A novel three-step assembly pathway is reported for the formation of a mesostructured alumina with framework pore walls made of crystalline, lathlike gamma-Al(2)O(3) nanoparticles. In the initial supramolecular assembly step of the pathway a mesostructured alumina with a wormhole framework morphology and amorphous pore walls is assembled through the hydrolysis of Al(13) oligocations and hydrated aluminum cations in the presence of a nonionic diblock or triblock poly(ethylene oxide) surfactant as the structure-directing porogen. The walls of the initial mesostructure are then transformed in a second hydrolysis step at a higher temperature to a surfactant-boehmite mesophase, denoted MSU-S/B, with a lathlike framework made of boehmite nanoparticles. A final thermal reaction step topochemically converts the intermediate boehmitic mesophase to a mesostructure with crystalline gamma-Al(2)O(3) pore walls, denoted MSU-gamma, with retention of the lathlike framework morphology. The boehmitic MSU-S/B intermediates formed from the chloride salts of aluminum incorporate chloride anions into the mesostructure. Chloride ion incorporation tends to disorder the nanoparticle assembly process, leading to a broadening of the slit-shaped framework pores in the final MSU-gamma phases and to the introduction of intra- and interparticle textural mesopores. However, the well-ordered MSU-gamma phases made from aluminum nitrate as the preferred aluminum reagent exhibit narrow framework pore size distributions and average pore sizes that are independent of the surfactant size and packing parameter, in accord with a lathlike framework assembled from nanoparticles of regular size and connectivity. The high surface areas ( approximately 300-350 m(2)/g) and pore volumes ( approximately 0.45-0.75 cm(3)/g) provided by these mesostructured forms of gamma-Al(2)O(3) should be useful in materials and catalytic applications where the availability of surface Lewis acid sites and the dispersion of supported metal centers govern reactivity.

gamma-Al2O3 is one of the most extensively utilized metal oxides in heterogeneous catalysis. Conventional forms of this oxide typically exhibit a surface area and pore volume less than 250 m2/g and 0.5 cm3/g, respectively. Previous efforts to prepare mesostructured forms of alumina resulted only in structurally unstable derivatives with amorphous framework walls. The present work reports mesostructured aluminas with walls made of gamma-Al2O3, denoted MSU-gamma. These materials are structurally stable and provide surface areas and pore volumes up to 370 m2/g and 1.5 cm3/g, respectively. The key to obtaining these structures is the formation of a mesostructured surfactant/boehmite precursor, denoted MSU-S/B, assembled through the hydrolysis of an aluminum cation, oligomer, or molecule in the presence of a nonionic surfactant. Mesostructured, gamma-aluminas offer the possibility of improving the catalytic efficiency of many heterogeneous catalytic processes, such as petroleum refining, petrochemical processing, and automobile exhaust control.

Improving product selectivity by controlling the spatial organization of functional sites at the nanoscale is a critical challenge in bifunctional catalysis. We present a series of composite bifunctional catalysts consisting of one‐dimensional zeolites (ZSM‐22 and mordenite) and a γ‐alumina binder, with platinum particles controllably deposited either on the alumina binder or inside the zeolite crystals. The hydroisomerization of n‐heptane demonstrates that the catalysts with platinum particles on the binder, which separates platinum and acid sites at the nanoscale, leads to a higher yield of desired isomers than catalysts with platinum particles inside the zeolite crystals. Platinum particles within the zeolite crystals impose pronounced diffusion limitations on reaction intermediates, which leads to secondary cracking reactions, especially for catalysts with narrow micropores or large zeolite crystals. These findings extend the understanding of the “intimacy criterion” for the rational design of bifunctional catalysts for the conversion of low‐molecular‐weight reactants.

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.

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