Omar El Hassan- Thesis June 2021
Abstract
Dry reforming of methane (DRM) is a promising process that can convert carbon dioxide and methane, two of the most abundant greenhouse gases, into synthesis gas or syngas (a mixture of hydrogen and carbon monoxide). This vital chemical precursor can then be transformed into several value-added products, including ultra-clean fuels. One of the main obstacles facing DRM is the rapid deactivation of economically desirable nickel-based catalysts due to carbon formation. Several studies have investigated the different combinations of supports and promotors, which could improve the performance of nickel catalysts. However, a limited number of studies have investigated the impact of varying preparation techniques on synthesized bimetallic catalysts. The current work aimed at studying the Ni-Cu/Al2O3 catalytic system in DRM, focusing on exploring the effect of copper loading on the catalyst characteristics and performance and the impact of the catalyst synthesis technique. Three main preparation techniques were investigated, incipient wetness impregnation (IWI), co-precipitation (CP), and the sol-gel (SG) method. A comprehensive set of characterization techniques (ICP, BET, H2-TPR, Chemisorption, XRD, XPS, SEM, TEM, EDS, TGA, TPO, DSC) was used to investigate crucial catalyst characteristics such as species reducibility, particle size distribution, crystallite diffraction patterns, and elemental composition. The study is divided into two sections. In the first section, titled optimization of copper loading, catalysts were synthesized by IWI only. It was found that medium copper loading (Ni: Cu=8:1) significantly improved catalyst performance compared to the monometallic variant and bimetallic catalysts with high and low copper loading. The formation of a Ni-Cu alloy reduced the amount of coke formed and increased catalyst stability. High copper loading (Ni:Cu=3:1) had an opposite effect as it reduced catalyst activity. In the second section of the study, monometallic and bimetallic catalysts (Ni:Cu=8:1) were synthesized using the SG and CP techniques. In the second section, titled impact of synthesis technique, it was found that bimetallic catalysts prepared by SG and CP were outperformed by their monometallic counterparts when tested for DRM. EDS analysis revealed that although the amount of copper introduced into the system aimed at creating a ‘medium’ loading, the synthesized catalyst had localized ‘high’ loading of copper encapsulating the active nickel sites in a core-shell shape. TGA of spent CP catalysts showed that the monometallic CP catalyst had a higher amount of carbon formed, indicating that the only logical reason for the underperformance of the bimetallic catalysts was copper segregation on the catalyst surface.
Subject
DRMImpact of catalyst preparation technique
Bi-metallic catalyst
Ni-Cu system
Catalyst deactivation
Catalyst characterization
Citation
El Hassan, Omar El (2021). Omar El Hassan- Thesis June 2021. Master's thesis, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /195388.