Thermal stability, SAPO

Akolekar, D.B. (1994) Thermal Stability, addity, catalytic properties, and deactivation behaviour of SAPO-5 catalysts effect of silicon content, add treatment and Na exchange. J. Catal., 149, 1 10. 

M. Briend, A. Lamy, M.J. Peltre, P.P. Man, and D. Barthomeuf, Thermal-Stability of Tetrapropylammonium (TPA) and Tetramethylammonium (TMA) Cations Occluded in SAPO-37 Molecular-Sieves. Zeolites, 1993, 13, 201-211. 

Ni-modified SAPO-5 molecular sieves have been prepared by addition of NiO or Ni acetate to the reaction mixture used for hydrothermal crystallization of SAPO-5. The crystallinity and thermal stability of the materials obtained are comparable with those of pure SAPO-5. 

K at the most. In a view of thermostability, AlPO-n-based molecular sieve is quite different from these zeolites, and its crystal structure is generally stable up to the temperature higher than 1,173 K. In spite of the high thermal stability of AlPO-n-based molecular sieves, studies on the application of these AlPO-n-based molecular sieves to high temperature reactions have been limited. The thermostability of the framework of AlPO-n-based molecular sieves and the application of SAPO to these high temperature reactions will be described in detail below. 

On the other hand, Briend et al. investigated the thermal stability of SAPO-5, -34, -37 by using XRD, IR, and Si MAS NMR. Thermal and hydrothermal stability of SAPOs strongly depends on the type of crystal structure. Figure 15 shows Si MAS NMR spectra of SAPO-34 after various treatments. Although the sharp peak of Si(4Al) at -91.6 ppm is broadened by hydration at room temperature, the intensity of these peaks was restored by the evacuation at 573 K. A similar decrease in the crystallinity of SAPO-34 by hydration at room temperature was also detected by XRD. However, this does not suggest that thermostability of SAPO-34 was poor in a wet... 

Application of Aluminophosphate- based Molecular Sieves for a Thermostable Catalyst. - Although the high thermal stability is a particularly interesting property of aluminophosphate molecular sieves compared to those of aluminosilicate zeolites, the application of aluminophosphate molecular sieves as thermostable catalysts has been limited. In this section, the application of SAPO as thermostable NO reduction catalysts... 

Furthermore, the high activity was sustained up to 873 K. Therefore, the conversion of NO into N2 is twice as high on Cu-SAPO-34 than on Cu-ZSM-5 at 873 K. Since Cu-SAPO-34 exhibited the highest activity to NO reduction with C3Hg among the catalysts examined, catalytic activity for NO reduction and thermal stability were investigated on SAPO-34 in detail. 

Defect free DD3R supported membranes have been newly prepared by NGK insulators (Japan).The great advantage of this zeolite type with respect to the SAPO-34 and T zeolites, should be the chemical and thermal stability because of its all silica structure. Kapteijn and co-workers studied the permeation of various gases (carbon dioxide, nitrous oxide, methane, nitrogen, oxygen. 

FIGURE 2.79 Concentration of bridging OH groups a function of the treatment temperature of silicoaluminophosphates H-SAPO-11, H-SAPO-18, H-SAPO-31, and H-SAPO-34 obtained by H MAS NMR spectroscopy. (Adapted from Micropor. Mesopor. Mater., 56, Buchholz, A., Wang, W., Xu, M., Arnold, A., and Hunger, M., Thermal stability and dehydroxylation of Brpnsted acid sites in silicoaluminophosphates H-SAPO-11, H-SAPO-18, H-SAPO-31, and H-SAPO-34 investigated by multi-nuclear solid-state NMR spectroscopy, 267-278, 2002, Copyright 2002, with permission from Elsevier.)... 

Small-pore molecular sieve SAPO-34 is known to exhibit exceptional thermal stability and maintain its crystalhne structure up to 1,000 °C [71]. Since the acid/ exchange sites in a SAPO-34 are associated with the Si tetrahedral sites, they are less susceptible than tetrahedral Al sites to H2O interaction and hence are more stable to hydrothermal aging [72]. 

Watanabe Y, Koiwai A, Takeuchi H et al (1993) Multinuclear NMR studies on the thermal stability of SAPO-34. Journal of Catalysis 143 430-436... 

An important group of catalysts for NOx reduction through anunonia SCR is represented by copper exchanged zeolites [1-9]. Many different zeolites have been investigated, for example, Cu-ZSM-5 [10-13], Cu-faujasite [14], Cu-Beta [15,16], and Cu-Y [17]. Recently, copper zeolites with chabazite (CHA) structure have received great attention due to their high thermal stability and hydro carbon resistance [18]. Both Cu-SAPO-34 [19] and Cu-SSZ-13 [18] have a CHA structure... 

The spectrum of adsorption pore sizes and pore volumes and the hydrophilic surface selectivity of the MeAPOs are similar to those described for the SAPOs. The observed catalytic properties vary from weakly to strongly acidic and are both metal- and structure-dependent. The thermal and hydrothermal stability of the MeAPO materials is somewhat less than that of the AIPO4 and SAPO molecular sieves. 

SAPO-37 molecular sieve which has the crystalline structure of faujasite differs from this zeolite by the presence of phosphorus in the structure (1). It was shown that this element increases the thermal and hydrothermal stability of the structure (2). With regards to acidity, the SAPO-37 materials have acidic properties (1,3,4) with two OH groups very similar to those of faujasites (1,4). It was also observed that the SAPO-37 materials have besides acid centers of medium strength a small number of protonic sites stronger than in HY or even than those of an ultrastable LZY-82 (4). 

The use of y-irradiation and controlled thermal annealing to produce silver clusters in zeolites and related materials was reviewed by Michalik [114]. Unusual stability was attributed to Ag + clusters formed in this way in dehydrated zeolite rho, which were found to persist for months at room temperature and could be observed up to 100°C. In the zeoHte A analogue, AgH-SAPO-42 (LTA), dehydrated at 300 °C in flowing oxygen, clusters such as AgJ and Agf" were detected in very low yield, but, in the presence of methanol, Agl" species were... 

The thermal and hydrothermal stabilities of the MeAPO, MeAPSO, ElAPO, and ElAPSO families identified in Tables II and III are more diverse than those of the AIPO4 and SAPO families. Here, the stability depends on both chemical composition and crystal form. Many species display stability similar to that of AlP04 s and SAPO s, while others show significantly reduced crystal retentions when exposed to high temperatures or severe hydrothermal conditions. 

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