The objective of this presentation is to give a characterization of aluminosilicate MCM-41, in particular with respect to acidity and the nature of the acid sites. Si-29 MAS NMR spectra of MCM-41 closely resemble those of amorphous silica, suggesting that the pore walls are amorphous. This fact could also imply that the types of acid sites in these materials are different from those generally found in zeolitic materials. The obtained results from H-1 MAS NMR and combined FTIR and temperature-programmed ammonia desorption (TPAD) investigations indicate that the washed, template-free MCM-41 and its protonic form behave as a solid-state acid with a broad acid strength distribution. With regard to the presence of bridging hydroxyl groups in the investigated MCM-41 materials, the findings of these two methods are not consistent. Therefore, it is assumed that the broad absorption between 3650 - 3400 cm(-1) in the FTIR spectra is connected with hydrogen-bonded vicinal silanol pairs. The results of the catalytic testing suggest that the weak Bronsted acid sites interact with neighbouring coordinatively unsaturated aluminium species and that synergistically stronger acid sites are formed.

The NMR signal intensity vs temperature (IT curve) of water confined in mesoporous materials (pore radius lager than 10 Angstrom) reveals one or more ''high-temperature'' transitions above 222 K, which are dependent on pore size, and an additional transition temperature below 209 K, which is independent of pore dimension. This latter transition shows no hysteresis effect or discontinuity and contributes to more than 65% of the total water content of the porous materials investigated and is explained as interfacial water in contact. with the surface of the matrix and the solid ice phase. The thickness of this interface water is estimated to be 5.4 +/- 1.0 Angstrom, (cylindrical pores). It is shown that the observed NMR intensity of water associated with the ''high-temperature'' transition phases has to be corrected in order to present the actual amount of water within these phases. It is further demonstrated that these intensity corrections must be implemented in the pore size distribution functions to give quantitative results. The significance of the correction factors increases with decreasing pore radius.

The catalytic properties of extra-large pore aluminosilicate MCM-41 and a silica-containing VPI-5 were investigated by MAT (Micro Activity Test) using n-hexadecane as a model feed and were then compared with the results obtained from a commercial FCC catalyst (FCC : Fluid Catalytic Cracking). It could be demonstrated that, by optimizing structural and chemical properties, the new mesoporous crystalline MCM-41 and related materials are suitable as active components in cracking catalysts for ''deeper'' cracking of high boiling hydrocarbons.

Publisher Summary The Fluid Catalytic Cracking process (FCC) is of paramount importance in petroleum refining. At present, besides an active matrix, the active component of the cracking catalyst is zeolite Y and/or ZSM-5, both of which are limited in the processing of heavier oil fractions due to the restriction caused by their pore dimensions. The new zeotype/mesoporous materials VPI-5, Cloverite, and MCM-41 open up interesting perspectives for the conversion of heavier feedstocks because of the accessibility of long-chain and/or bulky molecules to the active centers. This chapter presents the synthesis of and discusses the results obtained by using Si-VPI-5 and MCM-41 as catalysts in n-hexadecane cracking in comparison with a commercial FCC catalyst.