Influence of Different Palladium Precursors on the Properties of Solution‐Combustion‐Synthesized Palladium/Ceria Catalysts for Methane Combustion

Abstract

A series of Pd/CeO 2 catalysts was prepared by solution combustion synthesis (SCS) using different Pd precursors. The powders were characterized by complementary techniques such as BET surface area measurements, X-Ray diffraction analysis, XRay photoelectron spectroscopy, temperature-programmed reduction, temperature-programmed oxidation, and high-resolution TEM. The results obtained evidenced the formation of a Pd-Ce solid solution on all SCS samples. This solid solution is in the form of an ordered supercell structure only in the SCS catalyst prepared from palladium nitrate. This was correlated to the heat of reaction between Pd(NO3)2 and the fuel. The samples were tested for methane catalytic combustion, and the reaction rates on all SCS samples were approximately twice that of the impregnated counterpart, irrespective of the precursor. This was attributed to the presence of the Pd-O-Ce solid solution, which gave rise to strong Pd-ceria interactions.

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

“…Based on these results, it is reasonable to suggest that, in contrast to the conventional method, Pd was inserted into the ceria lattice during the SCS forming a non-stoichiometric Pd-O-Ce solid solution, which was segregated on the surface of the alumina support. This explanation corroborates the conclusions of the experimental work by Colussi et al [23,38] and Priolkar et al [36] as well as the theoretical prediction by Scanlon et al [54]. The insertion of Pd ion into the ceria lattice must be associated with oxygen vacancy formation and, consequently, with the generation of Ce 3+ ions.…”

“…A similar peak was assigned by Venezia et al and Bi et al to Pd 4+ , as in PdO 2 , due to the oxygen incorporation into the PdO crystal lattice during calcinations [52]. The highly ionized Pd ions of the samples prepared by the SCS can also be assigned to Pd ions which were inserted into the ceria lattice forming pallida/ceria solid solution [23,38,53]. The appearance of the three Pd XPS doublets, comparing to only two Pd XPS doublets for the impregnation catalyst, strongly indicated the formation of Pd/ceria solid solution as has already been reported in recent literature [23,36,38].…”

“…The highly ionized Pd ions of the samples prepared by the SCS can also be assigned to Pd ions which were inserted into the ceria lattice forming pallida/ceria solid solution [23,38,53]. The appearance of the three Pd XPS doublets, comparing to only two Pd XPS doublets for the impregnation catalyst, strongly indicated the formation of Pd/ceria solid solution as has already been reported in recent literature [23,36,38]. In the theoretical study by Scanlon et al [54], it was predicted that the ground state structure of Pd doped CeO 2 is a square planar with Pd ions having d 8 configuration; meaning that Pd 2+ rather than Pd 4+ is the predominant oxidation state in the Pd-O-Ce solid solution linkage.…”

Chemoselective hydrogenation of cinnamaldehyde at atmospheric pressure over combustion synthesized Pd catalysts

“…The samples have been pre-treated in air in order to remove all carbon containing species that may arise during the synthesis. The main thing to observe is that on Pd2Al the reduction starts at a lower temperature (-15 °C with respect to 0 °C for 2PdAlIWI), and the hydrogen consumption peak is clearly divided into more than one feature, indicating the coexistence of different PdO species with different interaction with the support [46]. Moreover, the negative peak observed at about 55 °C and corresponding to the decomposition of Pd hydrides is much more pronounced for Pd2Al; this might point to a higher affinity for hydrogen of Pd contained in the SCS sample with respect to the IWI sample, in accordance to the higher reducibility of Pd2Al at a lower temperature.…”

Uncovering the 3 D Structure of Combustion‐Synthesized Noble Metal‐Ceria Nanocatalysts

“…2 nm) was not affected by the reaction. Moreover, several groups have mentioned the possibility of a ionic dispersion and substitutional incorporation of noble metals in the ceria lattice from SCS . However, this state is unstable under reducing conditions and the powders thermally treated in hydrogen clearly show metal nanoparticles, the average size of which depends on the metal nature …”