Al-MCM-41 modified with carbonaceous deposits: characterisation by nitrogen adsorption measurements

Abstract

Aluminosilicate MCM-41 samples in the as-prepared form and modiÐed by deposition of carbonaceous compounds formed during conversion of cyclohexene were investigated by nitrogen adsorption. The amount of the deposits decreases with the reaction temperature and increases with the quantity of aluminium incorporated into the materials. The formation of coke occurs primarily in the aluminium-rich pores. The modiÐcation leads to a lowering of adsorption capacity, surface area, pore volume and relative pressure corresponding to the adsorption isotherm step that reÑects the capillary condensation. The nitrogen adsorption measurements appeared to be a useful tool for characterisation of structural and surface properties of both the original and the novel surface-modiÐed porous materials.

Expressiveness of Adsorption Measurements for Characterization of Zeolitic Materials—A Review

“…Mesoporous molecular sieves of the M41S family Kresge et al, 1992) exhibit the type IV isotherms (Kruk et al, 1997;Rozwadowski et al, 2000Rozwadowski et al, , 2001Rozwadowski et al, , 2002) of a sloped course and a flat, elongated hysteresis loop under higher pressures (Fig. 5), similar to the layered MCM-36 materials.…”

“…Substitution of metals (e.g. Corma et al, 1994) and other modifications, e.g., tailoring the pores by coke deposition (Rozwadowski et al, 2000(Rozwadowski et al, , 2001(Rozwadowski et al, , 2002, do not change the structure from the point of view of the course and mechanism of adsorption. This reminds the aluminophosphates: the main influence of the structure and properties of the skeleton cannot be overbalanced by even significant effects of non-numerous heterocentres.…”

“…The geometric pore volume of a mesoporous material cannot be calculated and an evaluation of the sorption capacity can be made by comparison to analogous materials. Higher perturbations in the capacities of mesoporous materials are rather seldom and indicate considerable problems with the structure (Rozwadowski et al, 2000(Rozwadowski et al, , 2001(Rozwadowski et al, , 2002.…”

Al-MCM-41: its acidity and activity in cyclohexene conversion

“…In a previous paper, 20 we have reported the preparation of Al-MCM-41. The direct synthesis of these aluminosilicate materials oers an easy way of tailoring the acidic properties.…”

“…Conversion of cyclohexene has been accepted 21±27 as a suitable reaction for testing the catalytic behaviour of various materials. We have applied this process to the Al-MCM-41 molecular sieves in order to characterise their properties after modi®cation by coking, 20 to determine sorption mechanisms for water, benzene, and nitrogen, 28 and to investigate the coke deposits 29 and the volatile products of the conversion. 30 In the present study, we aim at (i) determination of the probable mechanism of the relevant conversion reactions, (ii) characterisation of the active sites, and (iii) correlation between the postulated mechanisms and the nature of the sites.…”