Hydrogen production by methane decomposition and catalytic partial oxidation of methane over Pt/CexGd1−xO2 and Pt/CexZr1−xO2 (original) (raw)
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Chemical Engineering Journal, 2001
We have investigated the relationship between the reducibility of the support and the catalytic activity of supported Pt on a series of catalysts supported on ceria-zirconia mixed oxides. The supports were prepared by co-precipitation with varying Ce/Zr ratios. X-ray diffraction analysis indicated that, depending on the Ce/Zr ratio, solid solutions of cubic Ce x Zr 1−x O 2 can be formed. The reducibility of the supports was determined by X-ray photoelectron spectroscopy (XPS). After reduction at 773 K in hydrogen the fraction of reduced cerium (i.e. Ce 3+ ) was found to vary with the Ce content, exhibiting a maximum at a composition Ce 0.5 Zr 0.5 O 2 .
Applied Catalysis A: General, 2005
The effect of CeO2 loading (1-20 wt.%) on the properties and catalytic behaviors of CeO2-Al2O3-supported Pt catalysts on the partial oxidation of methane was studied. The catalysts were characterized by SBET, Xray diffraction (XRD), temperature-programmed reduction (TPR) and oxygen storage capacity (OSC). XRD and TPR results showed that the pretreatment temperature of the support influences on the amount of CeO2 with fluorite structure. The pretreatment temperature of the support and CeO2 loading influenced the morphology of Pt. OSC analysis showed a significant increase in the oxygen storage capacity per weight of CeO2 for samples with high CeO2 loading (12 and 20 wt.%). TPR analyses showed that the addition of Pt promotes the reduction of CeO2. This effect was more significant for the catalysts with high CeO2 loading (≥12 wt.%). The dispersion of Pt, measured by the rate of cyclohexane dehydrogenation, increases with increasing of the pretreatment temperature of the support. It was shown that the kind of the support is very important for obtaining of catalysts resistant to carbon formation. The catalysts with high CeO2 loading (≥12 wt.%) showed the highest catalytic activity and stability in the reaction of partial oxidation of methane due to a higher Pt-CeO2 interface.
Interactions of CO with Pt/ceria catalysts
Applied Catalysis B: Environmental, 1999
The interaction between CO and Pt/ceria catalysts was investigated by oxygen storage capacity measurements, CO and CO 2 isotope exchange and FT-IR measurements. A Pt/alumina sample was also investigated for comparison. The capacity to store and release oxygen as a function of ceria surface-area and Pt-ceria contact was estimated. The presence of chlorine from the Pt pre-cursor was found not to decrease the oxygen storage capacity. However, FT-IR measurements showed that chlorine hindered the carbonate formation during CO exposure, which was found to be the main form of carbon storage on the pre-oxidized sample. On a strongly reduced sample, CO disproportionation was found to occur to an increasing extent with increasing degree of reduction. CO and CO 2 isotope exchange showed that these molecules exchange their oxygen with Pt/ceria and ceria quite easily at 400 • C. CO chemisorption at −78 • C as a method to determine the metal dispersion was also investigated. At this temperature, the CO uptake on ceria was strongly suppressed, especially on the Cl-free sample, but not completely hindered.
Synthesis effects on activity and stability of Pt-CeO2 catalysts for partial oxidation of methane
Molecular Catalysis, 2017
The objective of this study is to explore the effect of catalyst synthesis procedure on the activity of catalysts for partial oxidation of methane. In this aspect, Pt-nanoparticles supported CeO 2 catalysts were prepared by Hydrothermal, co-precipitation, impregnation and by controlled deposition of platinum nanoparticles on hydrothermally prepared cerium oxide. Prepared catalysts were characterized by BET-surface area, X-ray diffraction, H 2-Chemisorption, Transmission electron microscopy, Temperature programmed reduction, Inductively coupled plasma atomic emission spectroscopy and X-ray photoelectron spectroscopy. The study revealed that the catalyst preparation procedure plays a very crucial role on morphology, catalyst particle size, metal support interaction and activity of the catalysts. Catalytic activities were tested for partial oxidation of methane in the temperature range 350-800 • C. The study revealed that the catalyst prepared by controlled deposition of Pt-nanoparticles on hydrothermally prepared cerium oxide showed better activity for partial oxidation of methane compared to the catalysts prepared by other conventional methods. Controlled deposition of Pt-nanoparticles generated better metal-support interaction compared to the catalysts prepared by conventional hydrothermal, coprecipitation and impregnation methods. All the catalysts showed excellent coke resisting ability but the deactivation of most of the catalyst was found to be caused by catalyst particles sintering and re-oxidation of the Pt particles during catalysis.
Electrochimica Acta, 2013
Different carbon materials with high electrical conductivity have been studied as electrocatalyst support for direct alcohol fuel cells (DAFCs). The aim of the work was to establish the influence of the support on the catalyst properties and to improve their efficiency in the fuel cell. Carbon nanofibers (CNFs), carbon nanocoils (CNCs) and ordered mesoporous carbons (gCMK-3) have been used for synthesizing platinum catalysts by the polyol method. Results have been compared with those obtained for a platinum catalyst supported on Vulcan XC-72R, prepared by the same method, and for the commercial Pt/C catalyst from E-TEK. It has been demonstrated that novel carbon supports could help to oxidize CO adsorbed on platinum particles more easily than the commercial carbon support and improve the alcohol oxidation reaction, both in terms of onset potential and current density. The catalyst supported on gCMK-3 carbon resulted to be the most effective in both the methanol and ethanol oxidation, which can be attributed to its ordered structure and high electrical conductivity.
Journal of Solid State Electrochemistry, 2013
Micro-and mesoporous carbide-derived carbons synthesized from molybdenum and tungsten carbides were used as porous supports for a platinum catalyst. Synthesized materials were compared with commercial Vulcan XC72R conducting furnace black. The scanning electron microscopy, X-ray diffraction, Raman spectroscopy, high-resolution transmission electron microscopy, and low-temperature N 2 adsorption methods were applied to characterize the structure of catalysts prepared. The kinetics of oxygen electroreduction in 0.5 M H 2 SO 4 solution was studied using cyclic voltammetry and rotating disk electrode methods. The synthesized carbidederived carbons exhibited high specific surface area and narrow pore size distribution. The platinum catalyst was deposited onto the surface of a carbon support in the form of nanoparticles or agglomerates of nanoparticles. Comparison of carbide-derived carbons and Vulcan XC72R as a support showed that the catalysts prepared using carbide-derived carbons are more active towards oxygen electroreduction. It was shown that the structure of the carbon support has a great influence on the activity of the catalyst towards oxygen electroreduction.
Journal of colloid and interface science, 2015
The effect of the metal precursor (presence or absence of chlorine) on the preferential oxidation of CO in the presence of H2 over Pt/CeO2 catalysts has been studied. The catalysts are prepared using (Pt(NH3)4)(NO3)2 and H2PtCl6, as precursors, in order to ascertain the effect of the chlorine species on the chemical properties of the support and on the catalytic behavior of these systems in the PROX reaction. The results show that chloride species exert an important effect on the redox properties of the oxide support due to surface chlorination. Consequently, the chlorinated catalyst exhibits a poorer catalytic activity at low temperatures compared with the chlorine-free catalyst, and this is accompanied by a higher selectivity to CO2 even at high reaction temperatures. It is proposed that the CO oxidation mechanism follows different pathways on each catalyst.
Journal of Catalysis, 2004
One crucial requirement for the operation of proton exchange membrane fuel cells (PEMFC) is to feed carbon monoxide free hydrogen to the anode. This need can be achieved by using catalysts able to selectively oxidize CO in the presence of excess hydrogen. Herein we report the preferential CO oxidation (PROX) in the presence of hydrogen over Pt/Ce x Zr x−1 O 2 (x = 0, 0.15, 0.5, 0.68, 1) catalysts. A comparison with results observed on a Pt/Al 2 O 3 catalyst is also presented. We examined the effect of temperature (90-300 • C) and O 2 excess (λ = 0.8-2). Ceria-supported platinum catalysts were more active than Pt/Al 2 O 3 in both CO and H 2 oxidation. The result was a sharp "light off" around 90 • C for the oxygen conversion. The maxima, which appeared in the CO conversion and in the selectivity toward CO oxidation as a function of temperature on Pt/Al 2 O 3 , did not show up in the case of ceria-supported samples. Chloride ion-containing Pt/CeO 2 catalysts showed lower performances in the PROX reaction, especially at low temperatures. Four types of reaction mechanisms were suggested for Pt/Ce x Zr x−1 O 2 samples: (i) competitive Langmuir-Hinshelwood CO and hydrogen oxidation on Pt particles, (ii) noncompetitive Langmuir-Hinshelwood mechanism on the metal/oxide interface, (iii) hydrogen oxidation on the support, and (iv) water-gas-shift reaction at high temperatures. The second reaction route predominated at low temperatures (90-130 • C) and was found preferential to CO oxidation rather than hydrogenoxygen reaction. This process was selectively blocked by Cl ions. The possible application of Pt/CeO 2 and Pt/Al 2 O 3 catalysts was discussed. Ceria appeared as a suitable support for the preferential CO oxidation catalysts at low temperatures.
Applied Catalysis B: Environmental, 2011
The ignition and extinction processes for total oxidation of CO, CH 4 and CO + CH 4 mixture in oxygen excess over Pt/Al 2 O 3 and Pt/CeO 2 catalysts with the platinum phase distributed either homogeneously or heterogeneously (i.e., locally high platinum concentration) in the support have been studied by temperature programmed oxidation experiments. Following the preparation methods by Arnby et al. , the samples have the same Pt load and dispersion. Generally the catalytic activity follows the order: Pt/CeO 2 (heterogeneous) > Pt/CeO 2 (homogeneous) > Pt/Al 2 O 3 (heterogeneous) > Pt/Al 2 O 3 (homogeneous) as indicated by lower ignition and/or extinction temperatures. For Pt/Al 2 O 3 , the addition of NO 2 to the reactant stream increases the rate of oxidation of CO in the pre-ignition regime although the light-off temperature T 50 is shifted towards higher temperatures (except for low CO concentrations). In the case of the Pt/CeO 2 , the CO conversion generally decreases. For CH 4 oxidation in the presence of NO 2 , the conversion increases for Pt/Al 2 O 3 and decreases for Pt/CeO 2 . The addition of CO 2 in the reactant stream has minor influence on CO oxidation over Pt/Al 2 O 3 while for Pt/CeO 2 , T 50 is shifted towards higher temperatures. For the simultaneous oxidation of CO and CH 4 , a reverse hysteresis for methane oxidation is observed, i.e., the extinction process occurs at higher temperature than the corresponding ignition process. The improved activity for CO oxidation over samples with heterogeneous Pt distribution is likely due to less tendency towards CO self-poisoning through the development of steeper concentration gradients in the Pt containing regions in the porous support material. The significant increase of activity for both reactions over ceria-supported Pt is here assigned to highly active sites at the platinum-ceria boundary but also, to some extent, the oxygen storage and release function and dynamics of the transport of oxygen in the Pt/CeO 2 system.