Making the TEM more Relevant for Catalysis Research

An interview with Jennifer McConnell, Product Manager at Protochips about how TEM can be made more relevant for catalysis research.

What are the current challenges with using the TEM for catalysis research?

The ability for a catalyst to do its job is highly dependent on its atomic-level structure and composition, which is why the transmission electron microscope (TEM) plays such a critical role in catalyst characterization today. During use, the structure and composition of the catalyst morphs which then affects its performance, usually in a detrimental way. For decades, catalyst characterization has generally been done in a 3-step process:

Step 1: Observe the catalyst in the TEM right after synthesis

Step 2: In an ex situ reactor, subject the catalyst to conditions similar to those used during real-world operation, possibly for a long period of time, while monitoring changes in gas conversion

Step 3: Observe the catalyst in the TEM again and note structural and compositional changes

The biggest challenge with this method is that the researchers can only speculate the pathway for the structural evolution observed in the before-and-after analysis as well as how this evolution relates to the changes in gas conversion recorded ex situ.

An analogy could be: Imagine being given a list of raw ingredients and a photo of a finished casserole and then you’re expected to outline the steps to make it.This would be a difficult task as there are thousands of ways to make casseroles that look alike, but they will all taste very different. How much easier would this task be if you could watch someone else cook it from beginning to end first? The Atmosphere in situ environmental TEM system enables researchers to watch the cooking from beginning to end before having to outline the recipe themselves.

Why is it so important to the catalysis field to overcome these challenges?

It is incredibly important for the catalysis field to overcome the inability to directly observe these evolutionary pathways over time and understand how they affect catalyst performance. This is the only way to understand how to improve upon the catalyst’s design. New areas of catalysis research, such as single atom catalysts and zeolites, show quite a bit of promise as far as improving efficiency and selectivity when looked at on a large scale, but we need to understand the behavior at the atomic scale first. The results of larger, bulk scale experiments are simply an average of millions of atomic-scale, localized reactions. True improvements in catalyst design will only come from understanding the localized structure-activity correlation under realistic operating conditions.

What is the Atmosphere in situ environmental TEM system that is designed by Protochips?

The Atmosphere in situ environmental TEM system is the first commercial solution for directly observing catalyst dynamics in conditions the closest possible to operando within a TEM. With the Atmosphere system, you can simultaneously gather a comprehensive set of data that allows for a full story: spatial resolution, crystallinity, chemical composition, and valence state with the ability to directly observe the evolution of these characteristics over time as the catalyst is exposed to harsh environmental conditions. In addition, the Atmosphere system has the first-of-its-kind integrated mass spectrometer specifically designed for use with the TEM, so changes in catalytic activity can also be observed in parallel to the structure, enabling researchers to fully understand the localized structure-activity correlation at the nanoscale. Researchers no longer have to speculate but can present solid proof instead. This level of data generates actionable conclusions that will help drive their research in a productive direction faster.

Copper nanoparticles undergoing fighting oxidation and reduction reactions in the presence of hydrogen and water vapor

How is the Atmosphere system different than other environmental TEM solutions on the market?

The need for dynamic data in more realistic conditions has not gone unnoticed in the electron microscopy field. Now-a-days there are differentially pumped TEMs that allow for gases to be introduced inside of the column at low pressure in an attempt to expose the sample to a more realistic environment. There are also additional TEM accessories that enable the introduction of gases and, with some of them, pressure and heat as well.  The Protochips Atmosphere system stands out from all of these instruments because it is the only fully integrated solution built with research needs in mind. Catalyst researchers are trying to solve real-world problems, meaning TEM experiments need to occur in real-world conditions or the results will not be considered relevant.

How does Atmosphere create the most realistic environments?

• Just about any gas or gas combination can be accurately flowed into the system, including custom exhausts captured in our customer’s own lab.
• Vapors such as water, alcohols, and organics can also be mixed and introduced to the reaction in a controlled and reproducible manner via software.
• The pressure gap created by the TEM can be closed by reaching pressures up to 1 atmosphere. Control your flow rate independently during the experiment for maximum residence time without altering experimental pressure.
• Apply heat up to 1000°C without worrying about metal contamination using a patented metal-free ceramic heating membrane.
• Monitor in real-time the effects the environmental variables have on catalyst activity using the integrated residual gas analyzer designed specifically for electron microscopy.

The combination of the above attributes can only be found in the Atmosphere system because we worked alongside real chemists when designing the system to ensure all needs would be met to generate truly relevant data.

EDS maps collected at 1 atmosphere of pressure in inert gas prior to exposing the sample to reactant gases. Sample is copper on zinc oxide.

How is the Atmosphere system uniquely suited to study the activation, deactivation and operation of a catalyst?

The different stages of a catalyst’s lifecycle are all equally important but require different considerations during the experiment to ensure data generated is scientifically valid, reproducible, and relevant. The Atmosphere system has strengths that are important to each of the stages​

Activation: The activation of a catalyst is typically achieved with some sort of reduction step, usually involving hydrogen gas, where the presence of oxidizers like air and water can quickly contaminate and ruin the experiment. The Atmosphere system is designed with the most thorough cleaning program on the market for in situ gas cell systems and includes capabilities like:

• pumping down to vacuum level pressure
• purging with inert gases
• baking out at elevated temperatures under low pressure

It is very difficult to completely remove air and water from any vacuum system, but they can be minimized to negligible levels with the right cleaning programs like that listed above. The integrated mass spectrometer then gives a system-wide look at the levels of water and oxygen after cleaning to ensure they have been reduced to a satisfactory level for the experiment at hand.

Operation, Deactivation, and Regeneration: These three stages can vary in their experimental requirements quite a bit because they require the catalyst to be present in conditions that best replicate its normal operating environment. The Atmosphere system excels in flexibility so the most realistic operating environment can be re-created within the TEM. The Atmosphere system uses a technique called volumetric blending to mix and flow gases, much like gas cylinder companies do when creating custom mixtures in high-pressure cylinders, because it is not limited by the type or mass of the gas. Dalton’s Law of Partial Pressures and sensitive pressure manometers are at the heart of volumetric blending, meaning you will never be restricted by an MFC’s required calibrations for specific gases. As your research evolves, your Atmosphere system will stay compatible.

The integrated mass spectrometer will also play a key role in all of these stages. Monitoring the relative change in gas conversion as conditions change is a critical indicator of the catalyst’s life cycle stage and how the conditions affect its overall performance. The unique integration of our mass spectrometer allows it to operate while imaging without degrading the imaging resolution. In addition, the response time from TEM to mass spectrometer is on the order of 3 seconds or less, allowing for seamless data correlation and the ability to make quick decisions on-the-fly during the experiment.

Are there other applications that can see the benefit of the Atmosphere in situ environmental TEM system?

Yes, there are several other applications that find the Atmosphere system useful in their research. The biggest one next to catalysis is corrosion. With the introduction of controllable water vapor combined with the robust metal-free heating membrane, researchers can really push the limits on different alloys to observe what makes them falter.  There are also researchers looking at thermal barrier coatings for gas turbine engine components, semi-conductor growth, and hydrogen storage materials.

Where can our readers go to find out more?

For more information regarding out Atmosphere system, please visit our product page on our website at www.protochips.com. For specific questions about your research project, please email [email protected] and we will be happy to talk to you.

The Atmosphere system was awarded an Innovation Award at the 2019 Microscopy and Microanalysis (M&M) conference in Portland, Oregon, USA for a breakthrough system to help advance research in the electron microscopy field.

About Jennifer McConnell

Jennifer McConnell is the Product Manager for the Atmosphere in situ environmental system at Protochips and is responsible for the evolution of the product over time to ensure it solves current market needs and transforms to solve future ones. She received her Bachelor of Science degree in Chemistry from North Carolina State University and Master of Forensic Chemistry degree from The George Washington University.

Before joining Protochips in early 2018, Jennifer held positions with the Drug Enforcement Administration as a forensic drug chemist with an expertise in methamphetamine synthesis and clandestine laboratory analysis and as a forensic scientist with the North Carolina State Crime Laboratory.