Strong Acidity of MFI-Type Ferrisilicate Determined by Temperature-Programmed Desorption of Ammonia

Abstract

Ammonia temperature-programmed desorption (TPD) with water vapor treatment method was applied to MFI-type ferrisilicate, and theoretical analysis was carried out to determine the acid amount and strength exactly. At the low iron content where isomorphous substitution of iron into the silicate matrix was predominant, a quite strong acid site with 150−180 kJ mol-1 adsorption heat of ammonia, which was stronger than that on aluminosilicate, was observed. The determined acidic property was in good agreement with microcalorimetry. Therefore, it is concluded that the isomorphous substitution of iron into the MFI structure generates a stronger acid site than that by aluminum.

IRMS-TPD of ammonia: Direct and individual measurement of Brønsted acidity in zeolites and its relationship with the catalytic cracking activity

“…The observation of S strongly supports measurement of the TPD of ammonia under equilibrium conditions. Moreover, it has been confirmed using mordenites [10] and ferrisilicate [11] that the measured H agrees well with that obtained by microcalorimetry. Thus, we have already measured the number and strength of the acid sites on various zeolites to arrive at the conclusion that the number of acid site is equal to Al in the framework of zeolite, and, as far as a zeolite species is concerned, the strength depends on the kind of zeolite, almost independent of the acid site concentration [10,12].…”

Improved performance of Mo-V-Te-Nb-O x catalysts prepared from a solution containing drying control chemical additives in propane oxidation to acrylic acid

“…7) show two peaks, an intensive one centered at about 200 o C and the other appearing as a broad shoulder at above 300 o C, representing the acidic sites of different strength [42,43]. The DCCA addition did not affect the position of the TPD peaks, which represented the acidic strength, but decreased the intensity of the peaks, which represented the amounts of the acidic sites.…”

“…6). In the case of FA-added catalyst, a significant decrease in the amounts of M2 phase will reduce the rates of propane oxidation because M2 is responsible for transferring lattice oxygen to the M1 phase [5,42,53].…”

Investigation of NH3 and NH4+ adsorbed on ZSM-5 zeolites by near and middle infrared spectroscopy

“…In recent years, the combination of IR mass spectroscopy and NH 3 -TPD is becoming one of the most powerful techniques to clarify the acid sites of catalyst surfaces. 1,4,[8][9][10] On the other hand, although NH 4 + also shows 4 vibration modes (symmetric stretching (ν 1 ): 3033 cm −1 , bending (doubly degenerated) (ν 2 ): 1685 cm −1 , asymmetric stretching (triply degenerated) (ν 3 ): 3134 cm −1 , bending (triply degenerated) (ν 4 ): 1397 cm −1 ), only its ν 3 and ν 4 modes are IR active. 1,4,[8][9][10] On the other hand, although NH 4 + also shows 4 vibration modes (symmetric stretching (ν 1 ): 3033 cm −1 , bending (doubly degenerated) (ν 2 ): 1685 cm −1 , asymmetric stretching (triply degenerated) (ν 3 ): 3134 cm −1 , bending (triply degenerated) (ν 4 ): 1397 cm −1 ), only its ν 3 and ν 4 modes are IR active.…”

“…15,16 In fact, all of the 4 vibration modes of a NH 3 molecule (symmetric stretching (ν 1 ): 3337 cm −1 , symmetric bending (ν 2 ): 950 cm −1 , asymmetric stretching (doubly degenerated) (ν 3 ): 3444 cm −1 , bending (doubly degenerated) (ν 4 ): 1627 cm −1 ) are IR active. 1,4,7,8,16 However, when NH 3 molecules and NH 4 + ions coexist on the catalyst surface, it is difficult to distinguish each stretching vibration mode of NH 3 and NH 4 + . 1,4,7,8,16 However, when NH 3 molecules and NH 4 + ions coexist on the catalyst surface, it is difficult to distinguish each stretching vibration mode of NH 3 and NH 4 + .…”