration membrane; Polystyrene grafts; Membrane reactor; Catalysis
Novel bidentate phosphine modified Pd(acac)2/BF3OEt2 catalyst system for the homopolymerization of alkylnorbornenes and copolymerization with norbornene by G. Myagmarsuren; O.-Yong Jeong; Son-Ki Ihm (pp. 21-29).
The Pd(acac)2+ nPh2P(CH2) mPPh2+25BF3OEt2, n=1–3, m=1–6, catalyst system has been successfully employed for the homopolymerization of 5-alkyl-2-norbornenes and their copolymerization with norbornene. For this series, the most efficient catalyst system was Pd(acac)2+2Ph2P(CH2)4PPh2+25BF3OEt2. The activity of the catalyst system is comparable to that of most active late transition metal catalysts described in the literature. Bidentate phosphines containing bridges larger than 1,4-butane are likely to act as monodentate ligands. The incorporations of flexible alkyl groups onto the main chain of norbornene, as well as copolymerization of 5-alkyl-2-norbornenes with norbornene, represent a useful method for lowering the glass transition temperature ( Tg), i.e. improving the processability. The introduction of bidentate phosphine ligand to the Pd(acac)2+25BF3OEt2 system switched the carbocationic polymerization mechanism to the coordination Ziegler–Natta polymerization. The simplicity of this catalytic system composition might be of industrial importance.
Keywords: Alkylnorbornene; Bidentate phosphine; Boron trifluoride; Copolymerization; Palladium; Polymerization
Competitive CO and CO2 methanation over supported noble metal catalysts in high throughput scanning mass spectrometer by Karin Yaccato; Ray Carhart; Alfred Hagemeyer; Andreas Lesik; Peter Strasser; Anthony F. Volpe Jr.; Howard Turner; Henry Weinberg; Robert K. Grasselli; Chris Brooks (pp. 30-48).
High-throughput synthesis and screening methods have been developed for the heterogeneously catalyzed gas phase hydrogenation of CO and CO2 (‘methanation’) over zirconia and ceria supported noble and base metal catalysts at 300–400°C and ambient pressure. The discovery libraries, for primary screening, consisted of 11×11 arrays of 111 catalysts on 3in. quartz wafers, and 16×16 arrays of 256 catalysts on 4in. quartz wafers. Catalysts were prepared by liquid dispensing techniques and screened for catalytic activity in scanning mass spectrometers (SMS). This primary screening tool uses quadrupole mass spectrometry for rapid serial detection. More than 500 potential catalysts could be screened in a single day. A kinetic model based on fast equilibration by the reverse water–gas-shift reaction in parallel with about an order of magnitude slower CO hydrogenation is in good agreement with CO x conversion data. CO2 is mainly reverse shifted to CO. Ru, Rh, and Ni were found to promote methanation whereas Pt tends to catalyze the reverse WGS reaction. Methanation activity can be enhanced by some acidic and redox dopants or suppressed by basic dopants. High conversions were achieved in SMS demonstrating the minimal scalability risk for short contact time reactions.
Keywords: Methanation; Water–gas-shift; High throughtput screening; Primary screening; Mass spectrometer; Scanning; Library; Wafer; Kinetic modeling
Influence of complexing agents on the adsorption of molybdate and nickel ions on alumina by K. Al-Dalama; B. Aravind; A. Stanislaus (pp. 49-53).
The effect of complexing agents such as NTA and EDTA on the adsorption characteristics of molybdate and nickel ions on γ-alumina supports was investigated. Complexing agents changed the nature of the charge on these metal ions and strongly influenced the extent of their adsorption on the support surface. In the presence of the complexing ligands, molybdenum uptake on alumina was reduced, but nickel adsorption was enhanced.
Keywords: Molybdenum adsorption; Nickel adsorption; Isotherm; Alumina support; Effect of complexing agent
In situ synthesis of ammonium salt of 12-molybdophosphoric acid on iron phosphate and the ammoxidation functionality of the catalyst in the transformation of 2-methylpyrazine to 2-cyanopyrazine by Ch. Srilakshmi; N. Lingaiah; I. Suryanarayana; P.S. Sai Prasad; K. Ramesh; B.G. Anderson; J.W. Niemantsverdriet (pp. 54-62).
The ammonium salt of 12-molybdophosphoric acid (AMPA) on iron phosphate was synthesized via in situ interaction between the phosphate species of the support and the molybdenum component of ammonium heptamolybdate. The concentration of AMPA was varied such that the nominal MoO3 content of the catalysts was in the range of 5–20wt.%. The formation of AMPA, possessing the typical Keggin structure, was confirmed by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and FT-Raman spectroscopy. Thermo-gravimetric and differential thermal (TG/DT) analyses were used to establish the stability of these catalysts. Whereas the support, FePO4, displayed low activity but maximum selectivity to 2-cyanopyrazine (CP), the in situ synthesized catalysts exhibited higher activity during the ammoxidation of 2-methylpyrazine (MP). At lower reaction temperatures and particularly, at lower AMPA loading, the in situ synthesized catalysts have shown higher activity and retained substantially high selectivity.
Keywords: 12-Molybdophosphoric acid; Ammoxidation; 2-Methyl pyrazine
Oxidative dehydrogenation of isobutane to isobutene III by Yusaku Takita; Xia Qing; Akihide Takami; Hiroyasu Nishiguchi; Katsutoshi Nagaoka (pp. 63-69).
Among rare earth phosphates, only CePO4 and LaPO4 exhibit very high activity for oxidative dehydrogenation (ODH) of isobutane. This phenomenon was studied in comparison with the corresponding oxides. Isobutene was formed over NdPO4, which was used as a representative of inactive phosphate catalysts, by simple dehydrogenation with 30–32% selectivity, C3H6 and CO2 were formed with a selectivity of 25–33% and 20–30%, respectively. Isobutene was obtained at a higher selectivity of 79–86% over CePO4 and LaPO4. No H2 formation suggests that the essential reaction was the ODH of isobutane. In the oxidation over metal oxides, isobutene selectivity was relatively high: 60–70% over CeO2; however, the essential reaction was considered to be a simple dehydrogenation. Isobutene was formed at 40–47% selectivity, but simple dehydrogenation of isobutane would proceed over Nd2O3 and La2O3. La2O3, Nd2O3, and NdPO4 have only weak acidic sites. CeO2 has weak acidic sites and those with intermediate strength; LaPO4 and CePO4 have relatively strong acidic sites in addition to the weak acidic sites and those of intermediate strength. Oxidative dehydrogenation activity was correlated with strong acidic sites. ODH of isobutane occurred in the reaction between lattice oxygen of CePO4 and isobutane. Introduction of NH3 into the reaction system reduced both ODH of isobutane and CO2 formation; and stopping the NH3 supply led to a resumption of the activity, which suggests the participation of acidic sites. CePO4 catalyst contained 2% excess Ce to P; in the prepared CePO4 sample, Ce4+ was detected by XPS. We conclude that acidic sites and redox between Ce4+ and Ce3+ play important roles in the ODH of isobutane.
Keywords: Oxidative dehydrogenation of isobutane; Acidic sites; Reaction mechanism; CePO; 4; Lattice oxygen
New size effect in the catalysis by interacting copper nanoparticles by T.N. Rostovshchikova; V.V. Smirnov; V.M. Kozhevin; D.A. Yavsin; M.A. Zabelin; I.N. Yassievich; S.A. Gurevich (pp. 70-79).
Highly active catalysts consisting of copper nanoparticles deposited on surface-oxidized silicon were prepared by a new method of laser electrodispersion. This method allows fabricating the stable monodispersive nanoparticles comprised of amorphous copper core (the size is ≈3.5nm) covered by the thin (<1nm) Cu2O oxide shell. Taking chlorohydrocarbon conversions (dichlorobutene isomerization, carbon tetrachloride addition to 1-octene and carbon tetrachloride reaction with decane) as examples the unusually high activity (104–105 product mol/(metal molh)) of closely packed ensembles of nanoparticles was observed. These catalysts are several orders of magnitude superior in activity than usual supported metal catalysts. In all the reactions studied, strong dependence of the catalytic activity on the particle surface density and on the polarity of the reactant solution was found. These results are in a good agreement with theoretical estimations indicating that nanoparticle charging, which occurs due to thermally activated electron tunneling between closely located particles is responsible for the formation of highly active catalytic system.
Keywords: Metal nanostructure; Charge state; High catalytic activity
Mechanistic study of water–gas-shift reaction over TiO2 supported Pt–Re and Pd–Re catalysts by Yasushi Sato; Keisuke Terada; Satoshi Hasegawa; Toshihiro Miyao; Shuichi Naito (pp. 80-89).
Water–gas-shift reactions over Pt–Re/TiO2 and Pd–Re/TiO2 catalysts were studied, using the closed gas circulation system and the fixed-bed flow-type reactor. The activity of Pd–Re/TiO2 catalysts was strongly affected by the Re content, while the activity of Pt–Re/TiO2 catalysts was less dependent on the addition ratio of Re, and more dependent on the temperature of reduction. The formation of certain bimetallic clusters between Pt and Re or Pd and Re was confirmed in the cases of Pt–Re(2:3) and Pd–Re(1:1)/TiO2 catalysts; however a different addition manner was suggested for the later acceleration effect over Pd–Re(1:10)/TiO2 catalysts. The FT-IR analyses of the adsorbed species during the reaction exhibited the enhancement of the adsorbed CO peaks in lower wavenumber region with the increase of Re content. Accordingly, Re is supposed to have some effect on these adsorbed CO, which accelerates the WGS reaction, especially in the case of Pd–Re/TiO2 catalysts.
Keywords: Water–gas-shift reaction; Pt–Re/TiO; 2; catalyst; Pd–Re/TiO; 2; catalyst; Bimetallic clusters
Platinum- and iron-doubly promoted tungstated zirconia catalyst for n-butane isomerization reaction by She-Tin Wong; Tao Li; Soofin Cheng; Jyh-Fu Lee; Chung-Yuan Mou (pp. 90-99).
The catalysis of n-butane isomerization over iron-promoted tungstated zirconia (F1.2WZ) and platinum–iron-promoted tungstated zirconia (P/F1.2WZ) catalysts was studied and correlated to the catalyst characterization results. In the singly promoted F1.2WZ catalyst, we suggest that the iron species promotes the n-butane isomerization reaction through a redox effect. The formation of W–O–Fe linkages optimized the surface reduction of WO x, thereby facilitating the formation of Brønsted acid sites necessary for the generation of carbenium ion. In addition, Fe3+ itself can also act as a redox site. In the case of the doubly promoted P/F1.2WZ catalyst, its catalytic activity is much higher than the sum of the singly promoted P/WZ and F1.2WZ catalysts. The exceptionally high activity of P/F1.2WZ catalyst in n-butane isomerization reaction is explained by a cooperative effect. The diffusion of activated n-butane species stabilized by iron promoter to the Brønsted acid sites created by platinum promoter will be improved as both promoters are in close proximity to each other. The interaction between iron promoter and n-butane or its activated species is shown by the influence of iron on the propane selectivity of the reaction. In addition, the close proximity of platinum and iron promoters in P/F1.2WZ catalyst is shown by TPR. The location and nature of iron promoter on WZ were also characterized. Results revealed that the iron promoter is located on the surface of F1.2WZ catalyst. XANES, EXAFS, and EPR studies suggest that the iron promoter exists as highly dispersed Fe3+ species either bound to WO x surface or located at the surface vacant sites of zirconia. In addition, EPR study indicates the presence of fine α-Fe2O3 clusters on the surface of catalyst; the TPR peak at 421°C is probably due to Fe–O–Fe of this species.
Keywords: Tungstated zirconia; Promoter; Platinum; Iron; n; -Butane isomerization; EXAFS
Catalytic performance of microtube-type copper-based catalyst for methanol steam reforming, prepared on the inner wall of an aluminum tube by electroless plating by Choji Fukuhara; Yoshiyuki Kamata; Akira Igarashi (pp. 100-107).
In order to construct a high-performance microreactor for conducting heterogeneous catalytic reactions, one must prepare a porous catalytic wall with high surface area on the microchannel. In this study, with the purpose of preparing such a catalyzed wall, microchannels plated with copper-based components by electroless plating were prepared on the inner walls of aluminum tubes with micron-order diameter. The electroless plating consisted of an activation of the inner walls of aluminum tubes by hydrogen chloride solution, a displacement plating of zinc, an intermediate plating of iron, and chemical reduction plating of copper. Each process solution was flowed into the aluminum tube by a suction pump system. The physicochemical properties and the steam reforming properties of methanol for the plated channel were then investigated. Scanning electron microscopy (SEM) photographs of the surface and section of the plated wall showed that the preparation used in this study produced catalytic components with a film thickness of about 100μm that were deposited porously on the inner surfaces of microtubes. An elemental analysis indicated that the plated walls consisted of copper and zinc, with the latter being detected in a wide area from the bulk to the surface of the wall. The microtube-type copper-based catalyst oxidized by air was significantly higher in activity of methanol reforming than that reduced by hydrogen, indicating that the conversion was 100% and the hydrogen production was about 0.07mol/h at 160°C with the channel length of 450mm. Even after the activity of the oxidized catalyst declined, its initial activity could be restored by reoxidation. The activity restoration by reoxidation could be repeated. These results show that the microtube-type catalysts prepared in this study have high catalytic performance for microreformer.
Keywords: Microreactor; Structured catalyst; Methanol steam reforming; Copper-based catalyst; Electroless plating; Oxidation
Vanadium incorporated ammonium salt of 12-molybdophosphoric acid supported on titania: Effect of loading on the activity and selectivity of the catalysts during ammoxidation of 2-methylpyrazine by K. Mohan Reddy; N. Lingaiah; K.N. Rao; Nilofer Rahman; P.S. Sai Prasad; I. Suryanarayana (pp. 108-113).
A series of catalysts was synthesized with varying quantities of vanadium incorporated into the ammonium salt of 12-molybdophosphoric acid (AMPV) supported on titanium dioxide. The catalysts were characterized by XRD, FT-IR, TPD of ammonia and XPS techniques. The characterization data derived from XRD, FT-IR and XPS techniques reveal that the AMPV on titania support exists in the Keggin structure. These catalysts are studied for the vapor phase ammoxidation of 2-methylpyrazine (MP) to cynopyrazine (CP). The conversion of methylpyrazine increased with increase in loading on titania showing a maximum at 20wt.% AMPV loading. A comparative study has been made among the catalytic functionalities of the 12-molybdophosphoric acid, its ammonium salt and vanadium incorporated ammonium salt. Vanadium incorporation led to substantial improvement in the selectivity to cynopyrazine.
Keywords: Ammonium salt of 12-molybdophosphoric acid; Vanadium incorporation; Titania; Ammoxidation; 2-Methylpyrazine
The reducing capability of palladium segregated from perovskite-type LaFePdO x automotive catalysts by Mari Uenishi; Hirohisa Tanaka; Masashi Taniguchi; Isao Tan; Yoshiyuki Sakamoto; Shin-ichi Matsunaga; Koji Yokota; Tetsuhiko Kobayashi (pp. 114-119).
In order to elucidate the activity of LaFePdO x-based automobile three-way catalysts at low-temperatures, the oxygen release capacity (ORC) and oxygen storage capacity (OSC) of LaFePdO x were measured by means of thermogravimetry (TG) in a hydrogen-containing atmosphere at 200–400°C and NO reduction activity was examined at 400°C by an NO-pulse technique. The catalyst weight-loss in reduction was attributed to oxygen release, leading to the formation of metallic Pd0. About 40% of Pd3+ in LaFe0.95Pd0.05O3 was converted into Pd0 at 200°C and about 90% at 400°C. ORC and OSC as observed for the LaFePdO x catalysts were found to be comparable to results seen when adding Ce-based oxides as an OSC material in a commercial catalytic converter. The reducing capability of Pd for NO reduction demonstrated by the reduced LaFePdO x catalysts can probably be attributed to the very fine dispersion of Pd0 species segregated from LaFe0.95Pd0.05O3 perovskite. The Pd0 species segregated from LaFePdO x by reduction was assessed to be metallic Pd0 particles with diameters smaller than 2nm. Highly dispersed Pd0 particles on the LaFePdO x catalyst were found to act as “breathing active sites� that combined high catalytic activity with OSC/ORC performance.
Keywords: Perovskite; Three-way catalyst; Self-regenerative function; Oxygen release capacity; Redox reaction; The intelligent catalyst
Investigation of a new oxidative catalytic system involving Jacobsen's catalyst in the absence of organic solvents by D.F.C. Guedes; T.C.O. Mac Leod; M.C.A.F. Gotardo; M.A. Schiavon; I.V.P. Yoshida; K.J. Ciuffi; M.D. Assis (pp. 120-127).
In this work, the commercially available Jacobsen's catalyst, Mn(salen), was occluded in a hybrid polymeric membrane based on poly(dimethylsiloxane) (PDMS). This system was used as a catalytic barrier between two different phases: an organic substrate phase (cyclohexane, cyclooctene, cyclohexene or styrene) in the absence of solvent, and an aqueous solution of either t-BuOOH or H2O2. Such system was characterized by UV–vis spectroscopy, TGA, DTA, DSC, and SEM techniques. The occluded complex proved to be an efficient catalyst for the oxidation of alkanes and alkenes when t-BuOOH was used as oxidant. However, the hybrid polymeric membrane was a barrier against H2O2, preventing this oxidant from reaching the bulk of the membrane and oxidizing the substrate.
Keywords: Jacobsen's catalyst; Mn(salen); Poly(dimethylsiloxane); Hybrid polymeric membrane; Oxidation; Catalyst; “Green chemistry�
Acetone condensation and selective hydrogenation to MIBK on Pd and Pt hydrotalcite-derived MgAl mixed oxide catalysts by A.A. Nikolopoulos; B.W.-L. Jang; J.J. Spivey (pp. 128-136).
The condensation and selective hydrogenation of acetone to methyl isobutyl ketone (MIBK) was studied on a directly comparable series of 0.1–1.5wt% Pd and Pt catalysts supported on hydrotalcite (HT)-derived MgAl mixed-oxides in a liquid-phase batch micro-reactor at 99–153°C and 400psig. The support catalyzes the condensation of acetone to diacetone alcohol (DAA) and its subsequent dehydration to mesityl oxide (MO); Pd and Pt catalyze the selective hydrogenation of MO to MIBK. The net yield of MIBK is independent of metal type and loading, depending only on the wt% of exposed metal. However, the by-products are quite different-Pt/HT is more selective for the direct hydrogenation to isopropanol (IPA) while Pd/HT forms more of the intermediate diacetone alcohol (DAA). Among the Pd- and Pt-based catalysts examined, the 0.1wt% Pd/HT gives the maximum MIBK yield of ∼32%, with an unusually low selectivity to IPA, 0.6mol% compared to 15mol% for the next best catalyst. This appears to be due to its higher basicity, and (to a lesser extent) to its minimal concentration of metal sites. This metal loading is sufficient to fully hydrogenate mesityl oxide to MIBK, and it also shows minimal acetone hydrogenation to isopropanol. A study of physically mixed Pd/silica+HT versus Pd/HT shows that the acid/base and hydrogenation functions need not be molecularly close.
Keywords: Acetone; Aldol condensation; Diacetone Alcohol; Hydrotalcite; Mesityl oxide; Methyl isobutyl Ketone; Palladium; Platinum