(199e) Uncovering a New Catalytic Pathway for Propylene-to-Butadiene Transformation

The rise in shale gas production has drastically reduced C₄ yields from traditional naphtha crackers, creating an urgent need for cost-competitive pathways to C₄ chemicals from light hydrocarbons. This study presents a selective, one-step gas-phase synthesis of 1,3-butadiene from propylene and formaldehyde. Using heteropolyacid (HPA) catalysts supported on silica, we demonstrate that Prins condensation proceeds with ~70–80% selectivity and high stability under continuous flow conditions.

Among the tested catalysts, silica-supported silicotungstic acid (H₄SiW₁₂O₄₀/SiO₂) delivered the highest activity and selectivity, reaching butadiene yields of up to 64% under optimized conditions. Detailed characterization (XRD, TEM, FTIR, NH₃-TPD, and ¹H MAS NMR) shows that SiW loadings above 40 wt% form dispersed yet intact Keggin structures with strong Brønsted acid sites essential for butadiene production. Kinetic and cofeeding experiments revealed a shared intermediate leading to both butadiene and butanal, the main by-product. Butadiene formation is favored at strong Brønsted sites, while weaker acid sites promote side reactions such as aldol condensation.

Importantly, small amounts of water enhance both activity and selectivity by improving proton accessibility and acid strength, while suppressing coke formation and undesired pathways. Optimal catalytic performance occurs between 280–320 °C; higher temperatures accelerate deactivation via coking and formaldehyde decomposition.

This work establishes clear structure–function relationships for Prins condensation over HPA catalysts and offers catalyst design principles for high-efficiency butadiene production. Beyond offering a practical route from light hydrocarbons to C₄ building blocks, our approach enables a new methanol-to-butadiene strategy paving the way toward scalable, petroleum-free synthetic rubber feedstocks.