Large Scale

							       New Large-Scale Synthesis Routes to Carbon Nanofibers: the
              Application of Ni-Fe Hydrotalcite Catalysts

                      Zhixin Yu1, De Chen1, Bård Tøtdal2, and Anders Holmen1
                                        1
                             Department of Chemical Engineering,
                                   2
                                     Department of Physics,
                        Norwegian University of Science and Technology,
                                 N-7491 Trondheim, Norway

Abstract

   Carbon nanofibers (CNFs) were synthesized on a series of Ni-Fe hydrotalcite (HT)
catalysts in order to achieve the optimization of productivity and quality. We have found
that only pure Fe catalyst is active in CO disproportionation, only pure Ni catalyst is
active in ethylene decomposition, but all catalysts are active in ethylene decomposition
when the reactants are the C2H4/CO mixture. The nature of the catalysts and as-
synthesized CNFs were fully examined by various characterization methods to correlate
the catalyst structure and CNF morphology and crystallinity. Based on the experimental
results a concerted reaction mechanism is inferred and the implications are discussed.
More importantly, we demonstrated that Ni-Fe HT catalysts uncovered a new promising
route to large-scale controlled synthesis of CNFs.



Some results :
                                                               TPO

                                       100
                                                                                   Ni
                                                                                   8:2
                                                                                   5:5
                                       80                                          2:8
                                                                                   Fe
                          Weight (%)




                                       60


                                       40


                                       20


                                            0
                                             500 520 540 560 580 600 620 640 660 680 700
                                                            Temperature

Fig. 1. Oxidation profiles of CNFs produced from C2H4 decomposition with C2H4/CO/H2 (30:10:10) over
various Ni-Fe catalysts at 600C.
                                                               SEM/TEM




                                                      10 m

                                                                            10 nm
Fig. 2. CO decomposition at 600C on Fe catalyst with CO/H2 (40:10); (a) SEM image of CNFs; (b) HR-
TEM image of CNFs. Fishbone structure with a hollow core.




                                                              CO-Conversion

                                            0.6
                                                                                           Ni
                                                                                           8:2
                                            0.5                                            5:5
                                                                                           2:8
                                                                                           Fe
                            CO Conversion




                                            0.4


                                            0.3
                                                                       C

                                            0.2


                                            0.1


                                             0
                                                  0     0.5      1         1.5   2   2.5         3
                                                                     Tim e (h)


Fig. 3. CO conversion as a function of reaction time over various Ni-Fe catalysts at 600C. For clarity the
conversion on Fe is only displayed for the first 2.5 hrs.
                                                   C2H4 - Conversion



                                      1
                                                                                 Ni
                                     0.9                                         8:2
                                                                                 5:5
                                     0.8                                         2:8
                                                                                 Fe

                   C2H4 Conversion
                                     0.7

                                     0.6

                                     0.5

                                     0.4

                                     0.3

                                     0.2

                                     0.1
                                           0   2    4        6         8   10       12
                                                         Tim e (h)
Fig. 4. C2H4 conversion as a function of reaction time over various Ni-Fe catalysts with C2H4/CO/H2
(30:10:10) at 600C.