Efficient synergistic catalysis of chlorinated aromatic hydrocarbons and NOx over novel low-temperature catalysts: Nano-TiO2 modification and interaction mechanism

For efficient and synergistic elimination of chlorinated aromatic hydrocarbons (e.g., dioxins and chlorobenzenes) and NOx at low temperatures, a novel VOx-CeOx-WOx/TiO2 catalyst was systemically studied, involving the nano-TiO2 modification and the interaction mechanism between 1,2-dichlorobenzen (1,2-DCB) catalytic oxidation (DCBCO) and NH3-SCR. The VOx-CeOx-WOx/TiO2 performed excellent oxygen storage/release capacity (OSRC) and desirable 1,2-DCB conversion efficiency (95.1-97.4%) at 160-200 ℃ via M‒K and L‒H mechanism. The nano-TiO2 modification slightly impaired the 1,2-DCB oxidation to 93.6-96.2% owing to the reduced surface area and Brønsted acidity, while it distinctly enhanced NO conversion and lowered the T50 (from 162 to 112 ℃) and T90 (from 232 to 205 ℃) by improving catalyst reducibility. Based on further synergistic catalysis evaluation and in-situ DRIFT analysis, NO enhanced the 1,2-DCB conversion and complete oxidation capacity of VOx-CeOx-WOx/TiO2 by promoting active oxygen (O2-, O-, O2-) generation and improving 1,2-DCB chemosorption and subsequent oxidation. In detail, the produced HCl and H2O improved the catalyst acidity and promoted the formation of HONO and HNO3. Moreover, their generation not only facilitated the chemisorption of NH3 but also participated in the NH3-SCR via L‒H mechanism. The ensuing problem was the competitive chemisorption among 1,2-DCB, NH3, and their subsequent intermediates. As a result, NH3 had distinct advantages in competing for acid sites and active oxygen species, especially at the higher temperature, resulting in the improved NO conversion with elevated reaction temperature but the reduced 1,2-DCB conversion. The results provided essential basics for developing new catalysts to synergistically control the emission of chloroaromatic organics and NOx at low temperature.