Carbon Dissolution and Segregation in Pd(110)

Abstract

The bulk-surface diffusion of carbon in Pd(110) has been investigated using molecular beams to examine the clean-off of carbon with gas-phase oxygen. The dominant product of the reaction above 600 K is CO; CO 2 is only produced at much lower temperatures where the lifetime of adsorbed CO is significant. The segregation from the bulk only occurs at a measurable rate at >750 K, while loss of carbon into the bulk can occur at much lower temperatures. The reaction of carbon at high temperatures shows two regimes: (i) a non steadystate evolution of CO due to the clean-off of surface carbon already present on the surface, followed by (ii) a near steady-state reaction due to the continuous diffusion of carbon to the surface.

Modulation Excitation X-Ray Absorption Spectroscopy to Probe Surface Species on Heterogeneous Catalysts

“…Under the CO pulse the Pd lattice undergoes expansion that is interpreted with the formation of PdC x . These data have been supported by independent hard-XRD experiments under similar conditions [18] and agree with other reports [28,29].…”

Carbidisation of Pd Nanoparticles by Ethene Decomposition with Methane Production

“…In our work we have observed that there are different processes occurring during the formation of PdC x . Surprisingly, together with dehydrogenation, and in contrast with the behaviour of single crystal Pd, we find that disproportionation of ethene to carbide and methane is a major reaction pathway. The stoichiometry of the carbide phase has been variously reported from a value of PdC 0.05 to PdC 0.16 (though higher levels are reported in the surface regions), but here we find the loading of the carbide to be much higher at ∼28 atom % C.…”

“…Pd is an important catalytic metal and it is used in a variety of processes, for instance, in the Wacker process for the selective oxidation of ethane to acetaldehyde, in vinyl acetate synthesis and in a wide range of fine chemicals hydrogenation reactions, which are often heterogeneous, liquid phase processes. The interaction of ethylene, ethanol, acetic acid and many other simple organic molecules with the surface of Pd can lead to the formation of palladium carbide . This can have an effect on the activity and selectivity of the reaction of interest.…”

“…This stoichiometry was based on the assumption that this was the maximum value of carbon incorporation achievable. More recently, efforts have focussed on using the XANES to discriminate between carbidic and hydridic forms of Pd; the formation of PdC x results in a broadening and a shift in position (+1 eV) of the main edge transition . The features of carbidic and hydridic Pd are readily apparent in the XANES difference spectra (e. g. PdC x ‐Pd 0 ) with characteristic features that allow them to be readily distinguished .…”

Carbon Segregation-Induced Highly Metallic Ni Nanoparticles for Electrocatalytic Oxidation of Hydrazine in Alkaline Media

“…The previous reports [20][21][22][23][24][25][26] and our comparative studies of Ni(acac) 2 and NiCl 2 led us to conclude that acetylacetonate was the source of carbon present into the solid matrix.…”