On stability and performance of highly c-oriented columnar AlPO4-5 and CoAPO-5 membranes

[EN] Continuous films comprised of highly c-oriented aluminophosphate AlPO4-5 or cobalt-substituted AlPO4-5 (CoAPO-5) were grown on porous supports and subjected to heat treatment in order to investigate the potential for membrane applications. A study in the early stages of in-plane crystalline intergrowth revealed a potential mechanism for flake-like crystal formation between the original oriented columnar crystals. Variations in metal substitution (AlPO4-5, CoAPO-5), support (glass, silicon, porous alumina), and calcination method (conventional, rapid thermal processing) were chosen to examine the conditions by which structural integrity was compromised following secondary (or tertiary) growth, resulting in reduced membrane functionality. Through the use of rapid thermal processing, the structure debilitation could be partially avoided. The membrane quality was inspected through pervaporation measurements consisting of a liquid hydrocarbon feed of n-heptane and 1,3,5-triisopropylbenzene. By investigating the effect of template removal on the oriented, columnar crystalline structure, useful insight is provided into the potential for the membranes to participate in applications such as molecular separations, catalysis, or host-guest assemblies. (C) 2011 Elsevier Inc. All rights reserved.Support by the American Chemical Society (ACS-PRF) and the European Community through the FP7 NextGTL project and a Marie Curie International Reintegration Grant (FP7, Grant agreement No. 210947) is greatly appreciated. M.P. thanks CSIC for a JAE doctoral fellowship. We would like to thank Kumar Varoon for assistance with membrane sectioning and imaging using the focused ion beam technique. Parts of this work were carried out in the Characterization Facility on the campus of the University of Minnesota-Twin Cities, which receives partial support from NSF through the MRSEC program.Stoeger, JA.; Veziri, CM.; Palomino Roca, M.; Corma Canós, A.; Kanellopoulos, NK.; Tsapatsis, M.; Karanikolos, GN. (2012). On stability and performance of highly c-oriented columnar AlPO4-5 and CoAPO-5 membranes. Microporous and Mesoporous Materials. 147(1):286-294. https://doi.org/10.1016/j.micromeso.2011.06.028286294147

Self-Pillared, Single-Unit-Cell Sn-MFI Zeolite Nanosheets and Their Use for Glucose and Lactose Isomerization

Single-unit-cell Sn-MFI, with the detectable Sn uniformly distributed and exclusively located at framework sites, is reported for the first time. The direct, single-step, synthesis is based on repetitive branching caused by rotational intergrowths of single-unit-cell lamellae. The self-pillared, meso- and microporous zeolite is an active and selective catalyst for sugar isomerization. High yields for the conversion of glucose into fructose and lactose to lactulose are demonstrated

Pillared Sn-MWW Prepared by a Solid-State-Exchange Method and its Use as a Lewis Acid Catalyst

Pillared Sn-MWW (Sn-MWW(SP)-SSE) was prepared through a solid-state-exchange (SSE) route. The pillared structure was inherited from pillared B-MWW, and Sn was inserted in the framework by boron leaching and solid-state-exchange with tin tetrachloride pentahydrate. The Sn-MWW(SP)-SSE with framework Sn sites exhibits Lewis acidity and good catalytic performance for the Baeyer–Villiger oxidation, and mono- and disaccharide isomerizations

Pillared Sn-MWW Prepared by a Solid-State-Exchange Method and its Use as a Lewis Acid Catalyst

Pillared Sn-MWW (Sn-MWW(SP)-SSE) was prepared through a solid-state-exchange (SSE) route. The pillared structure was inherited from pillared B-MWW, and Sn was inserted in the framework by boron leaching and solid-state-exchange with tin tetrachloride pentahydrate. The Sn-MWW(SP)-SSE with framework Sn sites exhibits Lewis acidity and good catalytic performance for the Baeyer–Villiger oxidation, and mono- and disaccharide isomerizations

A mathematical model for crystal growth by aggregation of precursor metastable nanoparticles

A mathematical model is developed to describe aggregative crystal growth, including oriented aggregation, from evolving pre-existing primary nanoparticles with composition and structure that are different from that of the final crystalline aggregate. The basic assumptions of the model are based on the ideas introduced in an earlier published report [Buyanov and Krivoruchko, Kinet. Katal. 1976, 17, 666−675] to describe the growth of low-solubility metal hydroxides (e.g., iron oxides) by oriented aggregation. It is assumed that primary particles can be described as pseudo-species A, B, and C, which have the following properties: (1) fresh primary particles (colloidally stable inert nanoparticles, denoted as A), (2) mature primary particles (partially transformed nanoparticles at an optimum stage of development for attachment to a growing crystal, denoted as B), and (3) nucleated primary particles (denoted as C1). The evolution of primary particles, A → B → C1, is treated as two first-order consecutive reactions. Crystal growth via crystal−crystal aggregation (Ci + ) is described using the Smoluchowski equation. The new element of this model is the inclusion of an additional crystal growth mechanism via the addition of primary particles (B) to crystals (Ci): (B + ). Two distinct, but constant, kernels (K ≠ K‘) are used. It is shown that, when K‘ = 0, a steplike crystal size distribution (CSD) is obtained. Within a range of K‘/K values (e.g., K‘/K = 103), CSD with multiple peaks are obtained. Comparison with predictions of models that do not include the intermediate stage of primary particles (B) indicates pronounced differences. Despite its simplicity, the model is able to capture the qualitative features of CSD evolution that have been obtained from crystal growth experiments in hematite, which is a system that is believed to undergo oriented aggregation

A mathematical model for crystal growth by aggregation of precursor metastable nanoparticles

A mathematical model is developed to describe aggregative crystal growth, including oriented aggregation, from evolving pre-existing primary nanoparticles with composition and structure that are different from that of the final crystalline aggregate. The basic assumptions of the model are based on the ideas introduced in an earlier published report [Buyanov and Krivoruchko, Kinet. Katal. 1976, 17, 666−675] to describe the growth of low-solubility metal hydroxides (e.g., iron oxides) by oriented aggregation. It is assumed that primary particles can be described as pseudo-species A, B, and C, which have the following properties: (1) fresh primary particles (colloidally stable inert nanoparticles, denoted as A), (2) mature primary particles (partially transformed nanoparticles at an optimum stage of development for attachment to a growing crystal, denoted as B), and (3) nucleated primary particles (denoted as C1). The evolution of primary particles, A → B → C1, is treated as two first-order consecutive reactions. Crystal growth via crystal−crystal aggregation (Ci + ) is described using the Smoluchowski equation. The new element of this model is the inclusion of an additional crystal growth mechanism via the addition of primary particles (B) to crystals (Ci): (B + ). Two distinct, but constant, kernels (K ≠ K‘) are used. It is shown that, when K‘ = 0, a steplike crystal size distribution (CSD) is obtained. Within a range of K‘/K values (e.g., K‘/K = 103), CSD with multiple peaks are obtained. Comparison with predictions of models that do not include the intermediate stage of primary particles (B) indicates pronounced differences. Despite its simplicity, the model is able to capture the qualitative features of CSD evolution that have been obtained from crystal growth experiments in hematite, which is a system that is believed to undergo oriented aggregation