Monolitos celulares cerámico-carbono como soportes de catalizadores de desnitrificación y adsorbentes

Resumen

[EN] A procedure to prepare carbon-ceramic cellular monoliths has been developed in this work. Optimisation of preparation conditions has been carried out so that materials with a homogeneous carbon distribution and a high pore volume in the micropore range have been obtained. The composite monoliths have been analysed as catalyst supports and adsorbents in diluted gaseous streams. First of all, these carbon-ceramic monoliths have been used as catalysts support for manganese oxides and vanadium oxides in order to study their performance in the selective catalytic reduction (SCR) of nitrogen oxides with ammonia at low temperature (T<200ºC). The catalyst preparation procedure was optimised via tailoring the superficial properties of the carbonaceous support. The effect of different variables on catalytic activity and selectivity of the previously developed catalyst has been analysed. The catalysts developed here show a high catalytic activity, higher than that of other catalysts reported in literature. Vanadium-based catalysts are more resistant to SO2 deactivation than manganese-based catalysts. The presence of water vapour in the gas stream produces a decrease in catalytic activity for both types of catalysts. The initial value of catalytic activity is recovered after removing water from the inlet stream. Vanadium-based catalysts have been kept in the exit duct of a power plant in order to analyse their long-term stability. An important deactivation is observed after ~200 days in the power plant, mainly provoked by arsenic poisoning. An exhaustive analysis of the species involved in the low temperature SCR (125ºC) has been performed over manganese-based catalysts. A reaction mechanism has been developed from this analysis based on ammonia reaction from an adsorbed state with nitrogen dioxide from the gas phase (Eley Rideal type mechanism). Strong though partial deactivation of the catalyst is associated to formation of stable surface nitrates. Carbon-ceramic monoliths have also been proposed in this work as adsorbents of n-butane in diluted streams. In these conditions, the adsorption capacity of the monoliths developed here is higher than that of granular active carbon packed beds. Moreover, monoliths are easier to handle with and produce a lower pressure drop in the system than packed beds of active carbon granules. A model to predict the behaviour of carbon-ceramic monoliths in dynamic adsorption processes has also been developed. This model permits to obtain an excellent fitting of the experimental data by considering the existence of a gas velocity profile in the adsorption chamber.