F and G are not clear. Further study is required. It has to be pointed out that due to the hydrogen spillover phenom- enon found in the above nickel dispersity measurements of samples D and E, the dispersion data listed in Tables 1 and
2 could be affected to some extent by the phenomenon. But those data are still very helpful for relatively estimat- ing their catalytic activities of hydrogenation. However, this phenomenon and its effects are needed for further investigation.
For comparative purposes, a nickel-doped activated car- bon sample with 0.54% of nickel loading (Ni/AC) was pre- pared using incipient wetness impregnation technique. Fig. 4 shows the TPR profiles of Ni–Ca/C, Ni/AC and bulk NiO samples. NiO isolated in the bulk is characterized at 310 C. In the cases of Ni–Ca/C and Ni/AC strong metal–carbon interactions were observed due to their much lower reduction temperatures than that of bulk NiO. The TPR profile of Ni/AC displays a broad peak with a maxi- mum at 270 C, which can be ascribed to diversification of the interaction of nickel with its support carbon and a broad NiO particle distribution. The TPR profile of Ni– Ca/C has two sharp peaks with maximums at 250 C and
300 C. The higher temperature peak is close to that of the bulk NiO in position and can be contributed to reduc- tion of NiO having weak interaction with its support. The lower temperature peak, which is much bigger than the for- mer, can be assigned to the reduction of NiO having inten- sive interaction with its support carbon (or we can say, forming Ni–C compounds). It is interesting that the effect of oxide supports (e.g. Al2O3, SiO2 and MgO) on reduction temperature of NiO is the reverse order of that in the case of Ni–Ca/C. The more intensive the interaction between nickel and oxides is, the higher the reduction temperature of NiO [18–20]. One of possible reasons may be the differ- ence of electronegativity between Ni(II) and its support molecules.
It is the strong Ni–C interaction to facilitate the catalytic activity of nickel loaded in Ni–Ca/C for methane produc- tion by gasification of carbon support, which occurred at
350 C (Fig. 4). In the case of Ni/AC, the start temperature of carbon gasification in H2 stream was around 400 C, which is much higher than that of Ni–Ca/C. Fig. 5 repre- sents the temperature-programmed oxidation (TPO) pro- files of Ni–Ca/C and Ni/AC. The peaks were due to the consumption of O2, which occurred from the reaction of nickel metal with O2. Henceforth, the consumption of O2 proportionally increased with the increase of temperature
F and G are not clear. Further study is required. It has to be pointed out that due to the hydrogen spillover phenom- enon found in the above nickel dispersity measurements of samples D and E, the dispersion data listed in Tables 1 and
2 could be affected to some extent by the phenomenon. But those data are still very helpful for relatively estimat- ing their catalytic activities of hydrogenation. However, this phenomenon and its effects are needed for further investigation.
For comparative purposes, a nickel-doped activated car- bon sample with 0.54% of nickel loading (Ni/AC) was pre- pared using incipient wetness impregnation technique. Fig. 4 shows the TPR profiles of Ni–Ca/C, Ni/AC and bulk NiO samples. NiO isolated in the bulk is characterized at 310 C. In the cases of Ni–Ca/C and Ni/AC strong metal–carbon interactions were observed due to their much lower reduction temperatures than that of bulk NiO. The TPR profile of Ni/AC displays a broad peak with a maxi- mum at 270 C, which can be ascribed to diversification of the interaction of nickel with its support carbon and a broad NiO particle distribution. The TPR profile of Ni– Ca/C has two sharp peaks with maximums at 250 C and
300 C. The higher temperature peak is close to that of the bulk NiO in position and can be contributed to reduc- tion of NiO having weak interaction with its support. The lower temperature peak, which is much bigger than the for- mer, can be assigned to the reduction of NiO having inten- sive interaction with its support carbon (or we can say, forming Ni–C compounds). It is interesting that the effect of oxide supports (e.g. Al2O3, SiO2 and MgO) on reduction temperature of NiO is the reverse order of that in the case of Ni–Ca/C. The more intensive the interaction between nickel and oxides is, the higher the reduction temperature of NiO [18–20]. One of possible reasons may be the differ- ence of electronegativity between Ni(II) and its support molecules.
It is the strong Ni–C interaction to facilitate the catalytic activity of nickel loaded in Ni–Ca/C for methane produc- tion by gasification of carbon support, which occurred at
350 C (Fig. 4). In the case of Ni/AC, the start temperature of carbon gasification in H2 stream was around 400 C, which is much higher than that of Ni–Ca/C. Fig. 5 repre- sents the temperature-programmed oxidation (TPO) pro- files of Ni–Ca/C and Ni/AC. The peaks were due to the consumption of O2, which occurred from the reaction of nickel metal with O2. Henceforth, the consumption of O2 proportionally increased with the increase of temperature
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