II International Symposium on Carbon for Catalysis ABSTRACTS

PP-I-30
EXPERIMENTAL VALUES OF THE ENERGY AND ENTROPY
CHARACTERISTICS OF THE HYDROGEN-CARBON INTERACTION,
RELEVANCE TO THE CARBON CATALYTIC ACTIVITY
Nechaev Yu.S.
I.P. Bardin Central Research Institute of Ferrous Metallurgy, Moscow, Russia
e-mail: netchaev@online.ru
The results of the thermodynamic analysis [1,2] of the most significant experimental data
on the hydrogen sorption by graphite and related novel carbon-based nanomaterials
(fullerenes, single- and multi-walled nanotubes (SWNT, MWNT), graphite nanofibers (GNF),
nanostructured graphites) are presented. The thermodynamic and kinetic (diffusion)
characteristics of sorption processes are refined (Table 1), which can be used for optimizing
and a better understanding of the carbon catalytic activity (in the Carbo-Cat processes).
Table 1. Some characteristics and mechanisms of chemisorption and diffusion of hydrogen in
isotropic graphite and related carbon nanostructures (processes I,<strong>II</strong>,<strong>II</strong>I,IV), [1,2]
Chemisorption
Models of chemisorption
Characteristics of chemisorption
Type of
of hydrogen
and diffusion of hydrogen in
and diffusion of hydrogen
the
in sp 2 carbon
the materials; energies of formation
in the materials
sorption
materials
of the chemical bonds
isotherm
Process <strong>II</strong>I
Dissociative chemisorption of
ΔH (7)<strong>II</strong>I ≈ (1/2 ∆H (diss.H2) +
(thermodesorp-
hydrogen between the graphene
∆H (form. C-H)<strong>II</strong>I ) ≈ -19 kJ/mol(H),
Sieverts-
tion peak) in
isotropic (Fig. 8,
in [1]) and
nanostructured
graphites, and
GNFs.
layers («reactions» (4)-(7) in [1]).
Bulk diffusion of hydrogen atoms,
accompanying with a reversible
trapping the diffusant by the
chemisorption “centers” on the
garphene layers, model F*
(Fig. 9, in [1]);
ΔH (form.C-H)<strong>II</strong>I ≈ -243 kJ/mol(H).
ΔS (7)<strong>II</strong>I /R ≈-14,7 (-15,4)
(X <strong>II</strong>I max = 0,5 (1,0)); (Eqs. (8)-(10)
in [1]).
D <strong>II</strong>I =D 0<strong>II</strong>I exp(-Q <strong>II</strong>I /RT),
D 0<strong>II</strong>I ≈ 3⋅10 -3 cm 2 /s, Q <strong>II</strong>I ≈ (Q (latt.) -
ΔH (form.C-H)<strong>II</strong>I ) ≈ 250 kJ /mol(H);
Q (latt.) ≈ 7 kJ/ mol(H);
(Eqs. (11), (12) in [1]).
Langmuir
(Eq. (9)
in [1]).
177