Crystal-facet effect of γ-Al2O3 on Fe–Al2O3 catalytic performance for the co-production of hydrogen and CNTs from catalytic reforming of toluene

The pyrolytic reforming of toluene to hydrogen and CNTs over the commercial and self-prepared Al 2 O 3 loaded with Fe through the impregnation method is investigated in a fixed bed reactor under the temperature from 600 °C to 800 °C. The physicochemical properties of Fe–Al 2 O 3 catalysts and Al 2 O 3 supports were characterized by XPS, H 2 -TPR, HRTEM and H 2 -pulse chemisorption . The reforming process over the catalyst of Fe loaded on self-prepared Al 2 O 3 gives the excellent H 2 yield of 27.8 mmol/(g-Fe) and graphite yield of 82.6 wt%, which is much higher than those from that over the catalyst of Fe loaded on the commercial Al 2 O 3 . It is evidenced by H 2 -pulse chemisorption that 5.1 % of Fe 0+ dispersion over the commercial Al 2 O 3 with mainly-exposed (110) facet while 11.2 % of Fe 0+ dispersion over self-prepared Al 2 O 3 with mainly-exposed (111) facet were obtained. The adsorption energy of iron cluster (Fe 4 ) with Al 2 O 3 (111) facet was estimated to be −14.5 eV through the DFT simulation, which is notably higher than that of iron cluster (Fe 4 ) with Al 2 O 3 (110) facet as −9.1 eV. With regard to the MD simulation along with XRD analysis of the Fe 3 C crystallite , Fe 0+ particles can be prominently molten at the high Fe 0+ dispersion over Al 2 O 3 facet, promoting the carbon solubility for the assembly of multi-wall CNTs without the deposition of unwanted amorphous carbon .