Bulk metal doping and surface phosphate modification were synergically adopted in a rational design to upgrade the CeO2 catalyst, which is highly active but easily deactivated for the catalytic oxidation of chlorinated volatile organic compounds (Cl-VOCs). The metal doping increased the redox ability and defect sites of CeO2, which mostly promoted catalytic activity and inhibited the formation of dechlorinated byproducts but generated polychlorinated byproducts. The subsequent surface modification of the metal-doped CeO2 catalysts with nonmetallic phosphate completely suppressed the formation of polychlorinated byproducts and, more importantly, enhanced the stability of the surface structure by forming a chainmail layer. A highly active, durable, and selective catalyst of phosphate-functionalized RuO x –CeO2 was the most promising among all the metal-doped (Ru, Pd, Pt, Cr, Mn, Fe, Co, and Cu) CeO2 catalysts investigated owing to the prominent chemical stability of RuO x and its superior versatility in the catalytic oxidation of different kinds of Cl-VOCs and other typical pollutants, including dimethyl sulfide, CO, and C3H8. Moreover, the chemical stability of the catalyst, including its bulk and surface structural stability, was investigated by combining intensive treatment with HCl/H2O or HCl with subsequent ex situ ultraviolet–visible light Raman spectroscopy and confirmed the superior resistance to Cl poisoning of the phosphate-functionalized RuO x –CeO2. This work exemplifies a promising strategy for developing ideal catalysts for the removal of Cl-VOCs and provides a catalyst with the superior catalytic performance in Cl-VOC oxidation to date.

MnO2 nanorods with exposed (110), (100), or (310) facets were prepared and investigated for catalytic oxidation of chlorobenzene, then the (110)-exposed MnO2 nanorod was screened as the candidate parent and further modified by Pt and/or Mo with different contents. The loading of Pt enhanced activity and versatility of the pristine MnO2, but the polychlorinated byproducts and Cl2 were promoted, conversely, as the decoration of Mo inhibited the polychlorinated byproducts and improved durability. Determination of structure and properties suggested that Pt facilitated the formation of more oxygen vacancies/Mn3+ and surface adsorbed oxygen weakened the bonds of surface lattice oxygen, while Mo stabilized surface lattice oxygen and increased acid sites, especially Brønsted acid sites. Expectedly, Pt and Mo bifunctionally modified MnO2 presented a preferable activity, selectivity, and durability along with the super resistance to H2O, high-temperature, and HCl, and no prominent deactivation was observed within 30 h at 300 °C under dry and humid conditions, even at high-temperature aging at 600 °C and HCl-pretreatment (7 h). In this work, the optimized Mo and Pt codecorated MnO2 was considered a promising catalyst toward practical applications for catalytic oxidation of actual Cl-VOCs emissions.

A phosphate-modified CeO2 nanosheet as a promising catalyst presenting high activity, durability, and selectivity for catalytic oxidation of chlorinated volatile organic compounds (CVOCs) was used to investigate mechanisms of dichloromethane (DCM) oxidation and monochloromethane (MCM) formation by comparison with Al2O3-based catalysts, and CeO2-based catalysts showed a higher activity for DCM oxidation and lower selectivity for MCM. A series of well-designed experiments including various isotopic experiments revealed that an acid–base pair catalysis was involved, that is, DCM mainly dissociated on Lewis acid sites and then dehydrochlorinated through hydroxyl groups/Brønsted acid sites, while the basicity was intrinsic to the generation of MCM via a hydride transfer reaction between DCM activated on basic sites and DCM dissociated on Lewis acid sites. Moreover, the superior redox ability could suppress the formation of MCM by a rapid catalytic oxidation but prompt the possible formation of Cl2 and polychlorinated byproducts.

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