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Investigation on Methane Catalytic Decomposition Reaction on Ni-based and Fe-based Catalysts

Author: LiDouXing
Tutor: LiYongDan
School: Tianjin University
Course: Industrial Catalysis
Keywords: Methane Catalytic Cracking Hydrotalcite Nickel catalyst Iron catalyst Hydrogen Production Single -walled carbon nanotubes Multi - walled carbon nanotubes Nano carbon onions DFT
CLC: O643.3
Type: PhD thesis
Year: 2009
Downloads: 256
Quote: 1
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Abstract

Methane catalytic cracking step in the system containing no carbon oxides pure hydrogen, and the nano-carbon material obtained has potential applications in the energy and process has obvious advantages. This article through basic research, design of Ni-based and Fe-based catalyst has high activity and stability of the catalyst, and explore a different reaction mode, and a variety of nano-carbon materials preparation and formation mechanism of research and analysis. Prepared using coprecipitation the hydrotalcite maternal the NiAl and NiCuAl-catalyst, and the effects of the reduction temperature, the reaction temperature, the amount of Ni load to improve the speed of the feed gas methane catalytic cracking reaction in the fluidized bed. And methane catalytic cracking in the Determination of Low of the intrinsic chemical reaction control area kinetics, found two kinds Ni/Al2O3 and NiCu/Al2O3 of catalyst activation energy is very similar, are in the 73 ± 2 kJ / mol of the range, which that Cu added did not affect the number of Ni atoms methane catalytic cleavage of the catalytic activity of the reactive sites. This point confirmed by the DFT of the methane adsorption process simulation, the simulation results indicate that of methane in the Ni (100) and of NiCu (100) is very close to the surface of the activation energy. However, due to the Cu added and the enrichment of the surface will cause the surface of such a rapid decline in the number of active sites, and to cause the same temperature for the reduction of activity, but this effect at high temperature can reduce the probability of carbon-coated particles, thereby improving high-temperature stability. Meanwhile, the CO content in the exhaust generated by gas chromatography with methanation converter were measured. Found dried deaerator means when not in use, the concentration of CO in the reaction in the exhaust gas of up to 1800-2500 ppm, initial reaction exhaust drying apparatus used alone in the CO concentration of approximately 1040 ppm, but the stabilization of the reaction could be reduced to 700 ppm or less. After drying and deaerating apparatus used simultaneously, CO concentration than before adding means significantly decreased, is stable up to about 250 ppm. Moreover, after 80 min of reaction when using pure methane feed to reach the level of 10 ppm or less. The results also show that the CO concentration is increased, and as the temperature rises, the highest concentration in the initial reaction. In a thermostatic reaction (CTR) and by comparing NiCu/Al2O3 Low boot two reaction processes of high-temperature reaction (PIR) and found that the stability of the catalyst can be significantly improved using a PIR. By HRTEM and EDS characterize the catalyst metal particles on the growth of carbon fibers, metal particles of the composition of the metal particles are generated by the PIR with cryogenic CTR similar composition, the Ni / Cu ratio of approximately 3:1, and the metal particles of the high temperature of CTR Ni / Cu is less than 1:1. View but also from the shape of the nano carbon fibers and metal particles generated, PIR both high and low temperatures CTR reaction generated when the characteristics of the product structure. Can be considered, in the reaction of the boot process, the formation of the copper-rich particles and the particles of the nickel-rich, when the catalytic cracking of methane when the reaction is carried out at a lower temperature, the copper-rich particles due to copper in an inert workability in the surface distribution nature, the catalytic activity is very low; while the nickel-rich particles have a structure suitable for the growth of carbon fibers and composition, and therefore have higher activity observed in the present experiment to the catalyst particles at the top of the carbon fibers and more with a high nickel content. When the reaction temperature is higher, the catalyst particles inactivation quickly, under such conditions, the nickel-rich particle stability is poor, not suitable for the catalytic growth of carbon fiber, and the copper particles can be maintained due to the modulation effect of the copper nickel a certain activity, it can be found in the experimental results the higher the copper content of the catalyst particles at the top of the high temperature carbon fiber, but even so, the catalytic activity of the copper-rich particles for the methane cracking reaction remains low. Under the heating conditions in the step-by-step of the boot process of the methane cracking reaction at a lower temperature, the restructuring of the catalyst particles can be carried out under low temperature, so that the nickel-rich particles remain active, and in a certain length of the carbon fiber wall to protect the nickel-rich particles has a better stability at high temperatures. The doped Mo, Cr and W on the catalytic activity of the iron-based catalyst as a result, the methane catalytic cleavage reaction does not occupy the surface position of the activity of Cr and W, to reduce the active site, and to reduce the methane conversion rate, but Cr The doping will lead to the generation of amorphous carbon, coke and inactivation likely to cause the surface of the metal particles. Doped Mo can significantly improve the activity of the catalyst can be a single metal Fe/Al2O3 catalyst 17% conversion rate was increased to about 40%, was found by XRD and TPR after the catalyst doping Mo catalyst in the catalyst oxide state and restore process has changed significantly, and help to improve the dispersion of the Fe. When the Mo / (Mo Fe) (mol ratio) was 10% of the catalyst having the highest activity. Was found by the reaction in a fixed bed, the catalyst may be provided at 973 K, and the methane conversion rate can be kept at 44% for approximately 180 min; up to 78% when the reaction temperature was raised to 1023 K, the initial conversion rate of methane, but the high The activity only keep 40 min. Methane catalytic cracking under high temperature conditions the reaction of nano-carbon material were studied. The use of citric acid were prepared the FeMo catalyst for methane catalytic cracking reaction. And use HRTEM and Raman characterization of nano-carbon generated. The active ingredient content of Fe: Mo: Al = 9:1:120 a catalyst to prepare a high purity, the diameter of 1-2.5 nm between the single-walled carbon nanotubes. Prepared by impregnation of the loading of 16% Fe / MgO, Mo / MgO was and FeMo / MgO for methane catalytic cracking reactions, respectively, has been a lot of a diameter of about 10 nm multi-walled carbon nanotubes, some multi-walled nanotubes carbon nanotubes and nano carbon onions. And found that the Mo / MgO-high temperature stability is good, and the methane conversion rate can always be maintained at around 31%, the XRD results confirmed the Mo2C the active center for the methane cracking reaction. The growth of single-wall carbon nanotube bundles according to the results observed in the HRTEM this article, the metal surface to form a protrusion for the growth center. The generation of nano-carbon onions excessive growth related with the high temperature graphite layer is also different, and the different particle size of the metallic particles, surface tension and into the intended degree of liquid, generate the nano-carbon of onion or graphite cage.

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CLC: > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > Chemical kinetics,catalysis > Catalytic
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