Bifunctional Catalytic Material Research Articles

Pincer ligands as powerful tools for catalysis in organic synthesis

Present trends in homogeneous catalysis are moving toward the development of multi-step, one-pot processes where salt waste is reduced to a minimum and in the lowest possible volumes of solvent. Energy efficiency is also maximized to produce the most cost-effective end product(s). However, these one pot cascade, tandem, or domino catalyzed reaction sequences rely on catalyst, substrate and solvent compatibility, on catalyst stability and on the possibility to protect these catalysts from mutual deactivation. This can be facilitated, for example, by binding these to suitable (in)soluble supports or by using compatible, stable catalysts that can be used to mediate a variety of different reactions.Pincer organometallics are powerful tools that can be used to achieve many of these objectives. The synthesis and properties of a variety of “molecularly enlarged” pincer organometallics displaying both surprising stability and versatile catalytic properties are discussed. A fascinating, recent development is the site-selective inhibition of a lipase, i.e., Cutinase, with a single pincer-metal catalytic site (see X-ray). Similarly, partial inhibition of lipases immobilized on beads with a Ru-based racemization catalyst yields a bio-organometallic hybrid catalyst, which in combination with still uninhibited lipase on these beads, can operate as a heterogeneous bifunctional catalytic material for the kinetic resolution of racemic alcohols to afford enantiopure product(s).

Hydrolytic hydrogenation of hemicellulose over metal modified mesoporous catalyst

The hydrolytic hydrogenation of hemicellulose arabinogalactan, into sugars, sugar alcohols and furfurals was carried out in a batch reactor using modified mesoporous MCM-48 material incorporated with ruthenium metal into the framework. The bi-functional catalytic materials, MCM-48 and Ru–MCM-48 were synthesized, characterized and investigated in the title reaction at total pressure of 20bar hydrogen, using an initial arabinogalactan concentration of 0.4wt%, at 458K. The transformation of the hemicellulose consists of arabinogalactan hydrolysis to the monosaccharides, l-arabinose and d-galactose followed by the subsequent hydrogenation to sugar alcohols, arabitol and galactitol or dehydration of the monomers to furfural and 5-hydroxymethylfurfural. The yields of the main products, i.e. sugars, sugar alcohols and furfurals were varied depending on the strength of the acid sites and the presence of metal in the structure of the ruthenium modified catalyst. Ru–MCM-48 displayed high catalytic activity and the sugar alcohols were obtained selectively from the hemicellulose. The catalytic performance of the mesoporous MCM-48 catalysts with respect to the catalyst structure, acidity and presence of the metal was evaluated.

Synthesis and characterization of NTS material and its oxidation desulfurization properties

The development of desulfurization technology involving the onsite direct generation of hydrogen peroxide (H 2O 2) from H 2 + O 2, followed by H 2O 2 oxidation to organic oxides without conventional refining is regarded as one promising approach for reducing capital and operating costs. The objective of our research is to provide bi-functional catalytic materials based on a combined process for the oxidative desulfurization (ODS) using H 2O 2 in situ generated. We have prepared a series of new bi-functional titanosilicate (NTS, titanium silicalite combined with noble-metal loading), which have been synthesized by combining noble-metal sources with modified titanium silicalite under basic conditions. Here, the synthesis and characterization of NTS samples, and their ODS properties are presented. The samples were characterized by various analytical techniques, and their direct ODS performances were investigated. The results indicate that NTS shows well ordered MFI topology and with hollow structure; NTS combined with noble-metal shows potential for application in direct ODS with H 2 + O 2 in one-step process.

NHTS: A Hollow, Noble‐Metal‐Modified Titanium Silicalite

AbstractThe major drawback of direct oxidation technology (onsite hydrogen peroxide production followed by its conversion into organic oxides without refining) is the design and preparation of the bifunctional catalysts used therein. Herein we present a bifunctional catalytic material (NHTS), which is synthesized by a revised semi‐in‐situ method that allows a noble metal to be distributed throughout the titanosilicate framework and also results in a redistribution of active Ti species throughout the crystals, thereby enriching the surface of the hollow crystals with catalytic species. This compound has been characterized by various techniques and its activity and selectivity for the direct epoxidation of propylene investigated. The results indicate that NHTS shows a very ordered MFI topology, with the noble metal incorporated in the framework, and a hollow structure, which makes it a good alternative for catalytic oxidations. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

MTS , modified titanium silicalite with hollow structure and precious-metal combined

Abstract Bi-functional catalytic materials, denoted as MTS n , are synthesized by supporting precious metal on hollow titanium silicalite, and become new modified titanium silicalites with hollow structure and precious metal being combined. The samples have been characterized by various instruments, their catalytic performances in the propylene direct epoxidation are also investigated. The results have indicated that the special modification treatment not only can introduce Pd into MTS n , but also can make the stable combination of precious metal with titanosilicate, and the hollow structure in MTS n can be convenient for molecular diffusions.