Moises A. Carreon

Highly Permeable Zeolite Imidazolate Framework-8 Membranes for CO2/CH4 Separation

ZIF-8 membranes, a type of zeolite imidazolate framework, were synthesized by secondary seeded growth on tubular alpha-Al(2)O(3) porous supports. The presence of small, highly crystalline, microporous crystals with narrow particle size distribution led to continuous thin membranes. The synthesized novel ZIF-8 membranes displayed unprecedented high CO(2) permeances and relatively high separation indexes for equimolar mixtures of CO(2) and CH(4).

Structural Evolution of Zeolitic Imidazolate Framework-8

We report the structural evolution of zeolitic imidazolate framework-8 (ZIF-8) as a function of time at room temperature. We have identified the different stages of ZIF-8 formation (nucleation, crystallization, growth, and stationary periods) and elucidated its kinetics of transformation. We hypothesize that the observed semicrystalline-to-crystalline transformation may take place via solution- and solid-mediated mechanisms, as suggested by the observed phase transformation evolution and Avramis kinetics, respectively. A fundamental understanding of ZIF-8 structural evolution as demonstrated in this study should facilitate the preparation of functional metal-organic framework phases with controlled crystal size and extent of crystallinity.

Alumina-Supported SAPO-34 Membranes for CO2/CH4 Separation

SAPO-34 membranes were prepared by in situ crystallization on alpha-Al2O3 porous supports. The crystal size of the seeds was effectively controlled in the 0.7 to 8.5 micron range by employing different structure-directing agents. Seeds smaller than 1 micron produced membranes with CO2/CH4 separation selectivities higher than 170 and unprecedented CO2 permeances as high as 2.0 x 10(-6) mol/m2.s.Pa at 295 K and a feed pressure of 224 kPa. The membranes effectively separated CO2/CH4 mixtures up to 1.7 MPa.

Amino-functionalized SAPO-34 membranes for CO2/CH4 and CO2/N2 separation.

SAPO-34 seeds and membranes were functionalized with several organic amino cations, such as ethylenediamine, hexylamine, and octylamine. The successful incorporation of the amino groups in the SAPO-34 framework was confirmed by Fourier transform infrared (FTIR) and X-ray photoemission (XPS) spectroscopies. The resultant SAPO-34 membranes were evaluated for the separation of CO2/CH4 and CO2/N2 gas mixtures. CO2/CH4 selectivities as high as 245, with CO2 permeances of ∼5 × 10(-7) mol m(-2) s(-1) Pa(-1) at 295K and 138 kPa, were observed for an optimum ethylenediamine-functionalized membrane, which corresponded to a ∼40% increase in the separation index, as compared to the nonfunctionalized SAPO-34 membrane. Similarly, the CO2/N2 separation performance was highly improved with the incorporation of ethylenediamine. CO2/N2 selectivities as high as 39, with CO2 permeances of ∼2.1 × 10(-7) mol m(-2) s(-1) Pa(-1) at 295K and 138 kPa, were observed for an optimum ethylenediamine-functionalized membrane, which corresponded to a ∼167% increase in the separation index, as compared to the nonfunctionalized SAPO-34 membrane.

Synthesis of SAPO-34 Crystals in the Presence of Crystal Growth Inhibitors

Microporous SAPO-34 molecular sieves were synthesized employing polyethylene glycol, polyoxyethylene lauryl ether, and methylene blue as crystal growth inhibitors. The synthesized SAPO-34 crystals displayed BET surface areas up to 700 m2/g, high CO2/CH4 adsorption ratios, and small crystal size in the approximately 0.6-0.9 microm range with narrow particle size distribution. The enhanced CO2/CH4 adsorption capacities were related to the high N/H ratios observed in the phases prepared in the presence of crystal growth inhibitors. The synthesized SAPO-34 crystals may find potential applications to prepare membranes for CO2 purification.

Hierarchical Sandwich-Like Structure of Ultrafine N-Rich Porous Carbon Nanospheres Grown on Graphene Sheets as Superior Lithium-Ion Battery Anodes

A sandwich-like, graphene-based porous nitrogen-doped carbon (PNCs@Gr) has been prepared through facile pyrolysis of zeolitic imidazolate framework nanoparticles in situ grown on graphene oxide (GO) (ZIF-8@GO). Such sandwich-like nanostructure can be used as anode material in lithium ion batteries, exhibiting remarkable capacities, outstanding rate capability, and cycling performances that are some of the best results among carbonaceous electrode materials and exceed most metal oxide-based anode materials derived from metal orgainc frameworks (MOFs). Apart from a high initial capacity of 1378 mAh g(-1) at 100 mA g(-1), this PNCs@Gr electrode can be cycled at high specific currents of 500 and 1000 mA g(-1) with very stable reversible capacities of 1070 and 948 mAh g(-1) to 100 and 200 cycles, respectively. At a higher specific current of 5000 mA g(-1), the electrode still delivers a reversible capacity of over 530 mAh g(-1) after 400 cycles, showing a capacity retention of as high as 84.4%. Such an impressive electrochemical performance is ascribed to the ideal combination of hierarchically porous structure, a highly conductive graphene platform, and high-level nitrogen doping in the sandwich-like PNCs@Gr electrode obtained via in situ synthesis.

Alumina-supported cobalt–adeninate MOF membranes for CO2/CH4 separation

The synthesis of continuous cobalt–adeninate MOF (bio-MOF-13 (I) and bio-MOF-14 (II)) membranes supported on porous alumina tubes is demonstrated. The membranes showed high CO2 permeabilities and low to moderate CO2 separation selectivities for CO2/CH4 gas mixtures. The observed CO2/CH4 selectivities are attributed to preferential CO2 adsorption within the framework.

Decarboxylation of oleic acid over Pt catalysts supported on small-pore zeolites and hydrotalcite

The catalytic decarboxylation and further conversions of oleic acid to paraffins, branched and aromatic hydrocarbons over Pt supported on small pore zeolites and hydrotalcite are demonstrated. The influence of the support, platinum source, and reaction temperature on the decarboxylation of oleic acid was investigated. An increase in reaction temperature increased the degree of decarboxylation and selectivity to heptadecane. Pt-SAPO-34 was a very effective catalyst. In addition to a high degree of decarboxylation, Pt-SAPO-34 displayed a high selectivity to heptadecane and dodecylbenzene among the products. Branched isomers, cracked (mostly <C17) paraffins, alkenes such as undecene and dodecene, and carboxylic acids such as nonanoic acid and decanoic acid were observed as side products. The further isomerization of the initially formed linear heptadecane (by decarboxylation of oleic acid) to branched isomers is suppressed in the narrow pores of SAPO-34 due to restricted transition state shape selectivity limitations in the pore system of SAPO-34. Catalyst acidity, dispersion of Pt and the pore diameter of the support played crucial roles in determining product selectivity.

Microwave assisted phase transformation of silicoaluminophosphate zeolite crystals

SAPO-34 zeolite displaying ∼0.5 µm crystal size with a narrow particle size distribution and preferential adsorption of CO2 over that of CH4 was prepared via phase transformation of SAPO-5 under microwave heating.

Mesostructured vanadium-phosphorus-oxide phases

Abstract Ordered mesostructured hexagonal, cubic and lamellar vanadium-phosphorus-oxide phases displaying improved thermal stability, desirable bulk compositions, and vanadium oxidation states (3.8–4.3) for the partial oxidation of lower alkanes were synthesized using cationic (alkyl trimethyl ammonium salts), anionic (alkyl sulfonates and phosphates) and primary alkylamines as structure-directing agents. It was found that hexagonal mesophases were favored at short carbon chain lengths (C 12 –C 16 ), while cubic phases were favored for longer chains (C 18 ). Structure-directing agents were removed by calcination or Soxhlet extraction in ethanol. When structure-directing agents were removed by extraction, phase transformations from hexagonal to cubic to lamellar structures were observed. The improved thermal stability of these mesophases was attributed to the acidic self-assembly conditions in the vicinity of the isoelectric point of V(V) oxocations.