دانلود رایگان مقاله کاهش برنامه ریزی شده دمای اصلاح کاتالیزور بخار نیکل با گلوکز

ABSTRACT

 Temperature-programmed reduction (TPR) of a NiO/-Al2O3 steam reforming catalyst with glucose under a N2 flow was investigated using TGA-FTIR technique. A series of catalyst samples obtained at different temperatures during the TPR were characterised by XRD, CHN elemental analysis, SEM-EDX and TPO. Results showed that the whole TPR covering from room temperature to 900 ◦C consisted of two reactive processes. They were glucose pyrolysis producing carbonaceous materials (char), and NiO reduction by the char resulting in CO2 as a main product. When the initial mass ratio of glucose to the catalyst was 1:10, the catalyst could be completely reduced without carbon remaining. Moreover, two mass loss peaks were observed at around 440 ◦C and 670 ◦C, respectively, during the reduction. Based on the experiments of char characterisation, H2 TPR and excess glucose TPR, a two-stage reduction mechanism was proposed. The first reduction stage was attributed to a solid reaction between NiO and char. The second stage was assigned to NiO being reduced by the CO produced by char gasification with CO2. Their apparent activation energies were 197 ± 19 kJ/mol and 316 ± 17 kJ/mol, respectively, estimated using the Kissinger method.

4. Conclusions

There is a growing interest in converting biomass to syngas by chemical looping reforming (CLR) technology. The reduction of an oxygen carrier by bio-feedstock is an important part of a CLR process. This paper investigated the reaction between a NiO/-Al2O3 catalyst and glucose in a batch pyrolysis mode using TGA-FTIR technique. A mixture of glucose and the catalyst was prepared by impregnation and then submitted to a slow temperatureprogrammed rise (5 ◦C/min) under a N2 flow. Such a condition enabled the separation of glucose pyrolysis and catalyst reduction. Through pyrolysis, about 64% of the carbon in glucose molecules was converted to char which later acted as reductant. The char was almost homogeneous and showed a H/C ratio of 0.6. It was unevenly distributed on the catalyst surface with some NiO uncovered. The catalyst reduction started at 420 ◦C, mainly producing CO2. A complete reduction without carbon remaining was achieved when the mass ratio of glucose to the catalyst was 1:10 under our experimental condition. The crystallite size of product Ni increased with temperature during the TPR and reached 44 nm at the end of TPR (900 ◦C). A two-stage reduction mechanism was proposed to explain the two reduction peaks observed during the TPR. NiO first reacted with the char deposited on NiO sites. The reaction was accelerated by the increasing temperature but slowed down by the decrease in the amount of char. As a result, a reduction peak centred at 440 ◦C was observed during TPR.When the temperature was raised to above 530 ◦C, the gasification of char by CO2 was initiated and produced CO, which acted as reductantfor the following reduction centred at 670 ◦C. The apparent activation energy for these two reduction stages was 197 ± 19 kJ/mol and 316 ± 17 kJ/mol, respectively. Such a mechanism made possible the transport of char from -Al2O3 sites to NiO sites and the reduction of the NiO uncovered by char. Future work on the reduction of NiO catalyst with other biomass derivatives such as citric acid is in progress.