Catalytic properties of beta zeolite exchanged with Pd and Fe for toluene total oxidation

Abstract

Dealuminated beta zeolites exchanged with Pd and Fe were prepared to investigate the influence of iron and dealumination on the activity and selectivity of Pd/BEA zeolite for toluene total oxidation. The specific areas determined by BET method and EPR studies allowed to know that the palladium would be more easily agglomerated on the BEA than on the DBEA. Moreover, a quantification of the palladium saturation on the BEA zeolite was deduced by EPR. Effects of dynamic and static oxidation and weak and strong reduction treatments were studied by EPR. Several isolated and interacted Pd + species and hole centers were detected. The Pd was much reduced after the catalytic test in dealuminated and Fe doped samples. This result could be directly correlated to the catalytic deactivation. The deactivation could be also explain by the type of coke deposed on the catalyst and by the hydroscopic behavior of the samples. Addition of Fe or dealumination could prevent the deactivation and then lead to better catalysts for VOCs oxidation.

Investigation of the modes of NO adsorption in Pd/H-CHA

“…The relative amounts of Pd + and Pd 2+ cations exchanged at NNN Al pairs can therefore be altered by varying the temperature and partial pressure of water. The question of whether or not Pd + is present in as-prepared and pretreated Pd/CHA remains open, as several authors have suggested based on evidence inferred from IR spectroscopy that Pd + only forms upon NO adsorption via the process Pd 2+ (Z -) 2 + 2 NO → (NO) Pd + Z -+ NO + Z -; however, direct evidence of Pd + in zeolites in the absence of adsorbates has been reported by electron paramagnetic resonance spectroscopy (EPR) [15,28,32].…”

Computational modeling predicts the stability of both Pd+ and Pd2+ ion-exchanged into H-CHA

“…Pd + had only been observed in a small number of binuclear Pd complexes, 20 until a family of mononuclear Pd + species was very recently characterized by Luo et al 21 In the zeolite literature, Jacquemin et al have reported the presence of Pd + cations based on observation of EPR signals consistent with the presence of paramagnetic species in their study of the catalytic properties of Pd and Fe-exchanged beta zeolites for toluene oxidation. 22 In a recent study, Paolucci et al assessed the speciation of Pd in zeolites under PNA conditions using both experiments and periodic DFT calculations. 23 For Pd/H-CHA, these authors conclude that at typical loadings, Pd will occur as Pd 2+ at specific proximate Al pairs (next-next-nearest neighbors, separated by two Si atoms) in the 6-ring on the basis of the favorable energetics of Pd 2+ at this ion-exchange site, combined with a model for the Al distribution in CHA introduced in previous work.…”

Moderate Temperature Treatment of Gas-Phase Volatile Organic Toluene Using NiO and NiO–TiO2 Nano-catalysts: Characterization and Kinetic Behaviors

“…The decrease in % TN Conv. during the preliminary oxidation time may be connected to the formation of coke [91], blocking of NiO active sites by water vapor, catalyst poisoning or fouling [92,93]. Previous studies have shown that the deactivation of the catalyst by water vapor is reversible [94][95][96].…”