Effect of mixed Al2O3 structure between θ- and α-Al2O3 on the properties of Pd/Al2O3 in the selective hydrogenation of 1,3-butadiene

The effect of mixed Al2O3 structure between θ- and α-Al2O3 on the properties of Pd/Al2O3 was investigated in the gas-phase selective hydrogenation of 1,3-butadiene under industrial simulated conditions. The mixed-phase Al2O3 supports containing 100/0, 80/20, 40/60, and 0/100 (%) θ/α Al2O3 were obtained by calcination of bayerites at 960–1200 °C for 3 h. The BET surface area and acidity of the Al2O3 supports decreased monotonically with increasing weight (%) of α-Al2O3. As revealed by X-ray photoelectron spectroscopy (XPS), there was no electronic modification of Pd surface and the hydrogenation of 1,3-butadiene on Pd/Al2O3 appeared to be dependent on Pd dispersion, support acidity, and Al2O3 structure. While high Pd dispersion/support acidity resulted in high hydrogenation rate, the bimodal pore structure of the mixed-phases Al2O3 (i.e., 80/20 θ/α-Al2O3) played important role in lowering butane selectivity at complete conversion of 1,3-butadiene without altering the 2-butene selectivity.