Hybrid Catalysis-Reactive Sorption Mechanism for 2-CEES and Sulfur Mustard Dehydrochlorination on Single Metal Atoms on Anatase-TiO2

Abstract

The threat posed by chemical warfare agents (CWAs) in the modern era necessitates increased innovation in understanding new mechanisms to neutralize their lethality. By identifying novel materials and chemical reaction pathways, better protection can be offered. Single metal atoms supported on TiO₂ represent a promising avenue of exploration in designing systems which can effectively capture and degrade the sulfur mustard agent. By modelling sulfur mustard and its simulant, 2-chloroethyl-ethylsulfide (2-CEES) this work brings a proof of concept for the facile decomposition pathways of sulfur-containing vesicant agents over Pt, Pd, and Ir single atom metal oxides on anatase TiO₂ (101) surface with and without the presence of water. Under ambient conditions, 2-CEES will favorably be transformed into ethyl-vinylsulfide (EVS) through a dehydrochlorination reaction involving C-H and C-Cl bond cleavages. Notably, the single atom metal oxide cleaves the α-C-H bond with a low calculated barrier. The reaction energetics are most favorable on the Pd system with barriers passable at a temperature of 298 K and with EVS desorption facilitated by adsorption and reaction of additional reactant molecules and with the produced H and Cl fragments stored on the titania support. The Pd single atom oxide is proposed to be able to degrade 2-CEES and sulfur mustard through a mechanism combining C-H bond cleavage at the Pd-O center and sorption of the H and Cl fragments from 2-CEES or mustard on TiO₂ , however with a larger reactivity for the removal of the second Cl of mustard than for dehydrochlorination of a second 2-CEES reactant. The reaction appears as a hybrid combination of catalytic steps evolving products in gas phase with reactive sorption of the remaining fraction of products on the support.