James C. Vartuli

Synthesis of mesoporous molecular sieves

This chapter discusses the synthesis of mesoporous molecular sieves. They are synthesized in the presence of surfactants and were recognized first in the silica-cationic surfactant systems. The study of the synthesis of mesoporous molecular sieves has become an interdisciplinary field with potential practical applications in catalysis and sorption. The chapter outlines the major advances in the synthesis of these mesoporous molecular sieves from discovery to the present, with a focus on the general trends and interplay between surfactant and oxide chemistries. Representative materials are discussed in detail for the convenient synthesis of a high quality useful product. The synthesis progressed in many directions affording both novel materials and methods for a large-scale manufacture. The M41S based catalyst is used in a commercial application and in one commercial process MCM-41 offers advantage over the state-of-the-art catalyst. The inherent flexibility and potential for modifications are the main drivers for continuing interest, innovation, and search for improvements in this field for future studies.

The discovery of ExxonMobil's M41S family of mesoporous molecular sieves

Publisher Summary This chapter discusses the discovery of ExxonMobils M41S family of mesoporous molecular sieves. The quest for new molecular sieves in the late 1980s led a team of mobil researchers to the discovery of a family of nanostructured mesoporous materials known as “M41S.” Mobil composition of matter (MCM)-41, the hexagonal phase, is undoubtedly the best known and most widely studied of this family of materials. Other discrete members of the M41S family are the cubic (MCM-48) and the lamellar (MCM-50) forms. Each is synthesized via a counterion initiated self assembled liquid crystal mechanism, involving oxide precursors, which form an inorganic equivalent to a liquid crystal-micelle structure. This manuscript describes the events that led to the discovery of M41S materials. It also summarizes the supporting characterization and mechanistic studies that led to a picture of how these materials are actually formed. The mechanistic and characterization studies involved many researchers from ExxonMobils Paulsboro and Princeton laboratories. ExxonMobil has very recently scaled-up the synthesis and commercialized MCM-41 for an undisclosed application.

Chapter 23 - Applications of Mesoporous Molecular Sieves in Catalysis and Separations

This chapter discusses the mesoporous molecular sieves in terms of their unique attributes as either catalysts or catalyst components or as adsorbents or materials otherwise used for separation. It attempts to identify the specific structure that has been used. The review of catalytic applications focuses on the recent studies, and the extensive patent literature that usually is not referenced, but provides a wealth of examples, observations, and historical background. The subject area of applications of structured mesoporous molecular sieves has expanded considerably with many interesting and exciting developments from the standpoint of fundamental science and potential uses. The synthesis has progressed in many directions affording many novel materials, methods for a large-scale manufacture, and new applications. For many new materials, traversing the path from discovery to commercial application can take as long as a decade.

The sorption properties of as-synthesized and calcined MCM-41 and MCM-48

The benzene sorption capacity of as-synthesized and calcined MCM-41 and MCM-48 were compared. The hydrocarbon sorption capacity increases with pore diameter for the calcined versions. As-synthesized samples sorb appreciable amounts of benzene but the quantity is invariant with respect to pore diameter. The sorption of hydrocarbon by as-synthesized M41S materials is a unique feature not observed with microporous molecular sieves.

The generation of shape selective intercalated kenyaites

Abstract Pillared clays, with pore openings in the 7–15 A range and possessing moderate acid activity have gained notoriety over the past 20 years as co-catalysts for the conversion of heavy feedstocks. [1-3]While “once through” catalysts, incorporating such pillared materials have shown important product selectivity improvements in FCC evaluations (in particular an increase in C 5 + gasoline/ conversion), their lack of hydrothermal stability under realistic FCC regeneration conditions have prevented their widespread use. We have synthesized active, pillared catalysts that have exhibited shape selectivity in model compound test reactions and reasonable hydrothermal stability under steaming conditions at temperatures up to 700°C. These molecular sieves have been developed based on the intercalation of metalloaluminophosphates gels into the layered silicate, kenyaite. Model compound reaction test results indicate that these molecular sieves exhibit product shape selectivity comparable to small 12-membered ring pore opening zeolites such as ZSM- 12 and mordenite. By variation of the reaction composition, various shape selectivities were realized suggesting methods for “tailoring” pore dimensions for particular reactions. Furthermore, the chemical nature of these phosphorus-containing materials suggests a method for the incorporation of catalytically important chemistry into the intercalated catalysts.

A comparison of the sorption properties of mesoporous molecular sieves MCM-41 and MCM-48

abstract The benzene and triisopropylbenzene sorption capacity and rates of adsorption for several samples of MCM-41 and MCM-48 were compared. The results indicate that for samples with similar pore diameters, MCM-41 has approximately 30% more total capacity for the two hydrocarbons than MCM-48. Pore sizes estimated from the benzene capacity measurements agree well with those calculated from argon adsorption. Estimates made from benzene capacity measurements indicate that for the MCM-41, samples the thickness of the pore walls is approximately 8 and is independent of pore diameter; the pore wall thickness of the MCM-48 sample is estimated to be slightly larger, approximately 10. Sorption rates for all samples were found to be indicative of macropore diffusion limitations rather than mesopore diffusion, hence, no conclusions can be drawn concerning the relative rates of diffusion of benzene through the mesoporous channels characteristic of these samples.

02-P-22 - Evidence for in-situ directing agent modification in zeolite syntheses

Publisher Summary This chapter presents evidence for in situ directing agent modification in zeolite syntheses. ZSM-22 can be produced from potassium based 1,6 hexamethylenediamine synthesis mixture while, ZSM-34 is synthesized from the same synthesis mixture with the addition of sodium. Nuclear magnetic resonance (NMR) analyses of the as-synthesized zeolite samples indicate the presence of a carbonyl species in all of the ZSM-34 samples but not in any of the preparations that produced ZSM-22. The carbonyl species is present only after the synthesis mixture is heated above ambient temperature. Molecular modeling studies calculate a favorable fit of the carbamic species within the pore system of the Erionite suggesting a reason for the formation of the OFF/ERI intergrowth.