With the increasing emphasis on carbon neutrality, carbon dioxide (CO₂) methanation has garnered significant attention due to its potential applications in renewable energy storage and carbon recycling. However, the strongly exothermic nature of this reaction poses considerable thermal management challenges, especially in controlling temperature distribution during reactor scale-up. Neglecting thermal management during scale-up may result in suboptimal reactor performance, including excessive carbon monoxide (CO) formation, decreased methane (CH₄) selectivity, thermal stress-induced material degradation, and accelerated catalyst deactivation. To address these issues, this dissertation systematically investigates the entire process, from micro-scale kinetic modeling to industrial-scale thermal management strategies, based on the performance of a highly active commercial 10%Ru/γ-Al₂O₃ catalyst and a cost-effective alternative, 15%Ni, 1%Ru/CeO₂–Al₂O₃, combining experimental characterization with multi-scale numerical simulations. This integrated approach enables a seamless link between intrinsic catalytic behavior and reactor-scale thermal performance, which is rarely achieved in previous studies on CO₂ methanation.

First, two-dimensional CFD models of packed-bed and wall-coated reactors were developed using 10%Ru/γ-Al₂O₃ as the catalyst, to compare temperature distribution and hot spot formation during CO₂ methanation. The results show that, compared to conventional packed-bed designs, wall-coated reactors offer significant advantages in thermal control, effectively suppressing local temperature rise and improving both reaction safety and product selectivity.

Subsequently, the research was extended to multi-tube heat exchanger-type reactors, where a conjugate heat transfer model coupling reaction and thermal transport processes was established. By simulating various cooling strategies, catalyst loading methods, and reactor geometries, the study demonstrated that coated reactors provide superior thermal management by reducing peak reactor temperatures by approximately 80 to 100 K compared to packed-bed reactors. In addition, extending the catalyst coating length allowed the coated reactors to maintain high methane yields while benefiting from improved thermal performance, demonstrating strong potential for scale-up.

While the initial thermal management analysis was based on a commercial 10%Ru/γ-Al₂O₃ catalyst, further work explored a cost-effective alternative. A bimetallic catalyst, 15%Ni, 1%Ru/CeO₂–Al₂O₃ which has been reported to exhibit high catalytic activity, was considered, and its kinetic parameters, including apparent activation energy (80.9 kJ/mol) and reaction orders, were determined. A reaction rate expression suitable for process simulation and optimization was established. The results indicated that CH₄ and H₂O as products have strong inhibitory effects on the reaction rate, while the influence of H₂ and CO₂ concentrations is relatively weaker.

Finally, incorporating kinetic data into CFD models, a comprehensive thermal optimization study was conducted on an industrial-scale multi-tube shell-and-tube reactor using the Ni-Ru catalyst. Key parameters such as catalyst coating length, inter-tube spacing, and coolant flow rate and temperature were investigated. The results demonstrate that temperature control, CO₂ conversion, and CH₄ selectivity in CO₂ methanation reactors are jointly influenced by the coupled effects of multiple operating parameters, including feed flow rate, feed temperature, coolant inlet temperature, coolant flow rate, and tube spacing. For the system studied under the given assumptions, the optimal performance was achieved with a catalyst coating length of 160 cm, a reaction temperature of 623 K, a coolant inlet temperature of 373 K, and a tube gap of 4 cm for a heat-exchanging coated reactor with 100 tubes and a 15%Ni, 1%Ru/CeO₂-Al₂O₃ catalyst, achieving a CO₂ conversion of 93.13%, a CH₄ selectivity of 99.78%, and a coolant temperature rise of 41.11 K. This highlights the need for integrated optimization of reactor design and operating conditions to achieve both thermal safety and high reaction performance.

This work establishes a comprehensive research framework linking micro-scale catalyst kinetics to macro-scale reactor thermal management, providing theoretical and engineering guidance for the safe and efficient scale-up of CO₂ methanation processes. Under optimal conditions, a cooling gas with the same composition as the reactants was employed, enabling the recovered reaction heat to both regulate reactor temperature and preheat the feed stream. This resulted in a temperature increase of 41.11 K under optimal design conditions, with a maximum of 66.19 K observed across all simulated scenarios. These results demonstrate the strong potential of the proposed design for integrated heat management and energy-efficient operation.