Cheap, but dirty petroleum causes premature failure of cracking catalyst

Utrecht chemists discover that the catalyst responsible for the production of petrol 'dies' like a rotting apple

Science Advances Bert Weckhuysen c.s.

The catalyst particles that convert cheap, but dirty crude petroleum into petrol 'die' in the same way as a rotting apple. The poisoning of the catalytic material by metal atoms present in the petroleum spreads from the surface to the core forming a largely impenetrable crust. At a certain point, the petroleum is no longer able to reach the still-active core. This surprising discovery was made by Utrecht University chemical experts, in cooperation with researchers from Stanford Synchrotron Radiation Lightsource and Albemarle Corporation, by recording, for the first time, the dying process of a catalytic particle in 3D down to the nanometre scale. Although it has long been known that the catalyst material loses its activity ('dies') during use, the exact nature of this process was still unknown.

"Understanding the deactivation process of this catalyst material is important, because we will become increasingly dependent on cheap, but dirty petroleum for making gasoline in the coming decades," explains Bert Weckhuysen, Professor of Inorganic Chemistry and Catalysis at Utrecht University. "Surprisingly enough, we now see that these catalytic cracking particles are close to being dead, even though the core of the particle is not yet poisoned by the metal ions present in cheap, crude petroleum. This means that we are not making optimal use of the inner part of the catalyst material. Now that we know this, we can work on a solution to make the conversion process more sustainable. Moreover, with our powerful measurement technique, we can also study the dying process of many other catalytic materials and take measures to prolong their lives."

Wide-angle camera with telephoto lens

The technique used by Utrecht chemical experts is that of X-ray computed tomography at the nanoscale: i.e. a three-dimensional X-ray scan with a precision of about ten millionth of a centimeter. Weckhuysen calls it a combination of a wide-angle camera and a telephoto lens. "You can compare it to taking a landscape photo, which has also captured all the ants in detail in the picture if you zoom in."

Big data

Such scans are technical feats in themselves; in addition, the extremely high resolution yields such a large amount of measurement data that processing them is a scientific challenge in itself. Initially, more than two years of computing time would have been needed to precisely determine the properties of the three-dimensional pore system of the catalytic particle. "However, thanks to an exceptionally intelligent approach to the big data problem, Dr Florian Meirer, the first author on the article, has managed to reduce this to just a few hours," says Weckhuysen.

Second-rate petroleum

The reason why researchers chose to study catalytic cracking materials for this cheap, but dirty petroleum in particular is because the largest available reserves are still of this type of petroleum. This 'advantageous feedstock' is cheap because of the many impurities it contains. For example, the feedstock contains a large amount of metal ions, mainly iron, nickel and vanadium. These metals 'poison' the catalytic particles by blocking the catalyst pores. This prevents easy access of petroleum molecules to the catalytic material, as a result of which the catalyst clogs up and loses its activity.

Publication

Florian Meirer, Sam Kalirai, Darius Morris, Santosh Soparawalla, Yijin Liu, Gerbrand Mesu, Joy C. Andrews, Bert M. Weckhuysen,
Life and death of a single catalytic cracking particle,
Science Advances 1, e1400199 (2015).

This research is partly funded by the NWO Gravitation programme Netherlands Center for Multiscale Catalytic Energy Conversion (MCEC) and a European Research Council Advanced Grant (no. 321140).

Further information

For other questions: Monica van der Garde, Faculty of Science Press Officer, m.vandergarde@uu.nl, +31 (0)613661438