Theoretical analysis and experimental investigation of hydrogen production by thermo-catalytic decomposition of methane

• Main Author: Chen, Qianqian
• Other Authors: Lua Aik Chong
• Format: Thesis-Master by Research
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Chemical engineering
• Online Access: https://hdl.handle.net/10356/143904
• Institution: Nanyang Technological University

One of the most promising alternative energy carriers and clean fuels would be hydrogen, which is widely considered. Therefore, significant effort has been focused on developing efficient, economic and environmental friendly approaches for the production of hydrogen. Among the many hydrogen generation techniques, the catalytic decomposition of methane (CDM) over supported nickel catalysts has gained much interest. This hydrogen generation method will eliminate the requirement for COx separation and subsequent processes altogether. The main objectives of this research project are to synthesis high efficient and long active-life catalysts and to optimize the experimental process in order to generate hydrogen by thermal decomposition of methane with high conversion ratio. In this thesis, a comprehensive study on a series of supported nickel nanoparticle catalysts was presented. These supported catalysts prepared in a novel and creative method showed comparable catalytic activity as the other supported catalysts prepared by traditional method such as coprecipitation and impregnation. These catalysts offered two major advantages by (1) providing high-loading supported nickel catalyst with tunable nanoparticle size and (2) preventing nickel nanoparticles from severe aggregation and loosing catalytic activity very rapidly, resulting from moderate interaction with support. To the best knowledge of the author, this study was the second time that investigated the catalytic activities and deactivation mechanisms of electroless nickel plating technique towards CDM systematically. The thesis consisted mainly of the two following parts: (1) Supported nickel nanoparticles were prepared by a creative method and these nanoparticles showed promising catalytic activity towards catalytic decomposition of methane. The addition of silver nanoparticles as seeds led to the formation of nickel particles with smaller crystalline size and high dispersion on the support than those of Ni particles prepared by another similar technique. Unlike the conventional supported catalysts, it was only required to introduce a small of amount of hydrogen to the reactor to reduce the surface oxidation of nickel particle and to avoid catalyst particles sintering into bigger ones during the reaction. The objective of this part of the project was to investigate the preparation of the active phase composition and the other physicochemical properties of catalyst synthesized by electroless nickel plating method. The textural and micro-structural properties of the deposited carbon were also characterized in detail. A series of decomposition atmospheres (CH4-N2 in different volumetric flow rate) were used to investigate their effects on the equilibrium between carbon diffusion among nickel bulk and the formation of carbon nanotubes. The effects of reaction temperatures on the catalytic activity were also studied. The resulting Ni particles with 32 wt.% loading on SBA-15 showed promising catalytic activities for methane decomposition at temperatures of 575°C. The stability of the catalysts was discussed and this work provided helpful guidance on the deactivation mechanism proposed in Chapter 4. (2) In Chapter 5, a detailed catalytic deactivation study was carried out. A series of kinetic experiments had been conducted using two types of catalysts (26 wt.% Ni/SBA-15 and 32 wt.% Ni/SBA-15). The effects of W/F ratio (the ratio of the weight of catalyst to the molar flow rate of methane) and reaction temperatures on the methane decomposition rate were studied. The reaction order and activation energy of 32 wt.% Ni/SBA-15 catalyst were calculated based on Genetic Algorithm, with correlation coefficient >0.99. Different deactivation mechanisms of 32 wt.% Ni/SBA-15 catalyst were proposed and discussed.