A Greener Route to Amines and Hydroxylamines: Pt/CeO₂–ZrO₂ Catalysis Under Ambient Conditions

Amines and hydroxylamines are essential building blocks in the chemical industry, widely used in pharmaceuticals, catalysts, polymers, and pigments. However, traditional methods for synthesizing these compounds often involve hazardous reagents like borohydrides and harsh conditions that contradict the principles of green chemistry. The selective hydrogenation of oximes using molecular hydrogen offers a more sustainable route—but until now, this transformation has required high pressure, elevated temperatures, and costly catalysts with limited reusability.

Our latest research presents a compelling alternative: a ceria–zirconia-supported platinum (Pt/CeO₂–ZrO₂) catalyst that efficiently hydrogenates oximes to hydroxylamines and primary amines under ambient conditions—room temperature and atmospheric pressure—while aligning with the core principles of green chemistry.

The Challenge

Oximes, derived easily from aldehydes and ketones, are attractive intermediates for producing amines. Yet, their low reactivity makes hydrogenation difficult. While homogeneous metal complexes have demonstrated good selectivity, they come with limitations: they are sensitive to moisture and air, hard to recycle, and involve complex purification steps. Heterogeneous systems, while more practical, typically require harsh conditions and still yield significant waste or undesired byproducts.

Our Solution: Pt/CeO₂–ZrO₂ Catalyst

Building on our previous work, we designed a recyclable heterogeneous catalyst using platinum supported on a mesoporous CeO₂–ZrO₂ oxide. What sets our approach apart is not just the catalyst's high activity and selectivity, but the entire synthesis strategy—from catalyst preparation to oxime hydrogenation—follows sustainable practices.

We used a straightforward calcination method to synthesize the CeO₂–ZrO₂ support, incorporating urea as a pore-forming agent. This yielded a high-surface-area material (70 m²/g) with a uniform mesoporous structure, crucial for maximizing catalytic efficiency. The mixed oxide formed a solid solution with a Ce:Zr ratio of 4:1, which we previously identified as optimal for promoting hydrogenation reactions.

Why It Matters

This catalyst effectively hydrogenates both aldoximes and ketoximes under mild conditions without the need for high pressures or excess reagents. It offers a 100% atom economy pathway to primary amines and hydroxylamines, drastically reducing chemical waste and improving safety. Moreover, the catalyst’s stability and reusability make it suitable for scale-up in industrial settings.

We also emphasize the green credentials of our approach. In addition to using benign solvents and mild conditions, we explored solvent-free, mechanochemical methods for oxime synthesis—further reducing the environmental footprint of the process.

Toward Greener Chemistry

The development of this Pt/CeO₂–ZrO₂ catalytic system represents a significant step toward more sustainable organic synthesis. By simplifying the hydrogenation of oximes and reducing dependency on toxic chemicals, our method opens the door to cleaner, safer, and more efficient production of valuable amine compounds.

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