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The selective catalytic reduction of N2O over steam-activated FeZSM-5 zeolite has been investigated at 473-823 K using C1-C3 hydrocarbons (methane, ethane, ethene, ethyne, propane, and propyne). The assessment of the hydrocarbons for nitrous oxide abatement is discussed according to different criteria: (i) de-N2O activity and operation temperature, (ii) hydrocarbon utilization, that is, the selectivity to react with N2O in O2 excess, (iii) emission of CO and CO2. (iv) sensitivity to NO and NH3, and (v) cost Alkanes are generally more effective reducing agents than unsaturated hydrocarbons. In particular, alkynes require higher temperature to activate N2O and are unselective because of their proneness to react with O2. Ethane is an optimal reductant, featuring a high de-N2O activity, high selectivity, and compared to methane, a lower degree of inhibition by NO. [ABSTRACT FROM AUTHOR]

A generalizedapproach to determine the complete distribution ofmacropores, mesopores, and micropores from argon adsorption and mercuryporosimetry is developed and validated for advanced zeolite catalystswith hierarchically structured pore systems in powder and shaped forms.Rather than using a fragmented approach of simple overlays from individualtechniques, a unified approach that utilizes a kernel constructedfrom model isotherms and model intrusion curves is used to calculatethe complete pore size distribution and the total pore volume of thematerial. An added benefit of a single full-range pore size distributionis that the cumulative pore area and the area distribution are alsoobtained without the need for additional modeling. The resulting completepore size distribution and the kernel accurately model both the adsorptionisotherm and the mercury porosimetry. By bridging the data analysisof two primary characterization tools, this methodology fills an existinggap in the library of familiar methods for porosity assessment inthe design of materials with multilevel porosity for novel technologicalapplications. [ABSTRACT FROM AUTHOR]

The manifestation of zeolite recrystallizationand the formationof amorphous aluminosilicate species during desilication are examinedto better understand the properties of alkaline-treated hierarchicalzeolites and their catalytic performance. This is achieved using asystematic experimental strategy, starting from treating the filtrateof alkaline-treated silicalite-1 in the presence of various externaladditives. No recrystallization is evidenced upon addition of tetrapropylammonium(TPA+) and/or aluminum hydroxide ions [Al(OH)4–], confirming the low probability of zeolite nucleationand/or growth during desilication. Conversely, ordered mesoporousmaterials (OMMs) form upon addition of cetyltrimethylammonium (CTA+) to the filtrate. By using other silicon sources, i.e., tetramethylorthosilicate or the organosilane dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium,we verify the facile formation of amorphous materials during alkalinetreatment of USY zeolites in the presence of hydrophobic micelle-formingalkyl moieties. A systematic characterization by X-ray diffraction,transmission electron microscopy, N2and Ar adsorption,inductively coupled plasma optical emission spectroscopy, and Fouriertransform infrared spectroscopy of pyridine adsorbed, demonstratesthat zeolites exposed to base solutions containing CTA+display weaker zeolitic properties, compared to those prepared usingTPA+, and should be considered as hierarchical zeolite/OMMcomposites. Catalytic tests in the alkylation of toluene with isopropylalcohol or benzyl alcohol evidence that CTA+-derived compositesdo not outperform the conventional USY zeolite. Only the hierarchicalUSY zeolite prepared by alkaline treatment in the presence of TPA+yielded a superior catalytic performance. [ABSTRACT FROM AUTHOR]

Hierarchical clinoptilolite and Lzeolites are prepared using optimizedtandem dealumination–desilication treatments. The main challengein the postsynthetic modification of these zeolites is the high Alcontent, requiring a tailored dealumination prior to the desilicationstep. For natural clinoptilolite, sequential acid treatments usingaqueous HCl solutions were applied, while for L a controlled dealuminationusing ammonium hexafluorosilicate is required. Subsequent desilicationby NaOH treatment yields mesopore surfaces of up to 4-fold (clinoptilolite,64 m2g–1; L, 135 m2g–1) relative to the parent zeolite (clinoptilolite,15 m2g–1; L, 45 m2g–1). A thorough characterization sheds light on thecomposition, crystallinity, porosity, morphology, coordination, andacidity of the modified clinoptilolite and L zeolites. It is elaboratedthat, besides the degree of dealumination, the resulting Al distributionis a critical precondition for the following mesopore formation bydesilication. Adsorption experiments of Cu2+and methyleneblue from aqueous solutions and the catalytic evaluation in alkylationsand Knoevenagel condensation evidence the superiority of the hierarchicalzeolites, as compared to their purely microporous counterparts. Finally,the postsynthetic routes for clinoptilolite and L are generalizedwith other recently reported modification strategies, and presentedin a comprehensive overview. [ABSTRACT FROM AUTHOR]