Effect of Al2O3 phase on the catalytic performance for HCHO oxidation over Ag/Al2O3 catalysts

The effect of different crystalline phases of Al2O3 (gamma-Al2O3, gamma, theta-Al2O3) on HCHO oxidation over Ag catalysts is investigated, and the silver state and particle size strongly depend on the Al2O3 crystalline phase. The various coordinatively unsaturated Al3+ (Al., Al.) involves in the formation of Ag-O-Al entities. Ag species is mainly anchored on Al. sites for gamma-Al2O3, whereas mainly on Al. sites for gamma, theta-Al2O3. The weaker interaction of Ag, O and Al. on gamma-Al2O3 compared with that of Ag, O and Al. on gamma, theta-Al2O3 and the larger surface area of gamma-Al2O3 result in the formation of more Ag-0 with high dispersion. The higher fraction of coordinated Al-VI on gamma-Al2O3 provides more adjacent hydroxyl groups for HCHO adsorption and formation of intermediates. And the synergistic effect of OH group and the high activation ability for oxygen on smaller Ag-0 particles give the high HCHO oxidation activity on Ag/gamma-Al2O3 (T-100 = 85 degrees C).