II International Symposium on Carbon for Catalysis ABSTRACTS

PP-I-30
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>
( TPD peak) in
isotropic (Fig. 8,
in [1]) and
nanostructured
graphites,
GNFs, defected
SWNTs and
MWNTs.
Process I
(TPD peak)
in isotropic
graphite (Fig. 8,
in [1]), SWNTs
and MWNTs.
Process IV
(TPD peak)
in isotropic
(Fig. 8, [1]),
pyrolytic and
nanustructured
graphites.
«Dissociative-associative» chemisorption
of H 2 in the intergrain or
defected (surface) regions
(“reactions” (13)-(16) in [1]).
Diffusion of H 2 in these regions,
accompanying with a reversible
dissociation and trapping of the
diffusant on the chemisorption
“centers”, model H (Fig. 9, [1]);
ΔH (form.C=2H)<strong>II</strong> ≈-570 kJ/mol(2H).
«Dissociative-associative»
chemisorption of H 2 in surface
layers of the material («reactions»
(13)-(16) in [1]).
Diffusion of H 2 in these layers,
accompanying with a reversible
dissociation and trapping of the
diffusant on the “centers”, model G
or F (Fig. 9, [3]); ΔH (form C=2H,C2=2H)I
≈ -460 kJ/mol(2H).
Dissociative chemisorption of H 2 in
defected regions of graphite lattice
(«reactions» (4)-(7) in [1]).
Bulk diffusion of H in the defected
regions, with the trapping by the
«centers», models C, D (Fig. 9, in
[1]); ΔH (form.C-H)IV ≈ -364 kJ/mol(H).
ΔH (16)<strong>II</strong> ≈ (∆H (diss.H2) +
∆H (form.C=2H)<strong>II</strong> ) ≈ -120 kJ/mol(H 2 ),
ΔS (16)<strong>II</strong> /R ≈ -30
(for X <strong>II</strong> max = 0,5 (0,25));
(Eqs. (25), (26) in [1]).
D <strong>II</strong> = D 0<strong>II</strong> exp(-Q <strong>II</strong> /RT),
D 0<strong>II</strong> ≈ 1,8·10 3 cm 2 /s, Q <strong>II</strong> ≈ (Q (def.) -
ΔH (16)<strong>II</strong> ) ≈ 120 k J/mol(H 2 );
Q (def.) ≈ 10 k J/mol(H 2 );
(Eqs. (22), (24), [1]).
ΔH (16)I ≈ (∆H (diss.H2) +
∆H (form. C=2H, C2=2H)I ) ≈
-10 kJ/mol(H 2 ), ΔS (16)I /R ≈ -20
(for X I max ≈ 0,5 (),25)); (Eqs. (20),
(21) in [1]). D I = D 0I exp(-Q I /RT),
D 0I ≈ 3⋅10 -3 cm 2 /s, Q I ≈ (Q (surf.) -
ΔH (16)I ) ≈ 20 kJ /mol(H 2 );
Q (surf.) ≈ 10 kJ /mol(H 2 );
(Eqs. (17), (19), [1]).
ΔH (7)IV ≈ (1/2 ΔH (diss.H2) +
ΔH (form.C-H)IV ) ≈ -140 kJ/mol(H);
(Eq. (27) in [1]).
D IV = D 0IV exp(-Q IV /RT),
D 0IV ≈ 6·10 2 cm 2 /s, Q IV ≈
-ΔH (form.C-H)IV ≈ 365 kJ /mol(H);
(Eq. (28) in [1]).
Henry-
Langmuir
(Eq. (25)
in [1]).
Henry-
Langmuir
(Eq. (20)
in [1]).
Sieverts-
Langmuir
(Eq. as
(9)
in [1]).
D 0<strong>II</strong>I , D 0<strong>II</strong> , D 0I , D 0IV - the pre-exponential (entropic) factors of the hydrogen diffusion coefficients
in the carbon materials corresponding to processes <strong>II</strong>I, <strong>II</strong>, I, IV.
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