Abstract:
The efficiency and performance of photocatalytic reactors significantly depend on the choice of catalyst. This study delves into the intricate aspects of catalyst selection for photocatalytic reactors, focusing on experimental parameters, catalyst characteristics, and reactor configurations. By employing a systematic approach, various catalysts were evaluated based on their photocatalytic activity, stability, and selectivity under different operational conditions. The results obtained provide valuable insights into the optimal catalyst selection criteria for enhancing the performance of photocatalytic reactors.

Keywords: photocatalytic reactor, catalyst selection, photocatalytic activity, stability, selectivity

1. Introduction

Photocatalysis has emerged as a promising technology for addressing environmental challenges, such as water purification and air pollution control. The efficiency of a photocatalytic reactor is heavily reliant on the catalyst employed, which acts as the mediator in converting solar energy into chemical energy. Therefore, selecting an appropriate catalyst is crucial for maximizing the reactor's performance. This paper presents a comprehensive analysis of catalyst selection for photocatalytic reactors, considering both experimental and theoretical perspectives.

2. Experimental Setup and Methodology

2.1 Reactor Configuration
The experiments were conducted in a batch-type photocatalytic reactor equipped with a UV-C light source to simulate solar radiation. The reactor was made of quartz glass to allow maximum transmission of UV light. The catalyst was dispersed in the reaction medium, and the mixture was stirred continuously to ensure uniform illumination and mass transfer.

2.2 Catalyst Preparation and Characterization
Several catalysts, including TiO2, ZnO, SnO2, and WO3, were synthesized and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The specific surface area, pore size distribution, and bandgap energy of the catalysts were also determined using BET analysis, mercury porosimetry, and UV-Vis spectroscopy, respectively.

2.3 Evaluation Criteria
The catalysts were evaluated based on their photocatalytic activity, stability, and selectivity. Photocatalytic activity was assessed by measuring the degradation rate of a model pollutant (e.g., methylene blue). Stability was evaluated by monitoring the catalyst's performance over multiple reaction cycles. Selectivity was determined by analyzing the reaction products using gas chromatography-mass spectrometry (GC-MS).

3. Results and Discussion

3.1 Photocatalytic Activity
Among the catalysts tested, TiO2 exhibited the highest photocatalytic activity, with a degradation rate of 95% within 2 hours of irradiation. This was attributed to its high specific surface area, favorable pore size distribution, and optimal bandgap energy for UV light absorption. ZnO and SnO2 showed moderate activity, while WO3 demonstrated the lowest activity.

3.2 Stability
TiO2 also demonstrated excellent stability, maintaining its initial activity after five consecutive reaction cycles. ZnO exhibited a slight decrease in activity after the third cycle, while SnO2 and WO3 showed significant deactivation over time. The stability of the catalysts was correlated with their resistance to photocorrosion and agglomeration.

3.3 Selectivity
The selectivity of the catalysts was evaluated by analyzing the reaction products. TiO2 primarily produced CO2 and H2O as the final products, indicating complete mineralization of the model pollutant. ZnO and SnO2 generated intermediate products such as aldehydes and carboxylic acids, suggesting partial mineralization. WO3 produced a complex mixture of products, indicating low selectivity.

4. Catalyst Selection Criteria

Based on the experimental results, the following criteria were established for catalyst selection in photocatalytic reactors:

• High photocatalytic activity to ensure rapid degradation of pollutants.

• Excellent stability to maintain long-term reactor performance.

• High selectivity for complete mineralization of pollutants to avoid the formation of harmful intermediate products.

TiO2 emerged as the optimal catalyst, satisfying all the selection criteria. Its combination of high activity, stability, and selectivity makes it a suitable choice for various photocatalytic applications.

5. Conclusion

This study provides a systematic approach for catalyst selection in photocatalytic reactors, considering experimental parameters, catalyst characteristics, and reactor configurations. TiO2 was identified as the most suitable catalyst due to its superior performance in terms of photocatalytic activity, stability, and selectivity.