Showing papers on "Catalyst support published in 2002"

Self-regeneration of a Pd-perovskite catalyst for automotive emissions control

Abstract: Catalytic converters are widely used to reduce the amounts of nitrogen oxides, carbon monoxide and unburned hydrocarbons in automotive emissions. The catalysts are finely divided precious-metal particles dispersed on a solid support. During vehicle use, the converter is exposed to heat, which causes the metal particles to agglomerate and grow, and their overall surface area to decrease. As a result, catalyst activity deteriorates. The problem has been exacerbated in recent years by the trend to install catalytic converters closer to the engine, which ensures immediate activation of the catalyst on engine start-up, but also places demanding requirements on the catalyst's heat resistance. Conventional catalyst systems thus incorporate a sufficient excess of precious metal to guarantee continuous catalytic activity for vehicle use over 50,000 miles (80,000 km). Here we use X-ray diffraction and absorption to show that LaFe0.57Co0.38Pd0.05O3, one of the perovskite-based catalysts investigated1,2,3,4 for catalytic converter applications since the early 1970s, retains its high metal dispersion owing to structural responses to the fluctuations in exhaust-gas composition that occur in state-of-the-art petrol engines5. We find that as the catalyst is cycled between oxidative and reductive atmospheres typically encountered in exhaust gas, palladium (Pd) reversibly moves into and out of the perovskite lattice. This movement appears to suppress the growth of metallic Pd particles, and hence explains the retention of high catalyst activity during long-term use and ageing.

A review of the selective reduction of NOx, with hydrocarbons under lean-burn conditions with non-zeolitic oxide and platinum group metal catalysts

Abstract: Research on the selective reduction of NOx with hydrocarbons under lean-burn conditions using non-zeolitic oxides and platinum group metal (PGM) catalysts has been critically reviewed. Alumina and silver-promoted alumina catalysts have been described in detail with particular emphasis on an analysis of the various reaction mechanisms that have been put forward in the literature. The influence of the nature of the reducing agent, and the preparation and structure of the catalysts have also been discussed and rationalised for several other oxide systems. It is concluded for non-zeolitic oxides that species that are strongly adsorbed on the surface, such as nitrates/nitrites and acetates, could be key intermediates in the formation of various reduced and oxidised species of nitrogen, the further reaction of which leads eventually to the formation of molecular nitrogen. For the platinum group metal catalysts, the different mechanisms that have been proposed in the literature have been critically assessed. It is concluded that although there is indirect, mainly spectroscopic, evidence for various reaction intermediates on the catalyst surface, it is difficult to confirm that any of these are involved in a critical mechanistic step because of a lack of a direct quantitative correlation between infrared and kinetic measurements. A simple mechanism which involves the dissociation of NO on a reduced metal surface to give N(ads) and O(ads), with subsequent desorption of N2 and N2O and removal of O(ads) by the reductant can explain many of the results with the platinum group metal catalysts, although an additional contribution from organo-nitro-type species may contribute to the overall NOx reduction activity with these catalysts. It is concluded, after the investigation of hundreds of catalyst formulations, that many of the fundamental questions relating to lean deNOx reactions have been addressed and the main boundary conditions have been established. It seems clear that catalysts with sufficient activity, selectivity or stability to satisfy the demanding conditions that appertain in automotive applications are still far away. The rapidly growing interest in NOx storage systems reflects this situation, and it now seems to be the case that acceptable direct NOx reduction catalysts may be very difficult to find for lean-burn applications.

Fischer–Tropsch synthesis: support, loading, and promoter effects on the reducibility of cobalt catalysts

Abstract: Temperature programmed reduction (TPR) and hydrogen chemisorption combined with reoxidation measurements were used to define the reducibility of supported cobalt catalysts. Different supports (e.g. Al2O3, TiO2, SiO2, and ZrO2 modified SiO2 or Al2O3) and a variety of promoters, including noble metals and metal cations, were examined. Significant support interactions on the reduction of cobalt oxide species were observed in the order Al2O3>TiO2>SiO2. Addition of Ru and Pt exhibited a similar catalytic effect by decreasing the reduction temperature of cobalt oxide species, and for Co species where a significant surface interaction with the support was present, while Re impacted mainly the reduction of Co species interacting with the support. For catalysts reduced at the same temperature, a slight decrease in cluster size was observed in H2 chemisorption/pulse reoxidation with noble metal promotion, indicating that the promoter aided in reducing smaller Co species that interacted with the support. On the other hand, addition of non-reducible metal oxides such as B, La, Zr, and K was found to cause the reduction temperature of Co species to shift to higher temperatures, resulting in a decrease in the percentage reduction. For both Al2O3 and SiO2, modifying the support with Zr was found to enhance the dispersion. Increasing the cobalt loading, and therefore the average Co cluster size, resulted in improvements to the percentage reduction. Finally, a slurry phase impregnation method led to improvements in the reduction profile of Co/Al2O3.

Fabrication of ordered uniform porous carbon networks and their application to a catalyst supporter.

Abstract: Ordered uniform porous carbon frameworks showing interesting morphology variations were synthesized against removable colloidal silica crystalline templates through simply altering acid catalyst sites for acid-catalyzed polymerization. These highly ordered uniform porous carbons as a catalyst supporter resulted in much improved catalytic activity for methanol oxidation in a fuel cell.

A systematic study of the synthesis conditions for the preparation of highly active gold catalysts

Abstract: Supported gold catalysts were prepared by a deposition–precipitation method in order to investigate the influence of the synthesis conditions on the difference in catalytic activities for CO oxidation. The optimization of the synthesis parameters resulted in highly active Au/TiO2, Au/Co3O4, Au/Al2O3 and Au/ZrO2 catalysts. SiO2 was found to be an unsuitable support material for the deposition–precipitation method. With increasing pH value during precipitation and decreasing temperature of calcination increasing catalytic activity was observed. The optimum pH was in the range of eight to nine and slightly dependent on the nature of the support. The optimum temperature of calcination was 200 °C. According to XRD and TEM the increasing catalytic activity could be attributed to a decrease in the gold particle size. However, comparing two samples with similar gold particle sizes, Au/TiO2 is more active than Au/Al2O3. This indicates that the catalytic activity is not only a particle size effect, but the role of the metal oxide is more than just the stabilization of the gold particles.

Development of supported bifunctional electrocatalysts for unitized regenerative fuel cells

Abstract: bUOP LLC, Des Plaines, Illinois 60017, USA Mixed metal catalysts containing Pt, Ir, Ru, Os, and Rh were synthesized on three different conductive oxide supports, Ebonex, which is a mixture of Ti4O7 and other phases, phase-pure microcrystalline Ti4O7 , and Ti09Nb01O2 , a doped rutile compound Ebonex-supported catalysts were prepared as arrays and screened combinatorially for activity and stability as bifunctional oxygen reduction/water oxidation catalysts The highest activity and stability was found in the Pt-Ru-Ir ternary region at compositions near Pt4Ru4Ir1 X-ray near edge absorption spectra indicated a significant electronic interaction between the catalyst and the support, and a substantial increase in catalyst utilization was observed, even though the support surface areas were relatively low Both Ebonex and Ti4O7 have short-lived electrochemical stability under conditions of oxygen evolution at 116 V vs RHE in 05 M H2SO4 Current at these supported catalysts gradually decreases, and the decrease is attributed to loss of electronic conductivity Ebonex and Ti4O7 are also thermally oxidized in air at temperatures above 400°C In contrast, Ti09Nb01O2 , which has a nondefective oxygen lattice, is quite resistant to electrochemical and thermal oxidation Conditioning of Ti 09Nb01O2-supported Pt4Ru4Ir1 at positive potentials had little effect on the activity of the catalyst © 2002 The Electrochemical Society @DOI: 101149/11491237# All rights reserved

Methane reforming over Ni/Ce-ZrO2 catalysts: effect of nickel content

Abstract: The effect of Ni content on the Ni/Ce-ZrO2 catalyst has been investigated in the methane conversion reactions to syngas, such as oxy-reforming, steam reforming and oxy-steam reforming. Among the catalysts examined, Ni/Ce-ZrO2 catalyst with 15% Ni loading exhibits not only the highest catalytic activity and selectivity but also remarkable stability. The TPR results reveal that strong interaction between support and metal exists and that some part of NiO incorporates into the surface of the Ce-ZrO2 support. Combined with H2 chemisorption results, one may deduce that Ni surface area and the chemical environment of nickel, as well as the properties of the Ce-ZrO2 support, play very important roles in the catalytic activity and stability of Ni/Ce-ZrO2 catalysts. It seems that two kinds of active sites, i.e. one for methane and the other for steam or oxygen, are well-balanced on 15% Ni/Ce-ZrO2 catalyst.

Highly active and stable Ni/Ce-ZrO2 catalyst for H2 production from methane

Abstract: Steam reforming of methane has been carried out aimed at the development of new and highly active catalysts for H2 production The catalytic properties of Ni catalysts supported on various supports have been investigated in connection with characterization results obtained from XRD, H2 chemisorption, TPR and CO2-TPD Among the catalysts examined, Ni/Ce–ZrO2 exhibited the best activity and stability The remarkable catalytic performance is interpreted as a combined result of high oxygen storage capacity of ceria in Ce–ZrO2, strong interaction between Ni and Ce–ZrO2, basic property of the catalyst and rather high capability of H2 uptake

Catalyst for purifying exhaust gases

Abstract: A catalyst for purifying exhaust gases exhibits not only effective purifying characteristics even in a low temperature range such as immediately after an engine starts but also high exhaust gas purifying ability. In the catalyst for purifying exhaust gases of a first aspect of the invention, HC adsorbed at low temperature are released at high temperature and the released HC are purified by a catalyst metal. This catalyst for purifying exhaust gases has an excellent advantage in purifying HC at low temperature as well as excellent exhaust gas purifying ability.

Design and fabrication of microfluidic devices for multiphase mixing and reaction

Abstract: Using silicon microfabrication technology, microchemical devices have been constructed for the purpose of conducting heterogeneously catalyzed multiphase reactions. The motivation behind the design, the fabrication approach, and the experimental characterization are presented for two classes of devices. The first design involves multiple parallel channels with integrated filter structures to incorporate standard catalytic materials. These catalysts are in the form of finely divided porous particles in a packed-bed arrangement. The second device involves the incorporation of porous silicon as a catalyst support, in the form of a thin layer covering microstructured channels. These microstructured channels simulate the structure of a packed bed and enhance mass transfer relative to an open channel. The ability to incorporate features at the tens-of-microns scale can reduce the mass-transfer limitations by promoting mixing and dispersion for the multiple phases. Directly integrating the catalyst support structures into the channels of the microreactor allows the precise definition of the bed properties, including the support's size, shape and arrangement, and the void fraction. Such a design would find broad applicability in enhancing the transport and active surface area for sensing, chemical, and biochemical conversion devices. Reaction rates for the gas-liquid-solid hydrogenation of cyclohexene using the integrated catalyst with porous silicon as a support compare favorably to those rates obtained with the packed-bed approach. In both cases, the mass transfer coefficient is at least 100 times better than conventional laboratory reactors.

Efficient evolution of hydrogen from liquid cycloalkanes over Pt-containing catalysts supported on active carbons under “wet–dry multiphase conditions”

Abstract: Highly efficient evolution of hydrogen is achieved in the dehydrogenation of cycloalkanes such as cyclohexane, methylcyclohexane, and decalin over Pt catalyst supported on active carbon (AC) under “wet–dry multiphase conditions”. Formation rate of hydrogen is largely dependent on reaction conditions such as reactant/catalyst ratio, temperature, and support. The highest initial rate of formation of hydrogen, k =8.0×10 −3 mol min −1 , was obtained in the dehydrogenation of cyclohexane over Pt/AC at 623 K and the reactant/catalyst ratio=3.3 ml g −1 . The addition of second metals such as Mo, W, Re, Rh, Ir, and Pd on the carbon-supported Pt catalysts enhances the dehydrogenation rate due to the promotion of CH bond cleavage and/or desorption of aromatic products. A physical mixture of Pt/AC and Pd/AC catalysts exhibits higher activities than the monometallic Pt/AC catalyst owing to the synergistic effects of spillover, migration, and recombination of hydrogen over Pt and Pd catalysts.

Theory and applications of ceramic foam catalysts

Abstract: Reticulated ceramic foams can now be prepared from a range of materials, and they have characteristics that make them desirable as substrates for structured heterogeneous catalysts. They exhibit extremely high porosities, with a significant degree of interconnectivity that results in low pressure-drop. High convection in the tortuous megapores gives enhanced mass and heat transfer. Furthermore, ceramic foam catalysts, unlike their honeycomb monolithic counterparts, have a considerable degree of radial mixing, which is an advantage in processes limited by heat transfer and can even out flow distribution. The low surface areas of ceramic foams means they have to be coated with a higher surface area material, and this increases the pressure drop and radial heat transfer conductivity in a predictable way. Reactions that require short contact times to control product selectivity and processes that are limited by heat transfer to or from the catalyst bed can benefit from the use of foam-based catalysts. This is particularly true if the effectiveness factor for a specific reaction with conventional catalyst particles is low. Examples of reactions of this type include many industrially important processes, such as the partial oxidation of hydrocarbons, water gas shift, methanol synthesis, methanation and Fischer-Tropsch synthesis. In this paper, the structure of ceramic foam catalysts, and correlations for estimating their transport properties are reviewed, and their use to potential applications are considered.

Gasoline conversion: reactivity towards cracking with equilibrated FCC and ZSM-5 catalysts

Abstract: Cracking of a straight-run FCC gasoline using either a steamed ZSM-5 catalyst or a base, FCC equilibrium, catalyst shows that the only significantly reactive components in the gasoline fraction are normal and branched olefins with a carbon number of seven and higher. Overall, the reactivity of gasoline is one to two orders of magnitude smaller than that of a normal FCC feedstock. The ZSM-5 catalyst produces light olefins (LPG-range and some ethene) through cracking of the gasoline-range olefins. The base catalyst produces these light olefins in lower amounts than ZSM-5 does. Further, the base catalyst produces small amounts of paraffins and products that are heavier than the gasoline feedstock. The overall reason for the differences between the two catalysts is a shape-selective mechanism; in the small pores of ZSM-5 only monomolecular cracking reactions take place, while in the larger pores of the FCC base catalyst also a bimolecular reaction mechanism is operative. As a result of the absence of bimolecular reactions, with ZSM-5, the average size of the products and the amount of hydrogen transfer products is smaller than with the base catalyst. On the other hand, because of the relatively small pore size of ZSM-5, the interaction between the catalytic surface of ZSM-5 and the reactants is larger resulting in a higher conversion of linear olefins and a higher production of ethene than with the base catalyst.

Ni–Ru bimetallic catalysts for the CO2 reforming of methane

Abstract: This paper reports the study on the effect of addition of various amounts of Ru to supported Ni catalysts towards the CO2 reforming of methane. Catalytic activity results have shown that in the case of silica supported samples addition of Ru strongly enhances the catalytic performance of the Ni sample, both in terms of activity and stability. The influence of Ru addition is instead much less remarkable on H-ZSM5 zeolite supported samples. On the basis of FT-IR spectra of adsorbed CO, H2 and O2 chemisorption and temperature-programmed reduction measurements, it has been proposed that the different trend observed on the two series of catalysts is related to different metal–metal and metal-support interactions occurring on the catalysts. In particular, the strong improvement in the activity and stability observed on silica supported Ni–Ru bimetallic samples has been attributed to an increase in the metallic dispersion of Ni as a consequence of the formation of Ni–Ru clusters with the surface mainly covered by Ni.

Supported nanoparticle catalyst

Abstract: A supported catalyst is provided comprising catalyst metal nanoparticles having an average particle size of 3.0 nm or less, or mo re typically 2.0 nm or less, and typically having a standard deviation of particle size of 0.5 nm or less, which are supported on support particles at a loading of 30% or more. Typical catalyst metals are selected from platinum, palladium, ruthenium, rhodium, iridium, osmium, molybdenum, tungsten, iron, nickel and tin. Typical support particles are carbon. A method of making a supported catalyst is provided comprising the steps of :a)providing a solution of metal chlorides of one or more catalyst metals in solvent system containing at least one polyalcohol, typically ethylene glycol containing less than 2% water; b)forming a colloidal suspension of unprotected catalyst metal nanoparticles by raising the pH of the solution, typically to a pH of 10 or higher, and heating said solution, typically to 125°C or higher; c)adding support particles to the colloidal suspension; and d)depositing the unprotected catalyst metal nanoparticles on the support particles by lowering the pH of said suspension, typically to a pH of 6.5 or lower.

The effect of CeO2 structure on the activity of supported Pd catalysts used for methane steam reforming

Abstract: Palladium (Pd) supported on CeO2-promoted γ-Al2O3 with various CeO2 (ceria) crystallinities, were used as catalysts in the methane steam reforming reaction. X-ray diffraction (XRD) analysis, FTIR spectroscopy of adsorbed CO, and X-ray photoelectron spectroscopy (XPS) were employed to characterize the samples in terms of Pd and CeO2 structure and dispersion on the γ-Al2O3 support. These results were correlated with the observed catalytic activity and deactivation process. Arrhenius plots at steady-state conditions are presented as a function of CeO2 structure. Pd is present on the oxidized CeO2-promoted catalysts as Pd0, Pd+ and Pd2+, at ratios strongly dependent on CeO2 structure. XRD measurements indicated that Pd is well dispersed (particles

Iron-containing catalysts of methane decomposition: accumulation of filamentous carbon

Abstract: Iron-containing catalysts were tested in methane decomposition reaction at moderate temperature and pressure 1 bar in order to evaluate their catalytic properties and produce catalytic filamentous carbon (CFC). Catalyst preparation method and composition of the catalysts were found to influence their properties. The best performance was found with coprecipitated Fe-Co-Al2O3 catalysts, where carbon capacity has achieved 52.4 g/gcat. TEM investigations have shown that carbon nanotubes were formed.

Effects of support on the activity of Co–Mo sulfide model catalysts

Abstract: The support effects of Co–Mo sulfide catalysts on the activities for hydrodesulfurization (HDS) and hydrogenation (HYD) were investigated by preparing model catalysts. CoS x –MoS 2 model catalysts were prepared by exposing supported Mo sulfide catalysts to a vapor of Co(CO) 3 NO, followed by a second sulfidation. The supports used here were Al 2 O 3 , TiO 2 , ZrO 2 and SiO 2 . XPS results showed that the Co sulfide species interacting with MoS 2 particles are formed by using Co(CO) 3 NO as a precursor. On the basis of a proportional correlation between Co/Mo and NO/Mo ratios, it is concluded that the Co sulfide species are located on the edge sites of MoS 2 particles, suggesting the formation of a CoMoS phase. The thiophene HDS activity was proportional to the amount of the Co species irrespective of the support for CoS x –MoS 2 /Al 2 O 3 , TiO 2 and ZrO 2 , indicating that the Co species form catalytically active sites and that no real support effects are observed in terms of the specific activity of the Co species. The higher activity of the Co sulfide phase supported on SiO 2 suggests that CoMoS(II) is formed on CoS x –MoS 2 /SiO 2 , whereas CoMoS(I) is formed on CoS x –MoS 2 /Al 2 O 3 , TiO 2 and ZrO 2 . On the other hand, the Co species on TiO 2 , ZrO 2 and SiO 2 showed the identical specific activity for the HYD of butadiene. The Co species on Al 2 O 3 , however, exhibited a higher activity for HYD. The HDS and HYD reactions over the Co–Mo sulfide catalysts are affected by the support in different ways. The NO adsorption property of the CoS x –MoS 2 model catalyst was also examined.