Oscillatory behaviour during the oxidation of methane over palladium metal catalysts

Abstract

Oscillatory reactions over palladium foil and wire catalysts during the oxidation of methane have been investigated over a wide range of reaction temperatures and argon/methane/oxygen feed gas compositions. Characterisation of the catalyst has also been carried out using scanning electron microscopy (SEM) techniques, which revealed the presence of a porous surface. This suggested that the metal surface has undergone a change since the reaction commenced, and using X-ray powder diffraction (XRD) techniques the palladium phase was shown to be the dominant phase present. Hysteresis phenomena were observed in the activity of the reaction as the temperature was cycled up and down, showing that the metal surface was continually changing throughout the reaction. The activation energies of the reaction during the high reactivity mode, PdO, and low reactivity mode, Pd, were also calculated. Oscillation rates were observed to depend on the dominant surface. Oscillations were frequent when the high reactivity mode was dominant while the activation energy of this mode was found to be low. When the low reactivity mode was dominant, the oscillations were slower and the activation energy was three times larger. The results obtained imply that the behaviour of the palladium surface, switching back and forth from the reduced state to the oxidised state, is responsible for the oscillatory behaviour seen in this system.

Oscillatory Behavior of Pd-Au Catalysts in Toluene Total Oxidation

“…Bychkov et al [21] also suggested the deposition/desorption of carbonaceous compounds on the catalysts' surfaces is directly related to a self-oscillatory process they investigated in the oxidation of methane and ethane. Along with Deng et al [15] and Zhang et al [16], they additionally correlated the oscillatory behaviour to changes in the oxidation state of active phase constituents. Therefore, and for a better understanding of changes occurring at the surface of the catalyst, it was inevitable to conduct operando DRIFT measurements throughout the whole duration of the catalytic test.…”

“…Other works by Zhang et al [17,18] concluded that oscillations may also be observed when using metallic nickel or cobalt foils. However, their intensities and frequencies were lower than what had been observed with palladium [16]. Furthermore, Bychkov et al [19][20][21] confirmed the latter results through witnessing self-oscillations on Pd-supported and Ni-supported catalysts as well as metal foils (Ni and Co).…”

“…Graham et al [14] first observed this oscillatory behaviour during methane oxidation over a thick Pd-film catalyst. Deng et al [15] and Zhang et al [16] also reported a periodical oscillatory conversion of methane using Pd-supported and metallic Pd foil catalysts, respectively. Both works attribute these oscillations to the use of palladium as an active phase constituent.…”

Efficient synthesis of palladium nanoparticles using guar gum as stabilizer and their applications as catalyst in reduction reactions and degradation of azo dyes

“…Its use in industrial process may give a new turn to the progress of new technologies [3]. Palladium as a catalyst is used in various industrial processes Petrolium cracking [4], alkaline oxidation, selective low oxide formation [5,6], reduction of C≡C to C=C without further reduction to carbon-carbon single bond (known as Landler's Catalyst) [7], Suzuki coupling [8], Heck reaction [9] and carbonfluoride bond formation [10]. For the oxidation of alcohols palladium is considered excellent electro-catalyst in alkaline medium [11][12][13][14].…”

Influence of the metal/metal oxide redox cycle on the catalytic activity of methane oxidation over Pd and Ni doped hydroxyapatite

“…This observation agreed with what has been reported elsewhere. [10] As the reaction proceeded to higher temperatures, catalytic activity increased for all the samples. On the other hand, Ni-based catalysts revealed a similar catalytic trend to that of Pd-based samples when Ni was reduced prior to reaction and showed general rise in catalytic activity with increased temperature ( Figure 3A) at 400°C.…”