Correlation of TPD and impedance measurements on the desorption of NH3 from zeolite H-ZSM-5

Rodríguez-González, L.; Rodríguez‐Castellón, Enrique; Jiménez‐López, Antonio; Simon, Ulrich

doi:10.1016/j.ssi.2008.06.007

Cited by 47 publications

(51 citation statements)

References 16 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The LT-peak represents intermediate strength, of acidic sites and assigned to the desorption of ammonia bound via hydrogen bonds to NH 4 + , i.e. (NH 3 ) n NH 4 + /Zeo − adsorbate, and proton transport is assumed to follow a Grotthus-like mechanism [30,31]. It can be seen from the TPD profiles that the NaP sample with the higher Na 2 O/SiO 2 molar ratio exhibited a large fraction of acid sites, contrary to that synthesized with the lower ratio.…”

Section: Morphology and Crystal Sizementioning

confidence: 99%

Controllable synthesis of NaP zeolite and its application in calcium adsorption

et al. 2015

View full text Add to dashboard Cite

functional performance of the different kinds of zeolites, many studies have been devoted to improving synthetic approaches to control crystal size, the size of the intracrystalline pore/channel system and morphology of zeolites [5,6].Among various types of zeolites, NaP (Na 6 [(AlO 2 ) 6 (SiO 2 ) 10 ]⋅15H 2 O) is one of the most interesting structured zeolite with two sets of intersecting channels: 0.31 nm × 0.44 nm and 0.26 nm × 0.49 nm. According to International Zeolite Association (IZA), this structure is called "Gismondine" (GIS) framework topology [7,8]. NaP zeolite offers the greatest promise for gas separation applications due to its small pore size [9,10], and is also useful for removal of toxic and radioactive waste species like Cs, Sr, Ba, Pb, U, heavy metals, and ammonium from wastewater, seawater potassium extraction and formation of environmental friendly detergent [11,12]. NaP zeolite can be synthesized from various precursor materials and various methods. It can be synthesized from: (i) clay at a crystallization temperature of 85ºC [13], (ii) sodium silicate solution [14], and (iii) high silicon fly ash of coal combustion at 120ºC for 4 h [15]. Among them the most common methods used for the synthesis of NaP zeolite are the sol-gel technique, hydrothermal synthesis and microwave heating synthesis [1]. The NaP zeolite with different morphologies can offer many intriguing properties: places to store the guest molecules and to perform chemical reactions with selected-sized molecules. Thus, the NaP zeolite morphology and its important correlation with properties is the need of the recent research.In this work, we attempted the template free hydrothermal synthesis of NaP under controlled conditions. Based on multiple paths that can be involved in the hydrothermal synthesis of NaP, optimization of crystallization conditions was adapted through variation of the following parameters: Na 2 O/SiO 2 and SiO 2 /Al 2 O 3 molar ratios, aging time and aging temperature. The characteristics of the synthesized gels NaP zeolite particles were prepared through a template-free hydrothermal condition at 100ºC. Parameters like Na2O/SiO2 and SiO2/Al2O3 molar ratios, gel aging time and aging temperature were investigated for regulating the crystallization of the final product. The samples at different synthesis stages were characterized with N2 adsorption at −196ºC, field emission scanning electron microscopy (FE-SEM), temperature programmed desorption of ammonia adsorption, X-ray diffraction, thermogravimetric and differential scanning calorimetry analysis and Fourier transform infrared spectroscopy. The experimental results evidenced that a high ordering crystallinity of NaP zeolite was obtained at Na2O/SiO2 and SiO2/Al2O3 molar ratios of 1.10 and 1.40, respectively, and a temperature of 100°C for 4 days of aging. FE-SEM image exhibited polycrystalline aggregates of NaP zeolite with crystallite sizes ranging up to 5.04 μm with cactus/cabbage like structures. The quantitative analysis of the total number of acid sites...

show abstract

Section: Morphology and Crystal Sizementioning

confidence: 99%

Controllable synthesis of NaP zeolite and its application in calcium adsorption

et al. 2015

View full text Add to dashboard Cite

show abstract

“…With decreasing Al content of the zeolite, the number of the Brønsted acid sites decreases and the distance between them increases. Consequently, the proton mobility due to proton hopping between neighboring Brønsted sites (Rodriguez-Gonzalez et al, 2008) decreases with increasing storage site distance. The part of the dielectric loss related to the proton mobility of the adsorbed NH 3 molecules increases with temperature, resulting in lower activation energies (thermal activation) for proton hopping, corresponding to the observed measurement results.…”

mentioning

confidence: 99%

Ammonia storage studies on H-ZSM-5 zeolites by microwave cavity perturbation: correlation of dielectric properties with ammonia storage

Dietrich

Rauch

Simon

et al. 2015

J. Sens. Sens. Syst.

View full text Add to dashboard Cite

Abstract.To meet today's emission standards, the ammonia-based selective catalytic reduction (SCR) has become the major NO x control strategy for light and heavy diesel engines. Before NO x reduction can proceed, adsorption of ammonia on the acidic sites of the catalyst is necessary. For improvements in efficiency and control of the exhaust gas aftertreatment, a better understanding of the ammonia storage on the acidic sites of zeolite-based SCR catalysts is needed. Thereby, the correlation of dielectric properties of the catalyst material itself with the ammonia storage is a promising approach. Recently, a laboratory setup using microwave cavity perturbation to measure the dielectric properties of catalyst material has been described. This study shows the first experimental data on zeolite-based SCR materials in their H-form. The SCR powder samples are monitored by microwave cavity perturbation while storing and depleting ammonia, both with and without admixed NO x at different temperatures. Its complex dielectric permittivity is found to correlate closely with the stored mass of ammonia. The influence of the temperature and the Si / Al ratio of the zeolite to the ammonia storage behavior are also examined. These measurements disclose different temperature dependencies and differing sensitivities to ammonia storage for both real and imaginary parts of the complex permittivity. The apparent constant sensitivity of the real part can be related to the polarity of the adsorbed ammonia molecules, whereas the imaginary part depends on the Si / Al ratio and is related to the conductivity mechanisms of the zeolite material by proton hopping. It provides information about the zeolite structure and the number of (and the distance between) acidic storage sites, in addition to the stored ammonia mass.

show abstract

“…Both NH4 + and NH4 + •(NH3)n complexes can provide additional paths or carriers for proton transport, which consequently increase the proton conductivity of zeolite catalysts [26,[32][33][34]. The physico-chemical features of NH3-supported proton transport were revealed by in situ studies over NH3-loaded zeolites using techniques combining IS with TPD or quantum chemical calculations [26][27][28][29]34,43], and are schematically illustrated in Figure 3 for proton-form zeolites. Four distinct temperature-dependent mechanisms can be distinguished, specifically (i) the Grothuss-like transport along condensed NH4 + •(NH3)n chains at low temperatures, i.e., below the desorption temperature of NH3; (ii) proton hopping along partially disintegrated chains of NH3 molecules (i.e., in the temperature range, where weakly bound solvent molecules desorb); (iii) vehicle-supported transfer of protons between the neighboring Brønsted sites with NH4 + carriers as "proton vehicles", and (iv) thermally activated proton hopping along the electron density located at the oxygen atoms of the zeolite lattice in the absence of solvate molecules (above 340 °C) [26,32,33].…”

Section: Nh3-supported Proton Transportmentioning

confidence: 99%

“…In NH 3 -SCR over zeolite catalysts, the adsorption of NH 3 molecules on Brønsted acid sites leads to the formation of ammonium ions (NH 4 + ), which interact further with NH 3 molecules forming NH 4 + ·(NH 3 ) n complexes at low temperatures [2]. The formed NH 4 + and NH 4 + ·(NH 3 ) n complexes, which can provide additional paths or carriers for proton transport [26,[32][33][34], lead to increased proton conductivities which can be monitored by IS in a broad frequency range (mHz-GHz) [27,[32][33][34][35][36]. The consumption of adsorbed NH 3 , either by desorption or SCR conversion, leads to decreased conductivity due to a loss of proton carriers [17,26].…”

Section: Introductionmentioning

confidence: 99%

In Situ Spectroscopic Studies of Proton Transport in Zeolite Catalysts for NH3-SCR

Chen

Simon

2016

Catalysts

View full text Add to dashboard Cite

Proton transport is an elementary process in the selective catalytic reduction of nitrogen oxides by ammonia (DeNO x by NH 3 -SCR) using metal-exchanged zeolites as catalysts. This review summarizes recent advancements in the study of proton transport in zeolite catalysts using in situ electrical impedance spectroscopy (IS) under NH 3 -SCR reaction conditions. Different factors, such as the metal cation type, metal exchange level, zeolite framework type, or formation of intermediates, were found to influence the proton transport properties of zeolite NH 3 -SCR catalysts. A combination of IS with diffuse reflection infrared Fourier transformation spectroscopy in situ (in situ IS-DRIFTS) allowed to achieve a molecular understanding of the proton transport processes. Several mechanistic aspects, such as the NH 3 -zeolite interaction, NO-zeolite interaction in the presence of adsorbed NH 3 , or formation of NH 4 + intermediates, have been revealed. These achievements indicate that IS-based in situ methods as complementary tools for conventional techniques (e.g., in situ X-ray absorption spectroscopy) are able to provide new perspectives for the understanding of NH 3 -SCR on zeolite catalysts.

show abstract

Correlation of TPD and impedance measurements on the desorption of NH3 from zeolite H-ZSM-5

Cited by 47 publications

References 16 publications

Controllable synthesis of NaP zeolite and its application in calcium adsorption

Controllable synthesis of NaP zeolite and its application in calcium adsorption

Ammonia storage studies on H-ZSM-5 zeolites by microwave cavity perturbation: correlation of dielectric properties with ammonia storage

In Situ Spectroscopic Studies of Proton Transport in Zeolite Catalysts for NH3-SCR

Contact Info

Product

Resources

About