Carbonylation — the chemical process of attaching carbon monoxide to hydrocarbon molecules — is a fundamental building block of the modern chemical industry, underpinning the production of bulk and fine chemicals such as acetic acid, plasticizers, fragrances, and pharmaceutical intermediates.

Now, Chinese scientists have developed a new route for this century-old reaction by using the precisely defined pore environments of zeolites as stand-alone catalysts. This eliminates the need for high-cost precious-metal catalyst, enables convenient separation of catalysts from products, and enhances production efficiency while avoiding the generation of acidic wastewater associated with conventional processes.

The breakthrough, published in the journal Nature on Wednesday, holds significant promise for green chemistry and industrial manufacturing. It offers new possibilities for chemical engineers to convert cheap, abundant feedstocks, such as carbon monoxide and olefins — a kind of hydrocarbons — into high-value chemicals with greater precision, fewer toxic byproducts, and lower energy consumption.

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Zeolites are crystalline materials that contain precisely defined pores and channels sized at the molecular scale. They act as microscopic sieves, selectively admitting or blocking molecules based on their shape and size, and play an irreplaceable role in petroleum refining and gas separation.

Building on two-decades of earlier work proving that zeolites can serve as stand-alone catalysts — driving large-scale anhydrous ethanol production without precious metals while enabling effortless catalyst-product separation due to their solid nature — researchers at the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences spent nearly three years exploring whether zeolites could catalyze a broader range of carbonylation reactions.

Led by Liu Zhongmin, a member of the Chinese Academy of Engineering and director of the Dalian Institute of Chemical Physics, the team established two new zeolite-catalyzed reactions. These processes produce isobutyric acid — widely used in cosmetics — from propylene, and propionic acid — widely used in food preservatives — from ethylene, with water as the only coreactant.‌

The researchers found that the confined pore environment not only promotes the desired carbonylation reactions, but also suppresses the competing side reaction of polymerization, as the narrow pores physically prevent molecules from clustering.

Moreover, as a solid catalyst, zeolite can be easily separated from the reaction products, potentially simplifying catalyst recovery and product purification compared to homogeneous liquid-phase systems.

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"Modern chemical system is already well-developed, leaving very little room for the discovery of new reactions," Liu said. "Yet, using zeolites as catalysts, our team has now found that olefin carbonylation can proceed directly in the presence of water to produce acids — a pathway fundamentally distinct from the conventional approach of obtaining acids through olefin oxidation."

Liu stressed the generality of this type of reaction, noting that, from a scientific standpoint, any olefin in principle can be amenable to carbonylation through this route.

Notably, the team discovered that different zeolite pore geometries function as precise molecular switches, dictating reaction pathways by matching specific reactants to distinct reactions. The findings challenge the conventional reliance on metals, which regulate catalysis by providing different active sites and instead establish pore geometry as a key design parameter for selective catalysis.

This means that future catalyst development can shift from trial-and-error screening to prediction. Researchers can now select suitable pore architectures based on substrate molecular size and synthesize and test only the most promising candidates.

"Our study provides a foundation for the rational design of zeolite catalysts for a broader range of olefin carbonylation reactions," Liu said, adding that the team will selectively advance the technological development and industrialization of these new reactions.