Catalytic activities and resistance to poisoning of tar reforming catalysts for syngas upgrading

• Main Author: Dara Khairunnisa Mohamed
• Other Authors: Grzegorz Lisak
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Science::Chemistry; Engineering::Chemical engineering; Engineering::Environmental engineering
• Online Access: https://hdl.handle.net/10356/157176
• Institution: Nanyang Technological University

Tar is formed from the thermal decomposition of organic compounds during the gasification of waste and biomass and is a major contaminant in syngas. For syngas to be utilized for further applications, such as in power generation, liquid fuel and chemical synthesis, removal of tar compounds is required. A preferred method of tar removal is the catalytic tar reforming using Ni catalysts. However, Ni catalysts for tar reforming of syngas suffer from loss of catalytic activity due to poisoning by other syngas impurities, such as sulfur and halide compounds. This has limited the industrial application of tar reforming integrated into gasification of waste and biomass. Therefore, this work focuses on the development and study of Ni catalysts with high activity and high resistance to poisoning by impurities in syngas. One strategy to increase the activity and durability of Ni catalysts was through the selection of suitable organic precipitants, such as urea, N,N’-dimethylformamide, N-methylurea, 1,1-dimethylurea and N,N’-dimethylurea, for hydrothermal synthesis. The formation of different reaction products during hydrolysis of precipitants influenced the distribution of Ni0, NiO and NiAl2O4 species, which played essential role in the tolerance towards poisoning during naphthalene reforming in the presence of H2S and HCl as impurities. Subsequently, the influence of HBr, which is an emerging impurity, on the activity of Ni catalysts was investigated. The negative HBr impact can be mitigated by developing a nanostructured catalyst with high porosity and Ni dispersion that ensure the strong Ni-support interaction. Finally, the effects of syngas impurities on the activities of pre-reduced and as-calcined NiAl2O4 catalysts prepared using hydrothermal synthesis for the reforming of a mixture of tar compounds was studied. Without pre-reduction treatment, the catalyst exhibited low catalyst activity in tar reforming attributing to the favourable reaction between H2S and Ni2+ species. Pre-reduction of catalysts resulted in their stable activity even in the presence of syngas impurities.