Engineering of Nanostructured Carbon Catalyst Supports for the Continuous Reduction of Bromate in Drinking Water

Abstract

Recent works in the development of nanostructured catalysts for bromate reduction in drinking water under hydrogen have highlighted the importance of the properties of the metallic phase support in their overall performance. Since most works in catalyst development are carried out in powder form, there is an overlooked gap in the correlation between catalyst support properties and performance in typical continuous applications such as fixed bed reactors. In this work, it is shown that the mechanical modification of commercially available carbon nanotubes, one of the most promising supports, can significantly enhance the activity of the catalytic system when tested in a stirred tank reactor, but upon transition to a fixed bed reactor, the formation of preferential pathways for the liquid flow and high pressure drops were observed. This effect could be minimized by the addition of an inert filler to increase the bed porosity; however, the improvement in catalytic performance when compared with the as-received support material was not retained. The operation of the continuous catalytic system was then optimized using a 1 wt.% Pd catalyst supported on the as-received carbon nanotubes. Effluent and hydrogen flow rates as well as catalyst loadings were systematically optimized to find an efficient set of parameters for the operation of the system, regarding its catalytic performance, capacity to treat large effluent flows, and minimization of catalyst and hydrogen requirements. Experiments carried out in the presence of distilled water as a reaction medium demonstrate that bromate can be efficiently removed from the liquid phase, whereas when using a real water matrix, a tendency for the deactivation of the catalyst over time was more apparent throughout 200 flow passages over the catalytic bed, which was mostly attributed to the competitive adsorption of inorganic matter on the catalyst active centers, or the formation of mineral deposits blocking access to the catalyst.

Magnetic Metallic Nanoparticles Coated with Carbon for the Catalytic Removal of Bromate from Water

“…The significance of this final factor is pivotal for the overall functionality of the catalyst. An investigation focused on determining the quantity of H 2 needed to activate the catalyst by varying H 2 flow rates from 5 to 75 cm 3 min −1 revealed a generally consistent activation pattern, except for a flow rate of 5 cm 3 min −1 [4]. Therefore, the determination of the H 2 flow rate is an important step since, as mentioned earlier and as suggested in the literature, the reaction mechanism involves the dissociative adsorption of H 2 on the surface of the metallic catalyst and the reaction between the adsorbed bromate ions and the atoms of hydrogen [3].…”

“…This indicates that the presence of other ions and organic matter influences the catalytic activity. The mechanism of bromate reaction is revealed to be a process controlled via adsorption, and therefore, the presence of ions can trigger competition for adsorption on the active sites of the metal, inhibiting the reduction of bromate [4]. Chen et al [20], when carrying out bromate reduction experiments in the presence of SO 4 2− , Cl − , and Br − ions to evaluate the impact of these anions, observed that the SO 4 2− ion, compared to Cl − and Br − , has a higher ionic charge.…”

“…Bromate is normally produced in treatment processes involving the ozonation or chlorination of water containing bromide [2,3]. To minimize bromate formation, water treatment plants must carefully control disinfection processes, adjusting reaction conditions and optimizing ozone dosage [4]. Several studies have confirmed that bromate is a carcinogen, posing a threat to humans [3,5].…”