Controlling the softness–hardness of Pd by strong metal–zeolite interaction: cyclisation of diallylmalonate as a test reaction

The cycloisomerisation of diallylmalonate to form cyclopentenes is demonstrated here to be a specific test reaction for hard Lewis acid sites in palladium-containing zeolites. We have found a correlation of the cycloisomerisation efficiency for a series of palladium-supported zeolites with the hardness of their framework as previously reported by quantum chemical calculations. Thus, the catalytic activity decreases and eventually disappears when the softness of the zeolite framework increases, the optimum in the activity being achieved when palladium is hosted in hard zeolite frameworks. In this way, the cycloisomerisation yield decreases in the series HY (Si/Al 15)≈HBeta (Si/Al 12.5)>HZSM-5 (Si/Al 15)>(Si)Beta (Si/Al ∞)>H,NaBeta (Si/Al 12.5)>HNaY (Si/Al 2.6)>NaY (Si/Al 2.6)>NaBeta (Si/Al 12.5)≈(Si,Ge)Beta.