M Mathieu

Molecular Dispersion of Metal Complexes within Zeolitic Solids: An Alternative Way to Prepare Supported MOx Catalysts

Molecular Designed Dispersion (MDD) of metal complexes on a highly porous support is a novel synthesis method to prepare high quality heterogeneous catalysts. The process basically consists of two steps: (1) the anchoring of the complex onto the support in a controlled way and (2) the mild oxidation of the grafted complex towards catalytically active metal-oxide surface structures.This article presents two typical case studies: (1) the incorporation of cationic Cu-complexes in a H-ZSM-5 zeolite from the liquid phase and (2) the gas phase modification of pure silica MCM-48, using the VO(acac)2 complex. In both cases, superior catalysts are obtained. Detailed chemical, physical and catalytical analyses of these catalysts are discussed in the text. Comparison is made with analogous catalysts, prepared by conventional methods.

The creation of MOx surface species on pure silica MCM-48, using gas- and liquid phase modification with M-acetylacetonate complexes

Pure silica MCM-48 is prepared by a novel synthesis method, using the [C18H37N+(CH3)(2) - (CH2)(12) - N+(CH3)(2)C18H37].2Br(-) surfactant, abbreviated as GEMINI 18-12-18. The MCM-48, obtained after careful calcination, is a highly crystalline, mesoporous material, with the characteristics of the Ia3d cubic phase, a surface area exceeding 1000 m(2)/g and a narrow mesoporous pore size distribution (r = 1.4 nm; FWHH < 0.2 nm). This MCM support is grafted with VOx species, using a designed dispersion of VO(acac)(2) in a gas deposition reactor. In a first step, the complex is anchored to the support, in a subsequent step the adsorbed complex is thermolyzed to yield chemically bonded VOx surface species. The final material contains 1.7 mmol V/g (8.7 w% V), still has narrow pore size distribution and a surface area of 800 m(2)/g. It is observed that all silanols are consumed during the adsorption of the VO(acac)(2) complex to the MCM support. Therefore, the maximum achievable number of surface V-species is limited by the silanol number, and not by the geometrical surface, which has a higher capacity. After calcination of the adsorbed complex, the supported VOx species are present in a strictly tetrahedral configuration, but mainly as chains of linked tetrahedra and not as isolated species.

06-O-04 - Pore size engineering of MCM-48: the use of different additives as expanders

Publisher Summary This chapter discusses the pore size engineering of mesoporous MCM-48 materials using several additives during the synthesis. Dimethyltetradecyl amine (DMTDA) is a convenient expander, resulting in a MCM-48 structure with a pore size enlargement from 1.7 nm to 2.4 nm pore radius. A wide range of dimethylalkyl amines, with varying chain length is applied as swelling agents. Other additives, such as ethanol and decane, are also found to be suitable for the synthesis of large pore MCM-48. The influence of the chain length and the effect of the molar ratio of amine or surfactant on the crystallinity and pore size of the MCM-48 are also studied.

06-P-06- Active MCM-48 supported catalysts: different strategies to increase the structural and chemical stability

Publisher Summary This chapter discusses different strategies for increasing the structural and chemical stability of pure silica MCM-48. Thickening of the walls, using tetrachlorosilane (SiCl 4 ) and water, results in a wall thickening of 50%. It also strongly improves the mechanical stability of the samples. A partial hydrophobization with an amphiphilic silane, such as dimethyldichlorosilane, has extremely beneficial effects on the thermal, mechanical, and hydrothermal stability of the samples and strongly reduces the leaching of the active centers. Both wall thickening and hydrophobization can be combined into one simple postsynthesis treatment. Such treatments will be necessary for allowing a practical (industrial) use of the MCM-48 support as catalysts support or adsorbent.