Showing papers on "Catalyst support published in 2004"

Electrocatalytic corrosion of carbon support in PEMFC cathodes

Abstract: The influence of platinum on the corrosion of carbon catalyst supports has been characterized by on-line mass spectroscopy during cyclic voltammetry, with varying Pt mass fraction, catalyst type, and temperature. The generation rates increased with higher Pt mass fraction (0, 10, and 39% balanced by Vulcan XC-72). A peak observed at approximately for Pt/C was lowered to for PtRu/C. An Arrenhius plot indicated higher apparent activation energy for production at the positive potential limit of the cyclic voltammogram on 0% Pt (carbon-only) electrode than on 39% Pt/C electrode. It was concluded that platinum accelerated the corrosion rate of the carbon catalyst support. © 2003 The Electrochemical Society. All rights reserved.

Dry reforming of methane over nickel catalysts supported on magnesium aluminate spinels

Abstract: Dry reforming of methane to synthesis gas was studied over Ni-based catalysts. Compared to Ni/γ-Al2O3, the Ni/MgO-γ-Al2O3 and Ni/MgAl2O4 catalysts exhibit higher activity and better stability using a stoichiometric feed ratio (1:1). The MgAl2O4 spinel layer in Ni/MgO-γ-Al2O3 can effectively suppress the phase transformation to form NiAl2O4 spinel phases and can stabilize the Ni tiny crystallites, to which the good stability of the catalyst contributes. The application of magnesium aluminate spinel (MgAl2O4) prepared by the co-precipitation method as a support of Ni catalysts can give a high active catalytic system with excellent stability under reaction conditions. The high sintering-resistance ability and low acidity of MgAl2O4 compared to γ-Al2O3 and the interactions between Ni and MgAl2O4 might be responsible for its high activity and resistant to coking and sintering, because it can produce a highly dispersed active Ni species.

A mini-review on ammonia decomposition catalysts for on-site generation of hydrogen for fuel cell applications

Abstract: Due to the drive for better environmental protection and energy conversion efficiency, on-site generation of CO x -free hydrogen from ammonia decomposition for fuel cell applications has attracted much attention. The development of high performance solid catalysts is essential for the supply of such hydrogen from ammonia. In this mini-review, we provide a summary of the reaction kinetics of catalytic ammonia decomposition. Comparisons are then made among the catalysts that have different active components, supports, and promoters. According to the works reported in the literature and our recent research results, Ru is the most active catalyst, carbon nanotubes (CNTs) are the most effective support, and KOH is the best promoter. An increase in Ru dispersion results in better catalytic performance. Both support basicity and conductivity are important criteria for a NH 3 decomposition catalyst of high efficiency; and it seems possible to generate novel advanced support, such as oxide-CNTs nanocomposite materials, that bears such characteristics. Also, proper removal of the electron-withdrawing entities that originate from the precursors of active component, support or promoter can be effective in enhancing the catalytic activity of a Ru catalyst.

Synthesis and characterization of mesoporous alumina with nickel incorporated for use in the partial oxidation of methane into synthesis gas

Abstract: Mesoporous alumina catalysts that incorporate nickel (Ni-Alumina) with different Ni/Al molar ratios of 1:2, 1:5 and 1:10 were synthesized by a one-step sol–gel method using lauric acid as a template The prepared Ni-Alumina catalysts showed a relatively high surface area with a narrow pore size distribution after calcination at 700 °C; these effects were independent of the Ni/Al molar ratio Although weak interactions between nickel oxide and alumina were observed in the Ni-Alumina catalysts with increasing the amounts of nickel precursor, nickel catalysts finely dispersed on an alumina support were obtained in all cases The Ni-Alumina catalysts were found to be highly active in the partial oxidation of methane For the purposes of comparison, a nickel catalyst impregnated on a commercially available alumina support was prepared (Ni-IMP) Various characterization results showed that the 1:10 Ni-Alumina catalyst had stronger metal-support interactions and a more favorable catalyst structure for obtaining finely dispersed nickel particles, compared to the Ni-IMP catalyst The deactivation of catalysts examined in this work was not due to catalyst sintering, but mainly to the carbon deposition The Ni-Alumina catalyst having smaller nickel particles and lower levels of carbon deposition had a more stable catalytic activity than the Ni-IMP catalyst

Photocatalytic degradation of orange II by TiO2 catalysts supported on adsorbents

Abstract: TiO 2 mediated semiconductor photocatalysis is an established advanced oxidation process for the treatment of contaminated aqueous and gaseous streams. However, TiO 2 exhibits low adsorption ability, especially for non-polar substances due to its polar structure. Low adsorption ability of non-porous TiO 2 particles can be improved by surface augmentation using inert supports. In this work, TiO 2 was impregnated on three different kinds of adsorbents, mesoporous (MCM-41), microporous (β-zeolite) and pillared structure (montmorillonite) where different loadings (10-80%) of TiO 2 were obtained using sol-gel method. The catalysts were characterized by several analytical techniques including XRD, SEM-EDX, XPS, and BET analyzer. Subsequent to the dark adsorption studies, photocatalytic efficiency of the supported catalysts was evaluated using an azo-dye, orange II in water as model compound under different operating conditions. All supported catalysts exhibit good photodegradation efficiency of orange II, and their overall removal efficiency was always better than that of bare TiO 2 produced by the sol-gel method and commercial catalyst, Degussa-P25.

Chemical Vapor Deposition Growth of Single-Walled Carbon Nanotubes at 600 °C and a Simple Growth Model

Abstract: A comparison of different catalysts (Ni, Co, Fe/Mo) has been performed in order to minimize the growth temperature for single-walled carbon nanotubes (SWCNTs). Dense SWCNT networks have been synthesized by thermal chemical vapor deposition (CVD) at temperatures as low as 600 °C using Ni catalyst layers of approximately 0.2 nm thickness. The dependence of the SWCNT growth on the most important parameters will be discussed exemplarily on the Ni catalyst system. On the basis of experimental observations, a phenomenological growth model for CVD synthesis of SWCNTs is proposed which is based on the interactions between the catalyst and its support. Further, it is suggested that only surface diffusion of hydrocarbons on the catalyst support or along the CNTs can explain the fast growth rates of SWCNTs during CVD synthesis.

Activity and Stability of Cu−CeO2 Catalysts in High-Temperature Water−Gas Shift for Fuel-Cell Applications

Abstract: Copper-containing cerium oxide materials are shown in this work to be suitable for the high-temperature water−gas shift (WGS) reaction integrated with hydrogen separation in a membrane reactor to generate pure hydrogen. Copper−ceria is a stable high-temperature shift catalyst, unlike iron−chrome catalysts that deactivate severely in CO2-rich gases. Such gas mixtures will prevail if a catalytic membrane reactor is used to remove hydrogen. We also found that iron oxide−ceria catalysts have much lower activities than copper−ceria catalysts. Ceria participates in the WGS reaction; its surface properties are crucial for high activity and are sensitive to the presence of dopants. The kinetics of the WGS reaction over 10 atom % Cu−Ce(30 atom % La)Ox were measured in the temperature range 300−450 °C. A strong dependence on CO and a weak dependence on H2O were found at 450 °C, whereas inhibition by the reaction products was weak. The apparent activation energy over the catalyst stabilized in the reaction gas mixtu...

Production of COx-free hydrogen and nanocarbon by direct decomposition of undiluted methane on Ni–Cu–alumina catalysts

Abstract: Active and stable coprecipitated Ni–Cu–alumina catalysts were employed for direct decomposition of undiluted methane to produce CO x -free hydrogen and nanocarbon at 773–1013 K in a tubular reactor. Methane conversion increased with the reaction temperature, however, the catalyst stability declined. The weight ratio of formed solid nanocarbon and the catalyst employed attained about 380 and 280 g C/g cat at 873 and 973 K, respectively. Simultaneously, 30 and 70 vol.% hydrogen could be produced steadily for approximately 70 and 20 h, respectively. The doping of copper enhanced the catalyst stability when employed in a suitable amount. However, it made the catalyst particles to become quasi-liquid state at 973–1013 K in methane decomposition. Consequently, the catalyst particles were easily cut into small particles and encapsulated by the growing carbon layers. The tendency became pronounced with the increase of copper content. This effect may play an important role for the deactivation at high temperature in methane decomposition.

Comparison of Au Catalysts Supported on Mesoporous Titania and Silica: Investigation of Au Particle Size Effects and Metal-Support Interactions

Abstract: Au catalysts supported on mesoporous silica and titania supports were synthesized and tested for the oxidation of CO. Two approaches were used to prepare the silica-supported catalysts utilizing complexing triamine ligands which resulted in mesoporous silica with wormhole and hexagonal structures. The use of triamine ligands is the key for the formation of uniformly sized 2–3 nm Au nanoparticles in the silica pores. On mesoporous titania, high gold dispersions were obtained without the need of a functional ligand. Au supported on titania exhibited a much higher activity for CO oxidation, even though the Au particle sizes were essentially identical on the titania and the wormhole silica supports. The results suggest that the presence of 2–3 nm particle size alone is not sufficient to achieve high activity in CO oxidation. Instead, the support may influence the activity through other possible ways including stabilization of active sub-nanometer particles, formation of active oxygen-containing reactant intermediates (such as hydroxyls or O2−), or stabilization of optimal Au structures.

Gold catalysts supported on mesoporous titania for low-temperature water–gas shift reaction

Abstract: Mesoporous titania with high surface area and uniform pore size distribution was synthesized using surfactant templating method through a neutral [C 13 (EO) 6 –Ti(OC 3 H 7 ) 4 ] assembly pathway. The different gold content (1–5 wt.%) was supported on the mesoporous titania by deposition–precipitation (DP) method. The catalysts were characterized by X-ray diffraction, TEM, SEM, N 2 adsorption analysis and TPR. The catalytic activity of gold supported mesoporous titania was evaluated for the first time in water–gas shift reaction (WGSR). The influence of gold content and particle size on the catalytic performance was investigated. The catalytic activity was tested at a wide temperature range (140–300 °C) and at different space velocities and H 2 O/CO ratios. It is clearly revealed that the mesoporous titania is of much interest as potential support for gold-based catalyst. The gold/mesoporous titania catalytic system is found to be effective catalyst for WGSR.