Hydrothermal treatment of metallic-monolith catalyst support with self-growing porous anodic-alumina film

Abstract

Metallic-monolith catalyst support with self-growing porous anodic alumina (PAA) film was prepared by anodizing Al plate. The effect of hydrothermal treatment (HTT) on the crystalline state and textural properties of PAA film was investigated by XRD, BET, SEM and TG. The HTT treatment above 50 °C and the subsequent calcination above 300 °C could convert the amorphous skeleton alumina into γ-alumina and increase the specific surface area ( S BET ). However, SEM images showed the HTT modification was a non-uniform process along the thickness of PAA film. The promotion effect of HTT on S BET was non-linear, and the slope of S BET gradually decreased with the HTT temperature or time increased. The limited HTT effect should be attributed to a changed pore structure caused by an unfavorable pore sealing limitation. Pore widening treatment (PWT) before HTT could break the pore sealing limitation, because of the reduced internal diffusion resistance of hydrothermal reaction. The synergistic combination of PWT and HTT developed a PAA support with a large S BET comparable to commercial γ-alumina. In the catalytic combustion of toluene, the Pt-based catalyst prepared by using the PWT and HTT co-modified PAA support gave higher Pt dispersion and more favorable catalytic activity than that treated by HTT alone. The presence of a bimodal pore structure was suggested to be a decisive reason.