A new imaging technique developed by Chinese researchers can measure the temperature distribution inside a single catalyst particle during chemical reactions, which can help optimize industrial catalysis.
What are catalysts and why are they important?
Catalysts are substances that speed up chemical reactions without being consumed or changed by them. They are widely used in various industrial processes, such as refining, petrochemicals, pharmaceuticals and environmental remediation. However, catalysts often have complex structures and compositions, and their performance can be affected by many factors, such as temperature, pressure, reactant concentration and catalyst loading.
What is the challenge in measuring catalyst temperature?
One of the challenges in catalyst research is to measure the temperature near or at the active sites inside a single catalyst particle during catalysis. Temperature is an important parameter that can affect the chemical thermodynamics and reaction kinetics of the system. Precise measurement of the temperature can help establish the reaction mechanism and develop the microscopic reaction kinetics.
However, most of the existing techniques for measuring catalyst temperature can only measure the surface temperature of the catalyst, and have low spatial resolution. For example, thermocouples and infrared thermal imaging can only achieve a spatial resolution of millimeters, while the size of typical industrial catalyst particles is tens to hundreds of microns.
How did the researchers solve this problem?
To overcome this limitation, a research team led by Prof. Ye Mao and Prof. Liu Zhongmin from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS) has developed a new imaging technique that can measure the three-dimensional spatiotemporal distribution of temperature inside a single industrial zeolite-catalyst particle during methanol-to-olefins (MTO) reactions.
How does the new imaging technique work?
The new imaging technique is based on up-conversion confocal microscopy, which uses a laser to excite up-conversion nanoparticles that emit visible light when exposed to near-infrared light. The up-conversion nanoparticles act as nano-thermometers that can measure the local temperature by changing their luminescence intensity or color.
The researchers implanted the up-conversion nanoparticles into industrial zeolite catalyst particles using a microfluidic chip. Then they used a confocal microscope to scan the catalyst particles and obtain images of their temperature distribution during MTO reactions.
The technique has a spatial resolution of 800 nm, which is much higher than the existing techniques. It can also measure the dynamic changes of temperature inside the catalyst particles over time.
What did the researchers find out?
The researchers found that the temperature distribution inside the catalyst particles was heterogeneous and affected by several factors, such as zeolite content, particle size, reaction time and reactant concentration. They also revealed how the temperature distribution influenced the utilization of active sites and the evolution of reaction intermediates during MTO reactions.
For example, they observed that higher zeolite content led to higher temperature gradients inside the catalyst particles, indicating higher catalytic activity and heat generation. They also found that smaller catalyst particles had more uniform temperature distribution than larger ones, suggesting better heat transfer and mass transport. Moreover, they discovered that higher reactant concentration resulted in higher temperature peaks inside the catalyst particles, reflecting faster reaction rates and more coke formation.
The researchers also compared their results with those obtained by confocal fluorescence microscopy and confocal infrared microscopy, which are two other multimodal imaging techniques that can measure the spatiotemporal distribution of reaction intermediates and coke deposition inside the catalyst particles. They found that their technique was complementary to these techniques and could provide more information on the relationship between temperature, catalytic activation and reaction mechanism.
What is the significance of this study?
“This technique provides a new path to understand the heat transfer in catalyst particles toward rational design and optimization of industrial catalysts and catalysis,” said Prof. Ye.
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