A Pore Man’s Solution for Customized Catalysts 

Zeolites prized as efficient and durable catalysts for chemical reactions

Starting with just a handful of ingredients—primarily aluminum and silicon atoms—one can produce a dizzying variety of zeolite crystals. To the untrained eye, these porous mineral structures may look superficially similar. But subtle differences at the molecular scale can give rise to specialized materials that are distinctively well suited for a variety of manufacturing and industrial chemical processing applications.

“Their performance can vary depending on where you place the aluminums in the structure, how many you place, or whether they’re in close proximity to each other,” explains Jeffrey Rimer, a chemical engineer at the University of Houston. “Even within a given structure, you can design that material in so many different ways to get very different performance out of it.”

Synthesis and characterization research

Rimer’s research is focused on the synthesis and characterization of novel zeolite materials, and he works extensively with LUDOX^® colloidal silica as a building block. Zeolites are particularly prized as efficient and durable catalysts for chemical reactions. The reactions include “fluidized catalytic cracking,” a procedure for converting petroleum into gasoline and other industrial chemicals. Zeolites are also finding their way into a variety of green technologies. For example, zeolites are a common component of the catalytic converters in automotive engines, breaking down harmful nitrogen-based pollutants. Zeolites also are a potential means for helping to convert biomass into environmentally friendly fuels.

A zeolite’s nanometer-scale network of pores plays a critical role in determining its utility for a given catalytic application. “You can tune these [pores] in terms of their size to allow for what we call ‘shape-selective catalysis,’” Rimer says. “Instead of getting a whole multitude of chemical products, the small confined regions narrow it down and give you greater selectivity for a desired product.” He estimates that about 250 zeolite structures have been identified to date. Only a handful of these are actually in routine use, however, partly because of the difficulties in reliably manufacturing novel zeolite subtypes.

This is where the work of Rimer’s group comes in. His team is trying to understand the mechanisms underlying zeolite formation and how to control these processes in a predictable fashion to get a wider range of specialized crystal structures. Even small alterations can have an outsize impact: just a 1% increase in pore-structure selectivity can lead to a markedly improved catalyst, according to Rimer. But these synthesis processes can be finicky and particular, so even subtle deviations in a protocol might lead to the wrong product. “We're still much more on the side of it being an art form than a science,” Rimer says. He notes that commercial colloidal silica formulations, like LUDOX^® colloidal silica, are very helpful in this respect, as they allow his team to obtain consistent and reproducible performance from their starting reagents.

Zeolite formation should become a lot more predictable in the future, allowing researchers to computationally design specialized catalysts that can then be directly manufactured and put to use. For now, though, Rimer is finding satisfaction in exploring the unknown. “Each zeolite presents new challenges, and not everything is translatable to the extent that you would like it to be,” he says. “It can be maddening, but it also makes it fun.”

What can you do with LUDOX^® colloidal silica?

Specialty coatings, catalysts, zeolites, insulation board, refractory fibers, precision investment casting, paper and cardboard, flooring, beverages, concrete densifiers, polished concrete, textiles, or electronic components? Something entirely different?

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