Approaches for CO₂ Utilization and CO₂ Efficient Processes

CO₂ utilization and CO₂ emission reduction are important for low-carbon economy. As one of the thermal approaches for CO₂ utilization, CO₂ hydrogenation to methanol has attracted a lot of attention in recent years. However, the feasibility of this process is limited by the low product selectivity and low catalyst stability when using the state-of-the-art catalyst. Therefore, studies on new materials and catalyst designs are necessary to overcome these difficulties.

This dissertation developed new catalysts that aid this purpose. The new catalysts include Ru-Mo bimetallic phosphide, In-Ru-Mo trimetallic phosphide and In-Ru bimetallic catalyst. Each unique design resolves a critical drawback of the previous catalyst and our final design, In-Ru bimetallic catalyst, is capable of catalyzing CO₂ hydrogenation to methanol with methanol selectivity of 85% while the state-of-the-art catalyst can only reach 35% at the same condition. The promotional effect of In-Ru bimetallic compounds was investigated further through in-situ techniques which aids in-depth understanding on the reaction mechanism.

The second part of this dissertation focuses on reducing CO₂ emission from distributed hydrogen production to fuel the future low-carbon economy. The main approach is to develop steam methane reforming (SMR) at low temperature where thermal catalytic approaches are limited by low thermal equilibrium conversion. Dielectric barrier discharge (DBD) plasma was utilized to promote methane conversion and hydrogen production at low temperature and high steam/methane ratio, where thermal catalytic approach cannot. With the assistance of 15W plasma, SMR can take place at 300-440 ^oC with up to 80% methane conversion. Further experiments were performed to identify the key parameters that favors high methane conversion and high CO₂/CO ratio in flue gas. In addition, a cascade reactor design was also made to effectively control the CO concentration in flue gas.