Recycling greenhouse gases: Nanoparticles on perovskite crystals avoid ‘coking’ effect

Wherever the production of harmful greenhouse gases cannot be prevented, they must be turned into something useful: this approach is called “carbon capture and utilization”. Special catalysts are required for this. However, until now, the problem has been that a layer of carbon quickly forms on these catalysts (this is called “coking”) and the catalyst loses its effect.

At TU Wien, a new approach was taken: tiny metal nanoparticles were produced in perovskite crystals by special pretreatment. The interaction between glass surface and the nanoparticles then ensure that the desired chemical reaction takes place without the feared coking effect. The researchers have published their work in Applied Catalysis B: Environmental.

Dry reforming: greenhouse gases are converted into synthesis gas

Carbon dioxide (CO_two) and methane are the two man-made greenhouse gases that contribute the most to climate change. Both gases often occur in combination, for example in biogas plants.

“The so-called dry reforming of methane is a method that can be used to convert both gases into useful synthesis gas at the same time,” says Professor Christoph Rameshan of the Institute for Materials Chemistry at TU Wien. “Methane and carbon dioxide are converted to hydrogen and carbon monoxide—and then it is relatively easy to produce other hydrocarbons from them, even biofuels”.

The big problem here is the stability of the catalysts: “The metal catalysts that have been used for this process so far tend to produce tiny carbon nanotubes,” explains Florian Schrenk, who is currently working on his dissertation in Rameshan’s team. These nanotubes are deposited as a black film on the surface of the catalyst and they block.

Perovskite crystals as a key to success

The TU Wien team has now created a catalyst with fundamentally different properties: “We use perovskites, which are oxygen-containing crystals, which can be doped with various metal atoms,” says Christoph Rameshan. “You can insert nickel or cobalt, for example, into perovskite, metals that have also been used in catalysis before.”

A special pretreatment of the glass with hydrogen at around 600 °C allows nickel or cobalt atoms to migrate to the surface and form nanoparticles there. The size of the nanoparticles is crucial: success has been achieved with nanoparticles with a diameter of 30 to 50 nanometers. The desired chemical reaction then takes place in these tiny grains, but at the same time the oxygen contained in the perovskite prevents the formation of carbon nanotubes.

“We were able to show in our experiments: If you choose the right nanoparticle size, no carbon film is created – coking is no longer a hazard,” says Florian Schrenk. “In addition, the nanoparticles are stable, the structure of the catalyst does not change, it can be used permanently.”

New perovskite catalysts could be used anywhere methane Y carbon dioxide occur simultaneously; this is often the case when it comes to biological substances, for example in biogas plants. Depending on the selected reaction temperature, the composition of the resulting synthesis gas can be influenced. In this way, post-processing of weather damage Greenhouse gases into valuable products could become an important component for a sustainable circular economy.