Mesocellular polymer foams with unprecedented uniform large mesopores and high surface areas

Mesocellular polymer foams with uniform approximately 17 nm cellular pores were fabricated using mesocellular silica foams as inorganic templates. The mesocellular polymer foams have high surface areas up to approximately 600 m(2)g(-1) and pore volumes of 1.6 cm(3)g(-1).     

In situ disorder-order transformation in synthetic gallosilicate zeolites with the NAT topology

Here, we report that synthetic gallosilicate molecular sieves with the NAT topology and Si/Ga ratios close to but slightly higher than 1.50 undergo an in situ transformation under their crystallization conditions. The materials have been studied ex situ by using powder X-ray diffraction, elemental and thermal analyses, and multinuclear MAS NMR. The transformation is characterized by a change in the distribution of Si and Ga of the NAT framework, from a quite (but not completely) disordered phase to a very highly (but not completely) ordered one, accompanied by a change from tetragonal to orthorhombic symmetry. During most of the solution-mediated transformation, no noticeable signs of fresh precipitation, phase segregation, or changes in the chemical composition are detected. Intermediate materials show variations in the degree of Si-Ga ordering and orthorhombic distortion and are not physical mixtures of the disordered and ordered phases. Ab initio calculations strongly suggest a preferential siting of Si in the tetrahedral sites involved in a smaller number of 4-rings in the NAT topology (i.e., the low multiplicity site). The cost of violations of Loewenstein's rule has also been calculated. For this topology and chemical composition the preferential siting and Loewenstein's rule drive together the system to the ordered configuration. A Monte Carlo sampling procedure affords a reasonable model for the initial, mainly disordered state, which fits well within the experimental disorder-order series.     

Oxidative Dehydrogenation of <Emphasis Type="Italic">n</Emphasis>-Butenes to 1,3-Butadiene over Bismuth Molybdate and Ferrite Catalysts: A Review

1,3-Butadiene, an important raw material for a variety of chemical products, can be produced via the oxidative dehydrogenation (ODH) of n-butenes over multicomponent oxide catalysts based on bismuth molybdates and ferrites. In this review, the basic concept, reaction mechanism, and catalysts typically used in an ODH reaction are discussed.     

Synthesis, crystal structure, characterization, and catalytic properties of TNU-9

The synthesis, crystal structure, characterization, and catalytic properties of the novel medium-pore zeolite TNU-9 (framework type TUN), one of the most crystallographically complex zeolites known to date, are described. TNU-9 was found to crystallize under hydrothermal conditions at the expense of a lamellar precursor over a very narrow range of SiO(2)/Al(2)O(3) and NaOH/SiO(2) ratios and in the presence of 1,4-bis(N-methylpyrrolidinium)butane and Na+ ions as structure-directing agents. A combination of molecular modeling and Rietveld refinement using synchrotron powder diffraction data confirms the proposed topology of as-made TNU-9 and suggests three or possibly four different sites for the organic within the complex pore structure. The proton form (H-TNU-9) of this new medium-pore zeolite exhibits exceptionally high hydrothermal stability, as well as very strong acidity. When compared to H-ZSM-5, H-MCM-22, H-mordenite, and H-Beta, H-TNU-9 displays unique shape selectivities for the acid-catalyzed reactions of monoaromatic hydrocarbons such as the disproportionation of toluene and the isomerization and disproportionation of m-xylene. In particular, for the isomerization of m-xylene, the ratio of isomerization to disproportionation increases steadily to values in excess of 50 with prolonged time on stream and a high p/o xylene ratio is observed in the products, achieving a value of ca. 6 after only a short time on stream. These results are rationalized on the basis of the unique pore topology of TNU-9.     

Rational design of ordered mesoporous carbon with controlled bimodal porosity via dual silica templating route

Combining both nano-replication and nano-imprinting techniques using dual silica templates provides a simple way to synthesize ordered mesoporous carbons with bimodal pore size distributions ( approximately 1.5 nm and approximately 3.5 nm).     

Molecular conformations of protonated dipropylamine in AlPO4-11, AlPO4-31, SAPO-34, and AlPO4-41 molecular sieves

The host-guest interactions in AlPO4-11, AlPO4-31, SAPO-34, and AlPO4-41 molecular sieves prepared using the same organic structure-directing agent, i.e., dipropylamine, are investigated by a combination of Raman, 13C and 1H MAS NMR, and computer modeling studies. It was found that the organic molecules trapped within the pores of these four AlPO4-based materials exist as their protonated form and adopt distinct conformations in order to fit well with the pore structure of each host. In particular, the presence of two different types of conformations of protonated dipropylamine in the circular 12-ring channels of AlPO4-31 has been ascertained.     

Synthesis, structure solution, characterization, and catalytic properties of TNU-10: a high-silica zeolite with the STI topology

A high-silica zeolite (Si/Al = 7.1) with the STI framework topology, denoted TNU-10, has been synthesized in the presence of 1,4-bis(N-methylpyrrolidinium)butane and Na(+) cations as structure-directing agents, and its structure in the proton form has been refined against laboratory powder X-ray data in space group Fmmm (a = 13.533(1) A, b = 17.925(2) A, c = 17.651(2) A). The space group symmetry is supported by electron diffraction and energy minimization studies. The as-made and proton form of TNU-10 are extensively characterized by elemental and thermal analyses, scanning electron microscopy, N(2) adsorption, multinuclear solid-state NMR, IR, and temperature-programmed desorption of ammonia, and the location of the organic structure-directing agent in the channel system is determined by molecular modeling. The catalytic properties of H-TNU-10 and Co-TNU-10 are evaluated for the skeletal isomerization of 1-butene to isobutene and the selective reduction of NO with methane, respectively. When compared to H-ferrierite, a low selectivity to isobutene is observed for H-TNU-10. However, it is found that Co-TNU-10 exhibits a maximum NO conversion of 93% at 823 K under conditions of high concentrations of methane (16,000 ppm) and water vapor (10%) and in the presence of 2.6% O(2), which is considerable higher than even the value (74%) obtained from Co-ferrierite, known as the best catalyst for this reaction, under the identical conditions.     

Effect of oxychlorination treatment on the regeneration of Pt–Sn/Al2O3 catalyst for propane dehydrogenation

Research on Chemical Intermediates - Propane dehydrogenation and regeneration of Pt–Sn/θ-Al2O3 catalysts was evaluated with oxychlorination treatment. It was observed that the catalytic...     

Dry Reforming of Methane Over Cobalt Catalysts: A Literature Review of Catalyst Development

Dry reforming of methane produces syngas with desirable H₂/CO ratio. Besides noble metal catalysts, the cobalt catalyst performs good activity in this reaction. However, carbon deposition and catalyst deactivation are becoming the main problems inhibiting the scale up of this process into industrial application. Recently, many scientists were trying to increase the activity as well as the stability toward coking by using variants of support, promoter, and combination of metal series catalyst. This paper presents a recent technology of methane dry reforming over cobalt metal-base catalyst, covering the catalyst activity and their resistance of catalyst deactivation.