Effect of large d0 cation doping on gamma-alumina's acid–base and catalytic properties

BACKGROUND: Catalysts based on alumina-supported metal oxides are of crucial importance in the field of heterogeneous catalysis for several applications requiring tuning of surface acidity. RESULTS: In this work, the effects of K+, Ca2+ and La3+ cation doping have been evaluated on a well-characterized commercial gamma-Al2O3 through morphological characterization and surface characterization (Brunauer–Emmet–Teller, X-ray diffraction, field emission scanning electron microscopy, Fourier transform infrared spectroscopy). The conversion of ethanol as a test reaction was performed over these catalysts. The impregnated oxide species essentially remain at the surface, resulting in the partial poisoning of the strongest alumina Lewis acid sites. Moreover, oxide anions may increase basicity at the surface. The doping results in a significant decrease in catalytic activity in ethanol conversion to diethyl ether and to ethylene, which is shifted at higher temperatures. On the other side, higher activity in the formation of C4 olefins was detected, namely on the K-doped alumina. CONCLUSION: The partial poisoning of the strongest alumina Lewis acid sites and the presence at the surface of new more basic cation–anion couples result in significant changes in catalytic ethanol conversion.