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

Abstract

The catalytic production of syngas by the partial oxidation of methane (POM) was investigated over Pd supported on ceria (0.5–2 Pd wt.%) prepared by incipient wetness impregnation and by mechanochemical methods. The performance of the Pd/CeO2 catalyst prepared by milling CeO2 and Pd acetate was superior to that prepared by milling CeO2 and Pd nitrate and to Pd/CeO2 prepared by impregnation from Pd acetate. The best catalytic activity of the Pd/CeO2 catalyst prepared from CeO2 and Pd acetate was obtained by milling at 50 Hz for 5 min. Two-step combustion and reforming reaction mechanism were identified. Remarkably, methane conversion increased progressively with Pd loading for the catalysts prepared by incipient wetness impregnation, whereas low metal loading showed better conversion of methane for the catalysts prepared by ball milling using Pd acetate. This was explained in terms of an impressive dispersion of Pd species with a strong interaction with the surface of ceria, as deduced from transmission electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy characterization, which revealed a large quantity of highly oxidized species at the surface.

Photocatalytic partial oxidation of methane to carbon monoxide and hydrogen over CIGS solar cell

“…Note that no products have been detected using visible light irradiation (Table S2, SI). The thermocatalytic partial oxidation of methane to syngas is challenging because it is difficult to control the reaction selectivity to CO and to avoid full oxidation to CO 2 at relatively low temperatures (400 -500 o C) [41]. Temperature and partial pressures of methane and oxygen are the key parameters for the selectivity control.…”

Identification of Highly Selective Surface Pathways for Methane Dry Reforming Using Mechanochemical Synthesis of Pd–CeO2

“…Pd-ceria contact promotes a similar low coordination arrangement, enhancing interfacial interactions and facilitating CH 4 activation, making Pd/CeO 2 suitable for DRM. , Colussi et al showed that the incorporation of Pd atoms into the CeO 2 lattice via solution combustion synthesis outperforms Pd/CeO 2 catalysts prepared by incipient wetness impregnation (IW) in methane oxidation and has remarkable resistance to steam deactivation. , Furthermore, the degree of interaction between Pd and Ce can greatly influence the overall catalytic activity of the material. − Thus, there is a continuous search for methods that enhance metal-oxide interactions and can be used in the preparation of more efficient catalysts, and among these, mechanochemical synthesis is receiving considerable attention. − In particular, the milling of Pd with CeO 2 is a novel and facile method to produce methane oxidation catalysts, forming an active Pd–Ce configuration at the nanoscale level. ,, Pd–Ce-based materials prepared by mechanochemical synthesis were also explored for the partial oxidation of methane, which showed that milling Pd with either an acetate or nitrate precursor resulted in increased activity relative to the preparation via incipient wetness, because of improved dry and steam reforming reactivity occurring at higher temperature. The enhanced performance was attributed to the unique Pd–Ce configuration and increased dispersion offered via milling . This produces a specific surface arrangement where Pd moieties are embedded in the outer layer of ceria particles with unique interfacial Pd–O–Ce sites that are highly effective for methane oxidation, which serves as a basis for extending the study under milder oxidative conditions such as those encountered when CO 2 is used in the presence of methane.…”

“…The enhanced performance was attributed to the unique Pd–Ce configuration and increased dispersion offered via milling. 25 This produces a specific surface arrangement where Pd moieties are embedded in the outer layer of ceria particles with unique interfacial Pd–O–Ce sites that are highly effective for methane oxidation, which serves as a basis for extending the study under milder oxidative conditions such as those encountered when CO 2 is used in the presence of methane. Here, we describe a highly active Pd/CeO 2 DRM catalyst prepared by mechanochemical milling, showing that its distinctive catalytic behavior and surface chemistry can only be traced applying in situ techniques to differentiate it from conventionally prepared Pd–CeO 2 based catalysts with the same composition and nominal Pd loading.…”

Water inhibition and role of palladium adatoms on Pd/Al2O3 catalysts during methane oxidation

“…However, there is no agreement on the assignment and the high-binding energy species (high-BE species) are associated with either palladium (IV) oxide [36,39] or, more often, Pd n+ (n > 2) [40][41][42][43]. Another possibility is that palladium strongly interacts with its support, leading to the formation of aluminum palladate [37,44] or palladium diffusing into the metal oxide lattice [45][46][47], depending on the support. Such a high-BE component in the Pd 3d signal is usually detected for catalysts with a low metal loading (<1% wt) [36,48].…”