Modified zeolites, characterization

Tables 5.1 and 5.2 hst the main physicochemical properties of the modified zeolite characterized by a series of analyzing methods. XRF, XRD, and Al NMR results listed in Table 5.1 showed that with the increasing intensity of CP treatment, nonframework aluminum was ranoved gradually with httle influence on zeohte framework (unit cell size (UCS) changed little), thus the relative crystallinity increased. The removal of nonframework aluminum can also be verified by the FT-IR results shown in Figure 5.1, in which it can be seen that after CP treatment the intensity of the small peak at wave number 3660-3690 cm characterizing nonframework hydroxyl groups decreased step by step.

Because BaO/NaX zeolite catalysts exhibited the best performance, further investigations have been carried out recently to characterize the oxidative methylation of toluene catalyzed by BaO-modified X- and Y-zeolites, mordenite, ZSM-5, sil-icalite, and ALPO4-5 (230). The authors found that activity and basicity of BaO-modified zeolites and zeolite-like catalysts depend on both the structural type and composition. Thus, for samples of the same structural type (BaO/NaX zeolite. 

Xylenes. Because of the practical significance of xylenes, isomerization of xylenes over zeolites is frequently studied.348 The aim is to modify zeolite properties to enhance shape selectivity, that is, to increase the selectivity of the formation of the para isomer, which is the starting material to produce terephthalic acid. In addition, m-xylene isomerization is used as a probe reaction to characterize acidic zeolites.349,350... 

The use of surfactant-modified zeolite (SMZ) as a permeable barrier sorbent may offer several unique advantages when dealing with mixed contaminant plumes. Zeolites are hydrated aluminosilicate minerals characterized by cage-like structures, high internal and external surface areas, and high cation exchange capacities. Both natural and synthetic zeolites find use in industry as sorbents, soil amendments, ion exchangers,... 

The thermal and catalytic conversion of different hydrocarbon fractions, often with hydrotreating and other reaction steps, is characterized by a broad variety of feeds and products (Table 1, entry 4). New processes starting from natural gas are currently under development these are mainly based on the conversion of methane into synthesis gas, further into methanol, and finally into higher hydrocarbons. These processes are mainly employed in the petrochemical industry and will not be described in detail here. Several new processes are under development and the formation of BTX aromatics from C3/C4 hydrocarbons employing modified zeolite catalysts is a promising example [10],... 

The triplet state photophysics of naphthalene and a,u-diphenylpolyenes photogenerated in trapped heavy cation exchanged zeolites have been characterized. 0 The application of the modified zeolite environment provides a powerful new method for induction and observation of external heavy atom effects. Triplet excitation energy transport kinetics in vapour deposited naphthalene has been followed by an analysis of the kinetics of phosphorescence and delayed fluorescence. The assorted decays... 

In this presentation our interest is focused on the characterization of modified zeolites samples and the effect in physical and chtsmical properties. The case of Ti and the effects of modification on catalytic featjres will be described in other papers of this book by G. Bellusi, V. Fattore (Milano) and by P.A. Jacobs (Leuven) respectively. 

A modified zeolite was used to support Pt particles derived from the cluster anions [PtsIGOIgl ( = 4-6). Mesoporous channels (2.7 and 4.7 nm pore size) of FSM-16 were modified with Ti02 or zirconia by the impregnation and hydrolysis of Ti or Zr alkoxides with subsequent calcination. The Pt carbonyl cluster anions were synthesized within the modified FSM-16 by the reaction of H2PtCl6 with CO and water, and then characterized by IR and UV-VIS spectroscopies. Pyrolysis under vacuum at 573 K gave supported nanoparticles, which were more active for CO hydrogenation and more selective for C2-C3 alkanes than the unmodified Pt/FSM-16 catalyst. 

The external surface Bronsted and Lewis acidity of modified zeolites were characterized by FTIR of OH groups and adsorbed CO molecules and ESR of adsorbed nitroxyi radicals. The catalytic properties of the samples were tested in reactions of aromatics conversion toluene, pseudocumene, and triisopropylbenzene. The correlation between acidity and catalytic activity has been found and discussed. The three methods of external surface characterization can lead to the entire view on zeolite acidity. 

Corma, A., del Pino, M., Iglesias, M., Sanchez, F. (1992) Synthesis and characterization of new chiral Rh(l) complexes with A, A -ligands and A,P-ligands-a study of anchoring on the modified zeolites and catal54ic properties of heterogenized complexes, J. Organomet. Chem. 431, 233-246. 

Tao, Y, Kanoh, H., Abrams, L., and Kaneko, K. 2006. Mesopore-modified zeolites Preparation, characterization, and applications. Chem. Rev. 106 896-910. 

Rolison DR (1990) Zeolite-modified electrodes and electrode-modified zeolites. Chem Rev 90(5) 867-878 Rossinyol E, Prim A, Pellicer E, Arbiol J, Hernandez-Ramirez F, Peiro F, Comet A, Morante JR, Solovyov LA, Tian B, Bo T, Zhao D (2007a) Synthesis and characterization of chromium-doped mesoporous tungsten oxide for gassensing apphcations. Adv Funct Mater 17 1801-1806... 

The stepwise conversion of N-cyclohexanone oxime into 6-caprolactam via the vapour-phase Beckmann rearrangement on a number of modified zeolite systems was studied by a variety of different solid-state NMR techniques, including N and CP MAS NMR spectroscopy. The zeolite materials are characterized by H, Si, and N MAS NMR... 

Aluminosilicate molecular sieves with the FAU structure have been crystallized in the presence of several metallophthalocyanines. A percentage of the complexes becomes included into the zeolites. The synthesis of NaX around the metal chelate represents a new method for encapsulating such complexes and modifying zeolite molecular sieves. The entrapped complexes were characterized by XRD, IR and UV-VIS spectroscopy. Preliminary results suggest the metal complexes may function as templates by modifying the gel chemistry. 

The synthesis procedure led to a highly crystalline MCM-22 zeolite, as indicated by XRD data (Fig. 1A, a). The introduction of platinum by ion exchange procedure does not modify the crystallinity of the zeolite (Fig. 1A, b). SEM micrographs show that the sample obtained in static hydrothermal conditions is characterized by the presence of homogeneous round-shaped particles of ca. 10 pm in diameter formed by aggregation of lamellar particles [7,8], The morphology of the zeolite is not modified after platinum introduction (Fig. IB). 

Lercher and coworkers studied xylene isomerization on surface modified HZSM-5 zeolites [133]. They used time-resolved in situ IR spectroscopy to monitor the concentration of reactants and product inside the pores of the zeolite. Massiani and coworkers studied the conversion of xylene over mordenites [134]. They used in operando IR to characterize the adsorbed surface species and evolution of the active sites as the reaction proceeded. 

Measurement of the thermokinetic parameter can be used to provide a more detailed characterization of the acid properties of solid acid catalysts, for example, differentiate reversible and irreversible adsorption processes. For example, Auroux et al. [162] used volumetric, calorimetric, and thermokinetic data of ammonia adsorption to obtain a better definition of the acidity of decationated and boron-modified ZSM5 zeolites (Figure 13.7). 

The first in situ MAS NMR investigation of the synthesis of MTBE on acidic zeolites was performed by Mildner et al. (228) under batch reaction conditions. In this investigation, the temperature-jump MAS NMR technique (stop-and-go experiment, see Section III.A) was applied to characterize the reaction dynamics under non-equilibrium conditions on a boron-modified pentasil zeolite ( si/... 

TTigh silica zeolites attract great attention since they are characterized by relatively high thermal stability and considerable acid resistance. Physicochemical properties of high silica zeolites, despite a number of investigations, have not been sufficiently studied. The same is true for L- and clinoptilolite zeolite. The data on synthesis, structure, adsorption properties, decationization, dealuminization, adsorption heats, and other properties of the above-mentioned zeolites have been given (1-15). Results of studies of physicochemical properties of L zeolites and of natural and modified clinoptilolite are given here. 

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