Characteristics of Copper Particles Supported on Various Types of Graphite Nanofibers

Catalysts containing metals such as Cu, Ni, Fe, Co in their reduced state are often subjected to passivation procedures prior to characterization. Passivation with N 2 O or O 2 to create a protective oxide layer also results in a certain degree of sub-surface oxidation. The heat released during oxidation is a critical parameter. The extent of bulk oxidation depends on the type of oxidant as well as on the size of the metal particles, as shown for copper catalysts. The final, meta-stable passivation layer requires a certain thickness to sustain exposure to ambient atmosphere. The encapsulation of metal particles in carbon is an efficient method for preserving the metallic state, as demonstrated for metallic nickel and iron with carbon nanofibers. The use of passivated samples for characterization of the active, i.e., reduced, catalyst has limited value.

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“…Copper dispersion and passivation measurements by means of N 2 O decomposition [22,27,35,36] according to the exothermic reaction…”

Section: Characterizationmentioning

confidence: 99%

Remarks on the passivation of reduced Cu-, Ni-, Fe-, Co-based catalysts

Huber

Lögdberg

et al. 2006

Catal Lett

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“…Carbon materials, especially those with a planar sp 2 structure, are oen considered as weakly interacting supports with Cu particles. 5,6 The stability could be improved by utilization of the supports with a signicant fraction of edge sites like carbon nanobers, but still the mean Cu particle size proved to be relatively big (20-40 nm) and the particle size distribution was broad.…”

Section: Introductionmentioning

confidence: 99%

Copper on carbon materials: stabilization by nitrogen doping

et al. 2017

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The applicability of Cu/C catalysts is limited by sintering of Cu leading to deactivation in catalytic reactions.We show that the problem of sintering could be resolved by N-doping of the carbon support. Cu nanocatalysts with 1 at% of metal were synthesized by Cu acetate decomposition on N-free and Ndoped (5.7 at% N) mesoporous carbon supports as well as on thermally expanded graphite oxide.Catalytic properties of these samples were compared in hydrogen production from formic acid decomposition. The N-doping leads to a strong interaction of the Cu species with the support providing stabilization of Cu in the form of clusters of less than 5 nm in size and single Cu atoms, which were observed in a significant ratio by atomic resolution HAADF/STEM even after testing the catalyst under harsh conditions of the reaction at 600 K. The mean size of the obtained Cu clusters was by a factor of 7 smaller than that of the particles in the N-free catalyst. The N-doped Cu catalyst possessed good stability in the formic acid decomposition at 478 K for at least 7 h on-stream and a significantly higher catalytic activity than the N-free Cu catalysts. The nature of the strongly interacting Cu species was studied by XPS, XRD and other methods as well as by DFT calculations. The presence of single Cu atoms in the N-doped catalysts should be attributed to their strong coordination by pyridinic nitrogen atoms at the edge of the graphene sheets of the support. We believe that the N-doping of the carbon support will allow expanding the use of Cu/C materials for different applications avoiding sintering and deactivation.

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“…The characteristics of these edge sites, especially for the form of tubular-type carbon (carbon nanotubes) [4]- [13], make it possible to utilize them in the fabrication of absorbent materials [14], catalyst-supports [15,16], field emitters, gas storage components [17] and polymer composites [18,19]. It is well known that highly reactive edge sites are transformed into stable multi-loops when heat treated at higher temperatures [5,12,20,21].…”

Section: Introductionmentioning

confidence: 99%