In traditional chemical reactions, reactants are primarily activated through heating, providing the energy required to overcome thermodynamic barriers and drive the conversion of reactants into products. In thermocatalytic systems, reactant molecules are adsorbed and activated on the catalyst surface, altering the chemical reaction pathway and thereby reducing the activation energy, making the reaction easier to proceed. On the other hand, photo catalysis utilizes the energy of photons to catalyze reactions. The reaction mechanisms and pathways in photo catalysis are fundamentally different from thermocatalysis. Photo catalysis occurs under mild conditions and is easy to operate.
In recent years, as catalysis research has delved deeper, scientists have discovered that photo-thermal synergistic catalysis can not only enhance the efficiency of catalytic reactions but also convert low-density solar energy into high-density chemical energy. The effective integration of both approaches can surpass the individual effects of thermocatalysis and photocatalysis. By adjusting reaction conditions, the activity and selectivity of reactions can be controlled. This has immense value in the fields of energy and the environment and has become a focal point in the research of new catalytic technologies.
However, in traditional tubular furnace thermocatalytic reaction setups, where the catalyst is packed within the core of the tube, three main reaction modes are employed to achieve photo-thermal synergistic catalysis:
Figure 1. Three reaction modes
While these reaction modes achieve photo-thermal synergistic catalysis, the side openings disrupt the heating structure of the furnace body, causing uneven heating of the catalyst. Additionally, to minimize heat loss, the diameter of the light window is usually 1~2 cm, much smaller than the spot diameter of the light source (50 cm). As a result, the utilization efficiency of light output by the light source is low, thereby affecting the effectiveness of photo-thermal synergistic catalysis.
1. Increase the light energy input to the device from the light source
Increasing the light energy input to the device from the light source involves two strategies:
① Increasing the light source power;
② Increasing the illuminated area of the device.
Perfectlight Technology has introduced the PLS-SME300E H1 Xenon Lamp Source, which employs a novel light-guiding enhancement structure to reduce light energy transmission loss. This structure focuses most of the light source's energy on the center region of the spot, effectively increasing the light power in the center region. Furthermore, the PLR-RP series photo-thermal catalytic reaction evaluation device increases the diameter of the entrance light window from the traditional 1 cm to 3 cm, resulting in a 9-fold increase in illuminated area. This ensures the maximized input of light energy from the light source into the reaction device while maintaining the traditional thermocatalytic reactor structure.
Figure 2. (a) PLS-SME300E H1 Xenon Lamp Source; (b) Internal light-guiding enhancement structure of PLS-SME300E H1 Xenon Lamp Source.
2. Minimize photon loss during transmission from the light source to the catalyst surface
To preserve the structure of the traditional thermocatalytic reactor and ensure the uniformity and stability of its temperature, the PLR-RP series photo-thermal catalytic reaction evaluation device abandons the common side-opening structure on the market and adopts a novel top-opening structure to introduce light from the top into the reaction device. Additionally, to prevent light loss due to longer light path distances caused by top-opening illumination, the PLR-RP series photo-thermal catalytic reaction evaluation device introduces a quartz light guide column for light transmission. The introduction of the quartz light guide column significantly enhances light transmission efficiency, measuring as high as 82%, effectively avoiding light transmission losses due to longer path distances. This performance surpasses the light guide reactor structure with shorter path distances.
Figure 3. Left: Traditional side illumination; Right: Innovative top illumination.
3. Increase the illuminated area of the catalyst to enhance photon utilization
Due to the poor transparency of solid catalysts, a thick catalyst bed reduces light absorption by the lower layers of the catalyst, leading to reduced absorption efficiency. The PLR-RP series photo-thermal catalytic reaction evaluation device recommends a maximum catalyst bed thickness of 3 mm for the flat-illumination reactor. At this thickness, the maximum catalyst filling volume is 0.9 mL. When the catalyst filling volume exceeds 0.9 mL, an annular illumination reactor can be used, paired with a specially designed side-emitting quartz light column. This setup guarantees a catalyst filling thickness of ≤3 mm and allows for a maximum catalyst filling volume of 9 mL. This design increases the illuminated area of the catalyst from 0.3 cm2 in the flat-illumination setup to approximately 20 cm2, boosting the catalyst's illuminated area by nearly 70 times and significantly enhancing its photon utilization efficiency.
Figure 4. Innovative annular illumination reactor unique to the PLR-RP series photo-thermal catalytic reaction evaluation device.
To ensure uniform side-emitting, Perfectlight Technology also conducted simulation and design on the light guide column's structure. The final measurement shows that the emission uniformity reaches as high as 73%, surpassing the emission uniformity of traditional xenon lamp sources. This ensures the uniformity of activity of catalysts at different filling positions.
Figure 5. Emission uniformity before (left) and after (right) optimization of the quartz light guide column within a 50 mm area.
4. Reduce light source divergence and minimize ineffective irradiation area of the light spot
After increasing the light energy input to the device from the light source, it is essential to enhance the catalyst's light absorption efficiency. As shown in the diagram below, taking the flat-illumination reaction as an example, when the light source and catalyst are positioned too far apart, some of the light cannot reach the catalyst's surface, resulting in wasted light energy. Conversely, if the light source is too close to the catalyst, the light spot might not completely cover the catalyst, leading to the incomplete excitation of some catalysts and reducing the apparent catalytic efficiency. The PLR-RP series photo-thermal catalytic reaction evaluation device accurately calculates the distance between the quartz light guide column and the catalyst, considering the emission angle of the quartz light guide column and the surface area of the catalyst bed. This ensures the maximum utilization efficiency of input light and catalyst.
Figure 6. Impact of light source-catalyst distance on light utilization efficiency.
Perfectlight Technology has fully utilized its 17 years of experience in designing photo-catalytic reaction devices. This includes aspects such as light source introduction, light transmission within the reactor, contact between light and catalyst, and the matching of light spot area and catalyst area. A large amount of simulation and experimentation was conducted to create the innovative top-opening design with a quartz light guide column structure in the PLR-RP series photo-thermal catalytic reaction evaluation device. The goal is to create a photo-thermal synergistic catalytic reaction device with the highest light energy utilization efficiency.
