Seminario: “CO2 methanation and NH3 synthesis. Towards a general model to explain the catalytic activity of noble metal supported nanoparticles ”
Prof. Patricio Ruiz.
Martes 11 de Marzo, 11 horas.
Facultad de Ingeniería Química, Aula Babini.
El Prof. Patricio Ruiz desarrolla su trabajos de investigación en el Institute of Condensed Matter and Nanosciences, Molecules, Solids and Reactivity (IMCN-MOST), Université catholique de Louvain, Louvain-la-Neuve, Bélgica.
One of the main challenges in heterogeneous catalysis is to perform reactions with high selectivity and reducing energetic consumption. This can be achieved performing processes under mild reaction conditions (low temperature and low pressure).
In order to reduce energy consumption, the synthesis of highly active catalysts at low temperature and low pressure is required. Very active catalysts under mild reaction conditions can be obtained when the active phase present nanoscale properties. Nanosized metallic particles are a key factor to develop processes under mild reaction conditions. Therefore, understand the role of catalytic nanoparticles in performances is priority for improving existing technologies and for designing new processes of low energy consumption.
We present new results which can contribute to explain the catalytic performance using noble supported nanoparticles. Two reactions were studied i) CO2methanation (over Rh/alumina) and ii) NH3 synthesis (over Ru/alumina). Both reactions are performed at low temperature (<200°C) and pressure (< 5 bars).
The transformation of CO2 into useful products is one of the major challenges in the development of environmentally friendly and sustainable processes. The recycling of CO2 to fuels or raw materials that are consumed in large scale can contribute to the solution to the current global warming problem. Methane can be produced by hydrogenation of CO2. It can be directly injected into already existing natural gas pipelines and it can be used as a fuel or raw material for the production of chemicals. The major challenges for an industrial implementation of this reaction are to increase the activity and selectivity to methane that can permit the operation at low temperature and pressures in compact units that should be close to CO2 emission sources.
Ammonia synthesis is one of the two highest energy consumer processes in the chemical (except cementer)and petrochemical industry. It is an exothermic reverse reaction limited at low temperatures by the kinetic of the reaction and at high temperatures by the thermodynamic equilibrium. At industrial scale, the reaction is performed at high temperatures, so high pressures are also required to favor the direct reaction.
It will be demonstrated that the size of metallic nanoparticles (2-18 nm) plays a determinant role in both reactions. Larger particles are more actives than small ones having a higher fraction of metallic noble metal. In CO2methanation, the reaction rate is limited over small Rh nanoparticles, because CO is strongly adsorbed and hardly hydrogented. In NH3 synthesis, the reaction rate is limited over small Ru nanoparticles by the adsorption of nitrogen. Large Ru (Rh) nanoparticles activate H2 with higher efficacy, promoting the hydrogenation of the adsorbed species on small particles. For the first time a catalytic cooperation between small and large noble metal nanoparticles is put in evidence.In this model the distribution of the size of particles plays also an important role. The proposed model could be generalized to other metallic nanoparticles.