High-Efficiency Ozone Synthesis By Hybrid Discharge Integrated With Nanocatalyst Coating And Its Mechanism Analysis

As a strong and green oxidant,ozone has been widely used in industrial and agricultural production.Small and medium-sized ozone generators can be flexibly used for pollution control,but how to get high ozone concentration at low energy consumption is a key challenge.Hence,it is very imperative to develop a flat plate small and medium-sized ozone generator possessing the features of simple operation and high ozone synthesis efficiency.In this work,a novel flat-plate hybrid discharge reactor is constructed by adopting the ultra-thin dielectric plate and narrow discharge gap,significantly improving the ozone concentration and energy yield;and through the integration of hybrid discharge and nanocatalyst,the effective regulation of hybrid discharge in ozone synthesis is realized.Further,the enhancement mechanism of ozone synthesis is discussed in detail based on photoelectric diagnostic and physicochemical characterization technologies.The main results are as follows:(1)Based on the ultra-thin dielectric plate with high dielectric constant,a flat-plate double surface discharge reactor with the narrow discharge gap is constructed,and the effects of important parameters,such as dielectric,discharge gap and electrode materials,etc.,on ozone synthesis are studied.Experiment results suggest that,when the dielectric thickness and discharge gap are 0.25 mm and 1 mm respectively,the reactor configrated with titanium electrodes and ZrO2 plate possesses the optimum performance of ozone synthesis.Photoelectric diagnosis results indicate that,there is an internal correlation between structure parameters of the reactor and plasma parameters that improving permittivity,reducing dielectric thickness and discharge gap benefit the acquirement of higher electron excitation temperature,electron density and vibration temperature,and lower rotational temperature.Stability test results show that the optimum double surface discharge reactor possesses an excellent stability during the process of high-efficiency ozone synthesis.(2)A novel flat-plate hybrid discharge reactor with ultra-thin ZrO2 dielectric plate(0.25 mm),a narrow discharge gap(1 mm)and titanium electrodes is designed by coupling volume and surface discharges into one discharge gap.Compared with the volume and surface discharges,the designed hybrid discharge possesses much higher electron excitation temperature,electron density and lower rotational temperature,thus achieving the high ozone energy yield at high ozone concentration.The results indicate that,at input power of 1?5 W,ozone concentration and energy yield of the designed hybrid discharge reactor are 14.7?41.1 g/Nm3 and 255.2?85.0 g/kWh respectively,which is respectively 2.3 times and 1.9 times of volume discharge,2.1 times and 1.4 times of surface discharge,as well as remarkably higher than other reported discharges for ozone synthesis.The hybrid discharge reactor possesses a good stability.(3)Combining a nanocatalyst coating with the novel hybrid discharge,the effect of nanocatalyst on discharge characteristics and the performance of ozone synthesis are systematically studied in pure O2.The results suggest that O3 synthesis strongly depends on the features of nanocatalysts.Hybrid discharge integrated with TiO2 coating obtained the highest ozone concentration(19.3?58.2 g/Nm3)and energy yield(320.0?121.8 g/kWh),about improving 41%and 38%respectively in comparison with the hybrid discharge alone;while MnOx coating significantly reduced the ozone concentration and energy yield.The comprehensive results of ozone synthesis,catalyst characterization and discharge characteristics diagnosis indicate that,the single-valent nanocatalysts(TiO2,SiO2,ZnO,ZrO2,etc.)can enhance surface reactions,then promoting ozone production because of their large surface area but low concentration of oxygen vacancies.In contrast,the multivalent nanocatalysts(MnOx,Co3O4,Fe2O3,CeO2,etc.)possess large numbers of oxygen vacancies and redox couples,which mainly lead to the fast O3 decomposition via surface catalytic reactions over oxygen vacancies and redox couples,and thus resulting in a decline in ozone synthesis.(4)A small-sized ozone generator is assembled by multiple hybrid discharge reactors with TiO2 coating,and the ozone synthesis was conducted in pure O2.At the input power of 250 W,the ozone concentration,energy yield and ozone production rate of the ozone generator are 61.0 g/Nm3,131.6 g/kWh and 20.0 g/h,respectively,and displaying an excellent stability during a long-term test,which provides a good foundation for its practical application.