Carbon Dioxide Hydrogenation Towards Methane with Ruthenium Nanoparticles in Ionic Liquid Media

• Autor(a) principal: Barbosa, Catarina Isabel Cabral de Carvalho e Melo Simões
• Data de Publicação: 2018
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/57016
• topic: Carbon Dioxide; Hydrogenation; Ionic Liquids; Methane; Nanoparticles; Ruthenium; Domínio/Área Científica::Engenharia e Tecnologia::Engenharia Química

Carbon dioxide (CO2) is a greenhouse gas of major environmental impact whose emissions continue to rise each year. Extensive research is being done to develop methods of capturing and utilization. Regarding CO2 utilization, its application towards fuel production is a very attractive strategy. This work focuses on the development of a chemical process that converts CO2 into methane. This process aims at using ionic liquids in the synthesis and stabilization of metal nanoparticles that catalyse CO2 hydrogenation in a biphasic CO2+H2/IL medium. In this work ruthenium nanoparticles with a mean size between 1.6-2.9 nm were synthesized insitu through a simple and straightforward process. These nanoparticles can convert CO2 into methane with a selectivity of 100%. These reactions were carried out at temperatures of 150℃ and below, a very low value for this kind of process. Reaction performance was assessed though its yield. The study was divided into three main parts: Optimization, where different reaction conditions were tested such as: type and quantity of precursor; temperature and duration of reaction; and reactant ratio. Study on the effect of several ILs, mostly imidazolium based with fluorinated anions, where it was observed that reaction performance depended mainly on nanoparticle stabilization. This was favoured by the presence of long alkyl chains in the cation and fluoride chains in the anion. 1- Octyl-3-methylimidazolium nonaflate, [C8min][NfO], presented the best results with 84.4% yield. When using low molar volume anions, their strong coordination led to a change of selectivity, towards the formation of carbon monoxide. Recyclability study, where it was possible to reuse the system, although the catalyst slightly deactivated after each reuse due to nanoparticle aggregation and water accumulation in the system. Overall, this reaction reveals potential for implementation in a continuous process.