Surface chemistry and reactivity of ceria–zirconia-supported palladium oxide catalysts for natural gas combustion

Specchia, Stefania; Finocchio, Elisabetta; Busca, Guido; Palmisano, Pietro; Specchia, Vito

doi:10.1016/j.jcat.2009.02.002

Cited by 89 publications

(46 citation statements)

References 76 publications

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“…On the basis of high resolution transmission electron microscopy (HRTEM) results the enhanced catalytic activity was ascribed to the existence of PdO x and nanosized zarovalent Pd particles. In the aforementioned reported work CeO 2 and CeO 2 -ZrO 2 were used as catalytic supports which are considerably expensive materials [35,65]. By contrast, the results of XPS and HRTEM analysis of the Pd-based SCS catalysts reported in this work suggested that most of the palladium and ceria (the key catalytic components) nanocrystallites were segregated on the surface of the alumina support.…”

Section: Catalytic Activitymentioning

confidence: 55%

“…Indeed, there is also reported literature to suggest that SCS synthesis methodology resulted in catalysts with comparatively higher activity than that of the catalysts prepared via conventional impregnation methods. For example S. Specchia et al reported the synthesis of 2% Pd supported over Ceria-Zirconia via the solution combustion (SCS) method [35]. From the results of surface chemical characterization techniques of oxygen temperature programmed desorption, hydrogen temperature programmed reduction and infrared spectroscopy of low temperature carbon monoxide adsorption, they concluded that the presence of small metallic palladium (Pd 0 ) particles together with well dispersed PdO x species were responsible for higher catalytic activity for methane combustion at low operating temperatures.…”

Section: Catalytic Activitymentioning

confidence: 99%

“…The reaction is exothermic in nature and proceeds auto-thermally without further external heating after initiation of combustion. A detailed description of the synthesis procedure is provided elsewhere [31][32][33]35,44,47,53,[67][68][69][70][71]. The synthesized nano-powder was then sintered in air by heating at a rate of 1 • C min −1 until it reached 800 • C where it was maintained for 3 h before cooling to room temperature at a rate of 1 • C min −1 .…”

Section: Catalyst Synthesismentioning

confidence: 99%

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Active and Stable Methane Oxidation Nano-Catalyst with Highly-Ionized Palladium Species Prepared by Solution Combustion Synthesis

et al. 2018

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We report on the synthesis and testing of active and stable nano-catalysts for methane oxidation. The nano-catalyst was palladium/ceria supported on alumina prepared via a one-step solution-combustion synthesis (SCS) method. As confirmed by X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HTEM), SCS preparative methodology resulted in segregating both Pd and Ce on the surface of the Al 2 O 3 support. Furthermore, HTEM showed that bigger Pd particles (5 nm and more) were surrounded by CeO 2 , resembling a core shell structure, while smaller Pd particles (1 nm and less) were not associated with CeO 2 . The intimate Pd-CeO 2 attachment resulted in insertion of Pd ions into the ceria lattice, and associated with the reduction of Ce 4+ into Ce 3+ ions; consequently, the formation of oxygen vacancies. XPS showed also that Pd had three oxidation states corresponding to Pd 0 , Pd 2+ due to PdO, and highly ionized Pd ions (Pd (2+x)+ ) which might originate from the insertion of Pd ions into the ceria lattice. The formation of intrinsic Ce 3+ ions, highly ionized (Pd 2+ species inserted into the lattice of CeO 2 ) Pd ions (Pd (2+x)+ ) and oxygen vacancies is suggested to play a major role in the unique catalytic activity. The results indicated that the Pd-SCS nano-catalysts were exceptionally more active and stable than conventional catalysts. Under similar reaction conditions, the methane combustion rate over the SCS catalyst was~18 times greater than that of conventional catalysts. Full methane conversions over the SCS catalysts occurred at around 400 • C but were not shown at all with conventional catalysts. In addition, contrary to the conventional catalysts, the SCS catalysts exhibited superior activity with no sign of deactivation in the temperature range between~400 and 800 • C.

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Section: Catalytic Activitymentioning

confidence: 55%

Section: Catalytic Activitymentioning

confidence: 99%

Section: Catalyst Synthesismentioning

confidence: 99%

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Active and Stable Methane Oxidation Nano-Catalyst with Highly-Ionized Palladium Species Prepared by Solution Combustion Synthesis

et al. 2018

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“…Among the various supports used, alumina and zirconia have been the most studied. 1,[3][4][5]9,11,13,[17][18][19][20][21][22][23][24] The support most commonly used for Pd catalysts is alumina and many studies focusing on Pd/alumina catalysts are available. 10,11,18 However, alumina is not fully stable at the high temperatures reached in methane combustion as it undergoes a phase change at 800 o C from γ-alumina to δ-alumina, resulting in a loss of surface area.…”

Section: Introductionmentioning

confidence: 99%

“…These authors found that nanocrystalline ZrO 2 and CeO 2 supports showed appreciable activities below 300 o C. ZrO 2 has also been used as a support by other researchers. [20][21][22] With respect to the active phase, a number of studies 20,[25][26][27][28][29][30] have attempted to define the chemical state of the active phase of the palladium species during catalytic combustion, and it is generally agreed that PdO x species are essential, at least below 700-800 °C, where PdO x species should be thermodynamically stable. Whether metallic palladium is also permanently present for the dissociative adsorption of methane or participates in the catalytic cycle, formed by the reduction of PdO x by methane and destroyed by reoxidation with oxygen, remains a matter of debate.…”

Section: Introductionmentioning

confidence: 99%

Palladium-supported catalysts in methane combustion: comparison of alumina and zirconia supports

Domingos¹,

Rodrigues²,

Brandão³

et al. 2012

Quím. Nova

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Recebido em 4/8/11; aceito em 6/2/12; publicado na web em 15/5/12Palladium catalysts supported on alumina and zirconia were prepared by the impregnation method and calcined at 600 and 1000 °C. Catalysts were characterized by BET measurements, XRD, XPS, O 2 -TPD and tested in methane combustion through temperature programmed surface reaction. Alumina supported catalysts were slightly more active than zirconia supported catalysts, but after initial heat treatment at 1000 °C, zirconia supported palladium catalyst showed better performance above 500 °C A pattern between temperature interval stability of PdOx species and activity was observed, where better PdOx stability was associated with more active catalysts.

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Combustion Synthesis

Specchia

Finocchio

Busca

et al. 2010

Handbook of Combustion

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Combustion synthesis (CS) is becoming one of the most important ways to produce a wide range of advanced porous ceramic or metallic materials. These include ceramic oxide like nanostructured catalysts. In CS, the heat released from the redox chemical reaction is used to produce useful materials. Depending upon the nature of the reactants, and the amount of heat made available during reaction, CS is in general mainly described as self‐propagating high temperature synthesis (SHS), solution combustion synthesis (SCS), and flame synthesis (FS). Among these, SCS is an attractive alternative for the production of particular materials of high value compared to the more conventional and expensive preparation routes. SCS processes are characterized by relatively medium heating oven temperatures (350–600 °C), fast heating rates, and short reaction times. SCS, in fact, offers a unique synthesis route via a highly exothermic redox reaction between metal nitrates and an organic fuel to produce multi‐component oxides. The reaction is self‐propagating and able to sustain high temperatures for a time long enough to complete the synthesis reaction and form the desired product. Therefore, the reaction is over in a few minutes without the use of high temperature furnaces. The final product is usually of high purity and well crystallized with nanometric size clusters, owing to the very small residence time at high temperature, a condition allowing the formation of a very large number of particles without huge growing effects. As a consequence, it is characterized by high values of both surface area and specific volume. Moreover, the significant gas rate produced during the synthesis process breaks up the large agglomerates and yields a porous mass that is easily crumbled into a fine powder. Furthermore, SCS, suitably adapted, is easily tunable to complex systems to produce directly in situ structured catalysts. In recent years this technique has been used to produce very fine, crystalline powders, without the intermediate steps that other conventional synthesis routes would require. These features make CS an attractive alternative for the production of ceramic materials compared to the conventional more expensive and time consuming processes. Examples of SCS and in situ SCS for the production of structured catalysts for combustion of natural gas and preferential oxidation of carbon monoxide are described.

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Surface chemistry and reactivity of ceria–zirconia-supported palladium oxide catalysts for natural gas combustion

Cited by 89 publications

References 76 publications

Active and Stable Methane Oxidation Nano-Catalyst with Highly-Ionized Palladium Species Prepared by Solution Combustion Synthesis

Active and Stable Methane Oxidation Nano-Catalyst with Highly-Ionized Palladium Species Prepared by Solution Combustion Synthesis

Palladium-supported catalysts in methane combustion: comparison of alumina and zirconia supports

Combustion Synthesis

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