Novel Design Strategies of Bimetallic Nano-catalysts for Enhanced Dry Reforming of Methane (DRM) Performance towards Synthesis Gas Production

Abstract

Dry Reforming of methane (DRM) is an endothermic process that uses CH4 and CO2 to produce CO and H2, also known as synthesis gas (syngas). However, this process has not been commercialized yet due to the lack of an economically feasible catalyst. Ni-based catalysts are economically feasible and they have good catalytic activity compared to their noble metal counterparts (Pt, Ir). However, they suffer from coking and sintering which leads to the catalyst’s deactivation. The carbon formation and deposition under DRM is attributed to two main reactions: (i) CH4 decomposition (CH4 (g) → C-s + 2H2 (g)) and (ii) Boudouard reaction (2CO (g) ↔ C-s + CO2 (g)). Literature has shown that the synthesis method, metal-support interaction, acidity and basicity of the catalytic system affect the activity and stability of a catalytic system. Ceria based catalysts are known for their oxygen storage capacity (OSC), oxygen vacancies (Oᵥ) and reducibility. In the first contribution, the effwqase presence of La3+ and Sm3+ heteroatoms in the 5 wt% Ni/45Ce-45(Sm or La)-10Cu-O catalytic system on the carbon deposition and removal reaction paths in DRM at 750 ◦C were investigated using transient kinetic and isotopic experiments. The exsolution of Cu resulted in the formation of NiCu alloy nanoparticles (NPs), which were partly responsible for lowering carbon deposition and increasing carbon oxidation rates to CO. In the second contribution, the effects of post-synthetic modification (ball-milling) of 45Ce-45(Sm or La)-10Cu-O supports in wet and dry environments were investigated. Wet ball-milling (WBM) resulted in phase heterogeneity of catalysts, which consequently caused the catalysts’ deterioration via coking. While, dry ball-milling (DBM) improved carbon inhibition and catalytic performance in the case of 5 wt% Ni/Ce-Sm-10Cu-O catalyst. Whereas, 5 wt% Ni/Ce-La-10Cu-O exhibited the best catalytic performance and stability amongst the catalysts. As a result, in the last contribution the surface area of Ce-La-10Cu-O support was increased to improve dispersion of metal active sites and confinement which ultimately enhances catalytic performance and reduces sintering. (i) SBA-15 was used as a carrier to X% (X=10, 20, 30, 40) of CeLa10Cu ternary metal oxide loading. 30% of Ce-La-10Cu-O loading improved the stability of catalyst. (ii) Chitosan (sacrificial template) was successfully able to increase the surface area of the Ce-La-10Cu-O support. Then NiₓCoᵧ (x:y = 0:1, 1:1, 9:1, 1:0) NPs were loaded on Ce-La-10Cu-O and the catalytic performance of the catalysts were evaluated. HR-TEM results showed the formation of Ni-Co-Cu trimelltic and bimetallic alloy formation. the NiₓCoᵧ (x:y = 1:0) catlyst exhibited the best catalytic performance towards DRM compared to the other NiₓCoᵧ catalysts. This is attributted to the formation of NiCu bimetallic alloy at high temperatures.

Date of Award	Jul 2022
Original language	American English
Supervisor	Kyriaki Polychronopoulou (Supervisor)