Zhaorong Zhang

Mesoporous γ-Alumina Formed Through the Surfactant-Mediated Scaffolding of Peptized Pseudoboehmite Nanoparticles

Mesoporous gamma-alumina with precisely controlled mesoporosity is synthesized through the scaffolding of pseudoboehmite nanoparticles in the presence of a nonionic surfactant as the porogen. In the initial step of the synthesis, a colloidal suspension of pseudoboehmite is prepared by peptizing pseudoboehmite in dilute acidic solution. The nanoparticles in the peptizate are then assembled into a scaffold structure using nonionic Tergitol 15-S-7 (C(15)H(33)(OC(2)H(4))(7)OH) as the surfactant porogen. Calcination of the resulting surfactant-containing composites at 500 degrees C removes the surfactant and concomitantly converts the pseudoboehmite crystallites to gamma-alumina through topochemical transformation with the retention of the scaffold structure. Depending on the surfactant to alumina ratio used to form the scaffold structures, the average pore size can be precisely controlled over the range of 3.5-15 nm. Also, the BET surface areas of the scaffold structures are substantially larger in comparison to the gamma-alumina formed from pseudoboehmite at the same calcination temperature in the absence of surfactant (296-321 vs 238 m(2) g(-1)). The substantial improvement in surface area provided by the scaffold structures, together with the ability to provide narrow pore size distributions over a wide range of average pore sizes by simply adjusting the surfactant content, should substantially improve the effectiveness of this oxide as an adsorbent and as a catalyst or catalyst support.

An overview of mesostructured forms of alumina with crystalline framework walls

Novel step-wise assembly pathways are demonstrated for the formation of mesostructured aluminas with framework walls made of crystalline nanoparticles of γ-alumina. In the initial step, a mesostructured composite comprised of amorphous aluminum hydroxide framework walls is prepared through supramolecular assembly involving a non-ionic surfactant, or an amine surfactant as the structure directing porogens. The amorphous framework components of this mesophase are then converted to a crystalline boehmite phase through hydrothermal treatment in the presence of the surfactant. Upon calcination, the boehmitic framework walls are topochemically transformed to γ-alumina with the retention of mesostructure. Direct removal of the surfactant from the boehmitic composites can also lead to the formation of a mesostructure with crystalline boehmite framework walls. In comparison with conventional compositions, the mesostructured forms of boehmite and γ-alumina have substantially improved textural properties associated with controlled pore structure and morphology. Application properties of the mesostructured γ-alumina as support for the Co/Mo sulfide catalyst in the hydrodesulfurization of dibenzothiophene are also explored. The status of current studies which address the mechanism of mesostructure formation and the factors that determine the framework pore size and framework crystallinity will be reported.

Mesoporous metal oxides with improved atomic ordering in the pore walls

Abstract Three general approaches to improving the atomic order of mesoporous and mesostructured metal oxides are described. These include (i) the post-synthesis thermal treatment of surfactant-assembled mesostructures, (ii) the incorporation of protozeolitic nanoclusters in the assembly of aluminosilicates, and (iii) the occlusion of carbon nanoparticles in crystalline oxides and the carbon nanocasting of crystalline frameworks.