Toluene Abatement by Simultaneous Adsorption and Oxidation over Mixed-Metal Oxides

Development of integrated processes that can concentrate and oxidize volatile organic compounds (VOCs) from process streams or polluted air in an adsorptive reactor provides a cost-effective alternative to current VOC abatement technologies. Here, we report simultaneous adsorption and oxidation of toluene as a VOC model compound over TiO2/SiO2 and ZrO2/SiO2 mixed-metal oxides (MMOs) with varied compositions. These MMOs were investigated for their equilibrium adsorption capacity and dynamic performance at room temperature (25 degrees C), as well as their catalytic activity at 250 degrees C. The adsorption isotherms indicated that equilibrium capacity varies dramatically with TiO2 and ZrO2 loading, and the highest toluene uptake was reached over TiO2/SiO2 with 8 wt % TiO2 and ZrO2/SiO2 with 13 wt % ZrO2 (3.9 and 2.9 mmol/g, respectively) at 27 mmHg and 25 degrees C. Moreover, the integrated capture-oxidation results revealed that Ti-based MMOs are more efficient than Zr-based materials by displaying higher dynamic capacity and toluene conversion as a result of higher surface area and pore volume, surface defects, and hydroxyl groups. The TiO2/SiO2 with 8 wt % TiO2 loading exhibited a dynamic (pseudoequilibrium) adsorption capacity of 3.8 mmol/g and a toluene conversion of 86%. Post oxidative chemical analysis further revealed the retention of materials structure with little coke formation, which highlighted the repeated and sustainable applicability of these materials in VOC abatement processes.