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Catalysts 2018, 8(2), 66; doi:10.3390/catal8020066

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

Gas Processing Centre, College of Engineering, Qatar University, Doha 2713, Qatar
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Received: 11 December 2017 / Revised: 26 January 2018 / Accepted: 29 January 2018 / Published: 7 February 2018
(This article belongs to the Special Issue Catalytic Oxidation of Methane)
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Abstract

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 Al2O3 support. Furthermore, HTEM showed that bigger Pd particles (5 nm and more) were surrounded by CeO2, resembling a core shell structure, while smaller Pd particles (1 nm and less) were not associated with CeO2. The intimate Pd-CeO2 attachment resulted in insertion of Pd ions into the ceria lattice, and associated with the reduction of Ce4+ into Ce3+ ions; consequently, the formation of oxygen vacancies. XPS showed also that Pd had three oxidation states corresponding to Pd0, Pd2+ 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 Ce3+ ions, highly ionized (Pd2+ species inserted into the lattice of CeO2) 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. View Full-Text
Keywords: methane oxidation; palladium oxide/ceria catalyst; palladium oxide/ceria solid solution; solution combustion synthesis methane oxidation; palladium oxide/ceria catalyst; palladium oxide/ceria solid solution; solution combustion synthesis
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MDPI and ACS Style

Khader, M.M.; Al-Marri, M.J.; Ali, S.; Abdelmoneim, A.G. Active and Stable Methane Oxidation Nano-Catalyst with Highly-Ionized Palladium Species Prepared by Solution Combustion Synthesis. Catalysts 2018, 8, 66.

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