Desorption of Acetone from Alkaline-Earth Exchanged Y Zeolite after Propane Selective Oxidation

Abstract

The desorption of products from a series of alkaline-earth exchanged Y zeolites after room-temperature propane selective oxidation was investigated by in situ infrared and mass spectroscopy. The intermediate product, isopropylhydroperoxide (IHP), did not desorb during temperature-programmed-desorption experiments but converted into acetone and water. Decomposition rate of IHP, produced from propane and oxygen at room temperature, into acetone increased in the order BaY < SrY < CaY (<MgY), which was attributed to the number of acid sites in the samples. TPD results on the CaY zeolite point to two acetone adsorption sites, which are tentatively assigned to Brönsted acid sites and Ca(OH) x species. Acetone mainly desorbs at higher temperatures (>250 °C) under dry conditions. Addition of water, however, results in gas phase acetone already at room temperature. From the results it can be concluded that water clearly facilitates acetone desorption, most likely via shielding of the electrostatic field and creation of additional sites.

Effect of Ca2+ Position in Zeolite Y on Selective Oxidation of Propane at Room Temperature

“…It has been discussed in our previous paper 11,14 that propane partial oxidation to acetone on alkaline-earth-exchanged Y zeolite proceeds via IHP as a reaction intermediate, which results in the overall reaction…”

“…11,14 It is not yet clear how many Ca 2+ ions in the supercage position are converted to Ca(OH) x species. This is currently under investigation.…”

“…Complete selectivity was reported due to (1) the diffusional constraints to avoid radical coupling reactions and (2) strong adsorption of partially oxidized products to avoid overoxidation. 9,[12][13][14] Activity was reported to increase in the order NaY < BaY < SrY < CaY caused by the increasing cation electrostatic field. 10,11 It must be stressed that the catalytic cycle has not yet been closed because the oxygenates formed are left adsorbed strongly in the zeolite.…”

Hydrocarbon oxidation and aldol condensation over basic zeolite catalysts

“…Usually an addition of excess initiator is needed to activate the free-radical chain reaction, but the reaction can be self-activated by mild thermal conditions due to the strong electrical field of the zeolite structure [1,17]. Researchers have demonstrated that alkali and alkaline earth exchanged zeolite Y selectively oxidizes alkanes at low temperature [1,6,8,19]. The reaction mechanism proposed by Frei and coworkers involved a charge-transfer complex RH + O 2 À [6].…”

A new ATR-IR microreactor to study electric field-driven processes

“…A c c e p t e d M a n u s c r i p t 4 activation of propane and O 2 , but unfortunately also for a strong adsorption of product molecules like acetone [24]. Closing the catalytic cycle at low temperature would be possible, if these electrostatic forces could be turned off, or at least reduced to a value where the adsorbed products can be released from the surface with minor thermal activation.…”