Transition metals-based catalysts for CO2 Utilization

CO₂ emission from fossil fuel combustion is one of the most common causes of global warming accounting for 36 Mton per year. When renewable hydrogen is available, the catalytic hydrogenation of CO₂ to methane or CO is an efficient way to reduce CO₂ emissions, considering the forecasted increase in energy demand. In this field, heterogeneous catalysis plays a crucial role in the development of such technologies. Among noble and transition metals, supported nickel and ruthenium catalysts are the most promising candidates for CO₂ methanation reaction; nickel is preferred for its high activity and relatively low cost while ruthenium is generally targeted for low-temperature applications. However, the role of support plays a central role in the activity and stability of the investigated materials. CO₂ hydrogenation catalysts are generally supported on various oxides such as Al2O3, SiO2, ZrO2, and CeO2 with quite variable loadings (5-50 wt% and 0.3-5 wt% for Ni and Ru, respectively) and suitable promoters. Carbon-supported catalysts are of timely interest for different green chemistry reactions and have been investigated in ethanol steam reforming reactions, organic oxygenated hydrogenation/dehydrogenation, etc. In addition, graphene-based materials have gained attention for dispersing monometallic and bimetallic nanoparticles, showing, in some cases, remarkable catalytic performances even though metal oxidation state and interaction with the support are still matters of debate. However, studies that use graphene as catalyst support in the heterogeneous catalysis field are still limited. This thesis focused not only on improving the performance of well-established catalysts for CO₂ hydrogenation, particularly for CO₂ methanation but also on designing and evaluating novel carbon-based catalysts. The objective was to explore their advantages and limitations, contributing to the development of more efficient and sustainable catalytic systems. Additionally, cutting-edge methods for synthesizing suitable carbon-based supports were reviewed and implemented to identify the most effective, cost-efficient, and sustainable approach, ensuring a comprehensive process from conceptualization to final application.