Influence of the synthesis method on the catalytic activity of mayenite for the oxidation of gas-phase trichloroethylene

Abstract

Catalytic oxidation of trichloroethylene (TCE) in heterogeneous phase (gas-solid) is an effective strategy for the conversion of this pollutant in less harmful compounds, namely CO2, CO and HCl. In this work, we have studied the use of mayenite, a cost-effective material, as an active catalyst for the TCE conversion. In particular, we have assessed the influence of the mayenite synthesis method (hydrothermal, sol-gel and ceramic) on the reaction performance. The materials have been characterized by different techniques, such as XRD, N2-sorption (BET), TPR, Raman spectroscopy, FESEM-EDX and TEM. The analysis of the light-off curves and product distribution, has shown that the use of the hydrothermal method for the mayenite synthesis results in the most active and selective catalyst. This has been related with a higher surface area and with a higher concentration of oxygen anions in the mayenite prepared by this method. It has been found that the presence of water in the stream do not influence the catalytic performance of the material. A mechanism for the reaction and for the partial deactivation of the catalyst has been proposed.

Oxidative Degradation of Trichloroethylene over Fe2O3-doped Mayenite: Chlorine Poisoning Mitigation and Improved Catalytic Performance

“…As reported in previous works, the deactivation mechanism of mayenite catalyst is related with the displacement of active oxygen species by chloride ions [19,20,24,25]. In particular, the formation of HCl during the reaction caused a partial irreversible substitution of the anionic oxygen species (O x x− ) by chloride ions forming chloromayenite [19,22], with consequent deactivation of the catalyst. It is observed that the presence of iron in mayenite modifies this mechanism, probably because the Fe species catalyze the interaction of the atmospheric O 2 to form O 2− and O 2 2− , making reversible the substitution of chloride ions by oxygen and avoiding or diminishing the formation of chloromayenite.…”

“…Similar results were obtained in the XPS analysis of the samples after reaction (see Supplementary Materials). This does not occur with pure mayenite [19,22], demonstrating that the redox properties of iron catalyze the regeneration of anionic oxygen by the O 2 present in the gas feed and avoid the irreversible chlorine poisoning of mayenite. These results clearly show that the presence of well-dispersed iron on the mayenite surface improves the redox properties of the mayenite together with its stability, due to the ability of iron to catalyse the regeneration of the anionic oxygen responsible for TCE oxidation.…”

“…These results reveal that after 12 h of reaction, part of the HCl formed in the reaction interacts with the mayenite and some chloride species are formed on the catalyst surface. Nevertheless, these species are not irreversibly adsorbed on the ionic vacancies (as in the case with pure mayenite [19,22]) and oxidant centres (anionic oxygen) are present after reaction. This is due to a synergic action of the iron present in the mayenite surface, which catalyses O x…”

“…In previous works, we reported about the oxidation of TCE by using the mesoporous calcium aluminate mayenite (Ca 12 Al 14 O 33 ) as a catalyst [18][19][20][21][22]; mayenite had a good overall performance, showing high activity and selectivity towards nontoxic compounds, and fair thermal stability and recyclability. As a main drawback, the material shows a certain tendency towards chlorine poisoning, leading to slow deactivation of the catalyst.…”

A Novel Synthetic Route to Prepare High Surface Area Mayenite Catalyst for TCE Oxidation

“…Solsona and coworkers employed PMMA as a soft templating agent during catalyst preparation for increasing their surface area, thus improving the oxidation yield of propane [17]. In a previous work, we reported the influence of the synthesis method on mayenite activity for the trichloroethylene (TCE) oxidation [18]. In particular, hydrothermal, ceramic, and sol-gel routes were employed for the synthesis of the mayenite and we found that the hydrothermal method yielded the material with the best catalytic performances due to an optimum combination of surface area and redox properties.…”