Shuo Wang,Zhenke Chen,Ying Zhao,Chenlu Sun,Jianye Li
In this work, the unique starlike La-doped ZnO–SiO 2 photocatalysts were constructed by an evaporation and calcination method and characterized in detail. UV–vis reflectance and DFT calculation confirm that the doping with La allows to obtain a decrease of band gap of ZnO/SiO 2 , which enhances visible light absorbance and oxidizing ability. The photoluminescence intensity reduces greatly, indicating more effective separation of the photogenerated carriers of La-doped ZnO-SiO 2 . Photocatalytic activities of La-doped ZnO-SiO 2 with different doping ratios under simulated visible light irradiation were evaluated with malachite green (MG) as a model pollutant. Under optimized conditions including solution pH of 8, 15 mg/L of MG solution and 15 mg of catalyst dosage, 0.2% La-ZnO-SiO 2 exhibits the best catalytic activity in photodegradations of MG in water. The removal and mineralization efficiency of MG can reach 96.1% and 70.9% in 140 min, respectively. The as-prepared catalysts present superior stability and recyclability after four times reuse. Moreover, selective quenching experiments indicate that hydroxyl radical (·OH), hole (h + ) and superoxide radical (·O 2 - ) are the main reactive species responsible for MG degradation. Possible mechanism for photocatalytic elimination of MG over La-doped ZnO/SiO 2 photocatalyst is finally proposed.
CuO-ZnO is a key catalyst widely used in catalytic processes such as dehydrogenation and hydrogenation. Hence, revealing the impact of H2O and H2 on the stability of CuO-ZnO catalysts is of critical importance. In this work, a CuO-ZnO/SiO2 catalyst with highly dispersed CuO-ZnO interface active sites was synthesized, and the structure-activity relationship and deactivation mechanism were systematically investigated using a model reaction (the cyclodehydrogenation of 1-amino-2-propanol to 2,5-dimethylpyrazine) that simultaneously generates H2O and H2. Under optimized reaction conditions (250 °C, space velocity: 1.5 h-1, and N2 flow rate: 8 mL/min), a 2,5-dimethylpyrazine yield of 68.1% was achieved over the 20%CuO-ZnO/SiO2-3:2 catalyst. The investigation into the deactivation mechanism reveals that Cu species agglomeration and carbon deposition are the primary reasons for the decline in activity. The roles of H2 and H2O in catalyst stability were found to be different: H2 suppressed the aggregation of metallic Cu0, while H2O enhanced stability by suppressing the formation of carbon deposits. Based on the understanding of the deactivation mechanism, catalyst regeneration was performed through air calcination, recovering the 2,5-dimethylpyrazine yield to 88.1% of the initial value. Overall, this work reveals the deactivation pathways and stabilization mechanisms of CuO-ZnO/SiO2 catalysts under reactive atmospheres containing H2 and H2O, offering theoretical guidance for industrial application and design of a highly stable CuO-ZnO catalyst.
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