Ernam Selin, Akgül Zeynep Ece, Üner Deniz
Department of Chemical Engineering, Faculty of Engineering, Middle East Technical University, Ankara, Turkiye.
Turk J Chem. 2023 Sep 30;47(5):1285-1295. doi: 10.55730/1300-0527.3612. eCollection 2023.
The photocatalytic nitric oxide (NO) oxidation reaction is used as a standard diagnostic tool for photocatalytic activity according to the well-defined protocol described by ISO Standard 22197-1-2007. This protocol identifies the negative peak showing a NO concentration drop during a gas flow switch from the calibration bypass to the reactor as adsorption of NO on the surface. Evidence is provided for this first transient to be due to a dilution effect in the gas phase within the reactor. With proper models of residence time distribution analysis, this transient revealed the internal hydrodynamics and it can be used to determine the internal volumes of the system. The second transient occurs immediately after the light is switched on. The conversions strongly depend on the time constant of this transient. Controlled measurements of the effect of illumination intensity revealed that at higher light intensities the transient takes longer to reach steady state. The longer transient was attributed to the time needed to reach a thermal steady state of the hot spots generated by the recombination of excess charge carriers. When the catalyst amount was investigated as a parameter, a saturation effect was observed. This saturation effect was correlated with the gas phase concentrations of NO and moisture and their ratios to the available specific surface area. Hence, additional constraints with respect to the illumination intensity and catalyst amounts are recommended for accurate measurements of photocatalytic activity by NO oxidation.
根据ISO标准22197-1-2007中规定的明确方案，光催化一氧化氮（NO）氧化反应被用作光催化活性的标准诊断工具。该方案将气流从校准旁路切换到反应器期间NO浓度下降所显示的负峰识别为NO在表面的吸附。有证据表明，这第一个瞬态是由于反应器内气相中的稀释效应所致。通过适当的停留时间分布分析模型，该瞬态揭示了内部流体动力学，并且可用于确定系统的内部体积。第二个瞬态在光开启后立即出现。转化率强烈依赖于该瞬态的时间常数。对照明强度影响的控制测量表明，在较高光强度下，瞬态达到稳态所需的时间更长。较长的瞬态归因于由过量电荷载流子复合产生的热点达到热稳态所需的时间。当将催化剂量作为一个参数进行研究时，观察到了饱和效应。这种饱和效应与NO和水分的气相浓度及其与可用比表面积的比率相关。因此，建议对光照强度和催化剂量施加额外限制，以便通过NO氧化准确测量光催化活性。
