IR Spectroscopy Analysis and Kinetic Modeling Study for NH₃ Adsorption and Desorption on H- and Fe-BEA Catalysts

Abstract

Among different types of Fe-exchanged zeolites, Fe-BEA exhibits very promising surface properties for developing efficient urea or NH 3 -SCR systems. In this work, dedicated experimental and kinetic modeling studies were performed in order to elucidate mechanistic aspects related to NH 3 storage and release on these catalysts. A series of NH 3 adsorption and desorption experiments were performed over both H-and Fe-exchanged BEA zeolites, taking into account a broad range of operating conditions. Coupling FTIR spectroscopy, surface NH 3 adspecies were characterized. NH 3 gaseous concentration profiles were subsequently simulated by means of a detailed multisite kinetic model, being able to account for low-temperature adsorption phenomena. Finally, correlations between surface acidity and model sites were enabled by comparing IR spectroscopy and model predicted results, leading to the development of a phenomenological semidetailed, multisite kinetic modeling approach.

Study of the Cycloaddition of CO2 with Styrene Oxide Over Six‐Connected spn Topology MOFs (Zr, Hf) at Room Temperature

“…When the sample is adsorbed by NH 3 saturation, there are vibration peaks at 1100-1300 cm À 1 , ~1325 cm À 1 and 1420-1500 cm À 1 . According to previous research, the characteristic peaks around ~1256, ~1100 and 1130-1200 cm À 1 belong to the symmetric bending vibrations and symmetric stretching vibrations of the NÀ H bond in NH 3 , respectively, [30][31][32] at 1420-1500 cm À 1 The nearby peaks are attributed to the asymmetric stretching vibration of the NÀ H bond in NH 4 + ; [33,34] the vibration peak at ~1325 cm À 1 may be related to the oxidation of adsorbed ammonia species, [35] it is almost the same throughout the temperature range. For all catalysts, the intensity of the peaks attributed to Lewis acid site is stronger than Brønsted acid site (little peak area), illustrating that the catalyst surface is almost Lewis acid sites, and there are few Brønsted acid sites.…”

A multi-site kinetic model for NH3-SCR over Cu/SSZ-13

“…This method resulted in linearly decreasing the heat of adsorption when increasing the ammonia coverage, which is in line with the Temkin isotherm. Both single site [31,36] kinetic models and multiple site [17,33,42,43] models have been developed for ammonia storage over zeolites. A reason for using multiple sites is to describe storage at low temperature, where large amount of physisorbed ammonia is present [33].…”

Zeo‐Click Synthesis: Copper‐Zeolite‐Catalyzed Synthesis of Ynamides

“…Indeed, incomplete catching of Cu species may explain the small erosion observed upon recycling. Such phenomena have been observed with other metals and supports,20 and seem related to hydrogen‐bonding and acid sites 20c,21. However, such a mechanism cannot account for the large reactivity differences observed with the various zeolites examined.…”