TABLE 2.

The DFT energy barrier heights and activation free energy values at 1200 K (inside parenthesis) obtained here and compared with theoretical values and experimental apparent activation energy available in the literature, in eV, for the reaction steps of CMD mechanism (S1: CH₄→ CH₃*+ H*; S2: CH₃*→ CH₂*+ H*; S3: CH₂*→ CH*+ H*; and S4: CH*→ C*+ H*. The catalyst adopted in the respective work is indicated.

Catalyst	S1	S2	S3	S4
12-ZGNR edges (this work)	0.45 (0.56)	1.16 (1.24)	1.57 (1.53)	1.1 (1.06)
Ni(111) (Li et al., 2014)	1.23	0.85	0.29	1.36
ZGNR edges w/vacancy a (Calderón et al., 2016)	2.82	1.69	3.322 b	0.45
Ni-γAl2O3 (Salam and Abdullah, 2017)	0.98	0.63	1.15	0.63
Pd-γAl2O3 (Salam and Abdullah, 2017)	0.003	0.34	0.33	0.21
Mo-γAl2O3 (Salam and Abdullah, 2017)	0.048	3.82	1.99	5.98
Stepped-Ru (0001) (Arevalo et al., 2017)	1.02	-	-	1.10
Cu-Bi (Palmer et al., 2019)	2.80	-	-	-

^a Reaction steps were retrieved from the inverse reactions of the methane formation mechanism.

^b Occurs concomitant with H₂ formation.