The effect of milling parameters on the mechanochemical synthesis of Pd–CeO₂ methane oxidation catalysts

Abstract

Pd–ceria interaction can be tuned by suitable milling intensity to obtain highly active methane oxidation catalysts.

Low-Temperature Methane Partial Oxidation over Pd Supported on CeO2: Effect of the Preparation Method and Precursors

“…As commonly occurs in catalysis, the intricate properties of the metal-support interaction depend on the method used for the preparation of the catalyst. In recent years, it has been demonstrated that different architectures of the Pd-CeO 2 interface are obtained by using conventional impregnation or solution combustion synthesis or mechanochemical methods, which strongly determine the performance of the resulting Pd/CeO 2 catalysts in the total oxidation of methane [20][21][22][23]. In particular, advanced operando characterization has recently shown that catalysts prepared by mechanical milling are clearly superior because they contain very stable palladium species [24].…”

Mechanochemical Synthesis of Catalytic Materials

“…In general, such a configuration is unusual for supported catalysts prepared by conventional routes, as the formation of nanoparticles located on the surface of the metal oxide is more often observed. The reasons for the results found for PdCeM are not easily elucidated, and thus this is the aim of ongoing studies [87, 88] . Nevertheless, it was speculated that the mechanochemical action might enhance the interaction between Pd and CeO 2 and, thus, promote phase reconstruction.…”

Structure-activity relationship in Pd/CeO2 methane oxidation catalysts

“…There are several papers, mostly published in the last decade, which report that catalysts showing a strong Pd-CeO2 interaction possess unique properties for methane oxidation and in general outperform conventional samples. Pd-based catalysts in which Pd and ceria are in strong physical contact and/or Pd is embedded into ceria lattice are nowadays regarded as the most active formulations for methane oxidation [20,22,41,75,92,93], also on the basis of repeated reaction cycles and exposure to high temperature which are important factors in light of practical applications. Cargnello et al [41] described the superior activity of a catalyst in which Pd-ceria core-shell nanoparticles were deposited on Si-functionalized hydrophobic alumina.…”

“…The configurations explored in the literature include the formation of a solid solution between Pd and ceria by solution combustion synthesis [20,40,54] (Fig. 7), the presence of highly dispersed cationic PdO + sites on ceria obtained by deposition precipitation [46] and a unique arrangement in which Pd and ceria are mixed to form an amorphous layer surrounding ceria nanoparticles realized by dry mechanical milling of Pd and CeO2 powders [22,75].…”

“…This aspect is very important and deserves further investigation, as it is known that ceria morphology can undergo restructuring under operating conditions and thermal treatments [73] thus potentially affecting palladium electronic/oxidation state and Pd-ceria interaction. Moreover, also the mutual interplay and physical arrangement of Pd entities and ceria support, which can be tuned by opportune tailoring of the synthesis procedure [20,22,41,46,74,75], has a strong influence on the chemical state of Pd nanoparticles. For example, palladium can be present as Pd 2+ in the form of PdO nanoparticles on the surface of CeO2, or as Pd δ+ (2 < δ ≤ 4) inserted into ceria lattice [4,20,40,43,54,55].…”