Acidity of substituted MCM-41-type mesoporous silicates probed by ammonia

On the reactive adsorption of ammonia on activated carbons modified by impregnation with inorganic compounds

“…Secondly, these types of interactions can be masked by other types of retention such as Lewis acidbase interactions. This is especially true when FTIR spectroscopy is applied since bands related to ammonia physisorbed and ammonia adsorbed on Lewis centers appear in a similar range [57,70]. This difficulty in analyzing the amount of ammonia adsorbed is for instance encountered for the C and S samples.…”

Comparative Study of the Acidic and Catalytic Properties of the Mesoporous Material H-MCM-41 and Zeolite H-Y

“…In the hydroxyl range, the FT-IR spectrum of the protonic form of MCM-41 shows a very intense band at 3740 cm ±1 , which is in accordance with observations of Corma et al [9], correlating with free Si-OH vibrations found on silicas [13] which appear superimposed on a broader absorption between 3750 and 3400 cm ±1 . After addition of ammonia, intense bands appear at 3352, 3285, and 3201 cm ±1 in the region of N-H bond stretching vibrations, indicating the interaction of ammonia and the surface of the MCM-41 material, also described by Kosslick et al [14]. The absorption bands at 3352 and 3285 cm ±1 could be assigned to ammonia bonded to coordinately unsaturated species and the asymmetric stretching vibration of the ammonium ion [15,16].…”

Mild acid MCM-41 promotes para-isomer in the vapour phase alkylation of isopropylbenzene with diethyl carbonate

“…The results of IPB-conversion and products selectivity over Al-MCM-41 are illustrated in Tables 4-6 [12,13]. Al-MCM-41 (33) show the highest conversion rate among the catalysts.…”

“…It is observed that two major weight losses occurred over all the catalysts at lower and higher temperature range, which may be due to the desorption of ammonia adsorbed on weak and strong acid sites, respectively. The first and second weight losses occurred between 200-225 and 385-420 8C, respectively, for all the catalytic systems [12,13]. …”

“…Compared to microporous zeolites, these mesoporous molecular sieves are more useful for regio-selective alkylation of aromatics as they have straight pores, very well scattered mild Brönsted acid sites [12,13] and large pore diameters. These features of the materials aid the reactants to experience www.elsevier.com/locate/apcata Applied Catalysis A: General 287 (2005) 116-128 an environment similar to that in the homogeneous liquid phase.…”