Unlocking the mysteries of crystal formation

Synthetic zeolites could be key to next-generation biofuels 

Unlocking the mysteries of crystal formation
August 28, 2018

Every time you pull up to the gas pump and fill your tank, you have zeolites to thank. These crystalline catalysts with tiny holes have been used since the 1960s to convert petroleum into high octane gasoline, and because of this huge application, they are the most used catalysts by weight on earth. Researchers have found various zeolites tremendously useful in applications from softening water to clotting wounds in war zones. Now they’ve set their sights on other big applications: capturing greenhouse gases, and making renewable biofuels. The only problem is that some of the most promising zeolites for these applications have only been imagined but have never actually been fabricated because lab scientists don’t know how. In fact, nobody knows how zeolites form in the first place.

The success of zeolites stems from their tight control over the sizes and shapes of molecules that can fit in their tiny “nanopores,” earning them the term "shape selective catalysts." Professor Scott AuerbachUMass Chemistry, explains, “Currently, synthesizing zeolites with tailor-made pores remains a huge challenge because we know very little about how zeolites actually form. The key question is how they form regular arrays of nanopores. Nature abhors a vacuum, so what’s filling the space?”

What do you do when you want to see how crystals form? You have to be able to see what atoms are doing, but that’s too small for microscopes. When they’re on their way to a crystal, those atoms are in disordered, chaotic structures, so they’re far too messy for x-rays to be of use. Science has been stuck looking for a way to witness the process of crystal formation.  

Auerbach and his colleague Professor Wei Fan, UMass Chemical Engineering, have proposed to combine experiments and theories to shed new light on this problem. They’ve just been awarded a $630,000 grant from the Department of Energy to combine Auerbach’s theories and Fan’s experiments to understand how zeolites form crystals from watery gels. Their approach combines information from different sources: theory, which works at the level of atoms, and experiments, which work at the level of visible systems. Auerbach and Fan can work together to connect the dots and finally see what’s happening in the middle, where crystal formation occurs.  

What else could we make with zeolites when we understand them better? “If we could control and select the molecule shapes that the zeolites allow,” says Auerbach, “then we might be able to use them as catalysts for converting molecules from plants into biofuels.”

Sometime in the future, a customized zeolite could make it possible for us to fill up our tanks with renewable, plant-based fuels instead of petroleum-based gasoline.